using VoxelEngine.World;
using Xunit;

namespace VoxelEngine.Tests;

public class ChunkMesherTests
{
    private const int FloatsPerVertex = 6; // pos.xyz, uv, shade
    private const int VerticesPerFace = 6; // quad = 2 triangles
    private const int FloatsPerFace = FloatsPerVertex * VerticesPerFace; // 36

    private static int FaceCount(float[] mesh) => mesh.Length / FloatsPerFace;

    [Fact]
    public void EmptyChunk_ProducesNoFaces()
    {
        var mesh = new ChunkMesher().Build(new Chunk(), new BlockRegistry());
        Assert.Empty(mesh);
    }

    [Fact]
    public void SingleBlockSurroundedByAir_Produces6Faces()
    {
        var chunk = new Chunk();
        chunk[8, 8, 8] = 1; // stone

        var mesh = new ChunkMesher().Build(chunk, new BlockRegistry());

        Assert.Equal(6, FaceCount(mesh));
    }

    [Fact]
    public void FullySolidChunk_ProducesOnlyOuterShell()
    {
        var chunk = new Chunk();
        for (int x = 0; x < Chunk.Size; x++)
        for (int y = 0; y < Chunk.Size; y++)
        for (int z = 0; z < Chunk.Size; z++)
            chunk[x, y, z] = 1; // stone

        var mesh = new ChunkMesher().Build(chunk, new BlockRegistry());

        // 6 sides * 16 * 16 visible faces
        Assert.Equal(6 * Chunk.Size * Chunk.Size, FaceCount(mesh));
    }

    [Fact]
    public void SingleBlock_EmitsExactInterleavedFloatCount()
    {
        var chunk = new Chunk();
        chunk[0, 0, 0] = 1; // corner block: all 6 neighbors are air/out-of-bounds -> 6 faces

        var mesh = new ChunkMesher().Build(chunk, new BlockRegistry());

        // Pins the layout: 6 faces * 6 vertices/face * 6 floats/vertex.
        Assert.Equal(6 * VerticesPerFace * FloatsPerVertex, mesh.Length);
        Assert.Equal(0, mesh.Length % FloatsPerVertex);
    }
}