encompass-cs/encompass-cs/EntitySetQuery.cs

using System.Collections;
using System.Collections.Generic;
using Encompass.Collections;

namespace Encompass
{
    internal struct EntitySetQuery
    {
        private BitSet WithPendingMask { get; }
        private BitSet WithExistingMask { get; }
        private BitSet WithoutPendingMask { get; }
        private BitSet WithoutExistingMask { get; }
        private BitSet NotWithMask { get; }

        internal EntitySetQuery(BitSet withPendingMask, BitSet withExistingMask, BitSet withoutPendingMask, BitSet withoutExistingMask, BitSet notWithMask)
        {
            WithPendingMask = withPendingMask;
            WithExistingMask = withExistingMask;
            WithoutPendingMask = withoutPendingMask;
            WithoutExistingMask = withoutExistingMask;
            NotWithMask = notWithMask;
        }

        public IEnumerable<Entity> FilterEntities(IEnumerable<Entity> entities, ComponentBitSet pendingBitLookup, ComponentBitSet existingBitLookup)
        {
            foreach (var entity in entities)
            {
                var pendingBits = pendingBitLookup.EntityBitArray(entity.ID);
                var existingBits = existingBitLookup.EntityBitArray(entity.ID);

                var pending = WithPendingMask.And(pendingBits);
                var existing = WithExistingMask.And(existingBits);
                var withCheck = pending.Or(existing).Or(NotWithMask);

                var pendingForbidden = WithoutPendingMask.And(pendingBits).Not();
                var existingForbidden = WithoutExistingMask.And(existingBits).Not();
                var withoutCheck = pendingForbidden.And(existingForbidden);

                if (withCheck.And(withoutCheck).AllTrue()) { yield return entity; }
            }
        }
    }
}