namespace VoxelEngine.World.WorldGen;

public sealed class TerrainSampler
{
    // Box-blur radius (in blocks) applied to the biome-height field to smooth
    // biome borders. A full (2R+1)x(2R+1) kernel at 1-block spacing bounds the
    // per-block height change to ~maxBiomeHeightDiff / (2R+1), preventing cliffs.
    // A sparse kernel does NOT bound it (axis-aligned borders flip several samples
    // at once), so the kernel must be dense.
    private const int BlendRadius = 6;

    private readonly NoiseSource _noise;
    private readonly BiomeMap _biomes;

    public TerrainSampler(NoiseSource noise, BiomeMap biomes)
    {
        this._noise = noise;
        this._biomes = biomes;
    }

    public int HeightAt(float worldX, float worldZ)
    {
        // For each kernel point find the biome THERE, but evaluate its height AT the
        // column. Averaging blurs the hard biome borders into smooth transitions.
        float sum = 0f;
        int count = 0;
        for (int dz = -TerrainSampler.BlendRadius; dz <= TerrainSampler.BlendRadius; dz++)
        for (int dx = -TerrainSampler.BlendRadius; dx <= TerrainSampler.BlendRadius; dx++)
        {
            IBiome biome = this._biomes.BiomeAt(worldX + dx, worldZ + dz);
            sum += biome.SampleHeight(this._noise, worldX, worldZ);
            count++;
        }
        float avg = sum / count;
        int h = (int)System.MathF.Round(avg);
        return System.Math.Clamp(h, 0, WorldConstants.WorldHeight - 1);
    }
}