using System;
using AcDream.App.Rendering;
using AcDream.App.Rendering.Gpu;
using AcDream.App.Rendering.Wb;
using AcDream.App.Tests.Rendering.Gpu;
using System.Threading;
using AcDream.Content;
using Chorizite.Core.Render.Enums;
using Microsoft.Extensions.Logging.Abstractions;

namespace AcDream.App.Tests.Rendering.Wb;

/// <summary>
/// Campaign V slice V6i-2: the mesh pipeline no longer names a backend.
///
/// <para>Plan §5.5.10 recorded the blocker as a fact about types — "WbMeshAdapter
/// owns an OpenGLGraphicsDevice, so it is not constructible on Vulkan" — which is
/// why <c>NullWbMeshAdapter</c> existed. §5.5.12 item 6 measured how wide the
/// dependency really was: a GL context, the retirement queue, the instance VBO,
/// and two capability flags. This suite proves the interface at that surface is
/// load-bearing rather than cosmetic, by building the object graph against a
/// device that has NO GL context at all.</para>
///
/// <para>It originally proved construction and nothing more, back when the
/// upload bodies were still raw GL and the world renderers still bound a GL
/// handle table. Campaign V slice V11 deleted both along with the rest of the
/// raw-GL arm (and the interface's own <c>Gl</c> member, which nothing read any
/// more once they were gone) — the arena-build and upload tests below now cover
/// what those slices only asserted would eventually fail loudly.</para>
/// </summary>
public sealed class MeshPipelineDeviceSeamTests
{
    /// <summary>A device with the mesh pipeline's whole surface and no GL behind it.</summary>
    private sealed class ContextFreeMeshPipelineDevice(
        IGpuResourceRetirementQueue retirement,
        bool modernPath = false)
        : IMeshPipelineDevice
    {
        public IGpuResourceRetirementQueue ResourceRetirement { get; } = retirement;

        public uint InstanceVBO => 0;

        public bool HasBindless => modernPath;

        public bool HasOpenGL43 => modernPath;

        public bool HasPendingWork => false;

        public int ProcessedQueues { get; private set; }

        public void ProcessQueue() => ProcessedQueues++;

        public void Dispose()
        {
        }
    }

    private static ObjectMeshManager Build(
        RecordingGpuDevice device,
        bool modernPath = false) =>
        new(
            new ContextFreeMeshPipelineDevice(device.Retirement, modernPath),
            device,
            new NullPreparedAssetSource(),
            NullLogger<ObjectMeshManager>.Instance);

    private sealed class NullPreparedAssetSource : IPreparedAssetSource
    {
        public PreparedAssetSourceStats Stats => default;

        public CacheStats DecodedTextureCacheStats => default;

        public PreparedAssetPresence Probe(
            AcDream.Content.Pak.PakAssetType type,
            uint sourceFileId) =>
            PreparedAssetPresence.Missing;

        public PreparedAssetReadResult Read(
            in PreparedAssetRequest request,
            CancellationToken cancellationToken = default) =>
            PreparedAssetReadResult.Missing;

        public void Dispose()
        {
        }
    }

    /// <summary>
    /// The whole point. Before this slice the constructor downcast the RHI device
    /// to <c>GlGpuDevice</c>, so this threw before running a statement.
    /// </summary>
    [Fact]
    public void TheMeshPipelineConstructsAgainstADeviceWithNoGlContext()
    {
        using var device = new RecordingGpuDevice();
        using ObjectMeshManager manager = Build(device);

        Assert.False(manager.IsDisposed);
    }

    /// <summary>
    /// The one branch the texture stack keeps: a GL pair yields the GL arm, and
    /// anything else yields the RHI arm. Selection happens once, at construction.
    /// </summary>
    [Fact]
    public void TheArrayFactorySelectsTheRhiArmWithoutAGlPair()
    {
        using var device = new RecordingGpuDevice();
        IWorldTextureArrayFactory arrays = IWorldTextureArrayFactory.For(
            new ContextFreeMeshPipelineDevice(device.Retirement),
            device,
            NullLogger.Instance);

        Assert.IsType<RhiWorldTextureArrayFactory>(arrays);
        using IWorldTextureArray array =
            arrays.CreateClampedArray(TextureFormat.RGBA8, 32, 32, 2);
        Assert.IsType<RhiWorldTextureArray>(array);
    }

    /// <summary>
    /// The seam's whole value is that it is NARROW — six members measured out
    /// of a 760-line class (seven until Campaign V slice V11 deleted the unread
    /// <c>Gl</c> member). A later slice that quietly widens it back out would
    /// re-couple the mesh pipeline to a backend without any other gate noticing,
    /// so the member set is pinned rather than described.
    /// </summary>
    [Fact]
    public void TheDeviceSeamStaysAtTheMeasuredSurface()
    {
        string[] members =
        [
            .. typeof(IMeshPipelineDevice)
                .GetMembers()
                // Property accessors are the same members under another name.
                .Where(member => member is not System.Reflection.MethodInfo
                {
                    IsSpecialName: true,
                })
                .Select(member => member.Name)
                .Order(StringComparer.Ordinal),
        ];

        Assert.Equal(
            [
                "HasBindless",
                "HasOpenGL43",
                "HasPendingWork",
                "InstanceVBO",
                "ProcessQueue",
                "ResourceRetirement",
            ],
            members);
    }

    /// <summary>
    /// Construction touched no GL object at all. The shared mesh arena is the
    /// only one the constructor would build, and it is gated on the two
    /// capability flags the interface carries — so a device reporting neither
    /// leaves it absent rather than dereferencing a null context.
    /// </summary>
    [Fact]
    public void ConstructionBuildsNoGlObject()
    {
        using var device = new RecordingGpuDevice();
        using ObjectMeshManager manager = Build(device);

        Assert.Null(manager.GlobalBuffer);
        // Read-only policy queries still answer, which is what lets streaming
        // residence accounting keep running on a backend with no world draws.
        Assert.Equal((0, 0, 0), manager.GetPendingTextureUpdateStats());
    }

    /// <summary>
    /// Campaign V slice V6i-3. V6i-2 could only prove construction, because the
    /// arena's own body still spoke GL — a device reporting the modern-path
    /// capabilities and no context would have dereferenced a null one. It now
    /// builds, and what it publishes is the contract's handle rather than a raw
    /// name: no vertex array, two live stores.
    /// </summary>
    [Fact]
    public void TheModernArenaBuildsWithoutAGlContext()
    {
        using var device = new RecordingGpuDevice();
        using ObjectMeshManager manager = Build(device, modernPath: true);

        GlobalMeshBuffer arena = Assert.IsType<GlobalMeshBuffer>(manager.GlobalBuffer);
        Assert.True(arena.HasStores);
        Assert.NotNull(arena.VertexStore);
        Assert.NotNull(arena.IndexStore);
    }

    /// <summary>
    /// And it UPLOADS. The vertex and index bytes land in the stores a pass
    /// encoder binds, at the offsets the allocator handed out — which is the
    /// whole of what a draw needs from this class and the thing V6i-2 could not
    /// claim.
    /// </summary>
    [Fact]
    public void AMeshUploadsIntoTheArenaWithoutAGlContext()
    {
        using var device = new RecordingGpuDevice();
        using ObjectMeshManager manager = Build(device, modernPath: true);
        GlobalMeshBuffer arena = manager.GlobalBuffer!;

        var vertices = new VertexPositionNormalTexture[3];
        vertices[0].Position = new System.Numerics.Vector3(1f, 2f, 3f);
        vertices[2].Position = new System.Numerics.Vector3(7f, 8f, 9f);
        ushort[] indices = [0, 1, 2];

        GlobalMeshAllocation allocation = arena.UploadMesh(vertices, [indices]);

        Assert.Equal(3, allocation.Vertices.Length);
        Assert.Equal(3, allocation.Indices.Length);
        Assert.Equal(1, arena.UploadCount);

        Span<byte> readback = stackalloc byte[3 * VertexPositionNormalTexture.Size];
        arena.VertexStore!.Read(
            (long)allocation.Vertices.Offset * VertexPositionNormalTexture.Size,
            readback);
        var uploaded = System.Runtime.InteropServices.MemoryMarshal
            .Cast<byte, VertexPositionNormalTexture>(readback);
        Assert.Equal(new System.Numerics.Vector3(1f, 2f, 3f), uploaded[0].Position);
        Assert.Equal(new System.Numerics.Vector3(7f, 8f, 9f), uploaded[2].Position);

        Span<byte> indexBytes = stackalloc byte[3 * sizeof(ushort)];
        arena.IndexStore!.Read((long)allocation.Indices.Offset * sizeof(ushort), indexBytes);
        Assert.Equal(
            indices,
            System.Runtime.InteropServices.MemoryMarshal.Cast<byte, ushort>(indexBytes).ToArray());
    }

    /// <summary>
    /// The production Vulkan implementation of the seam, checked against the
    /// same surface. Its two capability flags answer true because what they
    /// gate is the modern path, which Vulkan supplies unconditionally — see the
    /// type's own documentation for why the GL-shaped names survive.
    /// </summary>
    [Fact]
    public void TheVulkanMeshPipelineDeviceReportsTheModernPath()
    {
        using var device = new RecordingGpuDevice();
        using var vulkanDevice =
            new AcDream.App.Rendering.Gpu.Vk.VulkanMeshPipelineDevice(device.Retirement);

        Assert.True(vulkanDevice.HasBindless);
        Assert.True(vulkanDevice.HasOpenGL43);
        Assert.False(vulkanDevice.HasPendingWork);
        Assert.Equal(0u, vulkanDevice.InstanceVBO);
        Assert.Same(device.Retirement, vulkanDevice.ResourceRetirement);
    }
}