oecs-sharp/Game.CardWars/Commands/PlayCardCommand.cs

using MessagePack;
using OECS;

namespace Game.CardWars;

/// <summary>
/// Play a card from hand to the field, choosing a rank.
/// Resolves on-play effects via the CardEffectRegistry.
/// </summary>
[MessagePackObject]
public struct PlayCardCommand : ICommand
{
    [Key(0)] public Entity CardEntity;
    [Key(1)] public int Rank;
    [Key(2)] public bool FaceDown;
    [Key(3)] public Entity? TargetPlayer;

    public void Execute(World world)
    {
        var state = world.ReadSingleton<GameState>();
        if (state.Phase is not GamePhase.PlayPhase) return;
        if (!world.IsAlive(CardEntity)) return;

        Entity player = FindPlayerByIndex(world, state.CurrentPlayerIndex);
        if (player == Entity.Null) return;

        // Verify the card is in the player's hand.
        if (!world.HasComponent<HeldBy>(CardEntity)) return;
        var heldBy = world.ReadComponent<HeldBy>(CardEntity);
        if (heldBy.Target != player) return;

        var def = world.ReadComponent<CardDef>(CardEntity);

        // Determine target: Witch/Thief are played to another player's field.
        Entity fieldOwner = def.Effect is CardEffect.Witch or CardEffect.Thief
            ? (TargetPlayer ?? player)
            : player;

        // Move from hand to field.
        world.RemoveComponent<HeldBy>(CardEntity);
        world.AddComponent(CardEntity, new OnField { Target = fieldOwner });
        world.AddComponent(CardEntity, new Card { Rank = Rank, FaceDown = FaceDown });

        // Resolve on-play effects via registry.
        if (!FaceDown)
            CardEffectRegistry.Dispatch(world, def.Effect, CardEntity, player, fieldOwner);

        world.MarkModified<GameState>(World.SingletonEntity);
    }

    public static Entity FindPlayerByIndex(World world, int index)
    {
        using var iter = world.Select<Player>();
        while (iter.MoveNext())
        {
            if (iter.CurrentEntity == World.SingletonEntity) continue;
            if (iter.Current1.Index == index)
                return iter.CurrentEntity;
        }
        return Entity.Null;
    }
}