oecs-sharp/Game.TicTacToe/Commands/PlaceMarkCommand.cs

using MessagePack;
using OECS;

namespace Game.TicTacToe;

/// <summary>
/// Places the current player's mark on the cell at (Row, Col).
/// Validates that the cell is empty and the game is still playing.
/// </summary>
[MessagePackObject]
public struct PlaceMarkCommand : ICommand
{
    [Key(0)] public int Row;
    [Key(1)] public int Col;

    public void Execute(World world)
    {
        if (world.ReadSingleton<GameState>().Status != GameStatus.Playing)
            return;

        // Find the cell entity at (Row, Col) that has no Mark.
        Entity? target = null;

        ref var state = ref world.GetSingleton<GameState>();
        foreach(var iter in world.Select(new Query<Cell>().Without<Mark>())){
            if (iter.Val1.Row != Row || iter.Val1.Col != Col) continue;
            target = iter.Entity;
            break;
        }

        if (target == null)
            return;

        world.AddComponent(target.Value, new Mark { Player = state.CurrentPlayer });

        state.MoveCount++;
        state.CurrentPlayer = state.CurrentPlayer == Player.X ? Player.O : Player.X;
    }
}