oecs-sharp/Game.Blackjack/Systems/DeckSetupSystem.cs

using OECS;

namespace Game.Blackjack;

/// <summary>
/// Creates the deck (52 cards + deck/hand entities) and shuffles
/// using mulberry32 with the seed from the GameState singleton.
/// Runs once at the start of each round (during Dealing phase).
/// </summary>
public class DeckSetupSystem : ISystem
{
    public void RunImpl(World world)
    {
        var state = world.ReadSingleton<GameState>();
        if (state.Phase != GamePhase.Dealing)
            return;

        // Only create deck entities if they don't exist yet.
        bool hasDeck = false;
        using (var iter = world.Select<Deck>())
        {
            hasDeck = iter.MoveNext();
        }

        if (!hasDeck)
        {
            // Create deck entity.
            var deckEntity = world.CreateEntity();
            world.AddComponent(deckEntity, new Deck());

            // Create all 52 cards.
            foreach (Suit suit in Enum.GetValues<Suit>())
            {
                foreach (Rank rank in Enum.GetValues<Rank>())
                {
                    var cardEntity = world.CreateEntity();
                    world.AddComponent(cardEntity, new Card { Suit = suit, Rank = rank });
                    world.AddComponent(cardEntity, new InDeck { Target = deckEntity });
                }
            }

            // Create hand entities.
            var playerHand = world.CreateEntity();
            world.AddComponent(playerHand, new PlayerHand());

            var dealerHand = world.CreateEntity();
            world.AddComponent(dealerHand, new DealerHand());
        }

        // Shuffle the deck using mulberry32 with the current seed.
        ref var mutableState = ref world.GetSingleton<GameState>();
        var deckEntity2 = world.FindEntity<Deck>();
        var cards = world.GetSources<InDeck>(deckEntity2).ToArray();
        Shuffle(world, deckEntity2, cards, ref mutableState.Seed);
    }

    private static void Shuffle(World world, Entity deckEntity, Entity[] cardEntities, ref uint seed)
    {
        // Fisher-Yates shuffle using mulberry32.
        for (int i = cardEntities.Length - 1; i > 0; i--)
        {
            int j = Mulberry32.NextInt(ref seed, 0, i);
            (cardEntities[i], cardEntities[j]) = (cardEntities[j], cardEntities[i]);
        }

        // Reorder the source set in-place — no component add/remove needed.
        world.ReorderSources<InDeck>(deckEntity, cardEntities);
    }
}