namespace Voxel
{
    public class Chunk
    {
        public static int Size = 16;
        public static int Height = 256;
        public readonly int X;
        public readonly int Y;
        private ChunkMesh _chunkMesh;

        private Dictionary<ushort, BlockData> _blockData;
        private Blocks[] _blocks;

        public Chunk(int x, int y)
        {
            X = x;
            Y = y;

            _blockData = new Dictionary<ushort, BlockData>();
            _blocks = new Blocks[Size * Size * Height];
            _chunkMesh = new ChunkMesh(X, Y);

            Initialize();
        }

        public void SetBlock(int x, int y, int z, Blocks block)
        {
            int i = GetBlockIndex(x, y, z);
            if (i == -1) return;
            _blocks[i] = block;
            UpdateChunkMesh();

            Renderer.MarkBuffersDirty();
        }

        public void SetBlockIndex(int i, Blocks block)
        {
            _blocks[i] = block;
        }

        public Blocks GetBlock(int x, int y, int z)
        {
            int i = GetBlockIndex(x, y, z);
            if (i == -1) return Blocks.Air;
            return _blocks[i];
        }

        public BlockData GetBlockData(int x, int y, int z)
        {
            return new BlockData();
        }

        private void Initialize()
        {
            for (int i = 0; i < Size * Size; i++)
                _blocks[i] = Blocks.Bedrock;
            for (int i = Size * Size * 1; i < Size * Size * 15; i++)
                _blocks[i] = Blocks.Stone;
            for (int i = Size * Size * 15; i < Size * Size * 16; i++)
                _blocks[i] = Blocks.Grass;
            UpdateChunkMesh();
        }

        // todo
        public (int x, int y, int z) IndexToPosition(int i)
        {
            int x = 0;
            int y = 0;
            int z = 0;

            return (x, y, z);
        }

        private int GetBlockIndex(int x, int y, int z)
        {
            if (x < 0 || x > 15 || y < 0 || y > 255 || z < 0 || z > 15)
                return -1;

            return x + z * Size + y * Size * Size;
        }

        private static readonly (int dx, int dy, int dz)[] Offsets = new (int, int, int)[6]
        {
            ( 1,  0,  0), // +X
            (-1,  0,  0), // -X
            ( 0,  1,  0), // +Y
            ( 0, -1,  0), // -Y
            ( 0,  0,  1), // +Z
            ( 0,  0, -1)  // -Z
        };

        private void UpdateChunkMesh()
        {
            List<FaceData> faces = new List<FaceData>(Size * Size * Height / 2);

            for (int x = 0; x < Size; x++)
            {
                for (int z = 0; z < Size; z++)
                {
                    for (int y = 0; y < Height; y++)
                    {
                        for (byte face = 0; face < 6; face++)
                        {
                            int indexBase = y * Size * Size + z * Size + x;
                            Blocks block = _blocks[indexBase];

                            void AddFace()
                            {
                                FaceData faceData = new FaceData();

                                faceData.Facing = (Orientation)face;
                                faceData.Texture = BlockDefinitions.Blocks[block].FaceTextures[face];

                                faceData.X = (byte)x;
                                faceData.Y = (byte)y;
                                faceData.Z = (byte)z;

                                faces.Add(faceData);
                            }

                            if (block == Blocks.Air) continue; // ignore if air

                            int nx = x + Offsets[face].dx;
                            int ny = y + Offsets[face].dy;
                            int nz = z + Offsets[face].dz;

                            // check neighbor, ignore if at chunk edge

                            int ni = GetBlockIndex(nx, ny, nz);
                            if (GetBlockIndex(nx, ny, nz) == -1)
                            {
                                AddFace();
                                continue;
                            }

                            if (_blocks[ni] == Blocks.Air)
                            {
                                AddFace();
                                continue;
                            }
                        }
                    }
                }
            }
            _chunkMesh.SetFaces(faces);
        }

        public ChunkMesh GetChunkMesh()
        {
            return _chunkMesh;
        }
    }
}