oecs-sharp/examples/Blackjack/Systems/HandUtil.cs

using OECS;

namespace Blackjack;

/// <summary>
/// Helper to calculate the blackjack value of a hand.
/// Aces count as 11 unless that would bust, then they count as 1.
/// </summary>
public static class HandUtil
{
    public static int CalculateHand(World world, DealerHand hand)
    {
        return CalculateHandImpl(world, hand);
    }

    public static int CalculateHand(World world, PlayerHand hand)
    {
        return CalculateHandImpl(world, hand);
    }

    private static int CalculateHandImpl<T>(World world, T handTag)
        where T : struct
    {
        // Find the hand entity.
        Entity handEntity = Entity.Null;
        using (var iter = world.Select<T>())
        {
            while (iter.MoveNext())
            {
                if (iter.CurrentEntity != World.SingletonEntity)
                {
                    handEntity = iter.CurrentEntity;
                    break;
                }
            }
        }

        if (handEntity == Entity.Null)
            return 0;

        var cards = world.GetSources<Holds>(handEntity);
        int total = 0;
        int aceCount = 0;

        foreach (var cardEntity in cards)
        {
            var card = world.ReadComponent<Card>(cardEntity);
            int value = card.Rank switch
            {
                Rank.Ace => 11,
                Rank.Jack => 10,
                Rank.Queen => 10,
                Rank.King => 10,
                _ => (int)card.Rank
            };

            if (card.Rank == Rank.Ace)
                aceCount++;

            total += value;
        }

        // Downgrade aces from 11 to 1 as needed.
        while (total > 21 && aceCount > 0)
        {
            total -= 10;
            aceCount--;
        }

        return total;
    }
}