using Unity.Collections;
using Unity.Collections.LowLevel.Unsafe;
using Unity.Mathematics;

namespace GameCore.Network
{
    public readonly struct FrameHistoryItem
    {
        public readonly ulong mask;
        public readonly int frameId;

        public const int kMaxBitCount = 64;

        public bool IsDirty => mask != 0ul;
        
        private FrameHistoryItem(ulong mask, int frameId)
        {
            this.mask = mask;
            this.frameId = frameId;
        }

        public static unsafe FrameHistoryItem Make<T>(T baseData, T newData, NativeArray<int> fieldSizeArray, int frameId) where T : unmanaged
        {
            var basePtr = (byte*) &baseData;
            var newPtr = (byte*) &newData;

            ulong mask = 0ul;
            var offset = 0;
            for (int i = 0, n = math.min(64, fieldSizeArray.Length); i < n; ++i)
            {
                var nextOffset = fieldSizeArray[i];
                var fieldSize = nextOffset - offset;
                if (UnsafeUtility.MemCmp(basePtr + offset, newPtr + offset, fieldSize) != 0)
                {
                    mask |= 1ul << i;
                }

                offset = nextOffset;
            }

            return new FrameHistoryItem(mask, frameId);
        }
    }
}