using OpenTK.Mathematics;
using VoxelEngine.Core;
using VoxelEngine.World.Blocks;
using VoxelChunk = VoxelEngine.World.Chunk.Chunk;

namespace VoxelEngine.World.WorldGen;

// Carves caves into an already-terrain-filled chunk. Stateless after
// construction; the carve methods are pure functions of (chunk, chunkPos).
// Safe to share across worker threads.
public sealed class CaveCarver
{
    private readonly int _seed;
    private readonly BlockRegistry _blocks;
    private readonly Configuration _cfg;
    private readonly FastNoiseLite _caveNoise;

    public CaveCarver(int seed, BlockRegistry blocks, Configuration cfg)
    {
        this._seed = seed;
        this._blocks = blocks;
        this._cfg = cfg;

        this._caveNoise = new FastNoiseLite(seed + 100);
        this._caveNoise.SetNoiseType(FastNoiseLite.NoiseType.OpenSimplex2);
        this._caveNoise.SetFrequency(cfg.CaveNoiseFrequency);
    }

    public void Carve(VoxelChunk chunk, Vector3i chunkPos)
    {
        this.CarveNoiseCaves(chunk, chunkPos);
        // Worm pass added in Task 6.
    }

    // Per-voxel 3D simplex threshold. Public for direct testability,
    // matching the pattern of WorldGenerator.BlockAt.
    public void CarveNoiseCaves(VoxelChunk chunk, Vector3i chunkPos)
    {
        int baseX = chunkPos.X * VoxelChunk.Size;
        int baseY = chunkPos.Y * VoxelChunk.Size;
        int baseZ = chunkPos.Z * VoxelChunk.Size;

        for (int x = 0; x < VoxelChunk.Size; x++)
        for (int y = 0; y < VoxelChunk.Size; y++)
        for (int z = 0; z < VoxelChunk.Size; z++)
        {
            int worldY = baseY + y;
            if (worldY <= 0) continue;

            ushort id = chunk[x, y, z];
            if (id == this._blocks.Air.Id) continue;
            if (id == this._blocks.Water.Id) continue;

            float density = this._caveNoise.GetNoise(baseX + x, worldY, baseZ + z);
            if (density < this._cfg.CaveNoiseThreshold)
            {
                chunk[x, y, z] = this._blocks.Air.Id;
            }
        }
    }
}