using System.Numerics;
using System.Runtime.InteropServices;
using Hexa.NET.ImGui;
using SDL3;

namespace SDL3_TestingSuite.SDL3;

/// <summary>
/// Implementation of ImGui for SDL3 Renderer backend.
/// https://github.com/ocornut/imgui/blob/master/backends/imgui_impl_sdlrenderer3.h
/// </summary>
public unsafe static class ImGuiSDL3Renderer
{
    public static SDL3Window Parent;

    public class RendererData
    {
        public nint Renderer; // Main viewport's renderer
        public ImVector<SDL.FColor> ColorBuffer;

        // Render State
        public SDL.ScaleMode CurrentScaleMode;
    }

    private struct BackupSDLRendererState
    {
        public SDL.Rect Viewport;
        public bool ViewportEnabled;
        public bool ClipEnabled;
        public SDL.Rect ClipRect;
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void RendererCreateWindowFn(ImGuiViewportPtr viewport);

    private static readonly RendererCreateWindowFn RendererCreateWindowDelegate = RendererCreateWindow;

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void RendererDestroyWindowFn(ImGuiViewportPtr viewport);

    private static readonly RendererDestroyWindowFn RendererDestroyWindowDelegate = RendererDestroyWindow;

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void RendererRenderWindowFn(ImGuiViewportPtr viewport);

    private static readonly RendererRenderWindowFn RendererRenderWindowDelegate = RendererRenderWindow;

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void RendererSwapBuffersFn(ImGuiViewportPtr viewport);

    private static readonly RendererSwapBuffersFn RendererSwapBuffersDelegate = RendererSwapBuffers;

    public static RendererData Data => ImGui.GetCurrentContext().Handle != null ? ImGuiUserData<RendererData>.Get(ImGui.GetIO().BackendRendererUserData)! : null!;

    public static bool Init(nint renderer, SDL3Window parentWindow = null)
    {
        Parent = parentWindow;
        ImGuiIOPtr io = ImGui.GetIO();

        RendererData bd = new RendererData();
        io.BackendRendererUserData = ImGuiUserData<RendererData>.Store(bd);
        io.BackendRendererName = (byte*)Marshal.StringToHGlobalAnsi("NepImGuiSDL3Renderer");
        io.BackendFlags |= ImGuiBackendFlags.RendererHasVtxOffset; // We can honor the ImDrawCmd.VtxOffset field, allowing for large meshes.
        io.BackendFlags |= ImGuiBackendFlags.RendererHasTextures;  // We can honor ImGuiPlatformIO.Textures[] requests during render.
        io.BackendFlags |= ImGuiBackendFlags.RendererHasViewports;

        bd.Renderer = renderer;

        ImGuiPlatformIOPtr platformIO = ImGui.GetPlatformIO();
        platformIO.RendererCreateWindow = (void*)Marshal.GetFunctionPointerForDelegate(RendererCreateWindowDelegate);
        platformIO.RendererDestroyWindow = (void*)Marshal.GetFunctionPointerForDelegate(RendererDestroyWindowDelegate);
        platformIO.RendererRenderWindow = (void*)Marshal.GetFunctionPointerForDelegate(RendererRenderWindowDelegate);
        platformIO.RendererSwapBuffers = (void*)Marshal.GetFunctionPointerForDelegate(RendererSwapBuffersDelegate);

        return true;
    }

    public static void Dispose()
    {
        var io = ImGui.GetIO();
        var platformIO = ImGui.GetPlatformIO();

        DestroyDeviceObjects();

        io.BackendRendererName = null;
        io.BackendRendererUserData = null;
        io.BackendFlags &= ~(ImGuiBackendFlags.RendererHasVtxOffset | ImGuiBackendFlags.RendererHasTextures);
        platformIO.RendererTextureMaxWidth = 0;
        platformIO.RendererTextureMaxHeight = 0;
        platformIO.RendererRenderState = null;
        platformIO.RendererCreateWindow = null;
        platformIO.RendererDestroyWindow = null;
        platformIO.RendererSetWindowSize = null;
        platformIO.RendererRenderWindow = null;
        platformIO.RendererSwapBuffers = null;
    }

    public static void NewFrame() { }

    private static void RendererCreateWindow(ImGuiViewportPtr viewport)
    {
        ImGuiSDL3Platform.ViewPortData? vd = ImGuiUserData<ImGuiSDL3Platform.ViewPortData>.Get(viewport.PlatformUserData);
        if (vd == null || vd.Window == nint.Zero)
            return;

        if (vd.Renderer == nint.Zero)
        {
            vd.Renderer = SDL.CreateRenderer(vd.Window, null);
            vd.RendererOwned = true;
        }
    }

    private static void RendererDestroyWindow(ImGuiViewportPtr viewport)
    {
        ImGuiSDL3Platform.ViewPortData? vd = ImGuiUserData<ImGuiSDL3Platform.ViewPortData>.Get(viewport.PlatformUserData);
        if (vd == null)
            return;

        if (vd.RendererOwned && vd.Renderer != nint.Zero)
        {
            SDL.DestroyRenderer(vd.Renderer);
        }

        vd.Renderer = nint.Zero;
        vd.RendererOwned = false;
    }

    private static void RendererRenderWindow(ImGuiViewportPtr viewport)
    {
        ImGuiSDL3Platform.ViewPortData? vd = ImGuiUserData<ImGuiSDL3Platform.ViewPortData>.Get(viewport.PlatformUserData);
        if (vd == null || vd.Renderer == nint.Zero)
        {
            return;
        }

        if (Parent != null)
        {
            SDL.SetRenderDrawColorFloat(vd.Renderer, Parent.ClearColor.X, Parent.ClearColor.Y, Parent.ClearColor.Z, 0f);
            SDL.RenderClear(vd.Renderer);
        }

        RenderDrawData(viewport.DrawData, vd.Renderer);
    }

    private static void RendererSwapBuffers(ImGuiViewportPtr viewport)
    {
        ImGuiSDL3Platform.ViewPortData? vd = ImGuiUserData<ImGuiSDL3Platform.ViewPortData>.Get(viewport.PlatformUserData);
        if (vd == null || vd.Renderer == nint.Zero)
            return;

        SDL.RenderPresent(vd.Renderer);
    }

    public static void RenderDrawData(ImDrawDataPtr drawData, nint renderer)
    {
        // Skip if no data to render
        if (drawData.Handle == null || drawData.CmdListsCount == 0)
            return;

        SDL.GetRenderScale(renderer, out float renderScaleX, out float renderScaleY);
        Vector2 renderScale = new Vector2(renderScaleX == 1.0f ? drawData.FramebufferScale.X : 1.0f, renderScaleY == 1.0f ? drawData.FramebufferScale.Y : 1.0f);

        int fbWidth = (int)(drawData.DisplaySize.X * renderScale.X);
        int fbHeight = (int)(drawData.DisplaySize.Y * renderScale.Y);
        if (fbWidth <= 0 || fbHeight <= 0)
            return;

        for (int i = 0; i < drawData.Textures.Size; i++)
        {
            var texture = drawData.Textures[i];
            UpdateTexture(texture, renderer);
        }

        // Backup SDL renderer state
        BackupSDLRendererState old = new BackupSDLRendererState
        {
            ViewportEnabled = SDL.RenderViewportSet(renderer),
            ClipEnabled = SDL.RenderClipEnabled(renderer)
        };
        SDL.GetRenderViewport(renderer, out old.Viewport);
        SDL.GetRenderClipRect(renderer, out old.ClipRect);

        // Set up render state
        SDL.SetRenderViewport(renderer, nint.Zero);
        SDL.SetRenderClipRect(renderer, nint.Zero);

        // Set render state in platform IO
        ImGuiPlatformIOPtr platformIo = ImGui.GetPlatformIO();
        platformIo.RendererRenderState = (void*)renderer;

        Vector2 clipOffset = drawData.DisplayPos;

        // Render command lists
        for (int n = 0; n < drawData.CmdListsCount; n++)
        {
            ImDrawListPtr cmdList = drawData.CmdLists[n];

            for (int cmdIndex = 0; cmdIndex < cmdList.CmdBuffer.Size; cmdIndex++)
            {
                ImDrawCmd cmd = cmdList.CmdBuffer[cmdIndex];

                if (cmd.UserCallback != null)
                {
                    continue; // User callback not implemented
                }

                // Apply clipping rectangle
                Vector4 clipRect = cmd.ClipRect;
                Vector2 clipMin = new Vector2((clipRect.X - clipOffset.X) * renderScale.X, (clipRect.Y - clipOffset.Y) * renderScale.Y);
                Vector2 clipMax = new Vector2((clipRect.Z - clipOffset.X) * renderScale.X, (clipRect.W - clipOffset.Y) * renderScale.Y);

                clipMin.X = Math.Max(0, clipMin.X);
                clipMin.Y = Math.Max(0, clipMin.Y);
                clipMax.X = Math.Min(fbWidth, clipMax.X);
                clipMax.Y = Math.Min(fbHeight, clipMax.Y);
                if (clipMax.X <= clipMin.X || clipMax.Y <= clipMin.Y)
                    continue;

                SDL.Rect r = new SDL.Rect
                {
                    X = (int)clipMin.X,
                    Y = (int)clipMin.Y,
                    W = (int)(clipMax.X - clipMin.X),
                    H = (int)(clipMax.Y - clipMin.Y)
                };
                SDL.SetRenderClipRect(renderer, r);

                // Get texture
                nint texId = cmd.GetTexID();

                // Convert ImGui vertices to SDL vertices
                if (!RenderDrawCommand(cmdList, cmd, renderer, texId, renderScale, clipOffset))
                {
                    Console.WriteLine($"Failed to render ImGui draw command: {SDL.GetError()}");
                }
            }
        }

        // Reset render state
        platformIo.RendererRenderState = null;

        // Restore renderer state
        SDL.SetRenderViewport(renderer, old.ViewportEnabled ? old.Viewport : new SDL.Rect());
        SDL.SetRenderClipRect(renderer, old.ClipEnabled ? old.ClipRect : new SDL.Rect());
    }

    private static void UpdateTexture(ImTextureDataPtr tex, nint renderer)
    {
        if (tex.Status == ImTextureStatus.WantDestroy)
        {
            if (tex.TexID != ImTextureID.Null)
                SDL.DestroyTexture(tex.TexID);

            tex.SetTexID(ImTextureID.Null);
            tex.SetStatus(ImTextureStatus.Destroyed);
            return;
        }

        bool needsCreate = tex.TexID == ImTextureID.Null || SDL.GetRendererFromTexture(tex.TexID) != renderer;
        if (tex.Status == ImTextureStatus.WantCreate || needsCreate)
        {
            if (tex.TexID != ImTextureID.Null)
                SDL.DestroyTexture(tex.TexID);

            // Create texture on the renderer that is actually drawing this viewport.
            // SDL textures are renderer-owned and cannot be shared across renderer instances.
            nint sdlTexture = SDL.CreateTexture(renderer, SDL.PixelFormat.ABGR8888, SDL.TextureAccess.Static, tex.Width, tex.Height);
            SDL.UpdateTexture(sdlTexture, nint.Zero, (nint)tex.GetPixels(), tex.GetPitch());
            SDL.SetTextureBlendMode(sdlTexture, SDL.BlendMode.Blend);
            SDL.SetTextureScaleMode(sdlTexture, SDL.ScaleMode.Linear);

            tex.SetTexID(sdlTexture);
            tex.SetStatus(ImTextureStatus.Ok);
            return;
        }

        if (tex.Status == ImTextureStatus.WantUpdates)
        {
            // Update selected blocks. We only ever write to textures regions which have never been used before!
            // This backend choose to use tex.Updates[] but you can use tex.UpdateRect to upload a single region.
            nint sdlTexture = tex.TexID;
            for (int i = 0; i < tex.Updates.Size; i++)
            {
                var r = tex.Updates[i];
                SDL.Rect sdlR = new SDL.Rect { X = r.X, Y = r.Y, W = r.W, H = r.H };
                SDL.UpdateTexture(sdlTexture, sdlR, (nint)tex.GetPixelsAt(r.X, r.Y), tex.GetPitch());
            }
            tex.SetStatus(ImTextureStatus.Ok);
        }
    }


    private static bool RenderDrawCommand(ImDrawListPtr drawList, ImDrawCmd cmd, nint renderer, nint texId, Vector2 scale, Vector2 displayPos)
    {
        uint indexOffset = cmd.IdxOffset;
        uint vertexOffset = cmd.VtxOffset;
        uint elemCount = cmd.ElemCount;

        SDL.Vertex[] vertices = new SDL.Vertex[elemCount];
        int[] indices = new int[elemCount];

        for (int i = 0; i < elemCount; i++)
        {
            ushort idx = drawList.IdxBuffer[(int)indexOffset + i];
            int vertIdx = (int)(vertexOffset + idx);

            ImDrawVert srcVert = drawList.VtxBuffer[vertIdx];

            uint col = srcVert.Col;

            byte r = (byte)((col >> 0) & 0xFF);
            byte g = (byte)((col >> 8) & 0xFF);
            byte b = (byte)((col >> 16) & 0xFF);
            byte a = (byte)((col >> 24) & 0xFF);

            vertices[i] = new SDL.Vertex
            {
                Position = new SDL.FPoint
                {
                    X = (srcVert.Pos.X - displayPos.X) * scale.X,
                    Y = (srcVert.Pos.Y - displayPos.Y) * scale.Y
                },
                Color = new SDL.FColor
                {
                    R = r / 255f,
                    G = g / 255f,
                    B = b / 255f,
                    A = a / 255f
                },
                TexCoord = new SDL.FPoint
                {
                    X = srcVert.Uv.X,
                    Y = srcVert.Uv.Y
                }
            };

            indices[i] = i;
        }

        return SDL.RenderGeometry(renderer, texId, vertices, vertices.Length, indices, indices.Length);
    }

    public static void CreateDeviceObjects() { }

    public static void DestroyDeviceObjects()
    {
        var texures = ImGui.GetPlatformIO().Textures;
        for (int i = 0; i < texures.Size; i++)
        {
            var texture = texures[i];
            texture.Status = ImTextureStatus.WantDestroy;
            UpdateTexture(texture, Data.Renderer);
        }
    }
}