using System.Runtime.InteropServices;
using AcDream.App.Rendering;

namespace AcDream.App.Tests.Rendering;

public sealed class ParticleBindlessInstanceTests
{
    [Fact]
    public void BillboardGpuInstance_MatchesVertexAttributeAbi()
    {
        // Campaign V slice V2c (2026-07-27): TextureHandleLow/High (the split
        // halves of a raw 64-bit ARB_bindless_texture handle, 8 bytes) became
        // one TextureIndex (a binding=9 handle-table slot, 4 bytes), so the
        // struct shrank by 4 bytes; TextureIndex keeps TextureHandleLow's
        // former offset (64 — right after the four vec4 fields).
        Assert.Equal(68, Marshal.SizeOf<ParticleRenderer.BillboardGpuInstance>());
        Assert.Equal(
            new IntPtr(64),
            Marshal.OffsetOf<ParticleRenderer.BillboardGpuInstance>(
                nameof(ParticleRenderer.BillboardGpuInstance.TextureIndex)));
    }

    [Fact]
    public void BillboardShaders_ConsumeOneBindlessTextureHandlePerInstance()
    {
        string shadersDirectory = Path.Combine(
            AppContext.BaseDirectory,
            "Rendering",
            "Shaders");
        string vertex = File.ReadAllText(Path.Combine(shadersDirectory, "particle.vert"));
        string fragment = File.ReadAllText(Path.Combine(shadersDirectory, "particle.frag"));

        // Campaign V slice V2c: the per-instance attribute now carries a
        // binding=9 table slot, not the raw handle; particle.vert
        // reconstructs the SAME uvec2 handle via ACDREAM_TEXTURE_HANDLE
        // before handing it to particle.frag, so the fragment shader's half
        // (extension, reconstruction, varying type/name) is untouched.
        Assert.Contains("layout(location = 6) in uint aTextureIndex;", vertex);
        Assert.Contains("flat out uvec2 vTextureHandle;", vertex);
        Assert.Contains("#extension GL_ARB_bindless_texture : require", fragment);
        Assert.Contains("sampler2DArray(vTextureHandle)", fragment);
        Assert.DoesNotContain("uniform sampler2D uParticleTexture", fragment);
    }
}