card-game-engine/RuleEngine/Core/Deck.cs

namespace RuleEngine.Core;

public class MahjongDeck
{
    public List<int> Tiles { get; private set; } = new();

    public MahjongDeck(bool includeHonors = false, bool includeFlowers = false, int wildcardCount = 0)
    {
        var allTiles = MahjongTile.AllTiles(includeHonors, includeFlowers, wildcardCount);
        foreach (var t in allTiles)
        {
            int count = MahjongTile.IsFlower(t) ? 1 : 4;
            // Wildcards are handled by AllTiles already
            if (MahjongTile.IsWildcard(t)) continue;
            for (int i = 0; i < count; i++)
                Tiles.Add(t);
        }
        // Add wildcards separately
        for (int i = 0; i < wildcardCount; i++)
            Tiles.Add(MahjongTile.WildcardBase + i);
    }

    public void Shuffle(Random? rng = null)
    {
        rng ??= Random.Shared;
        int n = Tiles.Count;
        while (n > 1)
        {
            int k = rng.Next(n--);
            (Tiles[n], Tiles[k]) = (Tiles[k], Tiles[n]);
        }
    }

    public int Draw()
    {
        if (Tiles.Count == 0)
            throw new InvalidOperationException("Deck is empty");
        int last = Tiles[^1];
        Tiles.RemoveAt(Tiles.Count - 1);
        return last;
    }

    public int Count => Tiles.Count;
}