oecs-sharp/Game.Blackjack/Commands/HitCommand.cs

using MessagePack;
using OECS;

namespace Game.Blackjack;

/// <summary>
/// Player hits: draws one card from the deck to the player's hand.
/// </summary>
[MessagePackObject]
public struct HitCommand : ICommand
{
    public void Execute(World world)
    {
        var state = world.ReadSingleton<GameState>();

        if (state.Phase != GamePhase.PlayerTurn)
            return;

        DrawCard<PlayerHand>(world);
    }

    /// <summary>
    /// Draws the top card from the deck and adds it to the given hand.
    /// </summary>
    internal static void DrawCard<THand>(World world)
        where THand : struct
    {
        var deckEntity = world.FindEntity<Deck>();
        var handEntity = world.FindEntity<THand>();

        if (deckEntity == Entity.Null || handEntity == Entity.Null)
            return;

        // Find a card still in the deck.
        var cardsInDeck = world.GetSources<InDeck>(deckEntity);
        if (cardsInDeck.Count == 0)
            return;

        var cardEntity = cardsInDeck.First();

        // Remove from deck, add to hand.
        world.RemoveComponent<InDeck>(cardEntity);
        world.AddComponent(cardEntity, new Holds { Target = handEntity });

        // Flush so subsequent DrawCard calls see the updated state.
        world.FlushPendingMutations();
    }

    internal static Entity FindEntity<T>(World world)
        where T : struct
    {
        return world.FindEntity<T>();
    }
}