using System;
using System.Linq;
using AcDream.App.Rendering;
using AcDream.App.Rendering.Gpu;
using AcDream.App.Tests.Rendering.Gpu;

namespace AcDream.App.Tests.Rendering;

/// <summary>
/// Campaign V slice V6i-2: the composite array pool's backend-neutral arm.
///
/// <para>Plan §5.5.12 item 1 recorded that <c>ICompositeTextureArrayBackend</c>
/// "is already a seam and takes an RHI backend directly", which is why this arm
/// is four small methods rather than a port. What is worth pinning is the
/// contract the cache above depends on: create returns a resource whose slot is
/// live, the release order is entry-then-image, and a resource made by one
/// backend is never handed to the other.</para>
/// </summary>
public sealed class RhiCompositeTextureArrayBackendTests
{
    private static byte[] Rgba(int width, int height) => new byte[width * height * 4];

    [Fact]
    public void CreateProducesASingleLevelArrayRegisteredIntoTheTable()
    {
        using var device = new RecordingGpuDevice();
        var backend = new RhiCompositeTextureArrayBackend(device);

        CompositeTextureArrayResource resource = backend.Create(32, 32, 8);

        Assert.True(resource.Slot.IsAssigned);
        Assert.Equal(32 * 32 * 4 * 8, resource.Bytes);
        // The GL identity fields are meaningless on this arm and say so.
        Assert.Equal(0u, resource.Name);
        Assert.Equal(0ul, resource.Handle);

        RecordingGpuTexture image = Assert.IsType<RecordingGpuTexture>(resource.Image);
        Assert.Equal(GpuTextureKind.Texture2DArray, image.Kind);
        Assert.Equal(GpuTextureFormat.Rgba8Unorm, image.Format);
        Assert.Equal(8, image.LayerCount);
        // Composites are the surfaces retail releases the moment they are built;
        // a mip chain would be paid for nothing.
        Assert.Equal(1, image.MipLevelCount);
    }

    [Fact]
    public void UploadWritesLevelZeroOfTheNamedLayer()
    {
        using var device = new RecordingGpuDevice();
        var backend = new RhiCompositeTextureArrayBackend(device);
        CompositeTextureArrayResource resource = backend.Create(32, 32, 4);

        backend.Upload(resource, 3, Rgba(32, 32));

        RecordingGpuTexture image = Assert.IsType<RecordingGpuTexture>(resource.Image);
        Assert.Equal([(0, 3, 32 * 32 * 4)], image.Uploads);
    }

    [Fact]
    public void ReleaseRetiresTheTableEntryBeforeTheImage()
    {
        using var device = new RecordingGpuDevice();
        var backend = new RhiCompositeTextureArrayBackend(device);
        int before = device.LiveTextureSlotCount;
        CompositeTextureArrayResource resource = backend.Create(32, 32, 4);
        Assert.Equal(before + 1, device.LiveTextureSlotCount);

        backend.MakeNonResident(resource);
        Assert.Equal(before, device.LiveTextureSlotCount);
        Assert.False(Assert.IsType<RecordingGpuTexture>(resource.Image).IsDisposed);

        backend.Delete(resource);
        Assert.True(Assert.IsType<RecordingGpuTexture>(resource.Image).IsDisposed);
    }

    /// <summary>
    /// A GL-made resource reaching this backend is a composition error, not a
    /// runtime condition — and the message says which backend owns it rather
    /// than dereferencing null.
    /// </summary>
    [Fact]
    public void AGlResourceIsRefusedRatherThanDereferenced()
    {
        using var device = new RecordingGpuDevice();
        var backend = new RhiCompositeTextureArrayBackend(device);
        var foreign = new CompositeTextureArrayResource
        {
            Name = 7,
            Handle = 0xDEAD,
            Slot = new GpuTextureSlot(3),
            Width = 32,
            Height = 32,
            Capacity = 1,
            Bytes = 32 * 32 * 4,
        };

        Assert.Throws<InvalidOperationException>(() => backend.Upload(foreign, 0, Rgba(32, 32)));
        Assert.Throws<InvalidOperationException>(() => backend.Delete(foreign));
    }

    /// <summary>
    /// The cache caps every array at 64 layers, so the layer ceiling this
    /// backend reports is never the binding constraint — which is what lets it
    /// report Vulkan's guaranteed minimum instead of a capability field the
    /// pinned record does not carry.
    /// </summary>
    [Fact]
    public void TheReportedLayerCeilingExceedsTheCachesOwnCap()
    {
        using var device = new RecordingGpuDevice();
        var backend = new RhiCompositeTextureArrayBackend(device);

        Assert.True(backend.MaximumArrayLayers >= CompositeTextureArrayCache.MaximumLayersPerArray);
    }
}