Remove reference from Unit.Past

This is in preparation for removing province and location references from Unit

MDATC.html

@@ -236,17 +236,13 @@
 <a name="2.B"><h3>2.B. ORDER NOTATION</h3></a>
 <p>The order notation in this document is as in DATC, with the following additions for multiversal time travel.</p>
 <ul>
-<li>A season within a particular timeline is designated in the format X:Y, where X is the turn (starting from 0 and advancing with each movement phase) and Y is the timeline number (starting from 0 and advancing with each timeline fork).</li>
-<li>Adjudication is implied to be done between successive seasons. For example, if orders are listed for 0:0 and then for 1:0, it is implied that the orders for 0:0 were adjudicated.</li>
-<li>Units are designated by unit type, province, and season, e.g. "A Munich 1:0". A destination for a move order or support-to-move order is designated by province and season, e.g. "Munich 1:0".
+<li>Timelines are designated by letters, e.g. "a", "b". Turns are designated by numbers, e.g. 0, 1, 2. A board in a timeline X at turn N is designated XN. A location LOC on that board is designated X-LOC@N.</li>
+<li>In examples that cover multiple turns, orders are given in sets. Each order set is adjudicated before moving on to the next set.</li>
+<li>Units are fully designated by unit type and multiversal location, e.g. "A b-Munich@3". Destinations for move orders or support-to-move orders are fully designated by multiversal location, e.g. <code>a-Munich@1</code>. Where orders are not fully designated, the full designations are implied according to these rules:</li>
 <ul>
-<li>If season of the ordered unit is not specified, the season is the season to which the orders are being given.</li>
-<li>If the season of a unit supported to hold is not specified, the season is the same season as the supporting unit.</li>
-<li>If the season of the destination of a move order or the season of the destination of a supported move order is not specified, the season is the season of the moving unit.</li>
-<li>For example:
-<pre>Germany 2:0
-A Munich supports A Munich 1:1 - Tyrolia</pre>
-The order here is for Army Munich in 2:0. The move being supported is for Army Munich in 1:1 to move to Tyrolia in 1:1.</li>
+<li>If only the timeline of a location is specified, the turn is the latest turn in that timeline. E.g. if timeline "a" is at turn 2, <code>a-Munich</code> is interpreted as <code>a-Munich@2</code>.</li>
+<li>If the timeline or turn are unspecified for the target of a move or support-hold order, the timeline and turn are those of the ordered unit. E.g. if timeline "b" is at turn 1, <code>A b-Tyrolia - Munich</code> is interpreted as <code>b-Tyrolia@1 - b-Munich@1</code>.</li>
+<li>If only the province is specified for the target of a support-move order, the timeline and turn are those of the supported unit. E.g. if timeline "a" is at turn 2 and "b" at turn 1, <code>A a-Munich supports A b-Tyrolia - Munich</code> is interpreted as <code>A a-Munich@2 supports A b-Tyrolia@1 - b-Munich@1</code>.</li>
 </ul>
 </ul>
 
@@ -258,13 +254,15 @@ The order here is for Army Munich in 2:0. The move being supported is for Army M
 <summary><h4><a href="#3.A.1">3.A.1</a>. TEST CASE, MOVE INTO OWN PAST FORKS TIMELINE</h4></summary>
 <p>A unit that moves into its own immediate past causes the timeline to fork.</p>
 <pre>
-    Germany 0:0
-    A Munich hold
+    Germany:
+    A a-Munich hold
 
-    Germany 1:0
-    A Munich - Tyrolia 0:0
+    ---
+
+    Germany:
+    A a-Munich - a-Tyrolia@0
 </pre>
-<p>A Munich 1:0 moves to Tyrolia 0:0. The main timeline advances to 2:0 with an empty board. A forked timeline advances to 1:1 with armies in Munich and Tyrolia.</p>
+<p>A a-Munich@1 moves to a-Tyrolia@0. The main timeline advances to a2 with an empty board. A forked timeline advances to b1 with armies in Munich and Tyrolia.</p>
 <div class="figures">
     <canvas id="canvas-3-A-1-before" width="0" height="0"></canvas>
     <script>
@@ -311,19 +309,21 @@ The order here is for Army Munich in 2:0. The move being supported is for Army M
 <summary><h4><a href="#3.A.2">3.A.2</a>. TEST CASE, SUPPORT TO REPELLED PAST MOVE FORKS TIMELINE</h4></summary>
 <p>A unit that supports a move that previously failed in the past, such that it now succeeds, causes the timeline to fork.</p>
 <pre>
-    Austria 0:0
+    Austria:
     A Tyrolia hold
 
-    Germany 0:0
+    Germany:
     A Munich - Tyrolia
 
-    Austria 1:0
+    ---
+
+    Austria:
     A Tyrolia hold
 
-    Germany 1:0
-    A Munich supports A Munich 0:0 - Tyrolia 0:0
+    Germany:
+    A Munich supports A a-Munich@0 - Tyrolia
 </pre>
-<p>With the support from A Munich 1:0, A Munich 0:0 dislodges A Tyrolia 0:0. A forked timeline advances to 1:1 where A Tyrolia 0:0 has been dislodged. The main timeline advances to 2:0 where A Munich and A Tyrolia are in their initial positions.</p>
+<p>With the support from A a-Munich@1, A a-Munich@0 dislodges A a-Tyrolia@0. A forked timeline advances to b1 where A Tyrolia has been dislodged. The main timeline advances to a2 where A Munich and A Tyrolia are in their initial positions.</p>
 <div class="figures">
     <canvas id="canvas-3-A-2-before" width="0" height="0"></canvas>
     <script>
@@ -379,19 +379,21 @@ The order here is for Army Munich in 2:0. The move being supported is for Army M
 <summary><h4><a href="#3.A.3">3.A.3</a>. TEST CASE, FAILED MOVE DOES NOT FORK TIMELINE</h4></summary>
 <p>A unit that attempts to move into the past, but is repelled, does not cause the timeline to fork.</p>
 <pre>
-    Austria 0:0
+    Austria:
     A Tyrolia hold
 
-    Germany 0:0
+    Germany:
     A Munich hold
 
-    Austria 1:0
+    ---
+
+    Austria:
     A Tyrolia hold
 
-    Germany 1:0
-    A Munich - Tyrolia 0:0
+    Germany:
+    A Munich - a-Tyrolia@0
 </pre>
-<p>The move by A Munich 1:0 fails. The main timeline advances to 2:0 with both armies in their initial positions. No alternate timeline is created.</p>
+<p>The move by A a-Munich@1 fails. The main timeline advances to a2 with both armies in their initial positions. No alternate timeline is created.</p>
 <div class="figures">
     <canvas id="canvas-3-A-3-before" width="0" height="0"></canvas>
     <script>
@@ -441,15 +443,17 @@ The order here is for Army Munich in 2:0. The move being supported is for Army M
 <summary><h4><a href="#3.A.4">3.A.4</a>. TEST CASE, SUPERFLUOUS SUPPORT DOES NOT FORK TIMELINE</h4></summary>
 <p>A unit that supports a move that succeeded in the past and still succeeds after the additional future support does not cause the timeline to fork.</p>
 <pre>
-    Germany 0:0
+    Germany:
     A Munich - Tyrolia
     A Bohemia hold
 
-    Germany 1:0
+    ---
+
+    Germany:
     A Tyrolia hold
-    A Bohemia supports A Munich 0:0 - Tyrolia
+    A Bohemia supports A a-Munich@0 - Tyrolia
 </pre>
-<p>Both units in 1:0 continue to 2:0. No alternate timeline is created.</p>
+<p>Both units in a1 continue to a2. No alternate timeline is created.</p>
 <div class="figures">
     <canvas id="canvas-3-A-4-before" width="0" height="0"></canvas>
     <script>
@@ -501,15 +505,15 @@ The order here is for Army Munich in 2:0. The move being supported is for Army M
 <summary><h4><a href="#3.A.5">3.A.5</a>. TEST CASE, CROSS-TIMELINE SUPPORT DOES NOT FORK HEAD</h4></summary>
 <p>In this test case, a unit elsewhere on the map moves into the past to cause a timeline fork. Once there are two parallel timelines, a support from one to the head of the other should not cause any forking, since timeline forks only occur when the past changes, not the present.</p>
 <pre>
-    Austria
-    A Tyrolia 2:0 hold
-    A Tyrolia 1:1 hold
+    Austria:
+    A a-Tyrolia hold
+    A b-Tyrolia hold
 
     Germany
-    A Munich 2:0 - Tyrolia
-    A Munich 1:1 supports A Munich 2:0 - Tyrolia
+    A a-Munich - Tyrolia
+    A b-Munich supports A a-Munich - Tyrolia
 </pre>
-<p>A Munich 2:0 dislodges A Tyrolia 2:0. No alternate timeline is created.</p>
+<p>A a-Munich dislodges A a-Tyrolia. No alternate timeline is created.</p>
 <div class="figures">
     <canvas id="canvas-3-A-5-before" width="0" height="0"></canvas>
     <script>
@@ -567,19 +571,11 @@ The order here is for Army Munich in 2:0. The move being supported is for Army M
 <p>Following <a href="#3.A.5">3.A.5</a>, a cross-timeline support that previously succeeded is cut.</p>
 <pre>
     Germany
-    A Munich 2:0 - Tyrolia
-    A Munich 1:1 supports A Munich 2:0 - Tyrolia
+    A a-Tyrolia holds
+    A b-Munich holds
 
     Austria
-    A Tyrolia 2:0 holds
-    A Tyrolia 1:1 holds
-
-    Germany
-    A Tyrolia 3:0 holds
-    A Munich 2:1 holds
-
-    Austria
-    A Tyrolia 2:1 - Munich 1:1
+    A b-Tyrolia@2 - b-Munich@1
 </pre>
 <p>Cutting the support does not change the past or cause a timeline fork.</p>
 <div class="figures">

Makefile

@@ -0,0 +1,10 @@
+.PHONY: *
+
+help: ## display this help
+	@awk 'BEGIN{FS = ":.*##"; printf "\033[1m\nUsage\n \033[1;92m make\033[0;36m <target>\033[0m\n"} /^[a-zA-Z0-9_-]+:.*?##/ { printf "  \033[36m%-15s\033[0m %s\n", $$1, $$2 } ' $(MAKEFILE_LIST)
+
+tests: ## run all tests
+	dotnet test MultiversalDiplomacyTests
+
+test: ## name=[test name]: run a single test with logging
+	dotnet test MultiversalDiplomacyTests -l "console;verbosity=normal" --filter $(name)

MultiversalDiplomacy/Adjudicate/Decision/MovementDecisions.cs

@@ -61,25 +61,25 @@ public class MovementDecisions
                 case MoveOrder move:
                     AdvanceTimeline.Ensure(
                         move.Season,
-                        () => new(move.Season, world.OrderHistory[move.Season].Orders));
+                        () => new(move.Season, world.OrderHistory[move.Season.Designation].Orders));
                     AdvanceTimeline[move.Season].Orders.Add(move);
                     break;
 
                 case SupportHoldOrder supportHold:
                     AdvanceTimeline.Ensure(
                         supportHold.Target.Season,
-                        () => new(supportHold.Target.Season, world.OrderHistory[supportHold.Target.Season].Orders));
+                        () => new(supportHold.Target.Season, world.OrderHistory[supportHold.Target.Season.Designation].Orders));
                     AdvanceTimeline[supportHold.Target.Season].Orders.Add(supportHold);
                     break;
 
                 case SupportMoveOrder supportMove:
                     AdvanceTimeline.Ensure(
                         supportMove.Target.Season,
-                        () => new(supportMove.Target.Season, world.OrderHistory[supportMove.Target.Season].Orders));
+                        () => new(supportMove.Target.Season, world.OrderHistory[supportMove.Target.Season.Designation].Orders));
                     AdvanceTimeline[supportMove.Target.Season].Orders.Add(supportMove);
                     AdvanceTimeline.Ensure(
                         supportMove.Season,
-                        () => new(supportMove.Season, world.OrderHistory[supportMove.Season].Orders));
+                        () => new(supportMove.Season, world.OrderHistory[supportMove.Season.Designation].Orders));
                     AdvanceTimeline[supportMove.Season].Orders.Add(supportMove);
                     break;
             }
@@ -91,19 +91,33 @@ public class MovementDecisions
             .Distinct()
             .ToList();
 
+        (Province province, Season season) Point(Unit unit)
+            => (world.Map.GetLocation(unit.Location).Province, unit.Season);
+
         // Create a hold strength decision with an associated order for every province with a unit.
         foreach (UnitOrder order in relevantOrders)
         {
-            HoldStrength[order.Unit.Point] = new(order.Unit.Point, order);
+            HoldStrength[Point(order.Unit)] = new(Point(order.Unit), order);
         }
 
+        bool IsIncoming(UnitOrder me, MoveOrder other)
+            => me != other
+            && other.Season == me.Unit.Season
+            && other.Province == world.Map.GetLocation(me.Unit).Province;
+
+        bool AreOpposing(MoveOrder one, MoveOrder two)
+            => one.Season == two.Unit.Season
+            && two.Season == one.Unit.Season
+            && one.Province == world.Map.GetLocation(two.Unit).Province
+            && two.Province == world.Map.GetLocation(one.Unit).Province;
+
         // Create all other relevant decisions for each order in the affected timelines.
         foreach (UnitOrder order in relevantOrders)
         {
             // Create a dislodge decision for this unit.
             List<MoveOrder> incoming = relevantOrders
                 .OfType<MoveOrder>()
-                .Where(order.IsIncoming)
+                .Where(other => IsIncoming(order, other))
                 .ToList();
             IsDislodged[order.Unit] = new(order, incoming);
 
@@ -118,7 +132,7 @@ public class MovementDecisions
                 // Determine if this move is a head-to-head battle.
                 MoveOrder? opposingMove = relevantOrders
                     .OfType<MoveOrder>()
-                    .FirstOrDefault(other => other!.IsOpposing(move), null);
+                    .FirstOrDefault(other => AreOpposing(move, other!), null);
 
                 // Find competing moves.
                 List<MoveOrder> competing = relevantOrders
@@ -142,11 +156,11 @@ public class MovementDecisions
                 GivesSupport[support] = new(support, incoming);
 
                 // Ensure a hold strength decision exists for the target's province.
-                HoldStrength.Ensure(support.Target.Point, () => new(support.Target.Point));
+                HoldStrength.Ensure(Point(support.Target), () => new(Point(support.Target)));
 
                 if (support is SupportHoldOrder supportHold)
                 {
-                    HoldStrength[support.Target.Point].Supports.Add(supportHold);
+                    HoldStrength[Point(support.Target)].Supports.Add(supportHold);
                 }
                 else if (support is SupportMoveOrder supportMove)
                 {

MultiversalDiplomacy/Adjudicate/MovementPhaseAdjudicator.cs

@@ -50,7 +50,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
 
         // Invalidate any order given to a unit in the past.
         AdjudicatorHelpers.InvalidateIfNotMatching(
-            order => !order.Unit.Season.Futures.Any(),
+            order => !world.GetFutures(order.Unit.Season).Any(),
             ValidationReason.IneligibleForOrder,
             ref unitOrders,
             ref validationResults);
@@ -77,7 +77,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
 
         // Trivial check: a unit cannot move to where it already is.
         AdjudicatorHelpers.InvalidateIfNotMatching(
-            order => !(order.Location == order.Unit.Location && order.Season == order.Unit.Season),
+            order => !(order.Location.Designation == order.Unit.Location && order.Season == order.Unit.Season),
             ValidationReason.DestinationMatchesOrigin,
             ref moveOrders,
             ref validationResults);
@@ -90,11 +90,11 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         ILookup<bool, MoveOrder> moveOrdersByAdjacency = moveOrders
             .ToLookup(order =>
                 // Map adjacency
-                order.Unit.Location.Adjacents.Contains(order.Location)
+                world.Map.GetLocation(order.Unit).Adjacents.Contains(order.Location)
                 // Turn adjacency
                 && Math.Abs(order.Unit.Season.Turn - order.Season.Turn) <= 1
                 // Timeline adjacency
-                && order.Unit.Season.InAdjacentTimeline(order.Season));
+                && world.InAdjacentTimeline(order.Unit.Season, order.Season));
         List<MoveOrder> adjacentMoveOrders = moveOrdersByAdjacency[true].ToList();
         List<MoveOrder> nonAdjacentMoveOrders = moveOrdersByAdjacency[false].ToList();
 
@@ -138,7 +138,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         // Trivial check: cannot convoy a unit to its own location
         AdjudicatorHelpers.InvalidateIfNotMatching(
             order => !(
-                order.Location == order.Target.Location
+                order.Location.Designation == order.Target.Location
                 && order.Season == order.Target.Season),
             ValidationReason.DestinationMatchesOrigin,
             ref convoyOrders,
@@ -175,12 +175,12 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         AdjudicatorHelpers.InvalidateIfNotMatching(
             order =>
                 // Map adjacency with respect to province
-                order.Unit.Location.Adjacents.Any(
-                    adjLocation => adjLocation.Province == order.Target.Province)
+                world.Map.GetLocation(order.Unit).Adjacents.Any(
+                    adjLocation => adjLocation.Province == world.Map.GetLocation(order.Target).Province)
                 // Turn adjacency
                 && Math.Abs(order.Unit.Season.Turn - order.Target.Season.Turn) <= 1
                 // Timeline adjacency
-                && order.Unit.Season.InAdjacentTimeline(order.Target.Season),
+                && world.InAdjacentTimeline(order.Unit.Season, order.Target.Season),
             ValidationReason.UnreachableSupport,
             ref supportHoldOrders,
             ref validationResults);
@@ -195,7 +195,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         // Support-move orders are invalid if the unit supports a move to any location in its own
         // province.
         AdjudicatorHelpers.InvalidateIfNotMatching(
-            order => order.Unit.Province != order.Province,
+            order => world.Map.GetLocation(order.Unit).Province != order.Province,
             ValidationReason.NoSupportMoveAgainstSelf,
             ref supportMoveOrders,
             ref validationResults);
@@ -207,12 +207,12 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         AdjudicatorHelpers.InvalidateIfNotMatching(
             order =>
                 // Map adjacency with respect to province
-                order.Unit.Location.Adjacents.Any(
+                world.Map.GetLocation(order.Unit).Adjacents.Any(
                     adjLocation => adjLocation.Province == order.Province)
                 // Turn adjacency
                 && Math.Abs(order.Unit.Season.Turn - order.Season.Turn) <= 1
                 // Timeline adjacency
-                && order.Unit.Season.InAdjacentTimeline(order.Season),
+                && world.InAdjacentTimeline(order.Unit.Season, order.Season),
             ValidationReason.UnreachableSupport,
             ref supportMoveOrders,
             ref validationResults);
@@ -255,7 +255,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
 
         // Finally, add implicit hold orders for units without legal orders.
         List<Unit> allOrderableUnits = world.Units
-            .Where(unit => !unit.Season.Futures.Any())
+            .Where(unit => !world.GetFutures(unit.Season).Any())
             .ToList();
         HashSet<Unit> orderedUnits = validOrders.Select(order => order.Unit).ToHashSet();
         List<Unit> unorderedUnits = allOrderableUnits
@@ -312,9 +312,9 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
 
         // All moves to a particular season in a single phase result in the same future. Keep a
         // record of when a future season has been created.
-        Dictionary<Season, Season> createdFutures = new();
-        List<Unit> createdUnits = new();
-        List<RetreatingUnit> retreats = new();
+        Dictionary<Season, Season> createdFutures = [];
+        List<Unit> createdUnits = [];
+        List<RetreatingUnit> retreats = [];
 
         // Populate createdFutures with the timeline fork decisions
         logger.Log(1, "Processing AdvanceTimeline decisions");
@@ -324,9 +324,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
             if (advanceTimeline.Outcome == true)
             {
                 // A timeline that doesn't have a future yet simply continues. Otherwise, it forks.
-                createdFutures[advanceTimeline.Season] = !advanceTimeline.Season.Futures.Any()
-                    ? advanceTimeline.Season.MakeNext()
-                    : advanceTimeline.Season.MakeFork();
+                createdFutures[advanceTimeline.Season] = world.ContinueOrFork(advanceTimeline.Season);
             }
         }
 
@@ -339,7 +337,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
             Season moveSeason = doesMove.Order.Season;
             if (doesMove.Outcome == true && createdFutures.ContainsKey(moveSeason))
             {
-                Unit next = doesMove.Order.Unit.Next(doesMove.Order.Location, createdFutures[moveSeason]);
+                Unit next = doesMove.Order.Unit.Next(doesMove.Order.Location.Designation, createdFutures[moveSeason]);
                 logger.Log(3, "Advancing unit to {0}", next);
                 createdUnits.Add(next);
             }
@@ -368,7 +366,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
             if (isDislodged.Outcome == false)
             {
                 // Non-dislodged units continue into the future.
-                Unit next = order.Unit.Next(order.Unit.Location, future);
+                Unit next = order.Unit.Next(world.Map.GetLocation(order.Unit).Designation, future);
                 logger.Log(3, "Advancing unit to {0}", next);
                 createdUnits.Add(next);
             }
@@ -377,7 +375,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
                 // Create a retreat for each dislodged unit.
                 // TODO check valid retreats and disbands
                 logger.Log(3, "Creating retreat for {0}", order.Unit);
-                var validRetreats = order.Unit.Location.Adjacents
+                var validRetreats = world.Map.GetLocation(order.Unit).Adjacents
                     .Select(loc => (future, loc))
                     .ToList();
                 RetreatingUnit retreat = new(order.Unit, validRetreats);
@@ -386,11 +384,11 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         }
 
         // Record the adjudication results to the season's order history
-        Dictionary<Season, OrderHistory> newHistory = new();
+        Dictionary<string, OrderHistory> newHistory = [];
         foreach (UnitOrder unitOrder in decisions.OfType<IsDislodged>().Select(d => d.Order))
         {
-            newHistory.Ensure(unitOrder.Unit.Season, () => new());
-            OrderHistory history = newHistory[unitOrder.Unit.Season];
+            newHistory.Ensure(unitOrder.Unit.Season.Designation, () => new());
+            OrderHistory history = newHistory[unitOrder.Unit.Season.Designation];
             // TODO does this add every order to every season??
             history.Orders.Add(unitOrder);
             history.IsDislodgedOutcomes[unitOrder.Unit] = dislodges[unitOrder.Unit].Outcome == true;
@@ -401,7 +399,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         }
 
         // Log the new order history
-        foreach ((Season season, OrderHistory history) in newHistory)
+        foreach ((string season, OrderHistory history) in newHistory)
         {
             string verb = world.OrderHistory.ContainsKey(season) ? "Updating" : "Adding";
             logger.Log(1, "{0} history for {1}", verb, season);
@@ -411,7 +409,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
             }
         }
 
-        IEnumerable<KeyValuePair<Season, OrderHistory>> updatedHistory = world.OrderHistory
+        IEnumerable<KeyValuePair<string, OrderHistory>> updatedHistory = world.OrderHistory
             .Where(kvp => !newHistory.ContainsKey(kvp.Key))
             .Concat(newHistory);
 
@@ -486,7 +484,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         bool progress = false;
 
         // A season at the head of a timeline always advances.
-        if (!decision.Season.Futures.Any())
+        if (!world.GetFutures(decision.Season).Any())
         {
             progress |= LoggedUpdate(decision, true, depth, "A timeline head always advances");
             return progress;
@@ -496,7 +494,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         IEnumerable<MoveOrder> newIncomingMoves = decision.Orders
             .OfType<MoveOrder>()
             .Where(order => order.Season == decision.Season
-                && !world.OrderHistory[order.Season].DoesMoveOutcomes.ContainsKey(order));
+                && !world.OrderHistory[order.Season.Designation].DoesMoveOutcomes.ContainsKey(order));
         foreach (MoveOrder moveOrder in newIncomingMoves)
         {
             DoesMove doesMove = decisions.DoesMove[moveOrder];
@@ -513,7 +511,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         // 1. The outcome of a dislodge decision is changed,
         // 2. The outcome of an intra-timeline move decision is changed, or
         // 3. The outcome of an inter-timeline move decision with that season as the destination is changed.
-        OrderHistory history = world.OrderHistory[decision.Season];
+        OrderHistory history = world.OrderHistory[decision.Season.Designation];
         bool anyUnresolved = false;
         foreach (UnitOrder order in decision.Orders)
         {
@@ -635,11 +633,11 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
 
         // If the origin and destination are adjacent, then there is a path.
         if (// Map adjacency
-            decision.Order.Unit.Location.Adjacents.Contains(decision.Order.Location)
+            world.Map.GetLocation(decision.Order.Unit).Adjacents.Contains(decision.Order.Location)
             // Turn adjacency
             && Math.Abs(decision.Order.Unit.Season.Turn - decision.Order.Season.Turn) <= 1
             // Timeline adjacency
-            && decision.Order.Unit.Season.InAdjacentTimeline(decision.Order.Season))
+            && world.InAdjacentTimeline(decision.Order.Unit.Season, decision.Order.Season))
         {
             bool update = LoggedUpdate(decision, true, depth, "Adjacent move");
             return progress | update;

MultiversalDiplomacy/Adjudicate/PathFinder.cs

@@ -30,13 +30,13 @@ public static class PathFinder
         // also have coasts, and between those coasts there is a path of adjacent sea provinces
         // (not coastal) that are occupied by fleets. The move order is valid even if the fleets
         // belong to another power or were not given convoy orders; it will simply fail.
-        IDictionary<(Location location, Season season), Unit> fleets = world.Units
+        IDictionary<(string location, Season season), Unit> fleets = world.Units
             .Where(unit => unit.Type == UnitType.Fleet)
             .ToDictionary(unit => (unit.Location, unit.Season));
 
         // Verify that the origin is a coastal province.
-        if (movingUnit.Location.Type != LocationType.Land) return false;
-        IEnumerable<Location> originCoasts = movingUnit.Province.Locations
+        if (world.Map.GetLocation(movingUnit).Type != LocationType.Land) return false;
+        IEnumerable<Location> originCoasts = world.Map.GetLocation(movingUnit).Province.Locations
             .Where(location => location.Type == LocationType.Water);
         if (!originCoasts.Any()) return false;
 
@@ -60,7 +60,7 @@ public static class PathFinder
             (Location currentLocation, Season currentSeason) = toVisit.Dequeue();
             visited.Add((currentLocation, currentSeason));
 
-            var adjacents = GetAdjacentPoints(currentLocation, currentSeason);
+            var adjacents = GetAdjacentPoints(world, currentLocation, currentSeason);
             foreach ((Location adjLocation, Season adjSeason) in adjacents)
             {
                 // If the destination is adjacent, then a path exists.
@@ -69,7 +69,7 @@ public static class PathFinder
                 // If not, add this location to the to-visit set if it isn't a coast, has a fleet,
                 // and hasn't already been visited.
                 if (!adjLocation.Province.Locations.Any(l => l.Type == LocationType.Land)
-                    && fleets.ContainsKey((adjLocation, adjSeason))
+                    && fleets.ContainsKey((adjLocation.Designation, adjSeason))
                     && !visited.Contains((adjLocation, adjSeason)))
                 {
                     toVisit.Enqueue((adjLocation, adjSeason));
@@ -81,11 +81,11 @@ public static class PathFinder
         return false;
     }
 
-    private static List<(Location, Season)> GetAdjacentPoints(Location location, Season season)
+    private static List<(Location, Season)> GetAdjacentPoints(World world, Location location, Season season)
     {
-        List<(Location, Season)> adjacentPoints = new();
+        List<(Location, Season)> adjacentPoints = [];
         List<Location> adjacentLocations = location.Adjacents.ToList();
-        List<Season> adjacentSeasons = season.GetAdjacentSeasons().ToList();
+        List<Season> adjacentSeasons = GetAdjacentSeasons(world, season).ToList();
 
         foreach (Location adjacentLocation in adjacentLocations)
         {
@@ -105,4 +105,56 @@ public static class PathFinder
 
         return adjacentPoints;
     }
+
+    /// <summary>
+    /// Returns all seasons that are adjacent to a season.
+    /// </summary>
+    public static IEnumerable<Season> GetAdjacentSeasons(World world, Season season)
+    {
+        List<Season> adjacents = [];
+
+        // The immediate past and all immediate futures are adjacent.
+        if (season.Past != null) adjacents.Add(world.GetSeason(season.Past));
+        adjacents.AddRange(world.GetFutures(season));
+
+        // Find all adjacent timelines by finding all timelines that branched off of this season's
+        // timeline, i.e. all futures of this season's past that have different timelines. Also
+        // include any timelines that branched off of the timeline this timeline branched off from.
+        List<Season> adjacentTimelineRoots = [];
+        Season? current;
+        for (current = season;
+            current?.Past != null && world.GetSeason(current.Past).Timeline == current.Timeline;
+            current = world.GetSeason(current.Past))
+        {
+            adjacentTimelineRoots.AddRange(
+                world.GetFutures(current).Where(s => s.Timeline != current.Timeline));
+        }
+
+        // At the end of the for loop, if this season is part of the first timeline, then current
+        // is the root season (current.past == null); if this season is in a branched timeline,
+        // then current is the branch timeline's root season (current.past.timeline !=
+        // current.timeline). There are co-branches if this season is in a branched timeline, since
+        // the first timeline by definition cannot have co-branches.
+        if (current?.Past != null && world.GetSeason(current.Past) is Season past)
+        {
+            IEnumerable<Season> cobranchRoots = world
+                .GetFutures(past)
+                .Where(s => s.Timeline != current.Timeline && s.Timeline != past.Timeline);
+            adjacentTimelineRoots.AddRange(cobranchRoots);
+        }
+
+        // Walk up all alternate timelines to find seasons within one turn of this season.
+        foreach (Season timelineRoot in adjacentTimelineRoots)
+        {
+            for (Season? branchSeason = timelineRoot;
+                branchSeason != null && branchSeason.Turn <= season.Turn + 1;
+                branchSeason = world.GetFutures(branchSeason)
+                    .FirstOrDefault(s => s!.Timeline == branchSeason.Timeline, null))
+            {
+                if (branchSeason.Turn >= season.Turn - 1) adjacents.Add(branchSeason);
+            }
+        }
+
+        return adjacents;
+    }
 }

MultiversalDiplomacy/Model/Location.cs

@@ -1,3 +1,5 @@
+using System.Text.Json.Serialization;
+
 namespace MultiversalDiplomacy.Model;
 
 /// <summary>
@@ -9,17 +11,21 @@ public class Location
 {
     /// <summary>
     /// The province to which this location belongs.
+    /// </summary>
+    [JsonIgnore]
     public Province Province { get; }
 
+    public string ProvinceName => Province.Name;
+
     /// <summary>
     /// The location's full human-readable name.
     /// </summary>
-    public string? Name { get; }
+    public string Name { get; }
 
     /// <summary>
     /// The location's shorthand abbreviation.
     /// </summary>
-    public string? Abbreviation { get; }
+    public string Abbreviation { get; }
 
     /// <summary>
     /// The location's type.
@@ -29,10 +35,16 @@ public class Location
     /// <summary>
     /// The locations that border this location.
     /// </summary>
+    [JsonIgnore]
     public IEnumerable<Location> Adjacents => this.AdjacentList;
     private List<Location> AdjacentList { get; set; }
 
-    public Location(Province province, string? name, string? abbreviation, LocationType type)
+    /// <summary>
+    /// The unique name of this location in the map.
+    /// </summary>
+    public string Designation => $"{this.ProvinceName}/{this.Abbreviation}";
+
+    public Location(Province province, string name, string abbreviation, LocationType type)
     {
         this.Province = province;
         this.Name = name;
@@ -43,7 +55,7 @@ public class Location
 
     public override string ToString()
     {
-        return this.Name == null
+        return this.Name == "land" || this.Name == "water"
             ? $"{this.Province.Name} ({this.Type})"
             : $"{this.Province.Name} ({this.Type}:{this.Name}]";
     }

MultiversalDiplomacy/Model/Map.cs

@@ -0,0 +1,573 @@
+namespace MultiversalDiplomacy.Model;
+
+/// <summary>
+/// Encapsulation of the world map and playable powers constituting a Diplomacy variant.
+/// </summary>
+public class Map
+{
+    /// <summary>
+    /// The map type.
+    /// </summary>
+    public MapType Type { get; }
+
+    /// <summary>
+    /// The game map.
+    /// </summary>
+    public IReadOnlyCollection<Province> Provinces => _Provinces.AsReadOnly();
+
+    private List<Province> _Provinces { get; }
+
+    private Dictionary<string, Location> LocationLookup { get; }
+
+    /// <summary>
+    /// The game powers.
+    /// </summary>
+    public IReadOnlyCollection<Power> Powers => _Powers.AsReadOnly();
+
+    private List<Power> _Powers { get; }
+
+    private Map(MapType type, IEnumerable<Province> provinces, IEnumerable<Power> powers)
+    {
+        Type = type;
+        _Provinces = provinces.ToList();
+        _Powers = powers.ToList();
+
+        LocationLookup = Provinces
+            .SelectMany(province => province.Locations)
+            .ToDictionary(location => location.Designation);
+    }
+
+    /// <summary>
+    /// Get a province by name. Throws if the province is not found.
+    /// </summary>
+    public Province GetProvince(string provinceName)
+        => GetProvince(provinceName, this.Provinces);
+
+    /// <summary>
+    /// Get a province by name. Throws if the province is not found.
+    /// </summary>
+    private static Province GetProvince(string provinceName, IEnumerable<Province> provinces)
+        => provinces.SingleOrDefault(
+            p => p!.Name.Equals(provinceName, StringComparison.InvariantCultureIgnoreCase)
+                || p.Abbreviations.Any(
+                    a => a.Equals(provinceName, StringComparison.InvariantCultureIgnoreCase)),
+            null)
+            ?? throw new KeyNotFoundException($"Province {provinceName} not found");
+
+    /// <summary>
+    /// Get the location in a province matching a predicate. Throws if there is not exactly one
+    /// such location.
+    /// </summary>
+    private Location GetLocation(string provinceName, Func<Location, bool> predicate)
+        => GetProvince(provinceName).Locations.SingleOrDefault(
+            l => l != null && predicate(l), null)
+            ?? throw new KeyNotFoundException($"No such location in {provinceName}");
+
+    public Location GetLocation(string designation)
+        => LocationLookup[designation];
+
+    public Location GetLocation(Unit unit)
+        => GetLocation(unit.Location);
+
+    /// <summary>
+    /// Get the sole land location of a province.
+    /// </summary>
+    public Location GetLand(string provinceName)
+        => GetLocation(provinceName, l => l.Type == LocationType.Land);
+
+    /// <summary>
+    /// Get the sole water location of a province, optionally specifying a named coast.
+    /// </summary>
+    public Location GetWater(string provinceName, string? coastName = null)
+        => coastName == null
+            ? GetLocation(provinceName, l => l.Type == LocationType.Water)
+            : GetLocation(provinceName, l => l.Name == coastName || l.Abbreviation == coastName);
+
+    /// <summary>
+    /// Get a power by name. Throws if there is not exactly one such power.
+    /// </summary>
+    public Power GetPower(string powerName)
+        => Powers.SingleOrDefault(p => p!.Name == powerName || p.Name.StartsWith(powerName), null)
+            ?? throw new KeyNotFoundException($"Power {powerName} not found");
+
+    public static Map FromType(MapType type)
+        => type switch {
+            MapType.Test => Test,
+            MapType.Classical => Test,
+            _ => throw new NotImplementedException($"Unknown variant {type}"),
+        };
+
+    public static Map Test => _Test.Value;
+
+    private static readonly Lazy<Map> _Test = new(() => {
+        Province lef = Province.Time("Left", "Lef")
+            .AddLandLocation();
+        Province cen = Province.Empty("Center", "Cen")
+            .AddLandLocation();
+        Province rig = Province.Time("Right", "Rig")
+            .AddLandLocation();
+        Location center = cen.Locations.First();
+        center.AddBorder(lef.Locations.First());
+        center.AddBorder(rig.Locations.First());
+
+        Power a = new("Alpha");
+        Power b = new("Beta");
+
+        return new(MapType.Test, [lef, cen, rig], [a, b]);
+    });
+
+    public static Map Classical => _Classical.Value;
+
+    private static readonly Lazy<Map> _Classical = new(() => {
+        // Define the provinces of the standard world map.
+        List<Province> provinces =
+        [
+#region Provinces
+            Province.Empty("North Africa", "NAF")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Tunis", "TUN")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Bohemia", "BOH")
+                .AddLandLocation(),
+            Province.Supply("Budapest", "BUD")
+                .AddLandLocation(),
+            Province.Empty("Galacia", "GAL")
+                .AddLandLocation(),
+            Province.Supply("Trieste", "TRI")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Tyrolia", "TYR")
+                .AddLandLocation(),
+            Province.Time("Vienna", "VIE")
+                .AddLandLocation(),
+            Province.Empty("Albania", "ALB")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Bulgaria", "BUL")
+                .AddLandLocation()
+                .AddCoastLocation("east coast", "ec")
+                .AddCoastLocation("south coast", "sc"),
+            Province.Supply("Greece", "GRE")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Rumania", "RUM", "RMA")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Serbia", "SER")
+                .AddLandLocation(),
+            Province.Empty("Clyde", "CLY")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Edinburgh", "EDI")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Liverpool", "LVP", "LPL")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Time("London", "LON")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Wales", "WAL")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Yorkshire", "YOR")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Brest", "BRE")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Burgundy", "BUR")
+                .AddLandLocation(),
+            Province.Empty("Gascony", "GAS")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Marseilles", "MAR")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Time("Paris", "PAR")
+                .AddLandLocation(),
+            Province.Empty("Picardy", "PIC")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Time("Berlin", "BER")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Kiel", "KIE")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Munich", "MUN")
+                .AddLandLocation(),
+            Province.Empty("Prussia", "PRU")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Ruhr", "RUH", "RHR")
+                .AddLandLocation(),
+            Province.Empty("Silesia", "SIL")
+                .AddLandLocation(),
+            Province.Supply("Spain", "SPA")
+                .AddLandLocation()
+                .AddCoastLocation("north coast", "nc")
+                .AddCoastLocation("south coast", "sc"),
+            Province.Supply("Portugal", "POR")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Apulia", "APU")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Naples", "NAP")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Piedmont", "PIE")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Time("Rome", "ROM", "RME")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Tuscany", "TUS")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Venice", "VEN")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Belgium", "BEL")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Holland", "HOL")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Finland", "FIN")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Livonia", "LVN", "LVA")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Time("Moscow", "MOS")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Sevastopol", "SEV")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Saint Petersburg", "STP")
+                .AddLandLocation()
+                .AddCoastLocation("north coast", "nc")
+                .AddCoastLocation("west coast", "wc"),
+            Province.Empty("Ukraine", "UKR")
+                .AddLandLocation(),
+            Province.Supply("Warsaw", "WAR")
+                .AddLandLocation(),
+            Province.Supply("Denmark", "DEN")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Norway", "NWY")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Sweden", "SWE")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Ankara", "ANK")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Armenia", "ARM")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Time("Constantinople", "CON")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Supply("Smyrna", "SMY")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Syria", "SYR")
+                .AddLandLocation()
+                .AddOceanLocation(),
+            Province.Empty("Barents Sea", "BAR")
+                .AddOceanLocation(),
+            Province.Empty("English Channel", "ENC", "ECH")
+                .AddOceanLocation(),
+            Province.Empty("Heligoland Bight", "HEL", "HGB")
+                .AddOceanLocation(),
+            Province.Empty("Irish Sea", "IRS", "IRI")
+                .AddOceanLocation(),
+            Province.Empty("Mid-Atlantic Ocean", "MAO", "MID")
+                .AddOceanLocation(),
+            Province.Empty("North Atlantic Ocean", "NAO", "NAT")
+                .AddOceanLocation(),
+            Province.Empty("North Sea", "NTH", "NTS")
+                .AddOceanLocation(),
+            Province.Empty("Norwegian Sea", "NWS", "NWG")
+                .AddOceanLocation(),
+            Province.Empty("Skagerrak", "SKA", "SKG")
+                .AddOceanLocation(),
+            Province.Empty("Baltic Sea", "BAL")
+                .AddOceanLocation(),
+            Province.Empty("Guld of Bothnia", "GOB", "BOT")
+                .AddOceanLocation(),
+            Province.Empty("Adriatic Sea", "ADS", "ADR")
+                .AddOceanLocation(),
+            Province.Empty("Aegean Sea", "AEG")
+                .AddOceanLocation(),
+            Province.Empty("Black Sea", "BLA")
+                .AddOceanLocation(),
+            Province.Empty("Eastern Mediterranean Sea", "EMS", "EAS")
+                .AddOceanLocation(),
+            Province.Empty("Gulf of Lyons", "GOL", "LYO")
+                .AddOceanLocation(),
+            Province.Empty("Ionian Sea", "IOS", "ION", "INS")
+                .AddOceanLocation(),
+            Province.Empty("Tyrrhenian Sea", "TYS", "TYN")
+                .AddOceanLocation(),
+            Province.Empty("Western Mediterranean Sea", "WMS", "WES")
+                .AddOceanLocation(),
+#endregion
+        ];
+
+        // Declare some helpers for border definitions
+        Location Land(string provinceName) => GetProvince(provinceName, provinces)
+            .Locations.Single(l => l.Type == LocationType.Land);
+        Location Water(string provinceName) => GetProvince(provinceName, provinces)
+            .Locations.Single(l => l.Type == LocationType.Water);
+        Location Coast(string provinceName, string coastName)
+            => GetProvince(provinceName, provinces)
+                .Locations.Single(l => l.Name == coastName || l.Abbreviation == coastName);
+
+        static void AddBordersTo(Location location, Func<string, Location> LocationType, params string[] borders)
+        {
+            foreach (string bordering in borders)
+            {
+                location.AddBorder(LocationType(bordering));
+            }
+        }
+        void AddBorders(string provinceName, Func<string, Location> LocationType, params string[] borders)
+            => AddBordersTo(LocationType(provinceName), LocationType, borders);
+
+#region Borders
+        AddBorders("NAF", Land, "TUN");
+        AddBorders("NAF", Water, "MAO", "WES", "TUN");
+
+        AddBorders("TUN", Land, "NAF");
+        AddBorders("TUN", Water, "NAF", "WES", "TYS", "ION");
+
+        AddBorders("BOH", Land, "MUN", "SIL", "GAL", "VIE", "TYR");
+
+        AddBorders("BUD", Land, "VIE", "GAL", "RUM", "SER", "TRI");
+
+        AddBorders("GAL", Land, "BOH", "SIL", "WAR", "UKR", "RUM", "BUD", "VIE");
+
+        AddBorders("TRI", Land, "TYR", "VIE", "BUD", "SER", "ALB");
+        AddBorders("TRI", Water, "ALB", "ADR", "VEN");
+
+        AddBorders("TYR", Land, "MUN", "BOH", "VIE", "TRI", "VEN", "PIE");
+
+        AddBorders("VIE", Land, "TYR", "BOH", "GAL", "BUD", "TRI");
+
+        AddBorders("ALB", Land, "TRI", "SER", "GRE");
+        AddBorders("ALB", Water, "TRI", "ADR", "ION", "GRE");
+
+        AddBorders("BUL", Land, "GRE", "SER", "RUM", "CON");
+        AddBordersTo(Coast("BUL", "ec"), Water, "BLA", "CON");
+        AddBordersTo(Coast("BUL", "sc"), Water, "CON", "AEG", "GRE");
+
+        AddBorders("GRE", Land, "ALB", "SER", "BUL");
+        AddBorders("GRE", Water, "ALB", "ION", "AEG");
+        Water("GRE").AddBorder(Coast("BUL", "sc"));
+
+        AddBorders("RUM", Land, "BUL", "SER", "BUD", "GAL", "UKR", "SEV");
+        AddBorders("RUM", Water, "SEV", "BLA");
+        Water("RUM").AddBorder(Coast("BUL", "ec"));
+
+        AddBorders("SER", Land, "BUD", "RUM", "BUL", "GRE", "ALB", "TRI");
+
+        AddBorders("CLY", Land, "EDI", "LVP");
+        AddBorders("CLY", Water, "LVP", "NAO", "NWG", "EDI");
+
+        AddBorders("EDI", Land, "YOR", "LVP", "CLY");
+        AddBorders("EDI", Water, "CLY", "NWG", "NTH", "YOR");
+
+        AddBorders("LVP", Land, "CLY", "EDI", "YOR", "WAL");
+        AddBorders("LVP", Water, "WAL", "IRS", "NAO", "CLY");
+
+        AddBorders("LON", Land, "WAL", "YOR");
+        AddBorders("LON", Water, "WAL", "ENC", "NTH", "YOR");
+
+        AddBorders("WAL", Land, "LVP", "YOR", "LON");
+        AddBorders("WAL", Water, "LON", "ENC", "IRS", "LVP");
+
+        AddBorders("YOR", Land, "LON", "WAL", "LVP", "EDI");
+        AddBorders("YOR", Water, "EDI", "NTH", "LON");
+
+        AddBorders("BRE", Land, "PIC", "PAR", "GAS");
+        AddBorders("BRE", Water, "GAS", "MAO", "ENC", "PIC");
+
+        AddBorders("BUR", Land, "BEL", "RUH", "MUN", "MAR", "GAS", "PAR", "PIC");
+
+        AddBorders("GAS", Land, "BRE", "PAR", "BUR", "MAR", "SPA");
+        AddBorders("GAS", Water, "MAO", "BRE");
+        Water("GAS").AddBorder(Coast("SPA", "nc"));
+
+        AddBorders("MAR", Land, "SPA", "GAS", "BUR", "PIE");
+        AddBorders("MAR", Water, "LYO", "PIE");
+        Water("MAR").AddBorder(Coast("SPA", "sc"));
+
+        AddBorders("PAR", Land, "PIC", "BUR", "GAS", "BRE");
+
+        AddBorders("PIC", Land, "BEL", "BUR", "PAR", "BRE");
+        AddBorders("PIC", Water, "BRE", "ENC", "BEL");
+
+        AddBorders("BER", Land, "PRU", "SIL", "MUN", "KIE");
+        AddBorders("BER", Water, "KIE", "BAL", "PRU");
+
+        AddBorders("KIE", Land, "BER", "MUN", "RUH", "HOL", "DEN");
+        AddBorders("KIE", Water, "HOL", "HEL", "DEN", "BAL", "BER");
+
+        AddBorders("MUN", Land, "BUR", "RUH", "KIE", "BER", "SIL", "BOH", "TYR");
+
+        AddBorders("PRU", Land, "LVN", "WAR", "SIL", "BER");
+        AddBorders("PRU", Water, "BER", "BAL", "LVN");
+
+        AddBorders("RUH", Land, "KIE", "MUN", "BUR", "BEL", "HOL");
+
+        AddBorders("SIL", Land, "PRU", "WAR", "GAL", "BOH", "MUN", "BER");
+
+        AddBorders("SPA", Land, "POR", "GAS", "MAR");
+        AddBordersTo(Coast("SPA", "nc"), Water, "POR", "MAO", "GAS");
+        AddBordersTo(Coast("SPA", "sc"), Water, "POR", "MAO", "WES", "LYO", "MAR");
+
+        AddBorders("POR", Land, "SPA");
+        AddBorders("POR", Water, "MAO");
+        Water("POR").AddBorder(Coast("SPA", "nc"));
+        Water("POR").AddBorder(Coast("SPA", "sc"));
+
+        AddBorders("APU", Land, "NAP", "ROM", "VEN");
+        AddBorders("APU", Water, "VEN", "ADR", "IOS", "NAP");
+
+        AddBorders("NAP", Land, "ROM", "APU");
+        AddBorders("NAP", Water, "APU", "IOS", "TYS", "ROM");
+
+        AddBorders("PIE", Land, "MAR", "TYR", "VEN", "TUS");
+        AddBorders("PIE", Water, "TUS", "LYO", "MAR");
+
+        AddBorders("ROM", Land, "TUS", "VEN", "APU", "NAP");
+        AddBorders("ROM", Water, "NAP", "TYS", "TUS");
+
+        AddBorders("TUS", Land, "PIE", "VEN", "ROM");
+        AddBorders("TUS", Water, "ROM", "TYS", "LYO", "PIE");
+
+        AddBorders("VEN", Land, "APU", "ROM", "TUS", "PIE", "TYR", "TRI");
+        AddBorders("VEN", Water, "TRI", "ADR", "APU");
+
+        AddBorders("BEL", Land, "HOL", "RUH", "BUR", "PIC");
+        AddBorders("BEL", Water, "PIC", "ENC", "NTH", "HOL");
+
+        AddBorders("HOL", Land, "BEL", "RUH", "KIE");
+        AddBorders("HOL", Water, "NTH", "HEL");
+
+        AddBorders("FIN", Land, "SWE", "NWY", "STP");
+        AddBorders("FIN", Water, "SWE", "BOT");
+        Water("FIN").AddBorder(Coast("STP", "wc"));
+
+        AddBorders("LVN", Land, "STP", "MOS", "WAR", "PRU");
+        AddBorders("LVN", Water, "PRU", "BAL", "BOT");
+        Water("LVN").AddBorder(Coast("STP", "wc"));
+
+        AddBorders("MOS", Land, "SEV", "UKR", "WAR", "LVN", "STP");
+
+        AddBorders("SEV", Land, "RUM", "UKR", "MOS", "ARM");
+        AddBorders("SEV", Water, "ARM", "BLA", "RUM");
+
+        AddBorders("STP", Land, "MOS", "LVN", "FIN");
+        AddBordersTo(Coast("STP", "nc"), Water, "BAR", "NWY");
+        AddBordersTo(Coast("STP", "wc"), Water, "LVN", "BOT", "FIN");
+
+        AddBorders("UKR", Land, "MOS", "SEV", "RUM", "GAL", "WAR");
+
+        AddBorders("WAR", Land, "PRU", "LVN", "MOS", "UKR", "GAL", "SIL");
+
+        AddBorders("DEN", Land, "KIE", "SWE");
+        AddBorders("DEN", Water, "KIE", "HEL", "NTH", "SKA", "BAL", "SWE");
+
+        AddBorders("NWY", Land, "STP", "FIN", "SWE");
+        AddBorders("NWY", Water, "BAR", "NWG", "NTH", "SKA", "SWE");
+        Water("NWY").AddBorder(Coast("STP", "nc"));
+
+        AddBorders("SWE", Land, "NWY", "FIN", "DEN");
+        AddBorders("SWE", Water, "FIN", "BOT", "BAL", "DEN", "SKA", "NWY");
+
+        AddBorders("ANK", Land, "ARM", "SMY", "CON");
+        AddBorders("ANK", Water, "CON", "BLA", "ARM");
+
+        AddBorders("ARM", Land, "SEV", "SYR", "SMY", "ANK");
+        AddBorders("ARM", Water, "ANK", "BLA", "SEV");
+
+        AddBorders("CON", Land, "BUL", "ANK", "SMY");
+        AddBorders("CON", Water, "BLA", "ANK", "SMY", "AEG");
+        Water("CON").AddBorder(Coast("BUL", "ec"));
+        Water("CON").AddBorder(Coast("BUL", "sc"));
+
+        AddBorders("SMY", Land, "CON", "ANK", "ARM", "SYR");
+        AddBorders("SMY", Water, "SYR", "EAS", "AEG", "CON");
+
+        AddBorders("SYR", Land, "SMY", "ARM");
+        AddBorders("SYR", Water, "EAS", "SMY");
+
+        AddBorders("BAR", Water, "NWG", "NWY");
+        Water("BAR").AddBorder(Coast("STP", "nc"));
+
+        AddBorders("ENC", Water, "LON", "NTH", "BEL", "PIC", "BRE", "MAO", "IRS", "WAL");
+
+        AddBorders("HEL", Water, "NTH", "DEN", "BAL", "KIE", "HOL");
+
+        AddBorders("IRS", Water, "NAO", "LVP", "WAL", "ENC", "MAO");
+
+        AddBorders("MAO", Water, "NAO", "IRS", "ENC", "BRE", "GAS", "POR", "NAF");
+        Water("MAO").AddBorder(Coast("SPA", "nc"));
+        Water("MAO").AddBorder(Coast("SPA", "sc"));
+
+        AddBorders("NAO", Water, "NWG", "CLY", "LVP", "IRS", "MAO");
+
+        AddBorders("NTH", Water, "NWG", "NWY", "SKA", "DEN", "HEL", "HOL", "BEL", "ENC", "LON", "YOR", "EDI");
+
+        AddBorders("NWG", Water, "BAR", "NWY", "NTH", "EDI", "CLY", "NAO");
+
+        AddBorders("SKA", Water, "NWY", "SWE", "BAL", "DEN", "NTH");
+
+        AddBorders("BAL", Water, "BOT", "LVN", "PRU", "BER", "KIE", "HEL", "DEN", "SWE");
+
+        AddBorders("BOT", Water, "LVN", "BAL", "SWE", "FIN");
+        Water("BOT").AddBorder(Coast("STP", "wc"));
+
+        AddBorders("ADR", Water, "IOS", "APU", "VEN", "TRI", "ALB");
+
+        AddBorders("AEG", Water, "CON", "SMY", "EAS", "IOS", "GRE");
+        Water("AEG").AddBorder(Coast("BUL", "sc"));
+
+        AddBorders("BLA", Water, "RUM", "SEV", "ARM", "ANK", "CON");
+        Water("BLA").AddBorder(Coast("BUL", "ec"));
+
+        AddBorders("EAS", Water, "IOS", "AEG", "SMY", "SYR");
+
+        AddBorders("LYO", Water, "MAR", "PIE", "TUS", "TYS", "WES");
+        Water("LYO").AddBorder(Coast("SPA", "sc"));
+
+        AddBorders("IOS", Water, "TUN", "TYS", "NAP", "APU", "ADR", "ALB", "GRE", "AEG");
+
+        AddBorders("TYS", Water, "LYO", "TUS", "ROM", "NAP", "IOS", "TUN", "WES");
+
+        AddBorders("WES", Water, "LYO", "TYS", "TUN", "NAF", "MAO");
+        Water("WES").AddBorder(Coast("SPA", "sc"));
+#endregion
+
+        List<Power> powers =
+        [
+            new("Austria"),
+            new("England"),
+            new("France"),
+            new("Germany"),
+            new("Italy"),
+            new("Russia"),
+            new("Turkey"),
+        ];
+
+        return new(MapType.Classical, provinces, powers);
+    });
+}

MultiversalDiplomacy/Model/MapType.cs

@@ -0,0 +1,16 @@
+using System.Text.Json.Serialization;
+
+namespace MultiversalDiplomacy.Model;
+
+[JsonConverter(typeof(JsonStringEnumConverter<MapType>))]
+public enum MapType {
+    /// <summary>
+    /// A minimal test map.
+    /// </summary>
+    Test,
+
+    /// <summary>
+    /// The standard Diplomacy map.
+    /// </summary>
+    Classical,
+}

MultiversalDiplomacy/Model/ModelExtensions.cs

@@ -20,4 +20,10 @@ public static class ModelExtensions
     {
         return $"{coord.season.Timeline}-{coord.province.Abbreviations[0]}@{coord.season.Turn}";
     }
+
+    public static World ContinueOrFork(this World world, Season season, out Season future)
+    {
+        future = world.ContinueOrFork(season);
+        return world.Update(seasons: world.Seasons.Append(future));
+    }
 }

MultiversalDiplomacy/Model/OrderHistory.cs

@@ -13,7 +13,7 @@ public class OrderHistory
     public Dictionary<MoveOrder, bool> DoesMoveOutcomes;
 
     public OrderHistory()
-        : this(new(), new(), new())
+        : this([], [], [])
     {}
 
     public OrderHistory(

MultiversalDiplomacy/Model/Province.cs

@@ -37,7 +37,7 @@ public class Province
         this.Abbreviations = abbreviations;
         this.IsSupplyCenter = isSupply;
         this.IsTimeCenter = isTime;
-        this.LocationList = new List<Location>();
+        this.LocationList = [];
     }
 
     public override string ToString()
@@ -49,26 +49,26 @@ public class Province
     /// Create a new province with no supply center.
     /// </summary>
     public static Province Empty(string name, params string[] abbreviations)
-        => new Province(name, abbreviations, isSupply: false, isTime: false);
+        => new(name, abbreviations, isSupply: false, isTime: false);
 
     /// <summary>
     /// Create a new province with a supply center.
     /// </summary>
     public static Province Supply(string name, params string[] abbreviations)
-        => new Province(name, abbreviations, isSupply: true, isTime: false);
+        => new(name, abbreviations, isSupply: true, isTime: false);
 
     /// <summary>
     /// Create a new province with a time center.
     /// </summary>
     public static Province Time(string name, params string[] abbreviations)
-        => new Province(name, abbreviations, isSupply: true, isTime: true);
+        => new(name, abbreviations, isSupply: true, isTime: true);
 
     /// <summary>
     /// Create a new land location in this province.
     /// </summary>
     public Province AddLandLocation()
     {
-        Location location = new Location(this, name: null, abbreviation: null, LocationType.Land);
+        Location location = new(this, "land", "l", LocationType.Land);
         this.LocationList.Add(location);
         return this;
     }
@@ -78,19 +78,7 @@ public class Province
     /// </summary>
     public Province AddOceanLocation()
     {
-        Location location = new Location(this, name: null, abbreviation: null, LocationType.Water);
-        this.LocationList.Add(location);
-        return this;
-    }
-
-    /// <summary>
-    /// Create a new coastal location. Coastal locations must have names to disambiguate them
-    /// from the single land location in coastal provinces.
-    /// </summary>
-    public Province AddCoastLocation()
-    {
-        // Use a default name for provinces with only one coastal location
-        Location location = new Location(this, "coast", "c", LocationType.Water);
+        Location location = new(this, "water", "w", LocationType.Water);
         this.LocationList.Add(location);
         return this;
     }
@@ -101,7 +89,7 @@ public class Province
     /// </summary>
     public Province AddCoastLocation(string name, string abbreviation)
     {
-        Location location = new Location(this, name, abbreviation, LocationType.Water);
+        Location location = new(this, name, abbreviation, LocationType.Water);
         this.LocationList.Add(location);
         return this;
     }

MultiversalDiplomacy/Model/Season.cs

@@ -1,185 +1,41 @@
+using System.Text.Json.Serialization;
+
 namespace MultiversalDiplomacy.Model;
 
 /// <summary>
 /// Represents a state of the map produced by a set of move orders on a previous season.
 /// </summary>
-public class Season
+public class Season(string? past, int turn, string timeline)
 {
     /// <summary>
-    /// A shared counter for handing out new timeline numbers.
-    /// </summary>
-    private class TimelineFactory
-    {
-        private int nextTimeline = 0;
-
-        public int NextTimeline() => nextTimeline++;
-    }
-
-    /// <summary>
-    /// The first turn number.
+    /// The first turn number. This is defined to reduce confusion about whether the first turn is 0 or 1.
     /// </summary>
     public const int FIRST_TURN = 0;
 
     /// <summary>
-    /// The season immediately preceding this season.
+    /// The designation of the season immediately preceding this season.
     /// If this season is an alternate timeline root, the past is from the origin timeline.
     /// The initial season does not have a past.
     /// </summary>
-    public Season? Past { get; }
+    public string? Past { get; } = past;
 
     /// <summary>
     /// The current turn, beginning at 0. Each season (spring and fall) is one turn.
     /// Phases that only occur after the fall phase occur when Turn % 2 == 1.
     /// The current year is (Turn / 2) + 1901.
     /// </summary>
-    public int Turn { get; }
+    public int Turn { get; } = turn;
 
     /// <summary>
     /// The timeline to which this season belongs.
     /// </summary>
-    public int Timeline { get; }
+    public string Timeline { get; } = timeline;
 
     /// <summary>
-    /// The season's spatial location as a turn-timeline tuple.
+    /// The multiversal designation of this season.
     /// </summary>
-    public (int Turn, int Timeline) Coord => (this.Turn, this.Timeline);
+    [JsonIgnore]
+    public string Designation => $"{this.Timeline}{this.Turn}";
 
-    /// <summary>
-    /// The shared timeline number generator.
-    /// </summary>
-    private TimelineFactory Timelines { get; }
-
-    /// <summary>
-    /// Future seasons created directly from this season.
-    /// </summary>
-    public IEnumerable<Season> Futures => this.FutureList;
-    private List<Season> FutureList { get; }
-
-    private Season(Season? past, int turn, int timeline, TimelineFactory factory)
-    {
-        this.Past = past;
-        this.Turn = turn;
-        this.Timeline = timeline;
-        this.Timelines = factory;
-        this.FutureList = new();
-
-        if (past != null)
-        {
-            past.FutureList.Add(this);
-        }
-    }
-
-    public override string ToString()
-    {
-        return $"{this.Timeline}@{this.Turn}";
-    }
-
-    /// <summary>
-    /// Create a root season at the beginning of time.
-    /// </summary>
-    public static Season MakeRoot()
-    {
-        TimelineFactory factory = new TimelineFactory();
-        return new Season(
-            past: null,
-            turn: FIRST_TURN,
-            timeline: factory.NextTimeline(),
-            factory: factory);
-    }
-
-    /// <summary>
-    /// Create a season immediately after this one in the same timeline.
-    /// </summary>
-    public Season MakeNext()
-        => new Season(this, this.Turn + 1, this.Timeline, this.Timelines);
-
-    /// <summary>
-    /// Create a season immediately after this one in a new timeline.
-    /// </summary>
-    public Season MakeFork()
-        => new Season(this, this.Turn + 1, this.Timelines.NextTimeline(), this.Timelines);
-
-    /// <summary>
-    /// Returns the first season in this season's timeline. The first season is the
-    /// root of the first timeline. The earliest season in each alternate timeline is
-    /// the root of that timeline.
-    /// </summary>
-    public Season TimelineRoot()
-        => this.Past != null && this.Timeline == this.Past.Timeline
-            ? this.Past.TimelineRoot()
-            : this;
-
-    /// <summary>
-    /// Returns whether this season is in an adjacent timeline to another season.
-    /// Seasons are considered to be in adjacent timelines if they are in the same timeline,
-    /// one is in a timeline that branched from the other's timeline, or both are in timelines
-    /// that branched from the same point.
-    /// </summary>
-    public bool InAdjacentTimeline(Season other)
-    {
-        // Timelines are adjacent to themselves. Early out in that case.
-        if (this.Timeline == other.Timeline) return true;
-
-        // If the timelines aren't identical, one of them isn't the initial trunk.
-        // They can still be adjacent if one of them branched off of the other, or
-        // if they both branched off of the same point.
-        Season thisRoot = this.TimelineRoot();
-        Season otherRoot = other.TimelineRoot();
-        return // One branched off the other
-                thisRoot.Past?.Timeline == other.Timeline
-            || otherRoot.Past?.Timeline == this.Timeline
-                // Both branched off of the same point
-            || thisRoot.Past == otherRoot.Past;
-    }
-
-    /// <summary>
-    /// Returns all seasons that are adjacent to this season.
-    /// </summary>
-    public IEnumerable<Season> GetAdjacentSeasons()
-    {
-        List<Season> adjacents = new();
-
-        // The immediate past and all immediate futures are adjacent.
-        if (this.Past != null) adjacents.Add(this.Past);
-        adjacents.AddRange(this.FutureList);
-
-        // Find all adjacent timelines by finding all timelines that branched off of this season's
-        // timeline, i.e. all futures of this season's past that have different timelines. Also
-        // include any timelines that branched off of the timeline this timeline branched off from.
-        List<Season> adjacentTimelineRoots = new();
-        Season? current;
-        for (current = this;
-            current?.Past?.Timeline != null && current.Past.Timeline == current.Timeline;
-            current = current.Past)
-        {
-            adjacentTimelineRoots.AddRange(
-                current.FutureList.Where(s => s.Timeline != current.Timeline));
-        }
-
-        // At the end of the for loop, if this season is part of the first timeline, then current
-        // is the root season (current.past == null); if this season is in a branched timeline,
-        // then current is the branch timeline's root season (current.past.timeline !=
-        // current.timeline). There are co-branches if this season is in a branched timeline, since
-        // the first timeline by definition cannot have co-branches.
-        if (current?.Past != null)
-        {
-            IEnumerable<Season> cobranchRoots = current.Past.FutureList
-                .Where(s => s.Timeline != current.Timeline && s.Timeline != current.Past.Timeline);
-            adjacentTimelineRoots.AddRange(cobranchRoots);
-        }
-
-        // Walk up all alternate timelines to find seasons within one turn of this season.
-        foreach (Season timelineRoot in adjacentTimelineRoots)
-        {
-            for (Season? branchSeason = timelineRoot;
-                branchSeason != null && branchSeason.Turn <= this.Turn + 1;
-                branchSeason = branchSeason.FutureList
-                    .FirstOrDefault(s => s!.Timeline == branchSeason.Timeline, null))
-            {
-                if (branchSeason.Turn >= this.Turn - 1) adjacents.Add(branchSeason);
-            }
-        }
-
-        return adjacents;
-    }
+    public override string ToString() => Designation;
 }

MultiversalDiplomacy/Model/TimelineFactory.cs

@@ -0,0 +1,55 @@
+using System.Text.Json.Serialization;
+
+namespace MultiversalDiplomacy.Model;
+
+/// <summary>
+/// A shared counter for handing out new timeline designations.
+/// </summary>
+[JsonConverter(typeof(TimelineFactoryJsonConverter))]
+public class TimelineFactory(int nextTimeline)
+{
+    private static readonly char[] Letters = [
+        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
+        'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
+        'u', 'v', 'w', 'x', 'y', 'z',
+    ];
+
+    /// <summary>
+    /// Convert a string timeline identifier to its serial number.
+    /// </summary>
+    /// <param name="timeline">Timeline identifier.</param>
+    /// <returns>Integer.</returns>
+    public static int StringToInt(string timeline)
+    {
+        int result = Array.IndexOf(Letters, timeline[0]);
+        for (int i = 1; i < timeline.Length; i++) {
+            // The result is incremented by one because timeline designations are not a true base26 system.
+            // The "ones digit" maps a-z 0-25, but the "tens digit" maps a to 1, so "10" (26) is "aa" and not "a0"
+            result = (result + 1) * 26;
+            result += Array.IndexOf(Letters, timeline[i]);
+        }
+        return result;
+    }
+
+    /// <summary>
+    /// Convert a timeline serial number to its string identifier.
+    /// </summary>
+    /// <param name="designation">Integer.</param>
+    /// <returns>Timeline identifier.</returns>
+    public static string IntToString(int designation) {
+        static int downshift(int i ) => (i - (i % 26)) / 26;
+        IEnumerable<char> result = [Letters[designation % 26]];
+        for (int remainder = downshift(designation); remainder > 0; remainder = downshift(remainder) - 1) {
+            // We subtract 1 after downshifting for the same reason we add 1 above after upshifting.
+            // 
+            result = result.Prepend(Letters[(remainder % 26 + 25) % 26]);
+        }
+        return new string(result.ToArray());
+    }
+
+    public TimelineFactory() : this(0) { }
+
+    public int nextTimeline = nextTimeline;
+
+    public string NextTimeline() => IntToString(nextTimeline++);
+}

MultiversalDiplomacy/Model/TimelineFactoryJsonConverter.cs

@@ -0,0 +1,13 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace MultiversalDiplomacy.Model;
+
+internal class TimelineFactoryJsonConverter : JsonConverter<TimelineFactory>
+{
+    public override TimelineFactory? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        => new(reader.GetInt32());
+
+    public override void Write(Utf8JsonWriter writer, TimelineFactory value, JsonSerializerOptions options)
+        => writer.WriteNumberValue(value.nextTimeline);
+}

MultiversalDiplomacy/Model/Unit.cs

@@ -8,17 +8,12 @@ public class Unit
     /// <summary>
     /// The previous iteration of a unit. This is null if the unit was just built.
     /// </summary>
-    public Unit? Past { get; }
+    public string? Past { get; }
 
     /// <summary>
     /// The location on the map where the unit is.
     /// </summary>
-    public Location Location { get; }
-
-    /// <summary>
-    /// The province where the unit is.
-    /// </summary>
-    public Province Province => this.Location.Province;
+    public string Location { get; }
 
     /// <summary>
     /// The season in time when the unit is.
@@ -36,11 +31,11 @@ public class Unit
     public UnitType Type { get; }
 
     /// <summary>
-    /// The unit's spatiotemporal location as a province-season tuple.
+    /// A unique designation for this unit.
     /// </summary>
-    public (Province province, Season season) Point => (this.Province, this.Season);
+    public string Designation => $"{Type.ToShort()} {Season.Timeline}-{Location}@{Season.Turn}";
 
-    private Unit(Unit? past, Location location, Season season, Power power, UnitType type)
+    private Unit(string? past, string location, Season season, Power power, UnitType type)
     {
         this.Past = past;
         this.Location = location;
@@ -50,20 +45,18 @@ public class Unit
     }
 
     public override string ToString()
-    {
-        return $"{this.Power.Name[0]} {this.Type.ToShort()} {(this.Province, this.Season).ToShort()}";
-    }
+        => $"{Power.Name[0]} {Type.ToShort()} {Season.Timeline}-{Location}@{Season.Turn}";
 
     /// <summary>
     /// Create a new unit. No validation is performed; the adjudicator should only call this
     /// method after accepting a build order.
     /// </summary>
-    public static Unit Build(Location location, Season season, Power power, UnitType type)
-        => new Unit(past: null, location, season, power, type);
+    public static Unit Build(string location, Season season, Power power, UnitType type)
+        => new(past: null, location, season, power, type);
 
     /// <summary>
     /// Advance this unit's timeline to a new location and season.
     /// </summary>
-    public Unit Next(Location location, Season season)
-        => new Unit(past: this, location, season, this.Power, this.Type);
+    public Unit Next(string location, Season season)
+        => new(past: this.Designation, location, season, this.Power, this.Type);
 }

MultiversalDiplomacy/Model/World.cs

@@ -1,6 +1,4 @@
-using System.Collections.ObjectModel;
-
-using MultiversalDiplomacy.Orders;
+using System.Text.Json.Serialization;
 
 namespace MultiversalDiplomacy.Model;
 
@@ -9,67 +7,116 @@ namespace MultiversalDiplomacy.Model;
 /// </summary>
 public class World
 {
+    /// <summary>
+    /// The map variant of the game.
+    /// </summary>
+    [JsonIgnore]
+    public Map Map { get; }
+
+    /// <summary>
+    /// The map variant of the game.
+    /// </summary>
+    /// <remarks>
+    /// While this is serialized to JSON, deserialization uses it to populate <see cref="Map"/>
+    /// </remarks>
+    public MapType MapType => this.Map.Type;
+
     /// <summary>
     /// The game map.
     /// </summary>
-    public ReadOnlyCollection<Province> Provinces { get; }
+    [JsonIgnore]
+    public IReadOnlyCollection<Province> Provinces => this.Map.Provinces;
 
     /// <summary>
     /// The game powers.
     /// </summary>
-    public ReadOnlyCollection<Power> Powers { get; }
+    [JsonIgnore]
+    public IReadOnlyCollection<Power> Powers => this.Map.Powers;
 
     /// <summary>
     /// The state of the multiverse.
     /// </summary>
-    public ReadOnlyCollection<Season> Seasons { get; }
+    public List<Season> Seasons { get; }
+
+    /// <summary>
+    /// Lookup for seasons by designation.
+    /// </summary>
+    [JsonIgnore]
+    public Dictionary<string, Season> SeasonLookup { get; }
 
     /// <summary>
     /// The first season of the game.
     /// </summary>
-    public Season RootSeason { get; }
+    [JsonIgnore]
+    public Season RootSeason => GetSeason("a0");
 
     /// <summary>
     /// All units in the multiverse.
     /// </summary>
-    public ReadOnlyCollection<Unit> Units { get; }
+    public List<Unit> Units { get; }
 
     /// <summary>
     /// All retreating units in the multiverse.
     /// </summary>
-    public ReadOnlyCollection<RetreatingUnit> RetreatingUnits { get; }
+    public List<RetreatingUnit> RetreatingUnits { get; }
 
     /// <summary>
     /// Orders given to units in each season.
     /// </summary>
-    public ReadOnlyDictionary<Season, OrderHistory> OrderHistory { get; }
+    public Dictionary<string, OrderHistory> OrderHistory { get; }
+
+    /// <summary>
+    /// The shared timeline number generator.
+    /// </summary>
+    public TimelineFactory Timelines { get; }
 
     /// <summary>
     /// Immutable game options.
     /// </summary>
     public Options Options { get; }
 
+    [JsonConstructor]
+    public World(
+        MapType mapType,
+        List<Season> seasons,
+        List<Unit> units,
+        List<RetreatingUnit> retreatingUnits,
+        Dictionary<string, OrderHistory> orderHistory,
+        TimelineFactory timelines,
+        Options options)
+    {
+        this.Map = Map.FromType(mapType);
+        this.Seasons = seasons;
+        this.Units = units;
+        this.RetreatingUnits = retreatingUnits;
+        this.OrderHistory = orderHistory;
+        this.Timelines = timelines;
+        this.Options = options;
+
+        this.SeasonLookup = new(Seasons.ToDictionary(season => $"{season.Timeline}{season.Turn}"));
+    }
+
     /// <summary>
     /// Create a new World, providing all state data.
     /// </summary>
     private World(
-        ReadOnlyCollection<Province> provinces,
-        ReadOnlyCollection<Power> powers,
-        ReadOnlyCollection<Season> seasons,
-        Season rootSeason,
-        ReadOnlyCollection<Unit> units,
-        ReadOnlyCollection<RetreatingUnit> retreatingUnits,
-        ReadOnlyDictionary<Season, OrderHistory> orderHistory,
+        Map map,
+        List<Season> seasons,
+        List<Unit> units,
+        List<RetreatingUnit> retreatingUnits,
+        Dictionary<string, OrderHistory> orderHistory,
+        TimelineFactory timelines,
         Options options)
     {
-        this.Provinces = provinces;
-        this.Powers = powers;
+        this.Map = map;
         this.Seasons = seasons;
-        this.RootSeason = rootSeason;
         this.Units = units;
         this.RetreatingUnits = retreatingUnits;
         this.OrderHistory = orderHistory;
+        this.Timelines = timelines;
         this.Options = options;
+
+        this.SeasonLookup = new(Seasons.ToDictionary(season => $"{season.Timeline}{season.Turn}"));
     }
 
     /// <summary>
@@ -77,21 +124,18 @@ public class World
     /// </summary>
     private World(
         World previous,
-        ReadOnlyCollection<Province>? provinces = null,
-        ReadOnlyCollection<Power>? powers = null,
-        ReadOnlyCollection<Season>? seasons = null,
-        ReadOnlyCollection<Unit>? units = null,
-        ReadOnlyCollection<RetreatingUnit>? retreatingUnits = null,
-        ReadOnlyDictionary<Season, OrderHistory>? orderHistory = null,
+        List<Season>? seasons = null,
+        List<Unit>? units = null,
+        List<RetreatingUnit>? retreatingUnits = null,
+        Dictionary<string, OrderHistory>? orderHistory = null,
         Options? options = null)
         : this(
-            provinces ?? previous.Provinces,
-            powers ?? previous.Powers,
+            previous.Map,
             seasons ?? previous.Seasons,
-            previous.RootSeason,  // Can't change the root season
             units ?? previous.Units,
             retreatingUnits ?? previous.RetreatingUnits,
             orderHistory ?? previous.OrderHistory,
+            previous.Timelines,
             options ?? previous.Options)
     {
     }
@@ -99,17 +143,16 @@ public class World
     /// <summary>
     /// Create a new world with specified provinces and powers and an initial season.
     /// </summary>
-    public static World WithMap(IEnumerable<Province> provinces, IEnumerable<Power> powers)
+    public static World WithMap(Map map)
     {
-        Season root = Season.MakeRoot();
+        TimelineFactory timelines = new();
         return new World(
-            new(provinces.ToList()),
-            new(powers.ToList()),
-            new(new List<Season> { root }),
-            root,
-            new(new List<Unit>()),
-            new(new List<RetreatingUnit>()),
-            new(new Dictionary<Season, OrderHistory>()),
+            map,
+            new([new(past: null, Season.FIRST_TURN, timelines.NextTimeline())]),
+            new([]),
+            new([]),
+            new(new Dictionary<string, OrderHistory>()),
+            timelines,
             new Options());
     }
 
@@ -117,14 +160,14 @@ public class World
     /// Create a new world with the standard Diplomacy provinces and powers.
     /// </summary>
     public static World WithStandardMap()
-        => WithMap(StandardProvinces, StandardPowers);
+        => WithMap(Map.Classical);
 
     public World Update(
         IEnumerable<Season>? seasons = null,
         IEnumerable<Unit>? units = null,
         IEnumerable<RetreatingUnit>? retreats = null,
-        IEnumerable<KeyValuePair<Season, OrderHistory>>? orders = null)
-        => new World(
+        IEnumerable<KeyValuePair<string, OrderHistory>>? orders = null)
+        => new(
             previous: this,
             seasons: seasons == null
                 ? this.Seasons
@@ -149,7 +192,7 @@ public class World
         IEnumerable<Unit> units = unitSpecs.Select(spec =>
         {
             string[] splits = spec.Split(' ', 4);
-            Power power = this.GetPower(splits[0]);
+            Power power = Map.GetPower(splits[0]);
             UnitType type = splits[1] switch
             {
                 "A" => UnitType.Army,
@@ -157,11 +200,11 @@ public class World
                 _ => throw new ApplicationException($"Unknown unit type {splits[1]}")
             };
             Location location = type == UnitType.Army
-                ? this.GetLand(splits[2])
+                ? Map.GetLand(splits[2])
                 : splits.Length == 3
-                    ? this.GetWater(splits[2])
-                    : this.GetWater(splits[2], splits[3]);
-            Unit unit = Unit.Build(location, this.RootSeason, power, type);
+                    ? Map.GetWater(splits[2])
+                    : Map.GetWater(splits[2], splits[3]);
+            Unit unit = Unit.Build(location.Designation, this.RootSeason, power, type);
             return unit;
         });
         return this.Update(units: units);
@@ -198,562 +241,99 @@ public class World
         );
     }
 
+    /// <summary>
+    /// Create a continuation of this season if it has no futures, otherwise create a fork.
+    /// </summary>
+    public Season ContinueOrFork(Season season)
+        => GetFutures(season).Any()
+        ? new(season.Designation, season.Turn + 1, Timelines.NextTimeline())
+        : new(season.Designation, season.Turn + 1, season.Timeline);
+
     /// <summary>
     /// A standard Diplomacy game setup.
     /// </summary>
-    public static World Standard => World
-        .WithStandardMap()
-        .AddStandardUnits();
-
-    /// <summary>
-    /// Get a province by name. Throws if the province is not found.
-    /// </summary>
-    private Province GetProvince(string provinceName)
-        => GetProvince(provinceName, this.Provinces);
-
-    /// <summary>
-    /// Get a province by name. Throws if the province is not found.
-    /// </summary>
-    private static Province GetProvince(string provinceName, IEnumerable<Province> provinces)
-    {
-        string provinceNameUpper = provinceName.ToUpperInvariant();
-        Province? foundProvince = provinces.SingleOrDefault(
-            p => p!.Name.ToUpperInvariant() == provinceNameUpper
-                || p.Abbreviations.Any(a => a.ToUpperInvariant() == provinceNameUpper),
-            null);
-        if (foundProvince == null) throw new KeyNotFoundException(
-            $"Province {provinceName} not found");
-        return foundProvince;
-    }
-
-    /// <summary>
-    /// Get the location in a province matching a predicate. Throws if there is not exactly one
-    /// such location.
-    /// </summary>
-    private Location GetLocation(string provinceName, Func<Location, bool> predicate)
-    {
-        Location? foundLocation = GetProvince(provinceName).Locations.SingleOrDefault(
-            l => l != null && predicate(l), null);
-        if (foundLocation == null) throw new KeyNotFoundException(
-            $"No such location in {provinceName}");
-        return foundLocation;
-    }
-
-    /// <summary>
-    /// Get the sole land location of a province.
-    /// </summary>
-    public Location GetLand(string provinceName)
-        => GetLocation(provinceName, l => l.Type == LocationType.Land);
-
-    /// <summary>
-    /// Get the sole water location of a province, optionally specifying a named coast.
-    /// </summary>
-    public Location GetWater(string provinceName, string? coastName = null)
-        => coastName == null
-            ? GetLocation(provinceName, l => l.Type == LocationType.Water)
-            : GetLocation(provinceName, l => l.Name == coastName || l.Abbreviation == coastName);
+    public static World Standard => WithStandardMap().AddStandardUnits();
 
     /// <summary>
     /// Get a season by coordinate. Throws if the season is not found.
     /// </summary>
-    public Season GetSeason(int turn, int timeline)
+    public Season GetSeason(string timeline, int turn)
+        => GetSeason($"{timeline}{turn}");
+
+    /// <summary>
+    /// Get a season by designation.
+    /// </summary>
+    public Season GetSeason(string designation)
+        => SeasonLookup[designation];
+
+    /// <summary>
+    /// Get all seasons that are immediate futures of a season.
+    /// </summary>
+    /// <param name="present">A season designation.</param>
+    /// <returns>The immediate futures of the designated season.</returns>
+    public IEnumerable<Season> GetFutures(string present)
+        => Seasons.Where(future => future.Past == present);
+
+    /// <summary>
+    /// Get all seasons that are immediate futures of a season.
+    /// </summary>
+    /// <param name="present">A season.</param>
+    /// <returns>The immediate futures of the season.</returns>
+    public IEnumerable<Season> GetFutures(Season present) => GetFutures(present.Designation);
+
+    /// <summary>
+    /// Returns the first season in this season's timeline. The first season is the
+    /// root of the first timeline. The earliest season in each alternate timeline is
+    /// the root of that timeline.
+    /// </summary>
+    public Season GetTimelineRoot(Season season)
     {
-        Season? foundSeason = this.Seasons.SingleOrDefault(
-            s => s!.Turn == turn && s.Timeline == timeline,
-            null);
-        if (foundSeason == null) throw new KeyNotFoundException(
-            $"Season {turn}:{timeline} not found");
-        return foundSeason;
+        if (season.Past is null) {
+            return season;
+        }
+        Season past = SeasonLookup[season.Past];
+        return season.Timeline == past.Timeline
+            ? GetTimelineRoot(past)
+            : season;
     }
 
     /// <summary>
-    /// Get a power by name. Throws if there is not exactly one such power.
+    /// Returns whether this season is in an adjacent timeline to another season.
+    /// Seasons are considered to be in adjacent timelines if they are in the same timeline,
+    /// one is in a timeline that branched from the other's timeline, or both are in timelines
+    /// that branched from the same point.
     /// </summary>
-    public Power GetPower(string powerName)
+    public bool InAdjacentTimeline(Season one, Season two)
     {
-        Power? foundPower = this.Powers.SingleOrDefault(
-            p => p!.Name == powerName || p.Name.StartsWith(powerName),
-            null);
-        if (foundPower == null) throw new KeyNotFoundException(
-            $"Power {powerName} not found");
-        return foundPower;
+        // Timelines are adjacent to themselves. Early out in that case.
+        if (one == two) return true;
+
+        // If the timelines aren't identical, one of them isn't the initial trunk.
+        // They can still be adjacent if one of them branched off of the other, or
+        // if they both branched off of the same point.
+        Season rootOne = GetTimelineRoot(one);
+        Season rootTwo = GetTimelineRoot(two);
+        bool oneForked = rootOne.Past != null && GetSeason(rootOne.Past).Timeline == two.Timeline;
+        bool twoForked = rootTwo.Past != null && GetSeason(rootTwo.Past).Timeline == one.Timeline;
+        bool bothForked = rootOne.Past == rootTwo.Past;
+        return oneForked || twoForked || bothForked;
     }
 
     /// <summary>
     /// Returns a unit in a province. Throws if there are duplicate units.
     /// </summary>
-    public Unit GetUnitAt(string provinceName, (int turn, int timeline)? seasonCoord = null)
+    public Unit GetUnitAt(string provinceName, Season? season = null)
     {
-        Province province = GetProvince(provinceName);
-        seasonCoord ??= (this.RootSeason.Turn, this.RootSeason.Timeline);
-        Season season = GetSeason(seasonCoord.Value.turn, seasonCoord.Value.timeline);
+        Province province = Map.GetProvince(provinceName);
+        season ??= RootSeason;
         Unit? foundUnit = this.Units.SingleOrDefault(
-            u => u!.Province == province && u.Season == season,
-            null);
-        if (foundUnit == null) throw new KeyNotFoundException(
-            $"Unit at {province} at {season} not found");
+            u => Map.GetLocation(u!).Province == province && u!.Season == season,
+            null)
+            ?? throw new KeyNotFoundException($"Unit at {province} at {season} not found");
         return foundUnit;
     }
 
-    /// <summary>
-    /// The standard Diplomacy provinces.
-    /// </summary>
-    public static ReadOnlyCollection<Province> StandardProvinces
-    {
-        get
-        {
-            // Define the provinces of the standard world map.
-            List<Province> standardProvinces = new List<Province>
-            {
-                Province.Empty("North Africa", "NAF")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Tunis", "TUN")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Bohemia", "BOH")
-                    .AddLandLocation(),
-                Province.Supply("Budapest", "BUD")
-                    .AddLandLocation(),
-                Province.Empty("Galacia", "GAL")
-                    .AddLandLocation(),
-                Province.Supply("Trieste", "TRI")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Tyrolia", "TYR")
-                    .AddLandLocation(),
-                Province.Time("Vienna", "VIE")
-                    .AddLandLocation(),
-                Province.Empty("Albania", "ALB")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Bulgaria", "BUL")
-                    .AddLandLocation()
-                    .AddCoastLocation("east coast", "ec")
-                    .AddCoastLocation("south coast", "sc"),
-                Province.Supply("Greece", "GRE")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Rumania", "RUM", "RMA")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Serbia", "SER")
-                    .AddLandLocation(),
-                Province.Empty("Clyde", "CLY")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Edinburgh", "EDI")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Liverpool", "LVP", "LPL")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Time("London", "LON")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Wales", "WAL")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Yorkshire", "YOR")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Brest", "BRE")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Burgundy", "BUR")
-                    .AddLandLocation(),
-                Province.Empty("Gascony", "GAS")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Marseilles", "MAR")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Time("Paris", "PAR")
-                    .AddLandLocation(),
-                Province.Empty("Picardy", "PIC")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Time("Berlin", "BER")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Kiel", "KIE")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Munich", "MUN")
-                    .AddLandLocation(),
-                Province.Empty("Prussia", "PRU")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Ruhr", "RUH", "RHR")
-                    .AddLandLocation(),
-                Province.Empty("Silesia", "SIL")
-                    .AddLandLocation(),
-                Province.Supply("Spain", "SPA")
-                    .AddLandLocation()
-                    .AddCoastLocation("north coast", "nc")
-                    .AddCoastLocation("south coast", "sc"),
-                Province.Supply("Portugal", "POR")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Apulia", "APU")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Naples", "NAP")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Piedmont", "PIE")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Time("Rome", "ROM", "RME")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Tuscany", "TUS")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Venice", "VEN")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Belgium", "BEL")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Holland", "HOL")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Finland", "FIN")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Livonia", "LVN", "LVA")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Time("Moscow", "MOS")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Sevastopol", "SEV")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Saint Petersburg", "STP")
-                    .AddLandLocation()
-                    .AddCoastLocation("north coast", "nc")
-                    .AddCoastLocation("west coast", "wc"),
-                Province.Empty("Ukraine", "UKR")
-                    .AddLandLocation(),
-                Province.Supply("Warsaw", "WAR")
-                    .AddLandLocation(),
-                Province.Supply("Denmark", "DEN")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Norway", "NWY")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Sweden", "SWE")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Ankara", "ANK")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Armenia", "ARM")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Time("Constantinople", "CON")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Supply("Smyrna", "SMY")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Syria", "SYR")
-                    .AddLandLocation()
-                    .AddCoastLocation(),
-                Province.Empty("Barents Sea", "BAR")
-                    .AddOceanLocation(),
-                Province.Empty("English Channel", "ENC", "ECH")
-                    .AddOceanLocation(),
-                Province.Empty("Heligoland Bight", "HEL", "HGB")
-                    .AddOceanLocation(),
-                Province.Empty("Irish Sea", "IRS", "IRI")
-                    .AddOceanLocation(),
-                Province.Empty("Mid-Atlantic Ocean", "MAO", "MID")
-                    .AddOceanLocation(),
-                Province.Empty("North Atlantic Ocean", "NAO", "NAT")
-                    .AddOceanLocation(),
-                Province.Empty("North Sea", "NTH", "NTS")
-                    .AddOceanLocation(),
-                Province.Empty("Norwegian Sea", "NWS", "NWG")
-                    .AddOceanLocation(),
-                Province.Empty("Skagerrak", "SKA", "SKG")
-                    .AddOceanLocation(),
-                Province.Empty("Baltic Sea", "BAL")
-                    .AddOceanLocation(),
-                Province.Empty("Guld of Bothnia", "GOB", "BOT")
-                    .AddOceanLocation(),
-                Province.Empty("Adriatic Sea", "ADS", "ADR")
-                    .AddOceanLocation(),
-                Province.Empty("Aegean Sea", "AEG")
-                    .AddOceanLocation(),
-                Province.Empty("Black Sea", "BLA")
-                    .AddOceanLocation(),
-                Province.Empty("Eastern Mediterranean Sea", "EMS", "EAS")
-                    .AddOceanLocation(),
-                Province.Empty("Gulf of Lyons", "GOL", "LYO")
-                    .AddOceanLocation(),
-                Province.Empty("Ionian Sea", "IOS", "ION", "INS")
-                    .AddOceanLocation(),
-                Province.Empty("Tyrrhenian Sea", "TYS", "TYN")
-                    .AddOceanLocation(),
-                Province.Empty("Western Mediterranean Sea", "WMS", "WES")
-                    .AddOceanLocation(),
-            };
-
-            // Declare some helpers for border definitions
-            Location Land(string provinceName) => GetProvince(provinceName, standardProvinces)
-                .Locations.Single(l => l.Type == LocationType.Land);
-            Location Water(string provinceName) => GetProvince(provinceName, standardProvinces)
-                .Locations.Single(l => l.Type == LocationType.Water);
-            Location Coast(string provinceName, string coastName)
-                => GetProvince(provinceName, standardProvinces)
-                    .Locations.Single(l => l.Name == coastName || l.Abbreviation == coastName);
-
-            static void AddBordersTo(Location location, Func<string, Location> LocationType, params string[] borders)
-            {
-                foreach (string bordering in borders)
-                {
-                    location.AddBorder(LocationType(bordering));
-                }
-            }
-            void AddBorders(string provinceName, Func<string, Location> LocationType, params string[] borders)
-                => AddBordersTo(LocationType(provinceName), LocationType, borders);
-
-            AddBorders("NAF", Land, "TUN");
-            AddBorders("NAF", Water, "MAO", "WES", "TUN");
-
-            AddBorders("TUN", Land, "NAF");
-            AddBorders("TUN", Water, "NAF", "WES", "TYS", "ION");
-
-            AddBorders("BOH", Land, "MUN", "SIL", "GAL", "VIE", "TYR");
-
-            AddBorders("BUD", Land, "VIE", "GAL", "RUM", "SER", "TRI");
-
-            AddBorders("GAL", Land, "BOH", "SIL", "WAR", "UKR", "RUM", "BUD", "VIE");
-
-            AddBorders("TRI", Land, "TYR", "VIE", "BUD", "SER", "ALB");
-            AddBorders("TRI", Water, "ALB", "ADR", "VEN");
-
-            AddBorders("TYR", Land, "MUN", "BOH", "VIE", "TRI", "VEN", "PIE");
-
-            AddBorders("VIE", Land, "TYR", "BOH", "GAL", "BUD", "TRI");
-
-            AddBorders("ALB", Land, "TRI", "SER", "GRE");
-            AddBorders("ALB", Water, "TRI", "ADR", "ION", "GRE");
-
-            AddBorders("BUL", Land, "GRE", "SER", "RUM", "CON");
-            AddBordersTo(Coast("BUL", "ec"), Water, "BLA", "CON");
-            AddBordersTo(Coast("BUL", "sc"), Water, "CON", "AEG", "GRE");
-
-            AddBorders("GRE", Land, "ALB", "SER", "BUL");
-            AddBorders("GRE", Water, "ALB", "ION", "AEG");
-            Water("GRE").AddBorder(Coast("BUL", "sc"));
-
-            AddBorders("RUM", Land, "BUL", "SER", "BUD", "GAL", "UKR", "SEV");
-            AddBorders("RUM", Water, "SEV", "BLA");
-            Water("RUM").AddBorder(Coast("BUL", "ec"));
-
-            AddBorders("SER", Land, "BUD", "RUM", "BUL", "GRE", "ALB", "TRI");
-
-            AddBorders("CLY", Land, "EDI", "LVP");
-            AddBorders("CLY", Water, "LVP", "NAO", "NWG", "EDI");
-
-            AddBorders("EDI", Land, "YOR", "LVP", "CLY");
-            AddBorders("EDI", Water, "CLY", "NWG", "NTH", "YOR");
-
-            AddBorders("LVP", Land, "CLY", "EDI", "YOR", "WAL");
-            AddBorders("LVP", Water, "WAL", "IRS", "NAO", "CLY");
-
-            AddBorders("LON", Land, "WAL", "YOR");
-            AddBorders("LON", Water, "WAL", "ENC", "NTH", "YOR");
-
-            AddBorders("WAL", Land, "LVP", "YOR", "LON");
-            AddBorders("WAL", Water, "LON", "ENC", "IRS", "LVP");
-
-            AddBorders("YOR", Land, "LON", "WAL", "LVP", "EDI");
-            AddBorders("YOR", Water, "EDI", "NTH", "LON");
-
-            AddBorders("BRE", Land, "PIC", "PAR", "GAS");
-            AddBorders("BRE", Water, "GAS", "MAO", "ENC", "PIC");
-
-            AddBorders("BUR", Land, "BEL", "RUH", "MUN", "MAR", "GAS", "PAR", "PIC");
-
-            AddBorders("GAS", Land, "BRE", "PAR", "BUR", "MAR", "SPA");
-            AddBorders("GAS", Water, "MAO", "BRE");
-            Water("GAS").AddBorder(Coast("SPA", "nc"));
-
-            AddBorders("MAR", Land, "SPA", "GAS", "BUR", "PIE");
-            AddBorders("MAR", Water, "LYO", "PIE");
-            Water("MAR").AddBorder(Coast("SPA", "sc"));
-
-            AddBorders("PAR", Land, "PIC", "BUR", "GAS", "BRE");
-
-            AddBorders("PIC", Land, "BEL", "BUR", "PAR", "BRE");
-            AddBorders("PIC", Water, "BRE", "ENC", "BEL");
-
-            AddBorders("BER", Land, "PRU", "SIL", "MUN", "KIE");
-            AddBorders("BER", Water, "KIE", "BAL", "PRU");
-
-            AddBorders("KIE", Land, "BER", "MUN", "RUH", "HOL", "DEN");
-            AddBorders("KIE", Water, "HOL", "HEL", "DEN", "BAL", "BER");
-
-            AddBorders("MUN", Land, "BUR", "RUH", "KIE", "BER", "SIL", "BOH", "TYR");
-
-            AddBorders("PRU", Land, "LVN", "WAR", "SIL", "BER");
-            AddBorders("PRU", Water, "BER", "BAL", "LVN");
-
-            AddBorders("RUH", Land, "KIE", "MUN", "BUR", "BEL", "HOL");
-
-            AddBorders("SIL", Land, "PRU", "WAR", "GAL", "BOH", "MUN", "BER");
-
-            AddBorders("SPA", Land, "POR", "GAS", "MAR");
-            AddBordersTo(Coast("SPA", "nc"), Water, "POR", "MAO", "GAS");
-            AddBordersTo(Coast("SPA", "sc"), Water, "POR", "MAO", "WES", "LYO", "MAR");
-
-            AddBorders("POR", Land, "SPA");
-            AddBorders("POR", Water, "MAO");
-            Water("POR").AddBorder(Coast("SPA", "nc"));
-            Water("POR").AddBorder(Coast("SPA", "sc"));
-
-            AddBorders("APU", Land, "NAP", "ROM", "VEN");
-            AddBorders("APU", Water, "VEN", "ADR", "IOS", "NAP");
-
-            AddBorders("NAP", Land, "ROM", "APU");
-            AddBorders("NAP", Water, "APU", "IOS", "TYS", "ROM");
-
-            AddBorders("PIE", Land, "MAR", "TYR", "VEN", "TUS");
-            AddBorders("PIE", Water, "TUS", "LYO", "MAR");
-
-            AddBorders("ROM", Land, "TUS", "VEN", "APU", "NAP");
-            AddBorders("ROM", Water, "NAP", "TYS", "TUS");
-
-            AddBorders("TUS", Land, "PIE", "VEN", "ROM");
-            AddBorders("TUS", Water, "ROM", "TYS", "LYO", "PIE");
-
-            AddBorders("VEN", Land, "APU", "ROM", "TUS", "PIE", "TYR", "TRI");
-            AddBorders("VEN", Water, "TRI", "ADR", "APU");
-
-            AddBorders("BEL", Land, "HOL", "RUH", "BUR", "PIC");
-            AddBorders("BEL", Water, "PIC", "ENC", "NTH", "HOL");
-
-            AddBorders("HOL", Land, "BEL", "RUH", "KIE");
-            AddBorders("HOL", Water, "NTH", "HEL");
-
-            AddBorders("FIN", Land, "SWE", "NWY", "STP");
-            AddBorders("FIN", Water, "SWE", "BOT");
-            Water("FIN").AddBorder(Coast("STP", "wc"));
-
-            AddBorders("LVN", Land, "STP", "MOS", "WAR", "PRU");
-            AddBorders("LVN", Water, "PRU", "BAL", "BOT");
-            Water("LVN").AddBorder(Coast("STP", "wc"));
-
-            AddBorders("MOS", Land, "SEV", "UKR", "WAR", "LVN", "STP");
-
-            AddBorders("SEV", Land, "RUM", "UKR", "MOS", "ARM");
-            AddBorders("SEV", Water, "ARM", "BLA", "RUM");
-
-            AddBorders("STP", Land, "MOS", "LVN", "FIN");
-            AddBordersTo(Coast("STP", "nc"), Water, "BAR", "NWY");
-            AddBordersTo(Coast("STP", "wc"), Water, "LVN", "BOT", "FIN");
-
-            AddBorders("UKR", Land, "MOS", "SEV", "RUM", "GAL", "WAR");
-
-            AddBorders("WAR", Land, "PRU", "LVN", "MOS", "UKR", "GAL", "SIL");
-
-            AddBorders("DEN", Land, "KIE", "SWE");
-            AddBorders("DEN", Water, "KIE", "HEL", "NTH", "SKA", "BAL", "SWE");
-
-            AddBorders("NWY", Land, "STP", "FIN", "SWE");
-            AddBorders("NWY", Water, "BAR", "NWG", "NTH", "SKA", "SWE");
-            Water("NWY").AddBorder(Coast("STP", "nc"));
-
-            AddBorders("SWE", Land, "NWY", "FIN", "DEN");
-            AddBorders("SWE", Water, "FIN", "BOT", "BAL", "DEN", "SKA", "NWY");
-
-            AddBorders("ANK", Land, "ARM", "SMY", "CON");
-            AddBorders("ANK", Water, "CON", "BLA", "ARM");
-
-            AddBorders("ARM", Land, "SEV", "SYR", "SMY", "ANK");
-            AddBorders("ARM", Water, "ANK", "BLA", "SEV");
-
-            AddBorders("CON", Land, "BUL", "ANK", "SMY");
-            AddBorders("CON", Water, "BLA", "ANK", "SMY", "AEG");
-            Water("CON").AddBorder(Coast("BUL", "ec"));
-            Water("CON").AddBorder(Coast("BUL", "sc"));
-
-            AddBorders("SMY", Land, "CON", "ANK", "ARM", "SYR");
-            AddBorders("SMY", Water, "SYR", "EAS", "AEG", "CON");
-
-            AddBorders("SYR", Land, "SMY", "ARM");
-            AddBorders("SYR", Water, "EAS", "SMY");
-
-            AddBorders("BAR", Water, "NWG", "NWY");
-            Water("BAR").AddBorder(Coast("STP", "nc"));
-
-            AddBorders("ENC", Water, "LON", "NTH", "BEL", "PIC", "BRE", "MAO", "IRS", "WAL");
-
-            AddBorders("HEL", Water, "NTH", "DEN", "BAL", "KIE", "HOL");
-
-            AddBorders("IRS", Water, "NAO", "LVP", "WAL", "ENC", "MAO");
-
-            AddBorders("MAO", Water, "NAO", "IRS", "ENC", "BRE", "GAS", "POR", "NAF");
-            Water("MAO").AddBorder(Coast("SPA", "nc"));
-            Water("MAO").AddBorder(Coast("SPA", "sc"));
-
-            AddBorders("NAO", Water, "NWG", "CLY", "LVP", "IRS", "MAO");
-
-            AddBorders("NTH", Water, "NWG", "NWY", "SKA", "DEN", "HEL", "HOL", "BEL", "ENC", "LON", "YOR", "EDI");
-
-            AddBorders("NWG", Water, "BAR", "NWY", "NTH", "EDI", "CLY", "NAO");
-
-            AddBorders("SKA", Water, "NWY", "SWE", "BAL", "DEN", "NTH");
-
-            AddBorders("BAL", Water, "BOT", "LVN", "PRU", "BER", "KIE", "HEL", "DEN", "SWE");
-
-            AddBorders("BOT", Water, "LVN", "BAL", "SWE", "FIN");
-            Water("BOT").AddBorder(Coast("STP", "wc"));
-
-            AddBorders("ADR", Water, "IOS", "APU", "VEN", "TRI", "ALB");
-
-            AddBorders("AEG", Water, "CON", "SMY", "EAS", "IOS", "GRE");
-            Water("AEG").AddBorder(Coast("BUL", "sc"));
-
-            AddBorders("BLA", Water, "RUM", "SEV", "ARM", "ANK", "CON");
-            Water("BLA").AddBorder(Coast("BUL", "ec"));
-
-            AddBorders("EAS", Water, "IOS", "AEG", "SMY", "SYR");
-
-            AddBorders("LYO", Water, "MAR", "PIE", "TUS", "TYS", "WES");
-            Water("LYO").AddBorder(Coast("SPA", "sc"));
-
-            AddBorders("IOS", Water, "TUN", "TYS", "NAP", "APU", "ADR", "ALB", "GRE", "AEG");
-
-            AddBorders("TYS", Water, "LYO", "TUS", "ROM", "NAP", "IOS", "TUN", "WES");
-
-            AddBorders("WES", Water, "LYO", "TYS", "TUN", "NAF", "MAO");
-            Water("WES").AddBorder(Coast("SPA", "sc"));
-
-            return new(standardProvinces);
-        }
-    }
-
-    /// <summary>
-    /// The standard Diplomacy powers.
-    /// </summary>
-    public static ReadOnlyCollection<Power> StandardPowers
-    {
-        get => new(new List<Power>
-        {
-            new Power("Austria"),
-            new Power("England"),
-            new Power("France"),
-            new Power("Germany"),
-            new Power("Italy"),
-            new Power("Russia"),
-            new Power("Turkey"),
-        });
-    }
+    public Unit GetUnitByDesignation(string designation)
+        => Units.SingleOrDefault(u => u!.Designation == designation, null)
+        ?? throw new KeyNotFoundException($"Unit {designation} not found");
 }

MultiversalDiplomacy/MultiversalDiplomacy.csproj

@@ -7,4 +7,10 @@
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleTo">
+      <_Parameter1>MultiversalDiplomacyTests</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
+
 </Project>

MultiversalDiplomacy/Orders/MoveOrder.cs

@@ -39,15 +39,6 @@ public class MoveOrder : UnitOrder
         return $"{this.Unit} -> {(this.Province, this.Season).ToShort()}";
     }
 
-    /// <summary>
-    /// Returns whether another move order is in a head-to-head battle with this order.
-    /// </summary>
-    public bool IsOpposing(MoveOrder other)
-        => this.Season == other.Unit.Season
-        && other.Season == this.Unit.Season
-        && this.Province == other.Unit.Province
-        && other.Province == this.Unit.Province;
-
     /// <summary>
     /// Returns whether another move order has the same destination as this order.
     /// </summary>

MultiversalDiplomacy/Orders/UnitOrder.cs

@@ -16,12 +16,4 @@ public abstract class UnitOrder : Order
     {
         this.Unit = unit;
     }
-
-    /// <summary>
-    /// Returns whether a move order is moving into this order's unit's province.
-    /// </summary>
-    public bool IsIncoming(MoveOrder other)
-        => this != other
-        && other.Season == this.Unit.Season
-        && other.Province == this.Unit.Province;
 }

MultiversalDiplomacyTests/MDATC_A.cs

@@ -14,12 +14,12 @@ public class TimeTravelTest
         TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);
 
         // Hold to move into the future, then move back into the past.
-        setup[(0, 0)]
+        setup[("a", 0)]
             .GetReference(out Season s0)
             ["Germany"]
                 .Army("Mun").Holds().GetReference(out var mun0)
             .Execute()
-        [(1, 0)]
+        [("a", 1)]
             .GetReference(out Season s1)
             ["Germany"]
                 .Army("Mun").MovesTo("Tyr", season: s0).GetReference(out var mun1);
@@ -41,17 +41,17 @@ public class TimeTravelTest
             Is.EqualTo(1),
             "Failed to fork timeline when unit moved in");
 
-        // Confirm that there is a unit in Tyr 1:1 originating from Mun 1:0
-        Season fork = world.GetSeason(1, 1);
-        Unit originalUnit = world.GetUnitAt("Mun", s0.Coord);
-        Unit aMun0 = world.GetUnitAt("Mun", s1.Coord);
-        Unit aTyr = world.GetUnitAt("Tyr", fork.Coord);
-        Assert.That(aTyr.Past, Is.EqualTo(mun1.Order.Unit));
-        Assert.That(aTyr.Past?.Past, Is.EqualTo(mun0.Order.Unit));
+        // Confirm that there is a unit in Tyr b1 originating from Mun a1
+        Season fork = world.GetSeason("b1");
+        Unit originalUnit = world.GetUnitAt("Mun", s0);
+        Unit aMun0 = world.GetUnitAt("Mun", s1);
+        Unit aTyr = world.GetUnitAt("Tyr", fork);
+        Assert.That(aTyr.Past, Is.EqualTo(mun1.Order.Unit.Designation));
+        Assert.That(world.GetUnitByDesignation(aTyr.Past!).Past, Is.EqualTo(mun0.Order.Unit.Designation));
 
-        // Confirm that there is a unit in Mun 1:1 originating from Mun 0:0
-        Unit aMun1 = world.GetUnitAt("Mun", fork.Coord);
-        Assert.That(aMun1.Past, Is.EqualTo(originalUnit));
+        // Confirm that there is a unit in Mun b1 originating from Mun a0
+        Unit aMun1 = world.GetUnitAt("Mun", fork);
+        Assert.That(aMun1.Past, Is.EqualTo(originalUnit.Designation));
     }
 
     [Test]
@@ -60,7 +60,7 @@ public class TimeTravelTest
         TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);
 
         // Fail to dislodge on the first turn, then support the move so it succeeds.
-        setup[(0, 0)]
+        setup[("a", 0)]
             .GetReference(out Season s0)
             ["Germany"]
                 .Army("Mun").MovesTo("Tyr").GetReference(out var mun0)
@@ -75,7 +75,7 @@ public class TimeTravelTest
         Assert.That(tyr0, Is.NotDislodged);
         setup.UpdateWorld();
 
-        setup[(1, 0)]
+        setup[("a", 1)]
             ["Germany"]
                 .Army("Mun").Supports.Army("Mun", season: s0).MoveTo("Tyr").GetReference(out var mun1)
             ["Austria"]
@@ -91,16 +91,16 @@ public class TimeTravelTest
 
         // Confirm that an alternate future is created.
         World world = setup.UpdateWorld();
-        Season fork = world.GetSeason(1, 1);
-        Unit tyr1 = world.GetUnitAt("Tyr", fork.Coord);
+        Season fork = world.GetSeason("b1");
+        Unit tyr1 = world.GetUnitAt("Tyr", fork);
         Assert.That(
             tyr1.Past,
-            Is.EqualTo(mun0.Order.Unit),
-            "Expected A Mun 0:0 to advance to Tyr 1:1");
+            Is.EqualTo(mun0.Order.Unit.Designation),
+            "Expected A Mun a0 to advance to Tyr b1");
         Assert.That(
             world.RetreatingUnits.Count,
             Is.EqualTo(1),
-            "Expected A Tyr 0:0 to be in retreat");
+            "Expected A Tyr a0 to be in retreat");
         Assert.That(world.RetreatingUnits.First().Unit, Is.EqualTo(tyr0.Order.Unit));
     }
 
@@ -110,14 +110,14 @@ public class TimeTravelTest
         TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);
 
         // Hold to create a future, then attempt to attack in the past.
-        setup[(0, 0)]
+        setup[("a", 0)]
             .GetReference(out Season s0)
             ["Germany"]
                 .Army("Mun").Holds()
             ["Austria"]
                 .Army("Tyr").Holds().GetReference(out var tyr0)
             .Execute()
-        [(1, 0)]
+        [("a", 1)]
             .GetReference(out Season s1)
             ["Germany"]
                 .Army("Mun").MovesTo("Tyr", season: s0).GetReference(out var mun1)
@@ -128,7 +128,7 @@ public class TimeTravelTest
         Assert.That(mun1, Is.Valid);
         setup.AdjudicateOrders();
         Assert.That(mun1, Is.Repelled);
-        // The order to Tyr 0:0 should have been pulled into the adjudication set, so the reference
+        // The order to Tyr a0 should have been pulled into the adjudication set, so the reference
         // should not throw when accessing it.
         Assert.That(tyr0, Is.NotDislodged);
 
@@ -136,12 +136,12 @@ public class TimeTravelTest
         // change the past and therefore did not create a new timeline.
         World world = setup.UpdateWorld();
         Assert.That(
-            s0.Futures.Count(),
+            world.GetFutures(s0).Count(),
             Is.EqualTo(1),
             "A failed move incorrectly forked the timeline");
-        Assert.That(s1.Futures.Count(), Is.EqualTo(1));
-        Season s2 = world.GetSeason(s1.Turn + 1, s1.Timeline);
-        Assert.That(s2.Futures.Count(), Is.EqualTo(0));
+        Assert.That(world.GetFutures(s1).Count(), Is.EqualTo(1));
+        Season s2 = world.GetSeason(s1.Timeline, s1.Turn + 1);
+        Assert.That(world.GetFutures(s2).Count(), Is.EqualTo(0));
     }
 
     [Test]
@@ -150,7 +150,7 @@ public class TimeTravelTest
         TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);
 
         // Move, then support the past move even though it succeeded already.
-        setup[(0, 0)]
+        setup[("a", 0)]
             .GetReference(out Season s0)
             ["Germany"]
                 .Army("Mun").MovesTo("Tyr").GetReference(out var mun0)
@@ -162,7 +162,7 @@ public class TimeTravelTest
         Assert.That(mun0, Is.Victorious);
         setup.UpdateWorld();
 
-        setup[(1, 0)]
+        setup[("a", 1)]
             .GetReference(out Season s1)
             ["Germany"]
                 .Army("Tyr").Holds()
@@ -178,12 +178,12 @@ public class TimeTravelTest
         // ...since it succeeded anyway, no fork is created.
         World world = setup.UpdateWorld();
         Assert.That(
-            s0.Futures.Count(),
+            world.GetFutures(s0).Count(),
             Is.EqualTo(1),
             "A superfluous support incorrectly forked the timeline");
-        Assert.That(s1.Futures.Count(), Is.EqualTo(1));
-        Season s2 = world.GetSeason(s1.Turn + 1, s1.Timeline);
-        Assert.That(s2.Futures.Count(), Is.EqualTo(0));
+        Assert.That(world.GetFutures(s1).Count(), Is.EqualTo(1));
+        Season s2 = world.GetSeason(s1.Timeline, s1.Turn + 1);
+        Assert.That(world.GetFutures(s2).Count(), Is.EqualTo(0));
     }
 
     [Test]
@@ -192,51 +192,51 @@ public class TimeTravelTest
         TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);
 
         // London creates two timelines by moving into the past.
-        setup[(0, 0)]
-            .GetReference(out var s0_0)
+        setup[("a", 0)]
+            .GetReference(out var a0)
             ["England"].Army("Lon").Holds()
             ["Austria"].Army("Tyr").Holds()
             ["Germany"].Army("Mun").Holds()
             .Execute()
-        [(1, 0)]
-            ["England"].Army("Lon").MovesTo("Yor", s0_0)
+        [("a", 1)]
+            ["England"].Army("Lon").MovesTo("Yor", a0)
             .Execute()
-        // Head seasons: 2:0  1:1
+        // Head seasons: a2 b1
         // Both contain copies of the armies in Mun and Tyr.
         // Now Germany dislodges Austria in Tyr by supporting the move across timelines.
-        [(2, 0)]
-            .GetReference(out var s2_0)
-            ["Germany"].Army("Mun").MovesTo("Tyr").GetReference(out var mun2_0)
-            ["Austria"].Army("Tyr").Holds().GetReference(out var tyr2_0)
-        [(1, 1)]
-            .GetReference(out var s1_1)
-            ["Germany"].Army("Mun").Supports.Army("Mun", s2_0).MoveTo("Tyr").GetReference(out var mun1_1)
+        [("a", 2)]
+            .GetReference(out var a2)
+            ["Germany"].Army("Mun").MovesTo("Tyr").GetReference(out var mun_a2)
+            ["Austria"].Army("Tyr").Holds().GetReference(out var tyr_a2)
+        [("b", 1)]
+            .GetReference(out var b1)
+            ["Germany"].Army("Mun").Supports.Army("Mun", a2).MoveTo("Tyr").GetReference(out var mun_b1)
             ["Austria"].Army("Tyr").Holds();
 
-        // The attack against Tyr 2:0 succeeds.
+        // The attack against Tyr a2 succeeds.
         setup.ValidateOrders();
-        Assert.That(mun2_0, Is.Valid);
-        Assert.That(tyr2_0, Is.Valid);
-        Assert.That(mun1_1, Is.Valid);
+        Assert.That(mun_a2, Is.Valid);
+        Assert.That(tyr_a2, Is.Valid);
+        Assert.That(mun_b1, Is.Valid);
         setup.AdjudicateOrders();
-        Assert.That(mun2_0, Is.Victorious);
-        Assert.That(tyr2_0, Is.Dislodged);
-        Assert.That(mun1_1, Is.NotCut);
+        Assert.That(mun_a2, Is.Victorious);
+        Assert.That(tyr_a2, Is.Dislodged);
+        Assert.That(mun_b1, Is.NotCut);
 
         // Since both seasons were at the head of their timelines, there should be no forking.
         World world = setup.UpdateWorld();
         Assert.That(
-            s2_0.Futures.Count(),
+            world.GetFutures(a2).Count(),
             Is.EqualTo(1),
             "A cross-timeline support incorrectly forked the head of the timeline");
         Assert.That(
-            s1_1.Futures.Count(),
+            world.GetFutures(b1).Count(),
             Is.EqualTo(1),
             "A cross-timeline support incorrectly forked the head of the timeline");
-        Season s3_0 = world.GetSeason(s2_0.Turn + 1, s2_0.Timeline);
-        Assert.That(s3_0.Futures.Count(), Is.EqualTo(0));
-        Season s2_1 = world.GetSeason(s1_1.Turn + 1, s1_1.Timeline);
-        Assert.That(s2_1.Futures.Count(), Is.EqualTo(0));
+        Season a3 = world.GetSeason(a2.Timeline, a2.Turn + 1);
+        Assert.That(world.GetFutures(a3).Count(), Is.EqualTo(0));
+        Season b2 = world.GetSeason(b1.Timeline, b1.Turn + 1);
+        Assert.That(world.GetFutures(b2).Count(), Is.EqualTo(0));
     }
 
     [Test]
@@ -245,63 +245,63 @@ public class TimeTravelTest
         TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);
 
         // As above, only now London creates three timelines.
-        setup[(0, 0)]
-            .GetReference(out var s0_0)
+        setup[("a", 0)]
+            .GetReference(out var a0)
             ["England"].Army("Lon").Holds()
             ["Austria"].Army("Boh").Holds()
             ["Germany"].Army("Mun").Holds()
             .Execute()
-        [(1, 0)]
-            ["England"].Army("Lon").MovesTo("Yor", s0_0)
+        [("a", 1)]
+            ["England"].Army("Lon").MovesTo("Yor", a0)
             .Execute()
-        // Head seasons: 2:0  1:1
-        [(2, 0)]
-        [(1, 1)]
-            ["England"].Army("Yor").MovesTo("Edi", s0_0)
+        // Head seasons: a2, b1
+        [("a", 2)]
+        [("b", 1)]
+            ["England"].Army("Yor").MovesTo("Edi", a0)
             .Execute()
-        // Head seasons: 3:0  2:1  1:2
+        // Head seasons: a3, b2, c1
         // All three of these contain copies of the armies in Mun and Tyr.
-        // As above, Germany dislodges Austria in Tyr 3:0 by supporting the move from 2:1.
-        [(3, 0)]
-            .GetReference(out var s3_0)
+        // As above, Germany dislodges Austria in Tyr a3 by supporting the move from b2.
+        [("a", 3)]
+            .GetReference(out var a3)
             ["Germany"].Army("Mun").MovesTo("Tyr")
             ["Austria"].Army("Tyr").Holds()
-        [(2, 1)]
-            .GetReference(out Season s2_1)
-            ["Germany"].Army("Mun").Supports.Army("Mun", s3_0).MoveTo("Tyr").GetReference(out var mun2_1)
+        [("b", 2)]
+            .GetReference(out Season b2)
+            ["Germany"].Army("Mun").Supports.Army("Mun", a3).MoveTo("Tyr").GetReference(out var mun_b2)
             ["Austria"].Army("Tyr").Holds()
-        [(1, 2)]
+        [("c", 1)]
             ["Germany"].Army("Mun").Holds()
             ["Austria"].Army("Tyr").Holds()
             .Execute()
-        // Head seasons: 4:0 3:1 2:2
-        // Now Austria cuts the support in 2:1 by attacking from 2:2.
-        [(4, 0)]
+        // Head seasons: a4, b3, c2
+        // Now Austria cuts the support in b2 by attacking from c2.
+        [("a", 4)]
             ["Germany"].Army("Tyr").Holds()
-        [(3, 1)]
+        [("b", 3)]
             ["Germany"].Army("Mun").Holds()
             ["Austria"].Army("Tyr").Holds()
-        [(2, 2)]
+        [("c", 2)]
             ["Germany"].Army("Mun").Holds()
-            ["Austria"].Army("Tyr").MovesTo("Mun", s2_1).GetReference(out var tyr2_2);
+            ["Austria"].Army("Tyr").MovesTo("Mun", b2).GetReference(out var tyr_c2);
 
-        // The attack on Mun 2:1 is repelled, but the support is cut.
+        // The attack on Mun b2 is repelled, but the support is cut.
         setup.ValidateOrders();
-        Assert.That(tyr2_2, Is.Valid);
+        Assert.That(tyr_c2, Is.Valid);
         setup.AdjudicateOrders();
-        Assert.That(tyr2_2, Is.Repelled);
-        Assert.That(mun2_1, Is.NotDislodged);
-        Assert.That(mun2_1, Is.Cut);
+        Assert.That(tyr_c2, Is.Repelled);
+        Assert.That(mun_b2, Is.NotDislodged);
+        Assert.That(mun_b2, Is.Cut);
 
         // Though the support was cut, the timeline doesn't fork because the outcome of a battle
         // wasn't changed in this timeline.
         World world = setup.UpdateWorld();
         Assert.That(
-            s3_0.Futures.Count(),
+            world.GetFutures(a3).Count(),
             Is.EqualTo(1),
             "A cross-timeline support cut incorrectly forked the timeline");
         Assert.That(
-            s2_1.Futures.Count(),
+            world.GetFutures(b2).Count(),
             Is.EqualTo(1),
             "A cross-timeline support cut incorrectly forked the timeline");
     }

MultiversalDiplomacyTests/MapTests.cs

@@ -6,10 +6,10 @@ namespace MultiversalDiplomacyTests;
 
 public class MapTests
 {
-    IEnumerable<Location> LocationClosure(Location location)
+    static IEnumerable<Location> LocationClosure(Location location)
     {
-        IEnumerable<Location> visited = new List<Location>();
-        IEnumerable<Location> toVisit = new List<Location>() { location };
+        IEnumerable<Location> visited = [];
+        IEnumerable<Location> toVisit = [location];
 
         while (toVisit.Any())
         {
@@ -50,7 +50,7 @@ public class MapTests
     [Test]
     public void LandAndSeaBorders()
     {
-        World map = World.WithStandardMap();
+        Map map = Map.Classical;
         Assert.That(
             map.GetLand("NAF").Adjacents.Count(),
             Is.EqualTo(1),

MultiversalDiplomacyTests/Model/TimelineFactoryTest.cs

@@ -0,0 +1,38 @@
+using MultiversalDiplomacy.Model;
+
+using NUnit.Framework;
+
+namespace MultiversalDiplomacyTests.Model;
+
+public class TimelineFactoryTest
+{
+    [TestCase(0, "a")]
+    [TestCase(1, "b")]
+    [TestCase(25, "z")]
+    [TestCase(26, "aa")]
+    [TestCase(27, "ab")]
+    [TestCase(51, "az")]
+    [TestCase(52, "ba")]
+    [TestCase(53, "bb")]
+    [TestCase(77, "bz")]
+    [TestCase(78, "ca")]
+    public void RoundTripTimelineDesignations(int number, string designation)
+    {
+        Assert.That(TimelineFactory.IntToString(number), Is.EqualTo(designation), "Incorrect string");
+        Assert.That(TimelineFactory.StringToInt(designation), Is.EqualTo(number), "Incorrect number");
+    }
+
+    [Test]
+    public void NoSharedFactoryState()
+    {
+        TimelineFactory one = new();
+        TimelineFactory two = new();
+
+        Assert.That(one.NextTimeline(), Is.EqualTo("a"));
+        Assert.That(one.NextTimeline(), Is.EqualTo("b"));
+        Assert.That(one.NextTimeline(), Is.EqualTo("c"));
+
+        Assert.That(two.NextTimeline(), Is.EqualTo("a"));
+        Assert.That(two.NextTimeline(), Is.EqualTo("b"));
+    }
+}

MultiversalDiplomacyTests/MovementAdjudicatorTest.cs

@@ -171,8 +171,8 @@ public class MovementAdjudicatorTest
         // Confirm the future was created
         Assert.That(updated.Seasons.Count, Is.EqualTo(2));
         Season future = updated.Seasons.Single(s => s != updated.RootSeason);
-        Assert.That(future.Past, Is.EqualTo(updated.RootSeason));
-        Assert.That(future.Futures, Is.Empty);
+        Assert.That(future.Past, Is.EqualTo(updated.RootSeason.ToString()));
+        Assert.That(updated.GetFutures(future), Is.Empty);
         Assert.That(future.Timeline, Is.EqualTo(updated.RootSeason.Timeline));
         Assert.That(future.Turn, Is.EqualTo(Season.FIRST_TURN + 1));
 
@@ -186,7 +186,7 @@ public class MovementAdjudicatorTest
     public void Update_DoubleHold()
     {
         TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);
-        setup[(0, 0)]
+        setup[("a", 0)]
             .GetReference(out Season s1)
             ["Germany"]
                 .Army("Mun").Holds().GetReference(out var mun1);
@@ -199,20 +199,20 @@ public class MovementAdjudicatorTest
         World updated = setup.UpdateWorld();
 
         // Confirm the future was created
-        Season s2 = updated.GetSeason(1, 0);
-        Assert.That(s2.Past, Is.EqualTo(s1));
-        Assert.That(s2.Futures, Is.Empty);
+        Season s2 = updated.GetSeason("a1");
+        Assert.That(s2.Past, Is.EqualTo(s1.ToString()));
+        Assert.That(updated.GetFutures(s2), Is.Empty);
         Assert.That(s2.Timeline, Is.EqualTo(s1.Timeline));
         Assert.That(s2.Turn, Is.EqualTo(s1.Turn + 1));
 
         // Confirm the unit was created in the future
-        Unit u2 = updated.GetUnitAt("Mun", s2.Coord);
+        Unit u2 = updated.GetUnitAt("Mun", s2);
         Assert.That(updated.Units.Count, Is.EqualTo(2));
         Assert.That(u2, Is.Not.EqualTo(mun1.Order.Unit));
-        Assert.That(u2.Past, Is.EqualTo(mun1.Order.Unit));
+        Assert.That(u2.Past, Is.EqualTo(mun1.Order.Unit.Designation));
         Assert.That(u2.Season, Is.EqualTo(s2));
 
-        setup[(1, 0)]
+        setup[("a", 1)]
             ["Germany"]
                 .Army("Mun").Holds().GetReference(out var mun2);
 
@@ -227,16 +227,16 @@ public class MovementAdjudicatorTest
 
         // Update the world again
         updated = setup.UpdateWorld();
-        Season s3 = updated.GetSeason(s2.Turn + 1, s2.Timeline);
-        Unit u3 = updated.GetUnitAt("Mun", s3.Coord);
-        Assert.That(u3.Past, Is.EqualTo(mun2.Order.Unit));
+        Season s3 = updated.GetSeason(s2.Timeline, s2.Turn + 1);
+        Unit u3 = updated.GetUnitAt("Mun", s3);
+        Assert.That(u3.Past, Is.EqualTo(mun2.Order.Unit.Designation));
     }
 
     [Test]
     public void Update_DoubleMove()
     {
         TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);
-        setup[(0, 0)]
+        setup[("a", 0)]
             .GetReference(out Season s1)
             ["Germany"]
                 .Army("Mun").MovesTo("Tyr").GetReference(out var mun1);
@@ -249,20 +249,20 @@ public class MovementAdjudicatorTest
         World updated = setup.UpdateWorld();
 
         // Confirm the future was created
-        Season s2 = updated.GetSeason(s1.Turn + 1, s1.Timeline);
-        Assert.That(s2.Past, Is.EqualTo(s1));
-        Assert.That(s2.Futures, Is.Empty);
+        Season s2 = updated.GetSeason(s1.Timeline, s1.Turn + 1);
+        Assert.That(s2.Past, Is.EqualTo(s1.ToString()));
+        Assert.That(updated.GetFutures(s2), Is.Empty);
         Assert.That(s2.Timeline, Is.EqualTo(s1.Timeline));
         Assert.That(s2.Turn, Is.EqualTo(s1.Turn + 1));
 
         // Confirm the unit was created in the future
-        Unit u2 = updated.GetUnitAt("Tyr", s2.Coord);
+        Unit u2 = updated.GetUnitAt("Tyr", s2);
         Assert.That(updated.Units.Count, Is.EqualTo(2));
         Assert.That(u2, Is.Not.EqualTo(mun1.Order.Unit));
-        Assert.That(u2.Past, Is.EqualTo(mun1.Order.Unit));
+        Assert.That(u2.Past, Is.EqualTo(mun1.Order.Unit.Designation));
         Assert.That(u2.Season, Is.EqualTo(s2));
 
-        setup[(1, 0)]
+        setup[("a", 1)]
             ["Germany"]
                 .Army("Tyr").MovesTo("Mun").GetReference(out var tyr2);
 
@@ -277,8 +277,8 @@ public class MovementAdjudicatorTest
 
         // Update the world again
         updated = setup.UpdateWorld();
-        Season s3 = updated.GetSeason(s2.Turn + 1, s2.Timeline);
-        Unit u3 = updated.GetUnitAt("Mun", s3.Coord);
-        Assert.That(u3.Past, Is.EqualTo(u2));
+        Season s3 = updated.GetSeason(s2.Timeline, s2.Turn + 1);
+        Unit u3 = updated.GetUnitAt("Mun", s3);
+        Assert.That(u3.Past, Is.EqualTo(u2.Designation));
     }
 }

MultiversalDiplomacyTests/OrderReference.cs

@@ -108,8 +108,7 @@ public abstract class OrderReference
                 DefendStrength defend => defend.Order == this.Order,
                 PreventStrength prevent => prevent.Order == this.Order,
                 HoldStrength hold => this.Order is UnitOrder unitOrder
-                    ? hold.Province == unitOrder.Unit.Province
-                    : false,
+                    && hold.Province == Builder.World.Map.GetLocation(unitOrder.Unit).Province,
                 _ => false,
             }).ToList();
             return adjudications;

MultiversalDiplomacyTests/SeasonTests.cs

@@ -9,57 +9,54 @@ public class SeasonTests
     [Test]
     public void TimelineForking()
     {
-        Season a0 = Season.MakeRoot();
-        Season a1 = a0.MakeNext();
-        Season a2 = a1.MakeNext();
-        Season a3 = a2.MakeNext();
-        Season b1 = a1.MakeFork();
-        Season b2 = b1.MakeNext();
-        Season c1 = a1.MakeFork();
-        Season d1 = a2.MakeFork();
+        World world = World.WithMap(Map.Test);
+        Season a0 = world.GetSeason("a0");
+        world = world
+            .ContinueOrFork(a0, out Season a1)
+            .ContinueOrFork(a1, out Season a2)
+            .ContinueOrFork(a2, out Season a3)
+            .ContinueOrFork(a1, out Season b2)
+            .ContinueOrFork(b2, out Season b3)
+            .ContinueOrFork(a1, out Season c2)
+            .ContinueOrFork(a2, out Season d3);
 
-        Assert.That(a0.Timeline, Is.EqualTo(0), "Unexpected trunk timeline number");
-        Assert.That(a1.Timeline, Is.EqualTo(0), "Unexpected trunk timeline number");
-        Assert.That(a2.Timeline, Is.EqualTo(0), "Unexpected trunk timeline number");
-        Assert.That(a3.Timeline, Is.EqualTo(0), "Unexpected trunk timeline number");
-        Assert.That(b1.Timeline, Is.EqualTo(1), "Unexpected first alt number");
-        Assert.That(b2.Timeline, Is.EqualTo(1), "Unexpected first alt number");
-        Assert.That(c1.Timeline, Is.EqualTo(2), "Unexpected second alt number");
-        Assert.That(d1.Timeline, Is.EqualTo(3), "Unexpected third alt number");
+        Assert.That(
+            world.Seasons.Select(season => season.ToString()),
+            Is.EquivalentTo(new List<string> { "a0", "a1", "a2", "a3", "b2", "b3", "c2", "d3" }),
+            "Unexpected seasons");
+
+        Assert.That(a0.Timeline, Is.EqualTo("a"), "Unexpected trunk timeline");
+        Assert.That(a1.Timeline, Is.EqualTo("a"), "Unexpected trunk timeline");
+        Assert.That(a2.Timeline, Is.EqualTo("a"), "Unexpected trunk timeline");
+        Assert.That(a3.Timeline, Is.EqualTo("a"), "Unexpected trunk timeline");
+        Assert.That(b2.Timeline, Is.EqualTo("b"), "Unexpected first alt");
+        Assert.That(b3.Timeline, Is.EqualTo("b"), "Unexpected first alt");
+        Assert.That(c2.Timeline, Is.EqualTo("c"), "Unexpected second alt");
+        Assert.That(d3.Timeline, Is.EqualTo("d"), "Unexpected third alt");
 
         Assert.That(a0.Turn, Is.EqualTo(Season.FIRST_TURN + 0), "Unexpected first turn number");
         Assert.That(a1.Turn, Is.EqualTo(Season.FIRST_TURN + 1), "Unexpected next turn number");
         Assert.That(a2.Turn, Is.EqualTo(Season.FIRST_TURN + 2), "Unexpected next turn number");
         Assert.That(a3.Turn, Is.EqualTo(Season.FIRST_TURN + 3), "Unexpected next turn number");
-        Assert.That(b1.Turn, Is.EqualTo(Season.FIRST_TURN + 2), "Unexpected fork turn number");
-        Assert.That(b2.Turn, Is.EqualTo(Season.FIRST_TURN + 3), "Unexpected fork turn number");
-        Assert.That(c1.Turn, Is.EqualTo(Season.FIRST_TURN + 2), "Unexpected fork turn number");
-        Assert.That(d1.Turn, Is.EqualTo(Season.FIRST_TURN + 3), "Unexpected fork turn number");
+        Assert.That(b2.Turn, Is.EqualTo(Season.FIRST_TURN + 2), "Unexpected fork turn number");
+        Assert.That(b3.Turn, Is.EqualTo(Season.FIRST_TURN + 3), "Unexpected fork turn number");
+        Assert.That(c2.Turn, Is.EqualTo(Season.FIRST_TURN + 2), "Unexpected fork turn number");
+        Assert.That(d3.Turn, Is.EqualTo(Season.FIRST_TURN + 3), "Unexpected fork turn number");
 
-        Assert.That(a0.TimelineRoot(), Is.EqualTo(a0), "Expected timeline root to be reflexive");
-        Assert.That(a3.TimelineRoot(), Is.EqualTo(a0), "Expected trunk timeline to have root");
-        Assert.That(b1.TimelineRoot(), Is.EqualTo(b1), "Expected alt timeline root to be reflexive");
-        Assert.That(b2.TimelineRoot(), Is.EqualTo(b1), "Expected alt timeline to root at first fork");
-        Assert.That(c1.TimelineRoot(), Is.EqualTo(c1), "Expected alt timeline root to be reflexive");
-        Assert.That(d1.TimelineRoot(), Is.EqualTo(d1), "Expected alt timeline root to be reflexive");
+        Assert.That(world.GetTimelineRoot(a0), Is.EqualTo(a0), "Expected timeline root to be reflexive");
+        Assert.That(world.GetTimelineRoot(a3), Is.EqualTo(a0), "Expected trunk timeline to have root");
+        Assert.That(world.GetTimelineRoot(b2), Is.EqualTo(b2), "Expected alt timeline root to be reflexive");
+        Assert.That(world.GetTimelineRoot(b3), Is.EqualTo(b2), "Expected alt timeline to root at first fork");
+        Assert.That(world.GetTimelineRoot(c2), Is.EqualTo(c2), "Expected alt timeline root to be reflexive");
+        Assert.That(world.GetTimelineRoot(d3), Is.EqualTo(d3), "Expected alt timeline root to be reflexive");
 
-        Assert.That(b2.InAdjacentTimeline(a3), Is.True, "Expected alts to be adjacent to origin");
-        Assert.That(b2.InAdjacentTimeline(c1), Is.True, "Expected alts with common origin to be adjacent");
-        Assert.That(b2.InAdjacentTimeline(d1), Is.False, "Expected alts from different origins not to be adjacent");
-    }
+        Assert.That(world.InAdjacentTimeline(b3, a3), Is.True, "Expected alts to be adjacent to origin");
+        Assert.That(world.InAdjacentTimeline(b3, c2), Is.True, "Expected alts with common origin to be adjacent");
+        Assert.That(world.InAdjacentTimeline(b3, d3), Is.False, "Expected alts from different origins not to be adjacent");
 
-    [Test]
-    public void LookupTest()
-    {
-        World world = World.WithStandardMap();
-        Season s2 = world.RootSeason.MakeNext();
-        Season s3 = s2.MakeNext();
-        Season s4 = s2.MakeFork();
-        World updated = world.Update(seasons: world.Seasons.Append(s2).Append(s3).Append(s4));
-
-        Assert.That(updated.GetSeason(Season.FIRST_TURN, 0), Is.EqualTo(updated.RootSeason));
-        Assert.That(updated.GetSeason(Season.FIRST_TURN + 1, 0), Is.EqualTo(s2));
-        Assert.That(updated.GetSeason(Season.FIRST_TURN + 2, 0), Is.EqualTo(s3));
-        Assert.That(updated.GetSeason(Season.FIRST_TURN + 2, 1), Is.EqualTo(s4));
+        Assert.That(world.GetFutures(a0), Is.EquivalentTo(new List<Season> { a1 }), "Unexpected futures");
+        Assert.That(world.GetFutures(a1), Is.EquivalentTo(new List<Season> { a2, b2, c2 }), "Unexpected futures");
+        Assert.That(world.GetFutures(a2), Is.EquivalentTo(new List<Season> { a3, d3 }), "Unexpected futures");
+        Assert.That(world.GetFutures(b2), Is.EquivalentTo(new List<Season> { b3 }), "Unexpected futures");
     }
 }

MultiversalDiplomacyTests/SerializationTest.cs

@@ -0,0 +1,105 @@
+using System.Text.Json;
+
+using MultiversalDiplomacy.Adjudicate;
+using MultiversalDiplomacy.Model;
+
+using NUnit.Framework;
+
+namespace MultiversalDiplomacyTests;
+
+public class SerializationTest
+{
+    private JsonSerializerOptions Options = new() {
+        WriteIndented = true,
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+    };
+
+    [Test]
+    public void SerializeRoundTrip_NewGame()
+    {
+        World world = World.WithStandardMap();
+        string serialized = JsonSerializer.Serialize(world, Options);
+        World? deserialized = JsonSerializer.Deserialize<World>(serialized, Options);
+
+        Assert.That(deserialized, Is.Not.Null, "Failed to deserialize");
+        Assert.That(deserialized!.Map, Is.Not.Null, "Failed to deserialize map");
+        Assert.That(deserialized!.Seasons, Is.Not.Null, "Failed to deserialize seasons");
+        Assert.That(deserialized!.Units, Is.Not.Null, "Failed to deserialize units");
+        Assert.That(deserialized!.RetreatingUnits, Is.Not.Null, "Failed to deserialize retreats");
+        Assert.That(deserialized!.OrderHistory, Is.Not.Null, "Failed to deserialize history");
+        Assert.That(deserialized!.Timelines, Is.Not.Null, "Failed to deserialize timelines");
+        Assert.That(deserialized!.Options, Is.Not.Null, "Failed to deserialize options");
+        Assert.That(deserialized.Timelines.nextTimeline, Is.EqualTo(world.Timelines.nextTimeline));
+
+        JsonElement document = JsonSerializer.SerializeToDocument(world, Options).RootElement;
+        Assert.That(
+            document.EnumerateObject().Select(prop => prop.Name),
+            Is.EquivalentTo(new List<string> {
+                "mapType",
+                "seasons",
+                "units",
+                "retreatingUnits",
+                "orderHistory",
+                "options",
+                "timelines",
+            }));
+    }
+
+    [Test]
+    public void SerializeRoundTrip_MDATC_3_A_2()
+    {
+        // Set up MDATC 3.A.2
+        TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);
+        setup[("a", 0)]
+            .GetReference(out Season s0)
+            ["Germany"]
+                .Army("Mun").MovesTo("Tyr").GetReference(out var mun0)
+            ["Austria"]
+                .Army("Tyr").Holds().GetReference(out var tyr0);
+
+        setup.ValidateOrders();
+        Assert.That(mun0, Is.Valid);
+        Assert.That(tyr0, Is.Valid);
+        setup.AdjudicateOrders();
+        Assert.That(mun0, Is.Repelled);
+        Assert.That(tyr0, Is.NotDislodged);
+        setup.UpdateWorld();
+
+        // Serialize the world
+        string serialized = JsonSerializer.Serialize(setup.World, Options);
+
+        // Deserialize the world
+        Console.WriteLine(serialized);
+        World reserialized = JsonSerializer.Deserialize<World>(serialized, Options)
+            ?? throw new AssertionException("Failed to reserialize world");
+
+        // Resume the test case
+        setup = new(reserialized, MovementPhaseAdjudicator.Instance);
+        setup[("a", 1)]
+            ["Germany"]
+                .Army("Mun").Supports.Army("Mun", season: reserialized.GetSeason("a0")).MoveTo("Tyr").GetReference(out var mun1)
+            ["Austria"]
+                .Army("Tyr").Holds();
+
+        setup.ValidateOrders();
+        Assert.That(mun1, Is.Valid);
+        setup.AdjudicateOrders();
+        Assert.That(mun1, Is.NotCut);
+        Assert.That(mun0, Is.Victorious);
+        Assert.That(tyr0, Is.Dislodged);
+
+        // Confirm that an alternate future is created.
+        World world = setup.UpdateWorld();
+        Season fork = world.GetSeason("b1");
+        Unit tyr1 = world.GetUnitAt("Tyr", fork);
+        Assert.That(
+            tyr1.Past,
+            Is.EqualTo(mun0.Order.Unit.Designation),
+            "Expected A Mun a0 to advance to Tyr b1");
+        Assert.That(
+            world.RetreatingUnits.Count,
+            Is.EqualTo(1),
+            "Expected A Tyr a0 to be in retreat");
+        Assert.That(world.RetreatingUnits.First().Unit, Is.EqualTo(tyr0.Order.Unit));
+    }
+}

MultiversalDiplomacyTests/TestCaseBuilder.cs

@@ -19,7 +19,7 @@ public class TestCaseBuilder
         /// <summary>
         /// Choose a new season to define orders for.
         /// </summary>
-        public ISeasonContext this[(int turn, int timeline) seasonCoord] { get; }
+        public ISeasonContext this[(string timeline, int turn) seasonCoord] { get; }
 
         /// <summary>
         /// Get the context for defining the orders for a power.
@@ -40,7 +40,7 @@ public class TestCaseBuilder
         /// <summary>
         /// Choose a new season to define orders for.
         /// </summary>
-        public ISeasonContext this[(int turn, int timeline) seasonCoord] { get; }
+        public ISeasonContext this[(string timeline, int turn) seasonCoord] { get; }
 
         /// <summary>
         /// Get the context for defining the orders for another power.
@@ -188,7 +188,7 @@ public class TestCaseBuilder
         /// <summary>
         /// Choose a new season to define orders for.
         /// </summary>
-        public ISeasonContext this[(int turn, int timeline) seasonCoord] { get; }
+        public ISeasonContext this[(string timeline, int turn) seasonCoord] { get; }
 
         /// <summary>
         /// Get the context for defining the orders for another power.
@@ -234,13 +234,13 @@ public class TestCaseBuilder
     /// <summary>
     /// Get the context for defining the orders for a power. Defaults to the root season.
     /// </summary>
-    public IPowerContext this[string powerName] => this[(0, 0)][powerName];
+    public IPowerContext this[string powerName] => this[("a", 0)][powerName];
 
     /// <summary>
     /// Get the context for defining the orders for a season.
     /// </summary>
-    public ISeasonContext this[(int turn, int timeline) seasonCoord]
-        => new SeasonContext(this, this.World.GetSeason(seasonCoord.turn, seasonCoord.timeline));
+    public ISeasonContext this[(string timeline, int turn) seasonCoord]
+        => new SeasonContext(this, this.World.GetSeason(seasonCoord.timeline, seasonCoord.turn));
 
     /// <summary>
     /// Get a unit matching a description. If no such unit exists, one is created and added to the
@@ -262,7 +262,7 @@ public class TestCaseBuilder
         foreach (Unit unit in this.World.Units)
         {
             if (unit.Power == power
-                && unit.Province == location.Province
+                && World.Map.GetLocation(unit).Province == location.Province
                 && unit.Season == season)
             {
                 return unit;
@@ -270,7 +270,7 @@ public class TestCaseBuilder
         }
 
         // Not found
-        Unit newUnit = Unit.Build(location, season, power, type);
+        Unit newUnit = Unit.Build(location.Designation, season, power, type);
         this.World = this.World.Update(units: this.World.Units.Append(newUnit));
         return newUnit;
     }
@@ -327,11 +327,11 @@ public class TestCaseBuilder
             this.Season = season;
         }
 
-        public ISeasonContext this[(int turn, int timeline) seasonCoord]
-            => this.Builder[(seasonCoord.turn, seasonCoord.timeline)];
+        public ISeasonContext this[(string timeline, int turn) seasonCoord]
+            => this.Builder[(seasonCoord.timeline, seasonCoord.turn)];
 
         public IPowerContext this[string powerName]
-            => new PowerContext(this, this.Builder.World.GetPower(powerName));
+            => new PowerContext(this, this.Builder.World.Map.GetPower(powerName));
 
         public ISeasonContext GetReference(out Season season)
         {
@@ -353,7 +353,7 @@ public class TestCaseBuilder
             this.Power = Power;
         }
 
-        public ISeasonContext this[(int turn, int timeline) seasonCoord]
+        public ISeasonContext this[(string timeline, int turn) seasonCoord]
             => this.SeasonContext[seasonCoord];
 
         public IPowerContext this[string powerName]
@@ -363,8 +363,8 @@ public class TestCaseBuilder
         {
             Power power = powerName == null
                 ? this.Power
-                : this.Builder.World.GetPower(powerName);
-            Location location = this.Builder.World.GetLand(provinceName);
+                : this.Builder.World.Map.GetPower(powerName);
+            Location location = this.Builder.World.Map.GetLand(provinceName);
             Unit unit = this.Builder.GetOrBuildUnit(
                 power, location, this.SeasonContext.Season, UnitType.Army);
             return new UnitContext(this, unit);
@@ -374,8 +374,8 @@ public class TestCaseBuilder
         {
             Power power = powerName == null
                 ? this.Power
-                : this.Builder.World.GetPower(powerName);
-            Location location = this.Builder.World.GetWater(provinceName, coast);
+                : this.Builder.World.Map.GetPower(powerName);
+            Location location = this.Builder.World.Map.GetWater(provinceName, coast);
             Unit unit = this.Builder.GetOrBuildUnit(
                 power, location, this.SeasonContext.Season, UnitType.Fleet);
             return new UnitContext(this, unit);
@@ -413,8 +413,8 @@ public class TestCaseBuilder
             string? coast = null)
         {
             Location destination = this.Unit.Type == UnitType.Army
-                ? this.Builder.World.GetLand(provinceName)
-                : this.Builder.World.GetWater(provinceName, coast);
+                ? this.Builder.World.Map.GetLand(provinceName)
+                : this.Builder.World.Map.GetWater(provinceName, coast);
             Season destSeason = season ?? this.SeasonContext.Season;
             MoveOrder moveOrder = new MoveOrder(
                 this.PowerContext.Power,
@@ -451,8 +451,8 @@ public class TestCaseBuilder
         {
             Power power = powerName == null
                 ? this.PowerContext.Power
-                : this.Builder.World.GetPower(powerName);
-            Location location = this.Builder.World.GetLand(provinceName);
+                : this.Builder.World.Map.GetPower(powerName);
+            Location location = this.Builder.World.Map.GetLand(provinceName);
             Unit unit = this.Builder.GetOrBuildUnit(
                 power, location, this.SeasonContext.Season, UnitType.Army);
             return new ConvoyDestinationContext(this, unit);
@@ -465,8 +465,8 @@ public class TestCaseBuilder
         {
             Power power = powerName == null
                 ? this.PowerContext.Power
-                : this.Builder.World.GetPower(powerName);
-            Location location = this.Builder.World.GetWater(provinceName, coast);
+                : this.Builder.World.Map.GetPower(powerName);
+            Location location = this.Builder.World.Map.GetWater(provinceName, coast);
             Unit unit = this.Builder.GetOrBuildUnit(
                 power, location, this.SeasonContext.Season, UnitType.Fleet);
             return new ConvoyDestinationContext(this, unit);
@@ -492,7 +492,7 @@ public class TestCaseBuilder
 
         public IOrderDefinedContext<ConvoyOrder> To(string provinceName)
         {
-            Location location = this.Builder.World.GetLand(provinceName);
+            Location location = this.Builder.World.Map.GetLand(provinceName);
             ConvoyOrder order = new ConvoyOrder(
                 this.PowerContext.Power,
                 this.UnitContext.Unit,
@@ -526,8 +526,8 @@ public class TestCaseBuilder
         {
             Power power = powerName == null
                 ? this.PowerContext.Power
-                : this.Builder.World.GetPower(powerName);
-            Location location = this.Builder.World.GetLand(provinceName);
+                : this.Builder.World.Map.GetPower(powerName);
+            Location location = this.Builder.World.Map.GetLand(provinceName);
             Season destSeason = season ?? this.SeasonContext.Season;
             Unit unit = this.Builder.GetOrBuildUnit(
                 power, location, destSeason, UnitType.Army);
@@ -541,8 +541,8 @@ public class TestCaseBuilder
         {
             Power power = powerName == null
                 ? this.PowerContext.Power
-                : this.Builder.World.GetPower(powerName);
-            Location location = this.Builder.World.GetWater(provinceName, coast);
+                : this.Builder.World.Map.GetPower(powerName);
+            Location location = this.Builder.World.Map.GetWater(provinceName, coast);
             Unit unit = this.Builder.GetOrBuildUnit(
                 power, location, this.SeasonContext.Season, UnitType.Fleet);
             return new SupportTypeContext(this, unit);
@@ -582,8 +582,8 @@ public class TestCaseBuilder
             string? coast = null)
         {
             Location destination = this.Target.Type == UnitType.Army
-                ? this.Builder.World.GetLand(provinceName)
-                : this.Builder.World.GetWater(provinceName, coast);
+                ? this.Builder.World.Map.GetLand(provinceName)
+                : this.Builder.World.Map.GetWater(provinceName, coast);
             Season targetDestSeason = season ?? this.Target.Season;
             SupportMoveOrder order = new SupportMoveOrder(
                 this.PowerContext.Power,
@@ -623,7 +623,7 @@ public class TestCaseBuilder
             return this.Builder;
         }
 
-        public ISeasonContext this[(int turn, int timeline) seasonCoord]
+        public ISeasonContext this[(string timeline, int turn) seasonCoord]
             => this.SeasonContext[seasonCoord];
 
         public IPowerContext this[string powerName]

MultiversalDiplomacyTests/TestCaseBuilderTest.cs

@@ -14,7 +14,7 @@ class TestCaseBuilderTest
     {
         TestCaseBuilder setup = new(World.WithStandardMap());
 
-        Assert.That(setup.World.Powers.Count(), Is.EqualTo(7), "Unexpected power count");
+        Assert.That(setup.World.Powers.Count, Is.EqualTo(7), "Unexpected power count");
         Assert.That(setup.World.Units, Is.Empty, "Expected no units to be created yet");
 
         setup
@@ -40,7 +40,7 @@ class TestCaseBuilderTest
         Assert.That(fleetSTP.Type, Is.EqualTo(UnitType.Fleet), "Unit created with wrong type");
         Assert.That(
             fleetSTP.Location,
-            Is.EqualTo(setup.World.GetWater("STP", "wc")),
+            Is.EqualTo(setup.World.Map.GetWater("STP", "wc").Designation),
             "Unit created on wrong coast");
     }
 
@@ -49,7 +49,7 @@ class TestCaseBuilderTest
     {
         TestCaseBuilder setup = new(World.WithStandardMap());
 
-        Assert.That(setup.World.Powers.Count(), Is.EqualTo(7), "Unexpected power count");
+        Assert.That(setup.World.Powers.Count, Is.EqualTo(7), "Unexpected power count");
         Assert.That(setup.World.Units, Is.Empty, "Expected no units to be created yet");
         Assert.That(setup.Orders, Is.Empty, "Expected no orders to be created yet");
 
@@ -68,13 +68,13 @@ class TestCaseBuilderTest
         List<UnitOrder> orders = setup.Orders.OfType<UnitOrder>().ToList();
 
         Func<UnitOrder, bool> OrderForProvince(string name)
-            => order => order.Unit.Province.Name == name;
+            => order => setup.World.Map.GetLocation(order.Unit).Province.Name == name;
 
         UnitOrder orderBer = orders.Single(OrderForProvince("Berlin"));
         Assert.That(orderBer, Is.InstanceOf<MoveOrder>(), "Unexpected order type");
         Assert.That(
             (orderBer as MoveOrder)?.Location,
-            Is.EqualTo(setup.World.GetLand("Kiel")),
+            Is.EqualTo(setup.World.Map.GetLand("Kiel")),
             "Unexpected move order destination");
 
         UnitOrder orderPru = orders.Single(OrderForProvince("Prussia"));
@@ -88,7 +88,7 @@ class TestCaseBuilderTest
             "Unexpected convoy order target");
         Assert.That(
             (orderNth as ConvoyOrder)?.Location,
-            Is.EqualTo(setup.World.GetLand("Holland")),
+            Is.EqualTo(setup.World.Map.GetLand("Holland")),
             "Unexpected convoy order destination");
 
         UnitOrder orderKie = orders.Single(OrderForProvince("Kiel"));
@@ -99,7 +99,7 @@ class TestCaseBuilderTest
             "Unexpected convoy order target");
         Assert.That(
             (orderKie as SupportMoveOrder)?.Location,
-            Is.EqualTo(setup.World.GetLand("Holland")),
+            Is.EqualTo(setup.World.Map.GetLand("Holland")),
             "Unexpected convoy order destination");
 
         UnitOrder orderMun = orders.Single(OrderForProvince("Munich"));
@@ -124,11 +124,11 @@ class TestCaseBuilderTest
         Assert.That(orderMun, Is.Not.Null, "Expected order reference");
         Assert.That(
             orderMun.Order.Power,
-            Is.EqualTo(setup.World.GetPower("Germany")),
+            Is.EqualTo(setup.World.Map.GetPower("Germany")),
             "Wrong power");
         Assert.That(
             orderMun.Order.Unit.Location,
-            Is.EqualTo(setup.World.GetLand("Mun")),
+            Is.EqualTo(setup.World.Map.GetLand("Mun").Designation),
             "Wrong unit");
 
         Assert.That(

MultiversalDiplomacyTests/UnitTests.cs

@@ -10,29 +10,29 @@ public class UnitTests
     public void MovementTest()
     {
         World world = World.WithStandardMap();
-        Location Mun = world.GetLand("Mun"),
-            Boh = world.GetLand("Boh"),
-            Tyr = world.GetLand("Tyr");
-        Power pw1 = world.GetPower("Austria");
-        Season s1 = world.RootSeason;
-        Unit u1 = Unit.Build(Mun, s1, pw1, UnitType.Army);
+        Location Mun = world.Map.GetLand("Mun"),
+            Boh = world.Map.GetLand("Boh"),
+            Tyr = world.Map.GetLand("Tyr");
+        Power pw1 = world.Map.GetPower("Austria");
+        Season a0 = world.RootSeason;
+        Unit u1 = Unit.Build(Mun.Designation, a0, pw1, UnitType.Army);
 
-        Season s2 = s1.MakeNext();
-        Unit u2 = u1.Next(Boh, s2);
+        world = world.ContinueOrFork(a0, out Season a1);
+        Unit u2 = u1.Next(Boh.Designation, a1);
 
-        Season s3 = s2.MakeNext();
-        Unit u3 = u2.Next(Tyr, s3);
+        _ = world.ContinueOrFork(a1, out Season a2);
+        Unit u3 = u2.Next(Tyr.Designation, a2);
 
-        Assert.That(u3.Past, Is.EqualTo(u2), "Missing unit past");
-        Assert.That(u2.Past, Is.EqualTo(u1), "Missing unit past");
+        Assert.That(u3.Past, Is.EqualTo(u2.Designation), "Missing unit past");
+        Assert.That(u2.Past, Is.EqualTo(u1.Designation), "Missing unit past");
         Assert.That(u1.Past, Is.Null, "Unexpected unit past");
 
-        Assert.That(u1.Season, Is.EqualTo(s1), "Unexpected unit season");
-        Assert.That(u2.Season, Is.EqualTo(s2), "Unexpected unit season");
-        Assert.That(u3.Season, Is.EqualTo(s3), "Unexpected unit season");
+        Assert.That(u1.Season, Is.EqualTo(a0), "Unexpected unit season");
+        Assert.That(u2.Season, Is.EqualTo(a1), "Unexpected unit season");
+        Assert.That(u3.Season, Is.EqualTo(a2), "Unexpected unit season");
 
-        Assert.That(u1.Location, Is.EqualTo(Mun), "Unexpected unit location");
-        Assert.That(u2.Location, Is.EqualTo(Boh), "Unexpected unit location");
-        Assert.That(u3.Location, Is.EqualTo(Tyr), "Unexpected unit location");
+        Assert.That(u1.Location, Is.EqualTo(Mun.Designation), "Unexpected unit location");
+        Assert.That(u2.Location, Is.EqualTo(Boh.Designation), "Unexpected unit location");
+        Assert.That(u3.Location, Is.EqualTo(Tyr.Designation), "Unexpected unit location");
     }
 }