MultiversalDiplomacy/Adjudicate/Decision/MovementDecisions.cs

@@ -91,33 +91,19 @@ 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[Point(order.Unit)] = new(Point(order.Unit), order);
+            HoldStrength[order.Unit.Point] = new(order.Unit.Point, 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(other => IsIncoming(order, other))
+                .Where(order.IsIncoming)
                 .ToList();
             IsDislodged[order.Unit] = new(order, incoming);
 
@@ -132,7 +118,7 @@ public class MovementDecisions
                 // Determine if this move is a head-to-head battle.
                 MoveOrder? opposingMove = relevantOrders
                     .OfType<MoveOrder>()
-                    .FirstOrDefault(other => AreOpposing(move, other!), null);
+                    .FirstOrDefault(other => other!.IsOpposing(move), null);
 
                 // Find competing moves.
                 List<MoveOrder> competing = relevantOrders
@@ -156,11 +142,11 @@ public class MovementDecisions
                 GivesSupport[support] = new(support, incoming);
 
                 // Ensure a hold strength decision exists for the target's province.
-                HoldStrength.Ensure(Point(support.Target), () => new(Point(support.Target)));
+                HoldStrength.Ensure(support.Target.Point, () => new(support.Target.Point));
 
                 if (support is SupportHoldOrder supportHold)
                 {
-                    HoldStrength[Point(support.Target)].Supports.Add(supportHold);
+                    HoldStrength[support.Target.Point].Supports.Add(supportHold);
                 }
                 else if (support is SupportMoveOrder supportMove)
                 {

MultiversalDiplomacy/Adjudicate/MovementPhaseAdjudicator.cs

@@ -77,7 +77,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
 
         // Trivial check: a unit cannot move to where it already is.
         AdjudicatorHelpers.InvalidateIfNotMatching(
-            order => !(order.Location.Designation == order.Unit.Location && order.Season == order.Unit.Season),
+            order => !(order.Location == order.Unit.Location && order.Season == order.Unit.Season),
             ValidationReason.DestinationMatchesOrigin,
             ref moveOrders,
             ref validationResults);
@@ -90,7 +90,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         ILookup<bool, MoveOrder> moveOrdersByAdjacency = moveOrders
             .ToLookup(order =>
                 // Map adjacency
-                world.Map.GetLocation(order.Unit).Adjacents.Contains(order.Location)
+                order.Unit.Location.Adjacents.Contains(order.Location)
                 // Turn adjacency
                 && Math.Abs(order.Unit.Season.Turn - order.Season.Turn) <= 1
                 // Timeline adjacency
@@ -138,7 +138,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         // Trivial check: cannot convoy a unit to its own location
         AdjudicatorHelpers.InvalidateIfNotMatching(
             order => !(
-                order.Location.Designation == order.Target.Location
+                order.Location == order.Target.Location
                 && order.Season == order.Target.Season),
             ValidationReason.DestinationMatchesOrigin,
             ref convoyOrders,
@@ -175,8 +175,8 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         AdjudicatorHelpers.InvalidateIfNotMatching(
             order =>
                 // Map adjacency with respect to province
-                world.Map.GetLocation(order.Unit).Adjacents.Any(
+                order.Unit.Location.Adjacents.Any(
-                    adjLocation => adjLocation.Province == world.Map.GetLocation(order.Target).Province)
+                    adjLocation => adjLocation.Province == order.Target.Province)
                 // Turn adjacency
                 && Math.Abs(order.Unit.Season.Turn - order.Target.Season.Turn) <= 1
                 // Timeline adjacency
@@ -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 => world.Map.GetLocation(order.Unit).Province != order.Province,
+            order => order.Unit.Province != order.Province,
             ValidationReason.NoSupportMoveAgainstSelf,
             ref supportMoveOrders,
             ref validationResults);
@@ -207,7 +207,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
         AdjudicatorHelpers.InvalidateIfNotMatching(
             order =>
                 // Map adjacency with respect to province
-                world.Map.GetLocation(order.Unit).Adjacents.Any(
+                order.Unit.Location.Adjacents.Any(
                     adjLocation => adjLocation.Province == order.Province)
                 // Turn adjacency
                 && Math.Abs(order.Unit.Season.Turn - order.Season.Turn) <= 1
@@ -337,7 +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.Designation, createdFutures[moveSeason]);
+                Unit next = doesMove.Order.Unit.Next(doesMove.Order.Location, createdFutures[moveSeason]);
                 logger.Log(3, "Advancing unit to {0}", next);
                 createdUnits.Add(next);
             }
@@ -366,7 +366,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
             if (isDislodged.Outcome == false)
             {
                 // Non-dislodged units continue into the future.
-                Unit next = order.Unit.Next(world.Map.GetLocation(order.Unit).Designation, future);
+                Unit next = order.Unit.Next(order.Unit.Location, future);
                 logger.Log(3, "Advancing unit to {0}", next);
                 createdUnits.Add(next);
             }
@@ -375,7 +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 = world.Map.GetLocation(order.Unit).Adjacents
+                var validRetreats = order.Unit.Location.Adjacents
                     .Select(loc => (future, loc))
                     .ToList();
                 RetreatingUnit retreat = new(order.Unit, validRetreats);
@@ -633,7 +633,7 @@ public class MovementPhaseAdjudicator : IPhaseAdjudicator
 
         // If the origin and destination are adjacent, then there is a path.
         if (// Map adjacency
-            world.Map.GetLocation(decision.Order.Unit).Adjacents.Contains(decision.Order.Location)
+            decision.Order.Unit.Location.Adjacents.Contains(decision.Order.Location)
             // Turn adjacency
             && Math.Abs(decision.Order.Unit.Season.Turn - decision.Order.Season.Turn) <= 1
             // Timeline adjacency

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<(string location, Season season), Unit> fleets = world.Units
+        IDictionary<(Location 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 (world.Map.GetLocation(movingUnit).Type != LocationType.Land) return false;
+        if (movingUnit.Location.Type != LocationType.Land) return false;
-        IEnumerable<Location> originCoasts = world.Map.GetLocation(movingUnit).Province.Locations
+        IEnumerable<Location> originCoasts = movingUnit.Province.Locations
             .Where(location => location.Type == LocationType.Water);
         if (!originCoasts.Any()) return false;
 
@@ -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.Designation, adjSeason))
+                    && fleets.ContainsKey((adjLocation, adjSeason))
                     && !visited.Contains((adjLocation, adjSeason)))
                 {
                     toVisit.Enqueue((adjLocation, adjSeason));

MultiversalDiplomacy/Model/Location.cs

@@ -20,12 +20,12 @@ public class Location
     /// <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.
@@ -39,12 +39,7 @@ public class Location
     public IEnumerable<Location> Adjacents => this.AdjacentList;
     private List<Location> AdjacentList { get; set; }
 
-    /// <summary>
+    public Location(Province province, string? name, string? abbreviation, LocationType type)
-    /// 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;
@@ -55,7 +50,7 @@ public class Location
 
     public override string ToString()
     {
-        return this.Name == "land" || this.Name == "water"
+        return this.Name == null
             ? $"{this.Province.Name} ({this.Type})"
             : $"{this.Province.Name} ({this.Type}:{this.Name}]";
     }

MultiversalDiplomacy/Model/Map.cs

@@ -17,8 +17,6 @@ public class Map
 
     private List<Province> _Provinces { get; }
 
-    private Dictionary<string, Location> LocationLookup { get; }
-
     /// <summary>
     /// The game powers.
     /// </summary>
@@ -31,10 +29,6 @@ public class Map
         Type = type;
         _Provinces = provinces.ToList();
         _Powers = powers.ToList();
-
-        LocationLookup = Provinces
-            .SelectMany(province => province.Locations)
-            .ToDictionary(location => location.Designation);
     }
 
     /// <summary>
@@ -47,27 +41,29 @@ public class Map
     /// 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)
+        string provinceNameUpper = provinceName.ToUpperInvariant();
-                || p.Abbreviations.Any(
+        Province? foundProvince = provinces.SingleOrDefault(
-                    a => a.Equals(provinceName, StringComparison.InvariantCultureIgnoreCase)),
+            p => p!.Name.ToUpperInvariant() == provinceNameUpper
-            null)
+                || p.Abbreviations.Any(a => a.ToUpperInvariant() == provinceNameUpper),
-            ?? throw new KeyNotFoundException($"Province {provinceName} not found");
+            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)
-        => GetProvince(provinceName).Locations.SingleOrDefault(
+    {
-            l => l != null && predicate(l), null)
+        Location? foundLocation = GetProvince(provinceName).Locations.SingleOrDefault(
-            ?? throw new KeyNotFoundException($"No such location in {provinceName}");
+            l => l != null && predicate(l), null);
-
+        if (foundLocation == null) throw new KeyNotFoundException(
-    public Location GetLocation(string designation)
+            $"No such location in {provinceName}");
-        => LocationLookup[designation];
+        return foundLocation;
-
+    }
-    public Location GetLocation(Unit unit)
-        => GetLocation(unit.Location);
 
     /// <summary>
     /// Get the sole land location of a province.
@@ -125,10 +121,10 @@ public class Map
 #region Provinces
             Province.Empty("North Africa", "NAF")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Tunis", "TUN")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Bohemia", "BOH")
                 .AddLandLocation(),
             Province.Supply("Budapest", "BUD")
@@ -137,71 +133,71 @@ public class Map
                 .AddLandLocation(),
             Province.Supply("Trieste", "TRI")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Tyrolia", "TYR")
                 .AddLandLocation(),
             Province.Time("Vienna", "VIE")
                 .AddLandLocation(),
             Province.Empty("Albania", "ALB")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Bulgaria", "BUL")
                 .AddLandLocation()
                 .AddCoastLocation("east coast", "ec")
                 .AddCoastLocation("south coast", "sc"),
             Province.Supply("Greece", "GRE")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Rumania", "RUM", "RMA")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Serbia", "SER")
                 .AddLandLocation(),
             Province.Empty("Clyde", "CLY")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Edinburgh", "EDI")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Liverpool", "LVP", "LPL")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Time("London", "LON")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Wales", "WAL")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Yorkshire", "YOR")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Brest", "BRE")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Burgundy", "BUR")
                 .AddLandLocation(),
             Province.Empty("Gascony", "GAS")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Marseilles", "MAR")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Time("Paris", "PAR")
                 .AddLandLocation(),
             Province.Empty("Picardy", "PIC")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Time("Berlin", "BER")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Kiel", "KIE")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Munich", "MUN")
                 .AddLandLocation(),
             Province.Empty("Prussia", "PRU")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Ruhr", "RUH", "RHR")
                 .AddLandLocation(),
             Province.Empty("Silesia", "SIL")
@@ -212,43 +208,43 @@ public class Map
                 .AddCoastLocation("south coast", "sc"),
             Province.Supply("Portugal", "POR")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Apulia", "APU")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Naples", "NAP")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Piedmont", "PIE")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Time("Rome", "ROM", "RME")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Tuscany", "TUS")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Venice", "VEN")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Belgium", "BEL")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Holland", "HOL")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Finland", "FIN")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Livonia", "LVN", "LVA")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Time("Moscow", "MOS")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Sevastopol", "SEV")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Saint Petersburg", "STP")
                 .AddLandLocation()
                 .AddCoastLocation("north coast", "nc")
@@ -259,28 +255,28 @@ public class Map
                 .AddLandLocation(),
             Province.Supply("Denmark", "DEN")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Norway", "NWY")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Sweden", "SWE")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Ankara", "ANK")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Armenia", "ARM")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Time("Constantinople", "CON")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Supply("Smyrna", "SMY")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Syria", "SYR")
                 .AddLandLocation()
-                .AddOceanLocation(),
+                .AddCoastLocation(),
             Province.Empty("Barents Sea", "BAR")
                 .AddOceanLocation(),
             Province.Empty("English Channel", "ENC", "ECH")

MultiversalDiplomacy/Model/Province.cs

@@ -37,7 +37,7 @@ public class Province
         this.Abbreviations = abbreviations;
         this.IsSupplyCenter = isSupply;
         this.IsTimeCenter = isTime;
-        this.LocationList = [];
+        this.LocationList = new List<Location>();
     }
 
     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(name, abbreviations, isSupply: false, isTime: false);
+        => new Province(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(name, abbreviations, isSupply: true, isTime: false);
+        => new Province(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(name, abbreviations, isSupply: true, isTime: true);
+        => new Province(name, abbreviations, isSupply: true, isTime: true);
 
     /// <summary>
     /// Create a new land location in this province.
     /// </summary>
     public Province AddLandLocation()
     {
-        Location location = new(this, "land", "l", LocationType.Land);
+        Location location = new Location(this, name: null, abbreviation: null, LocationType.Land);
         this.LocationList.Add(location);
         return this;
     }
@@ -78,7 +78,19 @@ public class Province
     /// </summary>
     public Province AddOceanLocation()
     {
-        Location location = new(this, "water", "w", LocationType.Water);
+        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);
         this.LocationList.Add(location);
         return this;
     }
@@ -89,7 +101,7 @@ public class Province
     /// </summary>
     public Province AddCoastLocation(string name, string abbreviation)
     {
-        Location location = new(this, name, abbreviation, LocationType.Water);
+        Location location = new Location(this, name, abbreviation, LocationType.Water);
         this.LocationList.Add(location);
         return this;
     }

MultiversalDiplomacy/Model/Unit.cs

@@ -1,3 +1,5 @@
+using System.Text.Json.Serialization;
+
 namespace MultiversalDiplomacy.Model;
 
 /// <summary>
@@ -8,12 +10,18 @@ public class Unit
     /// <summary>
     /// The previous iteration of a unit. This is null if the unit was just built.
     /// </summary>
-    public string? Past { get; }
+    public Unit? Past { get; }
 
     /// <summary>
     /// The location on the map where the unit is.
     /// </summary>
-    public string Location { get; }
+    public Location Location { get; }
+
+    /// <summary>
+    /// The province where the unit is.
+    /// </summary>
+    [JsonIgnore]
+    public Province Province => this.Location.Province;
 
     /// <summary>
     /// The season in time when the unit is.
@@ -31,11 +39,11 @@ public class Unit
     public UnitType Type { get; }
 
     /// <summary>
-    /// A unique designation for this unit.
+    /// The unit's spatiotemporal location as a province-season tuple.
     /// </summary>
-    public string Designation => $"{Type.ToShort()} {Season.Timeline}-{Location}@{Season.Turn}";
+    public (Province province, Season season) Point => (this.Province, this.Season);
 
-    private Unit(string? past, string location, Season season, Power power, UnitType type)
+    private Unit(Unit? past, Location location, Season season, Power power, UnitType type)
     {
         this.Past = past;
         this.Location = location;
@@ -45,18 +53,20 @@ public class Unit
     }
 
     public override string ToString()
-        => $"{Power.Name[0]} {Type.ToShort()} {Season.Timeline}-{Location}@{Season.Turn}";
+    {
+        return $"{this.Power.Name[0]} {this.Type.ToShort()} {(this.Province, this.Season).ToShort()}";
+    }
 
     /// <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(string location, Season season, Power power, UnitType type)
+    public static Unit Build(Location 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(string location, Season season)
+    public Unit Next(Location location, Season season)
-        => new(past: this.Designation, location, season, this.Power, this.Type);
+        => new(past: this, location, season, this.Power, this.Type);
 }

MultiversalDiplomacy/Model/World.cs

@@ -1,3 +1,4 @@
+using System.Collections.ObjectModel;
 using System.Text.Json.Serialization;
 
 namespace MultiversalDiplomacy.Model;
@@ -204,7 +205,7 @@ public class World
                 : splits.Length == 3
                     ? Map.GetWater(splits[2])
                     : Map.GetWater(splits[2], splits[3]);
-            Unit unit = Unit.Build(location.Designation, this.RootSeason, power, type);
+            Unit unit = Unit.Build(location, this.RootSeason, power, type);
             return unit;
         });
         return this.Update(units: units);
@@ -327,13 +328,9 @@ public class World
         Province province = Map.GetProvince(provinceName);
         season ??= RootSeason;
         Unit? foundUnit = this.Units.SingleOrDefault(
-            u => Map.GetLocation(u!).Province == province && u!.Season == season,
+            u => u!.Province == province && u.Season == season,
             null)
             ?? throw new KeyNotFoundException($"Unit at {province} at {season} not found");
         return foundUnit;
     }
-
-    public Unit GetUnitByDesignation(string designation)
-        => Units.SingleOrDefault(u => u!.Designation == designation, null)
-        ?? throw new KeyNotFoundException($"Unit {designation} not found");
 }

MultiversalDiplomacy/Orders/MoveOrder.cs

@@ -39,6 +39,15 @@ 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

@@ -16,4 +16,12 @@ 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

@@ -46,12 +46,12 @@ public class TimeTravelTest
         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(aTyr.Past, Is.EqualTo(mun1.Order.Unit));
-        Assert.That(world.GetUnitByDesignation(aTyr.Past!).Past, Is.EqualTo(mun0.Order.Unit.Designation));
+        Assert.That(aTyr.Past?.Past, Is.EqualTo(mun0.Order.Unit));
 
         // 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));
+        Assert.That(aMun1.Past, Is.EqualTo(originalUnit));
     }
 
     [Test]
@@ -95,7 +95,7 @@ public class TimeTravelTest
         Unit tyr1 = world.GetUnitAt("Tyr", fork);
         Assert.That(
             tyr1.Past,
-            Is.EqualTo(mun0.Order.Unit.Designation),
+            Is.EqualTo(mun0.Order.Unit),
             "Expected A Mun a0 to advance to Tyr b1");
         Assert.That(
             world.RetreatingUnits.Count,

MultiversalDiplomacyTests/MovementAdjudicatorTest.cs

@@ -209,7 +209,7 @@ public class MovementAdjudicatorTest
         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.Designation));
+        Assert.That(u2.Past, Is.EqualTo(mun1.Order.Unit));
         Assert.That(u2.Season, Is.EqualTo(s2));
 
         setup[("a", 1)]
@@ -229,7 +229,7 @@ public class MovementAdjudicatorTest
         updated = setup.UpdateWorld();
         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));
+        Assert.That(u3.Past, Is.EqualTo(mun2.Order.Unit));
     }
 
     [Test]
@@ -259,7 +259,7 @@ public class MovementAdjudicatorTest
         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.Designation));
+        Assert.That(u2.Past, Is.EqualTo(mun1.Order.Unit));
         Assert.That(u2.Season, Is.EqualTo(s2));
 
         setup[("a", 1)]
@@ -279,6 +279,6 @@ public class MovementAdjudicatorTest
         updated = setup.UpdateWorld();
         Season s3 = updated.GetSeason(s2.Timeline, s2.Turn + 1);
         Unit u3 = updated.GetUnitAt("Mun", s3);
-        Assert.That(u3.Past, Is.EqualTo(u2.Designation));
+        Assert.That(u3.Past, Is.EqualTo(u2));
     }
 }

MultiversalDiplomacyTests/OrderReference.cs

@@ -108,7 +108,8 @@ 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 == Builder.World.Map.GetLocation(unitOrder.Unit).Province,
+                    ? hold.Province == unitOrder.Unit.Province
+                    : false,
                 _ => false,
             }).ToList();
             return adjudications;

MultiversalDiplomacyTests/SerializationTest.cs

@@ -94,7 +94,7 @@ public class SerializationTest
         Unit tyr1 = world.GetUnitAt("Tyr", fork);
         Assert.That(
             tyr1.Past,
-            Is.EqualTo(mun0.Order.Unit.Designation),
+            Is.EqualTo(mun0.Order.Unit),
             "Expected A Mun a0 to advance to Tyr b1");
         Assert.That(
             world.RetreatingUnits.Count,

MultiversalDiplomacyTests/TestCaseBuilder.cs

@@ -262,7 +262,7 @@ public class TestCaseBuilder
         foreach (Unit unit in this.World.Units)
         {
             if (unit.Power == power
-                && World.Map.GetLocation(unit).Province == location.Province
+                && unit.Province == location.Province
                 && unit.Season == season)
             {
                 return unit;
@@ -270,7 +270,7 @@ public class TestCaseBuilder
         }
 
         // Not found
-        Unit newUnit = Unit.Build(location.Designation, season, power, type);
+        Unit newUnit = Unit.Build(location, season, power, type);
         this.World = this.World.Update(units: this.World.Units.Append(newUnit));
         return newUnit;
     }

MultiversalDiplomacyTests/TestCaseBuilderTest.cs

@@ -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.Map.GetWater("STP", "wc").Designation),
+            Is.EqualTo(setup.World.Map.GetWater("STP", "wc")),
             "Unit created on wrong coast");
     }
 
@@ -68,7 +68,7 @@ class TestCaseBuilderTest
         List<UnitOrder> orders = setup.Orders.OfType<UnitOrder>().ToList();
 
         Func<UnitOrder, bool> OrderForProvince(string name)
-            => order => setup.World.Map.GetLocation(order.Unit).Province.Name == name;
+            => order => order.Unit.Province.Name == name;
 
         UnitOrder orderBer = orders.Single(OrderForProvince("Berlin"));
         Assert.That(orderBer, Is.InstanceOf<MoveOrder>(), "Unexpected order type");
@@ -128,7 +128,7 @@ class TestCaseBuilderTest
             "Wrong power");
         Assert.That(
             orderMun.Order.Unit.Location,
-            Is.EqualTo(setup.World.Map.GetLand("Mun").Designation),
+            Is.EqualTo(setup.World.Map.GetLand("Mun")),
             "Wrong unit");
 
         Assert.That(

MultiversalDiplomacyTests/UnitTests.cs

@@ -15,24 +15,24 @@ public class UnitTests
             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);
+        Unit u1 = Unit.Build(Mun, a0, pw1, UnitType.Army);
 
         world = world.ContinueOrFork(a0, out Season a1);
-        Unit u2 = u1.Next(Boh.Designation, a1);
+        Unit u2 = u1.Next(Boh, a1);
 
         _ = world.ContinueOrFork(a1, out Season a2);
-        Unit u3 = u2.Next(Tyr.Designation, a2);
+        Unit u3 = u2.Next(Tyr, a2);
 
-        Assert.That(u3.Past, Is.EqualTo(u2.Designation), "Missing unit past");
+        Assert.That(u3.Past, Is.EqualTo(u2), "Missing unit past");
-        Assert.That(u2.Past, Is.EqualTo(u1.Designation), "Missing unit past");
+        Assert.That(u2.Past, Is.EqualTo(u1), "Missing unit past");
         Assert.That(u1.Past, Is.Null, "Unexpected unit past");
 
         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.Designation), "Unexpected unit location");
+        Assert.That(u1.Location, Is.EqualTo(Mun), "Unexpected unit location");
-        Assert.That(u2.Location, Is.EqualTo(Boh.Designation), "Unexpected unit location");
+        Assert.That(u2.Location, Is.EqualTo(Boh), "Unexpected unit location");
-        Assert.That(u3.Location, Is.EqualTo(Tyr.Designation), "Unexpected unit location");
+        Assert.That(u3.Location, Is.EqualTo(Tyr), "Unexpected unit location");
     }
 }