using VoxelEngine.Core;
using VoxelEngine.World.Blocks;
using VoxelEngine.World.WorldGen;
using Xunit;

namespace VoxelEngine.Tests.WorldGen;

public class TerrainSamplerTests
{
    private static TerrainSampler Build(int seed = 42)
    {
        var blocks = new BlockRegistry();
        var biomes = new BiomeRegistry(seed, blocks, new Configuration());
        var noise = new NoiseSource(seed, new Configuration());
        var cells = new VoronoiCells(seed, 96f);
        var map = new BiomeMap(noise, cells, biomes, new Configuration());
        return new TerrainSampler(noise, map, new Configuration());
    }

    [Fact]
    public void Height_StaysWithinWorldBounds()
    {
        var sampler = Build();
        for (int x = -300; x < 300; x += 7)
        for (int z = -300; z < 300; z += 7)
        {
            int h = sampler.HeightAt(x, z);
            Assert.InRange(h, 0, WorldConstants.WorldHeight - 1);
        }
    }

    [Fact]
    public void Height_IsDeterministic()
    {
        var a = Build();
        var b = Build();
        Assert.Equal(a.HeightAt(120, 240), b.HeightAt(120, 240));
    }

    [Fact]
    public void AdjacentColumns_DoNotCliff()
    {
        var sampler = Build();
        for (int x = -200; x < 200; x += 3)
        for (int z = -200; z < 200; z += 3)
        {
            // The dense blur removes inter-biome cliffs. Remaining deltas are
            // rugged intra-Mountains ridged slopes, now ~4x larger after the
            // 128->512 rescale; 64 separates intended slopes from true cliffs.
            int dx = System.Math.Abs(sampler.HeightAt(x, z) - sampler.HeightAt(x + 1, z));
            Assert.True(dx <= 64, $"height jump {dx} at ({x},{z})");
        }
    }
}