5dplomacy/MultiversalDiplomacyTests/MDATC_A.cs

using MultiversalDiplomacy.Adjudicate;
using MultiversalDiplomacy.Adjudicate.Decision;
using MultiversalDiplomacy.Model;

using NUnit.Framework;

namespace MultiversalDiplomacyTests;

public class TimeTravelTest
{
    [Test]
    public void MDATC_3_A_1_MoveIntoOwnPastForksTimeline()
    {
        TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);

        // Hold to move into the future, then move back into the past.
        setup[("a", 0)]
            .GetReference(out Season s0)
            ["Germany"]
                .Army("Mun").Holds().GetReference(out var mun0)
            .Execute()
        [("a", 1)]
            .GetReference(out Season s1)
            ["Germany"]
                .Army("Mun").MovesTo("Tyr", season: s0).GetReference(out var mun1);

        setup.ValidateOrders();
        Assert.That(mun1, Is.Valid);
        setup.AdjudicateOrders();
        Assert.That(mun1, Is.Victorious);

        World world = setup.UpdateWorld();

        // Confirm that there are now four seasons: three in the main timeline and one in a fork.
        Assert.That(
            world.Timelines.Pasts.Keys.Select(key => new Season(key)).Where(s => s.Timeline == s0.Timeline).Count(),
            Is.EqualTo(3),
            "Failed to advance main timeline after last unit left");
        Assert.That(
            world.Timelines.Pasts.Keys.Select(key => new Season(key)).Where(s => s.Timeline != s0.Timeline).Count(),
            Is.EqualTo(1),
            "Failed to fork timeline when unit moved in");

        // Confirm that there is a unit in Tyr b1 originating from Mun a1
        Season fork = new("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.Key));
        Assert.That(world.GetUnitByKey(aTyr.Past!).Past, Is.EqualTo(mun0.Order.Unit.Key));

        // 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.Key));
    }

    [Test]
    public void MDATC_3_A_2_SupportToRepelledPastMoveForksTimeline()
    {
        TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);

        // Fail to dislodge on the first turn, then support the move so it succeeds.
        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();

        setup[("a", 1)]
            ["Germany"]
                .Army("Mun").Supports.Army("Mun", season: s0).MoveTo("Tyr").GetReference(out var mun1)
            ["Austria"]
                .Army("Tyr").Holds();

        // Confirm that history is changed.
        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 = new("b1");
        Unit tyr1 = world.GetUnitAt("Tyr", fork);
        Assert.That(
            tyr1.Past,
            Is.EqualTo(mun0.Order.Unit.Key),
            "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));
    }

    [Test]
    public void MDATC_3_A_3_FailedMoveDoesNotForkTimeline()
    {
        TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);

        // Hold to create a future, then attempt to attack in the past.
        setup[("a", 0)]
            .GetReference(out Season s0)
            ["Germany"]
                .Army("Mun").Holds()
            ["Austria"]
                .Army("Tyr").Holds().GetReference(out var tyr0)
            .Execute()
        [("a", 1)]
            .GetReference(out Season s1)
            ["Germany"]
                .Army("Mun").MovesTo("Tyr", season: s0).GetReference(out var mun1)
            ["Austria"]
                .Army("Tyr").Holds();

        setup.ValidateOrders();
        Assert.That(mun1, Is.Valid);
        setup.AdjudicateOrders();
        Assert.That(mun1, Is.Repelled);
        // 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);

        // There should only be three seasons, all in the main timeline, since the move failed to
        // change the past and therefore did not create a new timeline.
        World world = setup.UpdateWorld();
        Assert.That(
            world.Timelines.GetFutures(s0).Count(),
            Is.EqualTo(1),
            "A failed move incorrectly forked the timeline");
        Assert.That(world.Timelines.GetFutures(s1).Count(), Is.EqualTo(1));
        Season s2 = new(s1.Timeline, s1.Turn + 1);
        Assert.That(world.Timelines.GetFutures(s2).Count(), Is.EqualTo(0));
    }

    [Test]
    public void MDATC_3_A_4_SuperfluousSupportDoesNotForkTimeline()
    {
        TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);

        // Move, then support the past move even though it succeeded already.
        setup[("a", 0)]
            .GetReference(out Season s0)
            ["Germany"]
                .Army("Mun").MovesTo("Tyr").GetReference(out var mun0)
                .Army("Boh").Holds();

        setup.ValidateOrders();
        Assert.That(mun0, Is.Valid);
        setup.AdjudicateOrders();
        Assert.That(mun0, Is.Victorious);
        setup.UpdateWorld();

        setup[("a", 1)]
            .GetReference(out Season s1)
            ["Germany"]
                .Army("Tyr").Holds()
                .Army("Boh").Supports.Army("Mun", season: s0).MoveTo("Tyr").GetReference(out var boh1);

        // The support does work and the move does succeed, but...
        setup.ValidateOrders();
        Assert.That(boh1, Is.Valid);
        setup.AdjudicateOrders();
        Assert.That(boh1, Is.NotCut);
        Assert.That(mun0, Is.Victorious);

        // ...since it succeeded anyway, no fork is created.
        World world = setup.UpdateWorld();
        Assert.That(
            world.Timelines.GetFutures(s0).Count(),
            Is.EqualTo(1),
            "A superfluous support incorrectly forked the timeline");
        Assert.That(world.Timelines.GetFutures(s1).Count(), Is.EqualTo(1));
        Season s2 = new(s1.Timeline, s1.Turn + 1);
        Assert.That(world.Timelines.GetFutures(s2).Count(), Is.EqualTo(0));
    }

    [Test]
    public void MDATC_3_A_5_CrossTimelineSupportDoesNotForkHead()
    {
        TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);

        // London creates two timelines by moving into the past.
        setup[("a", 0)]
            .GetReference(out var a0)
            ["England"].Army("Lon").Holds()
            ["Austria"].Army("Tyr").Holds()
            ["Germany"].Army("Mun").Holds()
            .Execute()
        [("a", 1)]
            ["England"].Army("Lon").MovesTo("Yor", a0)
            .Execute()
        // 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.
        [("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 a2 succeeds.
        setup.ValidateOrders();
        Assert.That(mun_a2, Is.Valid);
        Assert.That(tyr_a2, Is.Valid);
        Assert.That(mun_b1, Is.Valid);
        setup.AdjudicateOrders();
        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(
            world.Timelines.GetFutures(a2).Count(),
            Is.EqualTo(1),
            "A cross-timeline support incorrectly forked the head of the timeline");
        Assert.That(
            world.Timelines.GetFutures(b1).Count(),
            Is.EqualTo(1),
            "A cross-timeline support incorrectly forked the head of the timeline");
        Season a3 = new(a2.Timeline, a2.Turn + 1);
        Assert.That(world.Timelines.GetFutures(a3).Count(), Is.EqualTo(0));
        Season b2 = new(b1.Timeline, b1.Turn + 1);
        Assert.That(world.Timelines.GetFutures(b2).Count(), Is.EqualTo(0));
    }

    [Test]
    public void MDATC_3_A_6_CuttingCrossTimelineSupportDoesNotFork()
    {
        TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);

        // As above, only now London creates three timelines.
        setup[("a", 0)]
            .GetReference(out var a0)
            ["England"].Army("Lon").Holds()
            ["Austria"].Army("Boh").Holds()
            ["Germany"].Army("Mun").Holds()
            .Execute()
        [("a", 1)]
            ["England"].Army("Lon").MovesTo("Yor", a0)
            .Execute()
        // Head seasons: a2, b1
        [("a", 2)]
        [("b", 1)]
            ["England"].Army("Yor").MovesTo("Edi", a0)
            .Execute()
        // 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 a3 by supporting the move from b2.
        [("a", 3)]
            .GetReference(out var a3)
            ["Germany"].Army("Mun").MovesTo("Tyr")
            ["Austria"].Army("Tyr").Holds()
        [("b", 2)]
            .GetReference(out Season b2)
            ["Germany"].Army("Mun").Supports.Army("Mun", a3).MoveTo("Tyr").GetReference(out var mun_b2)
            ["Austria"].Army("Tyr").Holds()
        [("c", 1)]
            ["Germany"].Army("Mun").Holds()
            ["Austria"].Army("Tyr").Holds()
            .Execute()
        // Head seasons: a4, b3, c2
        // Now Austria cuts the support in b2 by attacking from c2.
        [("a", 4)]
            ["Germany"].Army("Tyr").Holds()
        [("b", 3)]
            ["Germany"].Army("Mun").Holds()
            ["Austria"].Army("Tyr").Holds()
        [("c", 2)]
            ["Germany"].Army("Mun").Holds()
            ["Austria"].Army("Tyr").MovesTo("Mun", b2).GetReference(out var tyr_c2);

        // The attack on Mun b2 is repelled, but the support is cut.
        setup.ValidateOrders();
        Assert.That(tyr_c2, Is.Valid);
        setup.AdjudicateOrders();
        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(
            world.Timelines.GetFutures(a3).Count(),
            Is.EqualTo(1),
            "A cross-timeline support cut incorrectly forked the timeline");
        Assert.That(
            world.Timelines.GetFutures(b2).Count(),
            Is.EqualTo(1),
            "A cross-timeline support cut incorrectly forked the timeline");
    }
}