using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

[Tool]
[GlobalClass]
public partial class TerrainChunk
	: Resource
{
	// ChunkShift of 5 results in a ChunkSize of 32.
	public const int Shift = 5;
	public const int Mask = ~(~0 << Shift);
	public const int Size = Mask + 1;

	static readonly int SizeInBytes = Size * Size * Unsafe.SizeOf<Tile>();

	[Export] public byte[] Data { get; set; } = new byte[SizeInBytes];

	public bool IsEmpty { get {
		foreach (var b in Data)
			if (b != 0) return false;
		return true;
	} }

	public ref Tile this[TilePos pos] { get {
		var tiles = MemoryMarshal.Cast<byte, Tile>(Data);
		return ref tiles[GetIndex(pos)];
	} }

	public static Vector2I ToChunkPos(TilePos pos)
		=> new(pos.X >> Shift, pos.Z >> Shift);

	public static Vector2I ToTileOffset(Vector2I chunkPos)
		=> new(chunkPos.X << Shift, chunkPos.Y << Shift);

	static int GetIndex(TilePos pos)
		=> (pos.X & Mask) | ((pos.Z & Mask) << Shift);
}