using System.Numerics;
using AcDream.App.Rendering.Gpu;

namespace AcDream.App.Rendering;

/// <summary>
/// Restores the frame-global rendering convention shared by frame clear and
/// exceptional world-pass rollback. The raw-GL implementation this contract
/// used to have alongside it (<c>RenderFrameGlStateController</c>) was deleted
/// at Campaign V slice V11; <see cref="NullRenderFrameGlState"/> is the only
/// implementation left.
/// </summary>
internal interface IRenderFrameGlState
{
    void RestoreFrameDefaults();
}

/// <summary>
/// Campaign V slice V6j: the small graphics surface the two world pass executors
/// touch directly, expressed once so their ordering logic — which is retail's,
/// and heavily tested — is written once for both backends.
///
/// <para>Everything else those executors do is delegation to a renderer. What is
/// left is exactly this: the clip-frame publication, the doorway scissor,
/// <c>gl_ClipDistance</c> enablement, and retail's interior depth clear. Four
/// concerns, each of which genuinely differs between GL and Vulkan, and none of
/// which is expressible on the pinned RHI contract.</para>
/// </summary>
internal interface IWorldPassSurface
{
    /// <summary>
    /// Publishes this frame's per-cell clip-region table and terrain clip block,
    /// and routes both to the renderers that read them.
    ///
    /// <para><paramref name="terrainUploadCount"/> is how many distinct terrain
    /// clip blocks the frame will issue. GL reserves that many arena records
    /// before the first draw, because reallocating the arena while an earlier
    /// slice can still reference it is the hazard the reservation exists for. The
    /// RHI arm ignores it: a ring allocation is distinct memory by construction
    /// and lives until the frame retires.</para>
    /// </summary>
    void PrepareClipFrame(int terrainUploadCount);

    /// <summary>Replaces the terrain clip planes and republishes the block.</summary>
    void SetTerrainClip(ReadOnlySpan<Vector4> planes);

    /// <summary>
    /// Re-asserts the terrain clip block at its binding.
    ///
    /// <para>GL needs this because binding points are global and the sky and mesh
    /// shaders read the same uniform binding between two terrain slices. On the
    /// RHI arm every consumer binds the published section inside the pass, so
    /// there is no ambient binding to re-assert and this is a no-op.</para>
    /// </summary>
    void BindTerrainClip();

    /// <summary>
    /// Enables every <c>gl_ClipDistance</c> slot.
    ///
    /// <para>Vulkan activates every element the shader declares and has no
    /// enable, so this is a no-op there — and that is safe rather than a
    /// divergence: all three world vertex shaders already write <c>1.0</c>
    /// ("keep everything") into every slot past the active count, so a frame with
    /// no clip planes clips nothing on either backend (plan §5.5.14 item 4).</para>
    /// </summary>
    void EnableClipDistances();

    /// <summary>Disables every <c>gl_ClipDistance</c> slot. See <see cref="EnableClipDistances"/>.</summary>
    void DisableClipDistances();

    /// <summary>
    /// Scissors to a doorway slice's screen-space bounding box. Returns whether a
    /// scissor is now active, so the caller can pair it with <see cref="EndScissor"/>.
    /// </summary>
    bool BeginScissor(Vector4 ndcAabb);

    /// <summary>Restores the full drawable rectangle.</summary>
    void EndScissor();

    /// <summary>
    /// Retail's interior depth clear, between the landscape slice and the
    /// interior cells (<c>PView::DrawCells @ 0x005A4840</c>).
    /// </summary>
    void ClearInteriorDepth();
}

/// <summary>
/// The clip tables are ring sections published on the world pass scope, the
/// scissor is dynamic state on the borrowed encoder, and the depth clear is a
/// scoped <c>vkCmdClearAttachments</c>. The raw-GL implementation this used to
/// sit alongside (<c>GlWorldPassSurface</c>) was deleted at Campaign V slice
/// V11.
/// </summary>
internal sealed class RhiWorldPassSurface : IWorldPassSurface
{
    private readonly IWorldPassScope _scope;
    private readonly ICurrentGpuFrameSource _frames;
    private readonly ClipFrame _clipFrame;
    private readonly IRetailPViewFramebufferSource _framebuffer;

    public RhiWorldPassSurface(
        IWorldPassScope scope,
        ICurrentGpuFrameSource frames,
        ClipFrame clipFrame,
        IRetailPViewFramebufferSource framebuffer)
    {
        _scope = scope ?? throw new ArgumentNullException(nameof(scope));
        _frames = frames ?? throw new ArgumentNullException(nameof(frames));
        _clipFrame = clipFrame ?? throw new ArgumentNullException(nameof(clipFrame));
        _framebuffer = framebuffer ?? throw new ArgumentNullException(nameof(framebuffer));
    }

    public void PrepareClipFrame(int terrainUploadCount)
    {
        // The reservation count has no RHI counterpart: each publication below
        // takes its own ring slice, which is distinct memory that outlives every
        // draw recorded against it in this frame.
        _ = terrainUploadCount;
        _scope.Sections.ClipRegions = Publish(
            _clipFrame.RegionBytes,
            GpuRingUsage.Storage);
        PublishTerrainClip();
    }

    public void SetTerrainClip(ReadOnlySpan<Vector4> planes)
    {
        _clipFrame.SetTerrainClip(planes);
        PublishTerrainClip();
    }

    /// <summary>No-op: there is no ambient binding to re-assert. See the interface.</summary>
    public void BindTerrainClip()
    {
    }

    /// <summary>No-op: Vulkan activates every declared clip distance. See the interface.</summary>
    public void EnableClipDistances()
    {
    }

    /// <summary>No-op: Vulkan activates every declared clip distance. See the interface.</summary>
    public void DisableClipDistances()
    {
    }

    public bool BeginScissor(Vector4 ndcAabb)
    {
        RetailPViewFramebufferSize framebuffer = _framebuffer.Capture();
        var box = NdcScissorRect.ToPixels(
            ndcAabb,
            framebuffer.Width,
            framebuffer.Height);
        // GL convention on the way in; the backend performs its own Y flip.
        _scope.RequireEncoder().SetScissor(box.X, box.Y, box.Width, box.Height);
        return true;
    }

    public void EndScissor() =>
        _scope.RequireEncoder().SetScissor(
            0,
            0,
            _scope.AttachmentWidth,
            _scope.AttachmentHeight);

    public void ClearInteriorDepth()
    {
        // The GL arm drops the scissor before clearing so the clear covers the
        // whole target; vkCmdClearAttachments takes its own rectangle and is not
        // scissored, so the same coverage comes for free — but the scissor still
        // has to come off, because the interior cells drawn after it are not
        // confined to the doorway slice that was active.
        EndScissor();
        _scope.ClearInteriorDepth();
    }

    private void PublishTerrainClip() =>
        _scope.Sections.TerrainClip = Publish(
            _clipFrame.TerrainBytes,
            GpuRingUsage.Uniform);

    private GpuBufferSection Publish(ReadOnlySpan<byte> data, GpuRingUsage usage)
    {
        IGpuFrame frame = _frames.CurrentFrame
            ?? throw new InvalidOperationException(
                "The world clip frame requires an open IGpuFrame (see GpuDeviceFrameLifetime).");
        // A logically empty table still reserves one slot so the bound range is
        // never zero-length — the same rule the light buffers already state.
        int byteCount = Math.Max(data.Length, ClipFrame.CellClipStrideBytes);
        GpuRingAllocation allocation = frame.AllocateRing(byteCount, usage);
        allocation.Data.Clear();
        if (!data.IsEmpty)
            data.CopyTo(allocation.Data);
        return new GpuBufferSection(
            allocation.Buffer,
            allocation.OffsetBytes,
            (uint)byteCount);
    }
}

/// <summary>
/// Campaign V slice V6j: the frame-default restore on a backend with no ambient
/// state to restore.
///
/// <para>Both executors call <see cref="IRenderFrameGlState.RestoreFrameDefaults"/>
/// when aborting a failed frame. On Vulkan every piece of state that call
/// re-establishes is either baked into a pipeline or set per draw, so there is
/// nothing to put back and saying so is more honest than composing a GL
/// controller that would have no context to talk to.</para>
/// </summary>
internal sealed class NullRenderFrameGlState : IRenderFrameGlState
{
    public static NullRenderFrameGlState Instance { get; } = new();

    private NullRenderFrameGlState()
    {
    }

    public void RestoreFrameDefaults()
    {
    }
}

/// <summary>
/// Campaign V slice V6j: the GL state reader on a backend with no GL state.
///
/// <para><c>WorldRenderDiagnostics</c> reads live GL state for explicitly enabled
/// probes only. Every snapshot below is the truthful answer for a Vulkan frame —
/// there is no ambient capability state to sample — which keeps every other
/// diagnostic the class emits (render signature, PView input, out-stage routing,
/// phantom objects) working unchanged on both backends.</para>
/// </summary>
internal sealed class NullRenderGlStateReader : IRenderGlStateReader
{
    public static NullRenderGlStateReader Instance { get; } = new();

    private NullRenderGlStateReader()
    {
    }

    public RenderGlStateSnapshot CaptureState() => default;

    public RenderGlScissorSnapshot CaptureScissor() => default;
}