using VoxelEngine.Core;

namespace VoxelEngine.World.WorldGen;

public sealed class TerrainSampler
{
    private readonly NoiseSource _noise;
    private readonly BiomeMap _biomes;
    private readonly Configuration _cfg;

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

    public int HeightAt(float worldX, float worldZ)
    {
        // Blend the two nearest biomes' heights (each evaluated AT this column) by
        // how deep inside the nearer cell we are: exactly on the border they mix
        // 50/50, easing to 100% of the nearer biome over BiomeBlendWidth blocks.
        BiomeMap.BiomeBlend blend = this._biomes.NearestTwo(worldX, worldZ);
        float hNear = blend.Near.SampleHeight(this._noise, worldX, worldZ);
        float hFar = blend.Far.SampleHeight(this._noise, worldX, worldZ);

        float fracFar = 0.5f * (1f - SmoothStep01(blend.BorderDistance / this._cfg.BiomeBlendWidth));
        float avg = hNear * (1f - fracFar) + hFar * fracFar;

        int h = (int)MathF.Round(avg);
        return Math.Clamp(h, 0, WorldConstants.WorldHeight - 1);
    }

    // Hermite smoothstep on [0,1].
    private static float SmoothStep01(float t)
    {
        t = Math.Clamp(t, 0f, 1f);
        return t * t * (3f - 2f * t);
    }
}