PkmnLib.NET/Plugins/PkmnLib.Plugin.Gen7.Tests/Scripts/Moves/FollowMeTests.cs

using PkmnLib.Dynamic.Models;
using PkmnLib.Dynamic.Models.Choices;
using PkmnLib.Dynamic.ScriptHandling;
using PkmnLib.Plugin.Gen7.Common;
using PkmnLib.Plugin.Gen7.Scripts.Moves;
using PkmnLib.Plugin.Gen7.Scripts.Pokemon;
using PkmnLib.Static.Moves;
using PkmnLib.Static.Utils;

namespace PkmnLib.Plugin.Gen7.Tests.Scripts.Moves;

/// <summary>
/// Tests for the <see cref="FollowMe"/> script, and the <see cref="FollowMeEffect"/> it registers on its user.
/// Behavior is verified against the Bulbapedia page for Follow Me (Generation VII).
/// </summary>
public class FollowMeTests
{
    /// <summary>The side the center of attention and its ally are on.</summary>
    private const byte CenterSide = 0;

    /// <summary>The side the attacking opponents are on.</summary>
    private const byte OpposingSide = 1;

    /// <summary>
    /// A two-sided battle, each side carrying its own <see cref="IBattleSide.VolatileScripts"/>.
    /// </summary>
    private sealed class Arena
    {
        public IBattle Battle { get; } = Substitute.For<IBattle>();
        public IBattleSide[] Sides { get; } = [CreateSide(), CreateSide()];

        private static IBattleSide CreateSide()
        {
            var side = Substitute.For<IBattleSide>();
            side.VolatileScripts.Returns(Substitute.For<IScriptSet>());
            return side;
        }
    }

    /// <summary>
    /// Creates a mocked Pokémon standing on the given side of the given <see cref="Arena"/>.
    /// </summary>
    private static IPokemon CreatePokemon(Arena arena, byte sideIndex)
    {
        var pokemon = Substitute.For<IPokemon>();
        pokemon.Volatile.Returns(Substitute.For<IScriptSet>());

        var battleData = Substitute.For<IPokemonBattleData>();
        battleData.SideIndex.Returns(sideIndex);
        battleData.BattleSide.Returns(arena.Sides[sideIndex]);
        battleData.Battle.Returns(arena.Battle);
        pokemon.BattleData.Returns(battleData);
        return pokemon;
    }

    /// <summary>
    /// Creates a mocked move choice made by the given Pokémon, using the named move.
    /// </summary>
    private static IMoveChoice CreateMoveChoice(IPokemon user, string moveName = "tackle", bool noRedirection = false)
    {
        var moveData = Substitute.For<IMoveData>();
        moveData.Name.Returns(new StringKey(moveName));
        moveData.HasFlag(MoveFlags.NoRedirection).Returns(noRedirection);
        var learnedMove = Substitute.For<ILearnedMove>();
        learnedMove.MoveData.Returns(moveData);

        var moveChoice = Substitute.For<IMoveChoice>();
        moveChoice.User.Returns(user);
        moveChoice.ChosenMove.Returns(learnedMove);
        return moveChoice;
    }

    /// <summary>
    /// Returns the script that was handed to <see cref="IScriptSet.Add"/> or
    /// <see cref="IScriptSet.StackOrAdd"/> on the given set, or null if the set never received one.
    /// </summary>
    private static Script? RegisteredScript(IScriptSet set)
    {
        foreach (var call in set.ReceivedCalls())
        {
            var arguments = call.GetArguments();
            switch (call.GetMethodInfo().Name)
            {
                case "Add" when arguments[0] is Script script:
                    return script;
                case "StackOrAdd" when arguments[1] is Func<Script?> instantiation:
                    return instantiation();
            }
        }
        return null;
    }

    /// <summary>
    /// Executes <see cref="FollowMe"/> for the given user and returns the center-of-attention effect it
    /// registered, regardless of which script set it chose to register it on.
    /// </summary>
    private static Script? MakeCenterOfAttention(IPokemon user)
    {
        var followMe = new FollowMe();
        var move = Substitute.For<IExecutingMove>();
        move.User.Returns(user);

        followMe.OnSecondaryEffect(move, user, 0);

        return RegisteredScript(user.Volatile) ?? RegisteredScript(user.BattleData!.BattleSide.VolatileScripts);
    }

    /// <summary>
    /// Drives the registered effect through whichever target-redirection hook it implements, mirroring the two
    /// hooks the engine runs while resolving a move's targets.
    /// </summary>
    private static void Redirect(Script effect, IMoveChoice moveChoice, ref IReadOnlyList<IPokemon?> targets)
    {
        switch (effect)
        {
            case IScriptChangeIncomingTargets incomingTargets:
                incomingTargets.ChangeIncomingTargets(moveChoice, ref targets);
                break;
            case IScriptChangeTargets changeTargets:
                changeTargets.ChangeTargets(moveChoice, ref targets);
                break;
        }
    }

    /// <summary>
    /// Bulbapedia: "Follow Me ... makes the user the center of attention ... for the rest of the turn."
    /// Opposing Pokémon act in their own, later move choices, so using Follow Me must leave a persistent effect
    /// behind rather than only altering the targets of the Follow Me choice itself.
    /// </summary>
    [Test]
    public async Task OnSecondaryEffect_Used_MakesUserTheCenterOfAttention()
    {
        // Arrange
        var arena = new Arena();
        var user = CreatePokemon(arena, CenterSide);

        // Act
        var effect = MakeCenterOfAttention(user);

        // Assert
        await Assert.That(effect).IsNotNull();
    }

    /// <summary>
    /// Bulbapedia: "forcing opposing Pokémon to use their moves on the user rather than the intended target".
    /// The engine resolves a move's targets by running <see cref="IScriptChangeTargets"/> over the attacker's
    /// own script scope, and <see cref="IScriptChangeIncomingTargets"/> over each intended target's scope —
    /// which covers that target's own scripts and its <see cref="IBattleSide.VolatileScripts"/>. A redirection
    /// effect stored on the center of attention's <see cref="IPokemon.Volatile"/> therefore sits in neither
    /// scope when an opponent attacks the center's ally. It must live on the center's side, the way
    /// <see cref="PkmnLib.Plugin.Gen7.Scripts.Side.RagePowderEffect"/> does.
    /// </summary>
    [Test]
    public async Task OnSecondaryEffect_Used_RegistersEffectOnUsersSide()
    {
        // Arrange
        var arena = new Arena();
        var user = CreatePokemon(arena, CenterSide);

        // Act
        MakeCenterOfAttention(user);

        // Assert
        await Assert.That(RegisteredScript(arena.Sides[CenterSide].VolatileScripts)).IsNotNull();
    }

    /// <summary>
    /// Bulbapedia: "forcing opposing Pokémon to use their moves on the user rather than the intended target".
    /// The effect changes the targets of a move aimed at somebody else, so it has to hook
    /// <see cref="IScriptChangeIncomingTargets"/>, which the engine runs on each intended target.
    /// <see cref="IScriptChangeTargets"/> only ever runs within the attacker's own script scope, so a defending
    /// Pokémon's effect can never be reached through it.
    /// </summary>
    [Test]
    public async Task CenterOfAttentionEffect_ImplementsIncomingTargetsHook()
    {
        // Arrange
        var arena = new Arena();
        var user = CreatePokemon(arena, CenterSide);

        // Act
        var effect = MakeCenterOfAttention(user);

        // Assert
        await Assert.That(effect).IsAssignableTo<IScriptChangeIncomingTargets>();
    }

    /// <summary>
    /// Bulbapedia: "makes the user the center of attention, forcing opposing Pokémon to use their moves on the
    /// user rather than the intended target (even if it was a friendly target ...) for the rest of the turn."
    /// The core behavior: an opponent's single-target move aimed at the center's ally is drawn to the center.
    /// </summary>
    [Test]
    public async Task Redirect_OpposingMoveAimedAtAlly_RedirectsToCenterOfAttention()
    {
        // Arrange
        var arena = new Arena();
        var center = CreatePokemon(arena, CenterSide);
        var ally = CreatePokemon(arena, CenterSide);
        var opponent = CreatePokemon(arena, OpposingSide);
        var effect = MakeCenterOfAttention(center)!;
        var moveChoice = CreateMoveChoice(opponent);
        IReadOnlyList<IPokemon?> targets = [ally];

        // Act
        Redirect(effect, moveChoice, ref targets);

        // Assert
        await Assert.That(targets.Count).IsEqualTo(1);
        await Assert.That(targets[0]).IsEqualTo(center);
    }

    /// <summary>
    /// Bulbapedia: "Follow Me has no effect on moves which hit multiple Pokémon in a battle."
    /// </summary>
    [Test]
    public async Task Redirect_MultiTargetMove_TargetsUnchanged()
    {
        // Arrange
        var arena = new Arena();
        var center = CreatePokemon(arena, CenterSide);
        var ally = CreatePokemon(arena, CenterSide);
        var opponent = CreatePokemon(arena, OpposingSide);
        var effect = MakeCenterOfAttention(center)!;
        var moveChoice = CreateMoveChoice(opponent);
        IReadOnlyList<IPokemon?> targets = [center, ally];

        // Act
        Redirect(effect, moveChoice, ref targets);

        // Assert
        await Assert.That(targets.Count).IsEqualTo(2);
        await Assert.That(targets[0]).IsEqualTo(center);
        await Assert.That(targets[1]).IsEqualTo(ally);
    }

    /// <summary>
    /// Bulbapedia: "It does not affect allies."
    /// A move used by the center of attention's own ally keeps its intended target.
    /// </summary>
    [Test]
    public async Task Redirect_AllyMove_TargetsUnchanged()
    {
        // Arrange
        var arena = new Arena();
        var center = CreatePokemon(arena, CenterSide);
        var attackingAlly = CreatePokemon(arena, CenterSide);
        var targetedAlly = CreatePokemon(arena, CenterSide);
        var effect = MakeCenterOfAttention(center)!;
        var moveChoice = CreateMoveChoice(attackingAlly);
        IReadOnlyList<IPokemon?> targets = [targetedAlly];

        // Act
        Redirect(effect, moveChoice, ref targets);

        // Assert
        await Assert.That(targets.Count).IsEqualTo(1);
        await Assert.That(targets[0]).IsEqualTo(targetedAlly);
    }

    /// <summary>
    /// Bulbapedia: "forcing opposing Pokémon to use their moves on the user rather than the intended target."
    /// A move already aimed at the center of attention simply stays there.
    /// </summary>
    [Test]
    public async Task Redirect_MoveAimedAtCenterOfAttention_TargetsUnchanged()
    {
        // Arrange
        var arena = new Arena();
        var center = CreatePokemon(arena, CenterSide);
        var opponent = CreatePokemon(arena, OpposingSide);
        var effect = MakeCenterOfAttention(center)!;
        var moveChoice = CreateMoveChoice(opponent);
        IReadOnlyList<IPokemon?> targets = [center];

        // Act
        Redirect(effect, moveChoice, ref targets);

        // Assert
        await Assert.That(targets.Count).IsEqualTo(1);
        await Assert.That(targets[0]).IsEqualTo(center);
    }

    /// <summary>
    /// Creates a real <see cref="ScriptSet"/> hosting the given effect, so that
    /// <see cref="Script.RemoveSelf"/> calls can be observed through <see cref="IScriptSet.Contains"/>.
    /// </summary>
    private static IScriptSet CreateHostedSet(Script effect)
    {
        var owner = Substitute.For<IPokemon>();
        owner.GetScripts().Returns(_ => new ScriptIterator(Array.Empty<IEnumerable<ScriptContainer>>()));
        IScriptSet set = new ScriptSet(owner);
        set.Add(effect);
        return set;
    }

    /// <summary>
    /// Bulbapedia: "If the center of attention faints or switches out, it no longer draws moves."
    /// The effect removes itself from its host script set when the center of attention faints.
    /// </summary>
    [Test]
    public async Task OnFaint_CenterOfAttentionFaints_EffectRemovesItself()
    {
        // Arrange
        var arena = new Arena();
        var center = CreatePokemon(arena, CenterSide);
        var effect = MakeCenterOfAttention(center)!;
        var set = CreateHostedSet(effect);

        // Act
        ((IScriptOnFaint)effect).OnFaint(center, DamageSource.MoveDamage);

        // Assert
        await Assert.That(set.Contains(effect.Name)).IsFalse();
    }

    /// <summary>
    /// Bulbapedia: "If the center of attention faints or switches out, it no longer draws moves."
    /// The effect removes itself from its host script set when the center of attention switches out.
    /// </summary>
    [Test]
    public async Task OnSwitchOut_CenterOfAttentionSwitchesOut_EffectRemovesItself()
    {
        // Arrange
        var arena = new Arena();
        var center = CreatePokemon(arena, CenterSide);
        var effect = MakeCenterOfAttention(center)!;
        var set = CreateHostedSet(effect);

        // Act
        ((IScriptOnSwitchOut)effect).OnSwitchOut(center, 0);

        // Assert
        await Assert.That(set.Contains(effect.Name)).IsFalse();
    }

    /// <summary>
    /// The effect only concerns its own user: another Pokémon fainting leaves the center of attention in place.
    /// </summary>
    [Test]
    public async Task OnFaint_OtherPokemonFaints_EffectStays()
    {
        // Arrange
        var arena = new Arena();
        var center = CreatePokemon(arena, CenterSide);
        var ally = CreatePokemon(arena, CenterSide);
        var effect = MakeCenterOfAttention(center)!;
        var set = CreateHostedSet(effect);

        // Act
        ((IScriptOnFaint)effect).OnFaint(ally, DamageSource.MoveDamage);

        // Assert
        await Assert.That(set.Contains(effect.Name)).IsTrue();
    }

    /// <summary>
    /// Bulbapedia, Generation VI onwards: "Follow Me does not redirect Future Sight or Doom Desire."
    /// Both moves carry the <see cref="MoveFlags.NoRedirection"/> flag in the move data, which the effect
    /// checks to leave them alone.
    /// </summary>
    [Test, Arguments("future_sight"), Arguments("doom_desire")]
    public async Task Redirect_FutureSightOrDoomDesire_TargetsUnchanged(string moveName)
    {
        // Arrange
        var arena = new Arena();
        var center = CreatePokemon(arena, CenterSide);
        var ally = CreatePokemon(arena, CenterSide);
        var opponent = CreatePokemon(arena, OpposingSide);
        var effect = MakeCenterOfAttention(center)!;
        var moveChoice = CreateMoveChoice(opponent, moveName, true);
        IReadOnlyList<IPokemon?> targets = [ally];

        // Act
        Redirect(effect, moveChoice, ref targets);

        // Assert
        await Assert.That(targets.Count).IsEqualTo(1);
        await Assert.That(targets[0]).IsEqualTo(ally);
    }

    /// <summary>
    /// Technical test: an empty target list is left unchanged instead of throwing.
    /// </summary>
    [Test]
    public async Task Redirect_EmptyTargetList_TargetsUnchanged()
    {
        // Arrange
        var arena = new Arena();
        var center = CreatePokemon(arena, CenterSide);
        var opponent = CreatePokemon(arena, OpposingSide);
        var effect = MakeCenterOfAttention(center)!;
        var moveChoice = CreateMoveChoice(opponent);
        IReadOnlyList<IPokemon?> targets = [];

        // Act
        Redirect(effect, moveChoice, ref targets);

        // Assert
        await Assert.That(targets.Count).IsEqualTo(0);
    }

    /// <summary>
    /// Bulbapedia: "makes the user the center of attention ... for the rest of the turn."
    /// The effect has to clear itself once the turn ends, the way <see cref="PkmnLib.Plugin.Gen7.Scripts.Side.RagePowderEffect"/> does
    /// through <see cref="IScriptOnEndTurn"/>; otherwise the user stays the center of attention forever.
    /// </summary>
    [Test]
    public async Task CenterOfAttentionEffect_WearsOffAtEndOfTurn()
    {
        // Arrange
        var arena = new Arena();
        var user = CreatePokemon(arena, CenterSide);

        // Act
        var effect = MakeCenterOfAttention(user);

        // Assert
        await Assert.That(effect).IsAssignableTo<IScriptOnEndTurn>();
    }
}