namespace VoxelEngine.World.WorldGen;

public sealed class BiomeMap
{
    private readonly NoiseSource _noise;
    private readonly VoronoiCells _cells;
    private readonly BiomeRegistry _biomes;

    public BiomeMap(NoiseSource noise, VoronoiCells cells, BiomeRegistry biomes)
    {
        this._noise = noise;
        this._cells = cells;
        this._biomes = biomes;
    }

    public int CellId(float worldX, float worldZ) => this._cells.Nearest(worldX, worldZ).Id;

    public IBiome BiomeAt(float worldX, float worldZ)
    {
        VoronoiCells.Cell cell = this._cells.Nearest(worldX, worldZ);
        // Sample climate at the cell center so the biome is constant across the cell.
        float temperature = this._noise.Temperature(cell.CenterX, cell.CenterZ);
        float elevation = this._noise.Continent(cell.CenterX, cell.CenterZ);
        float forest = this._noise.Forest(cell.CenterX, cell.CenterZ);
        return BiomeMap.Classify(temperature, elevation, forest, this._biomes);
    }

    // Pure climate -> biome lookup. Thresholds in noise units (~[-1,1]).
    public static IBiome Classify(float temperature, float elevation, float forest, BiomeRegistry biomes)
    {
        if (elevation > 0.25f) return biomes.Mountains;          // high ground
        if (temperature > 0.33f) return biomes.Desert;           // hot, low
        if (temperature > -0.33f && forest > 0f) return biomes.Forest; // temperate, wooded
        return biomes.Plains;                                    // temperate/cold, low
    }
}