using System;
using System.Collections.Generic;
using System.Numerics;
using AcDream.App.Rendering.Wb;
using AcDream.Content;
using AcDream.Core.Meshing;
using AcDream.Core.Vfx;
using DatReaderWriter;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Enums;
using Silk.NET.OpenGL;

namespace AcDream.App.Rendering;

/// <summary>
/// Instanced renderer for retail particle emitters.
/// </summary>
public sealed unsafe class ParticleRenderer : IDisposable
{
    private readonly record struct BatchKey(uint TextureHandle, bool UseTexture, bool Additive);
    private readonly record struct ParticleDraw(BatchKey Key, ParticleInstance Instance);
    private readonly record struct MeshBatchKey(uint GfxObjId, int BatchIndex);
    private readonly record struct MeshParticleDraw(
        MeshBatchKey Key,
        ObjectRenderBatch Batch,
        MeshParticleInstance Instance);

    private readonly struct ParticleInstance
    {
        public readonly Vector3 Position;
        public readonly Vector3 AxisX;
        public readonly Vector3 AxisY;
        public readonly uint ColorArgb;
        public readonly float DistanceSq;

        public ParticleInstance(Vector3 position, Vector3 axisX, Vector3 axisY, uint colorArgb, float distanceSq)
        {
            Position = position;
            AxisX = axisX;
            AxisY = axisY;
            ColorArgb = colorArgb;
            DistanceSq = distanceSq;
        }
    }

    private readonly struct MeshParticleInstance
    {
        public readonly Matrix4x4 Model;
        public readonly uint ColorArgb;
        public readonly float DistanceSq;

        public MeshParticleInstance(Matrix4x4 model, uint colorArgb, float distanceSq)
        {
            Model = model;
            ColorArgb = colorArgb;
            DistanceSq = distanceSq;
        }
    }

    private readonly GL _gl;
    private readonly Shader _shader;
    private readonly Shader? _meshShader;
    private readonly TextureCache? _textures;
    private readonly DatCollection? _dats;
    private readonly WbMeshAdapter? _meshAdapter;
    private readonly ParticleSystem _particles;
    private readonly Dictionary<uint, ParticleGfxInfo> _particleGfxInfoByGfxObj = new();
    private readonly Dictionary<uint, RetailParticleGeometryKind> _geometryKindByGfxObj = new();
    private readonly Dictionary<uint, TranslucencyKind> _meshBlendBySurface = new();
    private readonly ParticleMeshReferenceTracker? _meshReferences;
    private readonly HashSet<uint> _meshLoadRequestedThisFrame = new();
    private readonly int _meshTextureHandleLoc = -1;
    private readonly int _meshTextureLayerLoc = -1;

    private readonly uint _quadVao;
    private readonly uint _quadVbo;
    private readonly uint _quadEbo;
    private readonly uint _instanceVbo;
    private readonly uint _meshVao;
    private readonly uint _meshInstanceVbo;

    private float[] _instanceScratch = new float[256 * 16];
    private float[] _meshInstanceScratch = new float[256 * 20];

    // MP-Alloc (2026-07-05): Draw() is called up to ~11 times per frame
    // (sky pre/post, scene, per-visible-cell, dynamics, unattached passes),
    // each previously `new`ing a List<ParticleDraw> (BuildDrawList) and a
    // List<ParticleInstance> (the per-batch `run` list) that became garbage
    // as soon as the call returned. All Draw() calls happen sequentially on
    // the render thread (verified: every call site in GameWindow.cs is a
    // plain synchronous invocation from the single-threaded OnRender chain,
    // none dispatched via Task.Run/Parallel) and each call fully drains its
    // lists before returning, so a single pair of reused fields is safe -
    // no call overlaps another's use of these buffers.
    private readonly List<ParticleDraw> _drawListScratch = new(64);
    private readonly List<ParticleInstance> _runScratch = new(64);
    private readonly List<MeshParticleDraw> _meshDrawListScratch = new(64);
    private readonly List<MeshParticleInstance> _meshRunScratch = new(64);
    private readonly List<ParticleSubmission> _submissionScratch = new(128);

    public ParticleRenderer(
        GL gl,
        string shadersDir,
        ParticleSystem particles,
        TextureCache? textures = null,
        DatCollection? dats = null,
        WbMeshAdapter? meshAdapter = null)
    {
        _gl = gl ?? throw new ArgumentNullException(nameof(gl));
        _textures = textures;
        _dats = dats;
        _meshAdapter = meshAdapter;
        _particles = particles ?? throw new ArgumentNullException(nameof(particles));
        if (_meshAdapter is not null)
        {
            _meshReferences = new ParticleMeshReferenceTracker(
                gfxObjId => _meshAdapter.IncrementRefCount(gfxObjId),
                gfxObjId => _meshAdapter.DecrementRefCount(gfxObjId));
        }
        _shader = new Shader(_gl,
            System.IO.Path.Combine(shadersDir, "particle.vert"),
            System.IO.Path.Combine(shadersDir, "particle.frag"));
        if (_meshAdapter?.MeshManager?.GlobalBuffer is not null)
        {
            _meshShader = new Shader(_gl,
                System.IO.Path.Combine(shadersDir, "particle_mesh.vert"),
                System.IO.Path.Combine(shadersDir, "particle_mesh.frag"));
            _meshTextureHandleLoc = _gl.GetUniformLocation(_meshShader.Program, "uTextureHandle");
            _meshTextureLayerLoc = _gl.GetUniformLocation(_meshShader.Program, "uTextureLayer");
        }

        float[] quadVerts =
        {
            -0.5f, -0.5f, 0f, 0f,
             0.5f, -0.5f, 1f, 0f,
             0.5f,  0.5f, 1f, 1f,
            -0.5f,  0.5f, 0f, 1f,
        };
        uint[] quadIdx = { 0, 1, 2, 0, 2, 3 };

        _quadVao = _gl.GenVertexArray();
        _gl.BindVertexArray(_quadVao);

        _quadVbo = _gl.GenBuffer();
        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, _quadVbo);
        fixed (void* p = quadVerts)
        {
            _gl.BufferData(
                BufferTargetARB.ArrayBuffer,
                (nuint)(quadVerts.Length * sizeof(float)),
                p,
                BufferUsageARB.StaticDraw);
        }

        _gl.EnableVertexAttribArray(0);
        _gl.VertexAttribPointer(0, 2, VertexAttribPointerType.Float, false, 4 * sizeof(float), (void*)0);
        _gl.EnableVertexAttribArray(1);
        _gl.VertexAttribPointer(1, 2, VertexAttribPointerType.Float, false, 4 * sizeof(float), (void*)(2 * sizeof(float)));

        _quadEbo = _gl.GenBuffer();
        _gl.BindBuffer(BufferTargetARB.ElementArrayBuffer, _quadEbo);
        fixed (void* p = quadIdx)
        {
            _gl.BufferData(
                BufferTargetARB.ElementArrayBuffer,
                (nuint)(quadIdx.Length * sizeof(uint)),
                p,
                BufferUsageARB.StaticDraw);
        }

        _instanceVbo = _gl.GenBuffer();
        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, _instanceVbo);
        _gl.BufferData(BufferTargetARB.ArrayBuffer, (nuint)(256 * 16 * sizeof(float)), (void*)0, BufferUsageARB.DynamicDraw);

        _gl.EnableVertexAttribArray(2);
        _gl.VertexAttribPointer(2, 4, VertexAttribPointerType.Float, false, 16 * sizeof(float), (void*)0);
        _gl.VertexAttribDivisor(2, 1);
        _gl.EnableVertexAttribArray(3);
        _gl.VertexAttribPointer(3, 4, VertexAttribPointerType.Float, false, 16 * sizeof(float), (void*)(4 * sizeof(float)));
        _gl.VertexAttribDivisor(3, 1);
        _gl.EnableVertexAttribArray(4);
        _gl.VertexAttribPointer(4, 4, VertexAttribPointerType.Float, false, 16 * sizeof(float), (void*)(8 * sizeof(float)));
        _gl.VertexAttribDivisor(4, 1);
        _gl.EnableVertexAttribArray(5);
        _gl.VertexAttribPointer(5, 4, VertexAttribPointerType.Float, false, 16 * sizeof(float), (void*)(12 * sizeof(float)));
        _gl.VertexAttribDivisor(5, 1);

        _gl.BindVertexArray(0);

        _meshVao = _gl.GenVertexArray();
        _meshInstanceVbo = _gl.GenBuffer();
        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, _meshInstanceVbo);
        _gl.BufferData(
            BufferTargetARB.ArrayBuffer,
            (nuint)(256 * 20 * sizeof(float)),
            (void*)0,
            BufferUsageARB.DynamicDraw);
        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, 0);

        _particles.EmitterDied += OnEmitterDied;
    }

    /// <summary>
    /// Starts one render frame. Wb point-of-use recovery is limited to one
    /// request per missing GfxObj even though portal slicing may invoke Draw
    /// many times during the frame.
    /// </summary>
    public void BeginFrame()
        => _meshLoadRequestedThisFrame.Clear();

    public void Draw(
        ICamera camera,
        Vector3 cameraWorldPos,
        ParticleRenderPass renderPass = ParticleRenderPass.Scene,
        Func<AcDream.Core.Vfx.ParticleEmitter, bool>? emitterFilter = null)
    {
        if (camera is null)
            return;

        Matrix4x4.Invert(camera.View, out var invView);
        Vector3 cameraRight = Vector3.Normalize(new Vector3(invView.M11, invView.M12, invView.M13));
        Vector3 cameraUp = Vector3.Normalize(new Vector3(invView.M21, invView.M22, invView.M23));
        BuildDrawLists(cameraWorldPos, renderPass, cameraRight, cameraUp, emitterFilter);
        if (_submissionScratch.Count > 0)
            DrawOrdered(camera);
    }

    private void DrawOrdered(ICamera camera)
    {
        ParticleSubmissionOrdering.Sort(_submissionScratch);
        GlobalMeshBuffer? global = _meshAdapter?.MeshManager?.GlobalBuffer;

        _gl.Enable(EnableCap.DepthTest);
        _gl.Enable(EnableCap.Blend);
        _gl.DepthMask(false);
        _gl.ActiveTexture(TextureUnit.Texture0);

        ParticleSubmissionKind? activeKind = null;
        for (int i = 0; i < _submissionScratch.Count;)
        {
            ParticleSubmission submission = _submissionScratch[i];
            if (submission.Kind == ParticleSubmissionKind.Billboard)
            {
                ParticleDraw draw = _drawListScratch[submission.DrawIndex];
                BatchKey key = draw.Key;
                if (activeKind != ParticleSubmissionKind.Billboard)
                {
                    PrepareBillboardPipeline(camera);
                    activeKind = ParticleSubmissionKind.Billboard;
                }

                _runScratch.Clear();
                do
                {
                    _runScratch.Add(_drawListScratch[submission.DrawIndex].Instance);
                    i++;
                    if (i >= _submissionScratch.Count)
                        break;
                    submission = _submissionScratch[i];
                }
                while (submission.Kind == ParticleSubmissionKind.Billboard
                    && _drawListScratch[submission.DrawIndex].Key == key);

                _gl.BlendFunc(
                    BlendingFactor.SrcAlpha,
                    key.Additive ? BlendingFactor.One : BlendingFactor.OneMinusSrcAlpha);
                _shader.SetInt("uUseTexture", key.UseTexture ? 1 : 0);
                _gl.BindTexture(TextureTarget.Texture2D, key.UseTexture ? key.TextureHandle : 0);
                DrawInstances(_runScratch);
                continue;
            }

            if (_meshShader is null || global is null)
            {
                i++;
                continue;
            }

            MeshParticleDraw meshDraw = _meshDrawListScratch[submission.DrawIndex];
            MeshBatchKey meshKey = meshDraw.Key;
            ObjectRenderBatch batch = meshDraw.Batch;
            if (activeKind != ParticleSubmissionKind.Mesh)
            {
                PrepareMeshPipeline(camera, global);
                activeKind = ParticleSubmissionKind.Mesh;
            }

            _meshRunScratch.Clear();
            do
            {
                _meshRunScratch.Add(_meshDrawListScratch[submission.DrawIndex].Instance);
                i++;
                if (i >= _submissionScratch.Count)
                    break;
                submission = _submissionScratch[i];
            }
            while (submission.Kind == ParticleSubmissionKind.Mesh
                && _meshDrawListScratch[submission.DrawIndex].Key == meshKey);

            ApplyMeshCullMode(batch.CullMode);
            TranslucencyKind blend = ResolveMeshBlend(batch);
            _gl.BlendFunc(
                blend == TranslucencyKind.InvAlpha
                    ? BlendingFactor.OneMinusSrcAlpha
                    : BlendingFactor.SrcAlpha,
                blend switch
                {
                    TranslucencyKind.Additive => BlendingFactor.One,
                    TranslucencyKind.InvAlpha => BlendingFactor.SrcAlpha,
                    _ => BlendingFactor.OneMinusSrcAlpha,
                });

            _gl.ProgramUniform2(
                _meshShader.Program,
                _meshTextureHandleLoc,
                (uint)(batch.BindlessTextureHandle & 0xFFFFFFFFu),
                (uint)(batch.BindlessTextureHandle >> 32));
            _gl.ProgramUniform1(_meshShader.Program, _meshTextureLayerLoc, batch.TextureIndex);

            UploadMeshInstances(_meshRunScratch);
            _gl.DrawElementsInstancedBaseVertex(
                PrimitiveType.Triangles,
                (uint)batch.IndexCount,
                DrawElementsType.UnsignedShort,
                (void*)(batch.FirstIndex * sizeof(ushort)),
                (uint)_meshRunScratch.Count,
                (int)batch.BaseVertex);
        }

        _gl.BindTexture(TextureTarget.Texture2D, 0);
        _gl.BindVertexArray(0);
        _gl.DepthMask(true);
        _gl.Disable(EnableCap.Blend);
        _gl.Disable(EnableCap.CullFace);
    }

    private void PrepareBillboardPipeline(ICamera camera)
    {
        _shader.Use();
        _shader.SetMatrix4("uViewProjection", camera.View * camera.Projection);
        _shader.SetInt("uParticleTexture", 0);
        _gl.Disable(EnableCap.CullFace);
        _gl.BindVertexArray(_quadVao);
    }

    private void PrepareMeshPipeline(ICamera camera, GlobalMeshBuffer global)
    {
        _meshShader!.Use();
        _meshShader.SetMatrix4("uViewProjection", camera.View * camera.Projection);
        _gl.FrontFace(FrontFaceDirection.CW);
        _gl.BindVertexArray(_meshVao);

        // GlobalMeshBuffer may grow and replace either backing buffer. Bind
        // today's buffer names on every pipeline switch instead of caching
        // them in this VAO at construction time.
        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, global.VBO);
        int vertexStride = VertexPositionNormalTexture.Size;
        _gl.EnableVertexAttribArray(0);
        _gl.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, (uint)vertexStride, (void*)0);
        _gl.EnableVertexAttribArray(1);
        _gl.VertexAttribPointer(1, 3, VertexAttribPointerType.Float, false, (uint)vertexStride, (void*)(3 * sizeof(float)));
        _gl.EnableVertexAttribArray(2);
        _gl.VertexAttribPointer(2, 2, VertexAttribPointerType.Float, false, (uint)vertexStride, (void*)(6 * sizeof(float)));
        _gl.BindBuffer(BufferTargetARB.ElementArrayBuffer, global.IBO);

        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, _meshInstanceVbo);
        const int instanceStride = 20 * sizeof(float);
        for (uint column = 0; column < 4; column++)
        {
            uint location = 3 + column;
            _gl.EnableVertexAttribArray(location);
            _gl.VertexAttribPointer(
                location,
                4,
                VertexAttribPointerType.Float,
                false,
                instanceStride,
                (void*)(column * 4 * sizeof(float)));
            _gl.VertexAttribDivisor(location, 1);
        }
        _gl.EnableVertexAttribArray(7);
        _gl.VertexAttribPointer(7, 4, VertexAttribPointerType.Float, false, instanceStride, (void*)(16 * sizeof(float)));
        _gl.VertexAttribDivisor(7, 1);
    }

    private void BuildDrawLists(
        Vector3 cameraWorldPos,
        ParticleRenderPass renderPass,
        Vector3 cameraRight,
        Vector3 cameraUp,
        Func<AcDream.Core.Vfx.ParticleEmitter, bool>? emitterFilter)
    {
        var draws = _drawListScratch;
        draws.Clear();
        _meshDrawListScratch.Clear();
        _submissionScratch.Clear();
        int sequence = 0;
        foreach (var em in _particles.EnumerateEmitters())
        {
            if (!em.PresentationVisible || !em.ViewEligible)
                continue;
            if (em.RenderPass != renderPass)
                continue;
            if (emitterFilter is not null && !emitterFilter(em))
                continue;

            for (int idx = 0; idx < em.Particles.Length; idx++)
            {
                ref var p = ref em.Particles[idx];
                if (!p.Alive)
                    continue;
                // `p.Position` is already in world coordinates: AttachLocal
                // emitters get their AnchorPos refreshed each frame by the
                // owning subsystem (sky-PES driver, animation tick, etc.) which
                // mirrors retail's live-parent-frame read at
                // ParticleEmitter::UpdateParticles 0x0051d2d4 for is_parent_local=1.
                Vector3 pos = p.Position;
                float distSq = Vector3.DistanceSquared(pos, cameraWorldPos);
                uint gfxObjId = em.Desc.HwGfxObjId != 0 ? em.Desc.HwGfxObjId : em.Desc.GfxObjId;
                if (gfxObjId != 0
                    && ResolveGeometryKind(gfxObjId) == RetailParticleGeometryKind.FullMesh
                    && TryAppendMeshDraws(em, p, gfxObjId, distSq, ref sequence))
                {
                    continue;
                }

                var gfxInfo = ResolveParticleGfxInfo(em.Desc);
                uint texture = gfxInfo.TextureHandle;
                bool useTexture = texture != 0;
                bool additive = gfxInfo.HasMaterial
                    ? gfxInfo.Additive
                    : (em.Desc.Flags & EmitterFlags.Additive) != 0;
                var key = new BatchKey(texture, useTexture, additive);
                Vector3 axisX;
                Vector3 axisY;
                if (gfxInfo.IsBillboard)
                {
                    pos += Vector3.UnitZ * (gfxInfo.CenterOffset.Z * p.Size);
                    axisX = cameraRight * (gfxInfo.Size.X * p.Size);
                    axisY = cameraUp * (gfxInfo.Size.Y * p.Size);
                }
                else
                {
                    Quaternion orientation = ParticleOrientation(em, p);
                    pos += Vector3.Transform(gfxInfo.CenterOffset * p.Size, orientation);
                    axisX = Vector3.Transform(gfxInfo.AxisX, orientation) * (gfxInfo.Size.X * p.Size);
                    axisY = Vector3.Transform(gfxInfo.AxisY, orientation) * (gfxInfo.Size.Y * p.Size);
                }

                int drawIndex = draws.Count;
                draws.Add(new ParticleDraw(key, new ParticleInstance(pos, axisX, axisY, p.ColorArgb, distSq)));
                _submissionScratch.Add(new ParticleSubmission(
                    ParticleSubmissionKind.Billboard,
                    drawIndex,
                    distSq,
                    sequence++));
            }
        }
    }

    private bool TryAppendMeshDraws(
        AcDream.Core.Vfx.ParticleEmitter emitter,
        Particle particle,
        uint gfxObjId,
        float distanceSq,
        ref int sequence)
    {
        if (_meshAdapter is null || _meshShader is null)
            return true;

        _meshReferences!.Register(emitter.Handle, gfxObjId);
        ObjectRenderData? renderData = _meshAdapter.TryGetRenderData(gfxObjId);
        if (renderData is null)
        {
            if (_meshLoadRequestedThisFrame.Add(gfxObjId))
                _meshAdapter.EnsureLoaded(gfxObjId);
            return true;
        }

        Quaternion orientation = ParticleOrientation(emitter, particle);
        Matrix4x4 model = Matrix4x4.CreateScale(particle.Size)
            * Matrix4x4.CreateFromQuaternion(orientation)
            * Matrix4x4.CreateTranslation(particle.Position);
        var instance = new MeshParticleInstance(model, particle.ColorArgb, distanceSq);

        for (int batchIndex = 0; batchIndex < renderData.Batches.Count; batchIndex++)
        {
            ObjectRenderBatch batch = renderData.Batches[batchIndex];
            if (batch.IndexCount <= 0 || batch.BindlessTextureHandle == 0)
                continue;

            int drawIndex = _meshDrawListScratch.Count;
            _meshDrawListScratch.Add(new MeshParticleDraw(
                new MeshBatchKey(gfxObjId, batchIndex),
                batch,
                instance));
            _submissionScratch.Add(new ParticleSubmission(
                ParticleSubmissionKind.Mesh,
                drawIndex,
                distanceSq,
                sequence++));
        }

        return true;
    }

    private void DrawInstances(List<ParticleInstance> instances)
    {
        if (instances.Count == 0)
            return;

        int needed = instances.Count * 16;
        if (_instanceScratch.Length < needed)
            _instanceScratch = new float[needed + 256 * 16];

        for (int i = 0; i < instances.Count; i++)
        {
            var p = instances[i];
            int o = i * 16;
            _instanceScratch[o + 0] = p.Position.X;
            _instanceScratch[o + 1] = p.Position.Y;
            _instanceScratch[o + 2] = p.Position.Z;
            _instanceScratch[o + 3] = 0f;

            _instanceScratch[o + 4] = p.AxisX.X;
            _instanceScratch[o + 5] = p.AxisX.Y;
            _instanceScratch[o + 6] = p.AxisX.Z;
            _instanceScratch[o + 7] = 0f;

            _instanceScratch[o + 8] = p.AxisY.X;
            _instanceScratch[o + 9] = p.AxisY.Y;
            _instanceScratch[o + 10] = p.AxisY.Z;
            _instanceScratch[o + 11] = 0f;

            _instanceScratch[o + 12] = ((p.ColorArgb >> 16) & 0xFF) / 255f;
            _instanceScratch[o + 13] = ((p.ColorArgb >> 8) & 0xFF) / 255f;
            _instanceScratch[o + 14] = (p.ColorArgb & 0xFF) / 255f;
            _instanceScratch[o + 15] = ((p.ColorArgb >> 24) & 0xFF) / 255f;
        }

        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, _instanceVbo);
        fixed (void* bp = _instanceScratch)
        {
            _gl.BufferData(
                BufferTargetARB.ArrayBuffer,
                (nuint)(instances.Count * 16 * sizeof(float)),
                bp,
                BufferUsageARB.DynamicDraw);
        }

        _gl.BindVertexArray(_quadVao);
        _gl.DrawElementsInstanced(PrimitiveType.Triangles, 6, DrawElementsType.UnsignedInt, (void*)0, (uint)instances.Count);
    }

    private void UploadMeshInstances(List<MeshParticleInstance> instances)
    {
        int needed = instances.Count * 20;
        if (_meshInstanceScratch.Length < needed)
            _meshInstanceScratch = new float[needed + 256 * 20];

        for (int i = 0; i < instances.Count; i++)
        {
            MeshParticleInstance instance = instances[i];
            Matrix4x4 model = instance.Model;
            int o = i * 20;
            _meshInstanceScratch[o + 0] = model.M11;
            _meshInstanceScratch[o + 1] = model.M12;
            _meshInstanceScratch[o + 2] = model.M13;
            _meshInstanceScratch[o + 3] = model.M14;
            _meshInstanceScratch[o + 4] = model.M21;
            _meshInstanceScratch[o + 5] = model.M22;
            _meshInstanceScratch[o + 6] = model.M23;
            _meshInstanceScratch[o + 7] = model.M24;
            _meshInstanceScratch[o + 8] = model.M31;
            _meshInstanceScratch[o + 9] = model.M32;
            _meshInstanceScratch[o + 10] = model.M33;
            _meshInstanceScratch[o + 11] = model.M34;
            _meshInstanceScratch[o + 12] = model.M41;
            _meshInstanceScratch[o + 13] = model.M42;
            _meshInstanceScratch[o + 14] = model.M43;
            _meshInstanceScratch[o + 15] = model.M44;
            _meshInstanceScratch[o + 16] = ((instance.ColorArgb >> 16) & 0xFF) / 255f;
            _meshInstanceScratch[o + 17] = ((instance.ColorArgb >> 8) & 0xFF) / 255f;
            _meshInstanceScratch[o + 18] = (instance.ColorArgb & 0xFF) / 255f;
            _meshInstanceScratch[o + 19] = ((instance.ColorArgb >> 24) & 0xFF) / 255f;
        }

        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, _meshInstanceVbo);
        fixed (void* bp = _meshInstanceScratch)
        {
            _gl.BufferData(
                BufferTargetARB.ArrayBuffer,
                (nuint)(instances.Count * 20 * sizeof(float)),
                bp,
                BufferUsageARB.DynamicDraw);
        }
    }

    private void ApplyMeshCullMode(CullMode mode)
    {
        _gl.FrontFace(FrontFaceDirection.CW);
        switch (mode)
        {
            case CullMode.None:
                _gl.Disable(EnableCap.CullFace);
                break;
            case CullMode.Clockwise:
                _gl.Enable(EnableCap.CullFace);
                _gl.CullFace(TriangleFace.Front);
                break;
            case CullMode.CounterClockwise:
            case CullMode.Landblock:
                _gl.Enable(EnableCap.CullFace);
                _gl.CullFace(TriangleFace.Back);
                break;
        }
    }

    private TranslucencyKind ResolveMeshBlend(ObjectRenderBatch batch)
    {
        uint surfaceId = batch.Key.SurfaceId;
        if (surfaceId == 0 || _dats is null)
            return batch.IsAdditive ? TranslucencyKind.Additive : TranslucencyKind.AlphaBlend;
        if (_meshBlendBySurface.TryGetValue(surfaceId, out TranslucencyKind blend))
            return blend;

        blend = RetailParticleBlendResolver.Resolve(
            surfaceId,
            batch.IsAdditive,
            id => _dats.Get<Surface>(id),
            Console.Error.WriteLine);
        _meshBlendBySurface[surfaceId] = blend;
        return blend;
    }

    private RetailParticleGeometryKind ResolveGeometryKind(uint gfxObjId)
    {
        if (_geometryKindByGfxObj.TryGetValue(gfxObjId, out RetailParticleGeometryKind kind))
            return kind;

        uint? firstDegradeMode = null;
        try
        {
            if (_dats?.Get<GfxObj>(gfxObjId) is { } gfx
                && gfx.Flags.HasFlag(GfxObjFlags.HasDIDDegrade)
                && gfx.DIDDegrade != 0
                && _dats.Get<GfxObjDegradeInfo>(gfx.DIDDegrade) is { Degrades.Count: > 0 } degrade)
            {
                firstDegradeMode = degrade.Degrades[0].DegradeMode;
            }
        }
        catch (Exception ex)
        {
            // Missing/corrupt content must not invent a billboard. Cache the
            // retail full-mesh choice and let WbMeshAdapter's normal missing-
            // asset diagnostics decide whether geometry can be presented.
            Console.Error.WriteLine(
                $"[particle-geometry] Failed to decode GfxObj 0x{gfxObjId:X8} degrade metadata: {ex.Message}");
        }

        kind = RetailParticleGeometryClassifier.Classify(firstDegradeMode);
        _geometryKindByGfxObj[gfxObjId] = kind;
        return kind;
    }

    private void OnEmitterDied(int handle)
        => _meshReferences?.Release(handle);

    private ParticleGfxInfo ResolveParticleGfxInfo(EmitterDesc desc)
    {
        if (_textures is null)
            return ParticleGfxInfo.Default;

        if (desc.TextureSurfaceId != 0)
            return ParticleGfxInfo.Billboard(
                _textures.GetOrUpload(desc.TextureSurfaceId),
                Vector2.One,
                Vector3.Zero,
                additive: (desc.Flags & EmitterFlags.Additive) != 0,
                hasMaterial: false);

        uint gfxObjId = desc.HwGfxObjId != 0 ? desc.HwGfxObjId : desc.GfxObjId;
        if (gfxObjId == 0 || _dats is null)
            return ParticleGfxInfo.Default;

        if (!_particleGfxInfoByGfxObj.TryGetValue(gfxObjId, out var info))
        {
            info = ReadParticleGfxInfo(gfxObjId);
            _particleGfxInfoByGfxObj[gfxObjId] = info;
        }

        return info.TextureHandle != 0 ? info : ParticleGfxInfo.Default;
    }

    private ParticleGfxInfo ReadParticleGfxInfo(uint gfxObjId)
    {
        try
        {
            var gfx = _dats?.Get<GfxObj>(gfxObjId);
            if (gfx is null)
                return ParticleGfxInfo.Default;

            uint surfaceId = gfx.Surfaces.Count > 0 ? gfx.Surfaces[0].DataId : 0u;
            uint texture = surfaceId != 0 && _textures is not null ? _textures.GetOrUpload(surfaceId) : 0u;
            bool additive = false;
            if (surfaceId != 0)
            {
                var surface = _dats?.Get<Surface>(surfaceId);
                additive = surface is not null && surface.Type.HasFlag(SurfaceType.Additive);
            }
            return AuthoredParticleGfxInfo(gfx, texture, additive, surfaceId != 0);
        }
        catch
        {
            return ParticleGfxInfo.Default;
        }
    }

    private ParticleGfxInfo AuthoredParticleGfxInfo(GfxObj gfx, uint texture, bool additive, bool hasMaterial)
    {
        if (gfx.VertexArray.Vertices.Count == 0)
            return ParticleGfxInfo.Billboard(texture, Vector2.One, Vector3.Zero, additive, hasMaterial);

        var min = new Vector3(float.PositiveInfinity);
        var max = new Vector3(float.NegativeInfinity);
        foreach (var (_, v) in gfx.VertexArray.Vertices)
        {
            min = Vector3.Min(min, v.Origin);
            max = Vector3.Max(max, v.Origin);
        }

        var size = max - min;
        var center = (min + max) * 0.5f;
        if (IsPointSprite(gfx))
        {
            float sx = FallbackParticleExtent(size.X) * 0.9f;
            float sy = FallbackParticleExtent(size.Z) * 0.9f;
            return ParticleGfxInfo.Billboard(texture, new Vector2(sx, sy), center, additive, hasMaterial);
        }

        Vector3 axisX;
        Vector3 axisY;
        Vector2 planeSize;
        if (size.Y > size.X && size.Y > size.Z)
        {
            if (size.X > size.Z)
            {
                axisX = Vector3.UnitX;
                axisY = Vector3.UnitY;
                planeSize = new Vector2(size.X, size.Y);
            }
            else
            {
                axisX = Vector3.UnitY;
                axisY = Vector3.UnitZ;
                planeSize = new Vector2(size.Y, size.Z);
            }
        }
        else if (size.X > size.Y && size.X > size.Z)
        {
            if (size.Z > size.Y)
            {
                axisX = Vector3.UnitX;
                axisY = Vector3.UnitZ;
                planeSize = new Vector2(size.X, size.Z);
            }
            else
            {
                axisX = Vector3.UnitX;
                axisY = Vector3.UnitY;
                planeSize = new Vector2(size.X, size.Y);
            }
        }
        else
        {
            if (size.X > size.Y)
            {
                axisX = Vector3.UnitX;
                axisY = Vector3.UnitZ;
                planeSize = new Vector2(size.X, size.Z);
            }
            else
            {
                axisX = Vector3.UnitY;
                axisY = Vector3.UnitZ;
                planeSize = new Vector2(size.Y, size.Z);
            }
        }

        planeSize.X = FallbackParticleExtent(planeSize.X);
        planeSize.Y = FallbackParticleExtent(planeSize.Y);
        return new ParticleGfxInfo(texture, planeSize, axisX, axisY, center, false, additive, hasMaterial);
    }

    private bool IsPointSprite(GfxObj gfx)
    {
        if (!gfx.Flags.HasFlag(GfxObjFlags.HasDIDDegrade) || gfx.DIDDegrade == 0 || _dats is null)
            return false;

        try
        {
            var degrade = _dats.Get<GfxObjDegradeInfo>(gfx.DIDDegrade);
            return degrade?.Degrades.Count > 0 && degrade.Degrades[0].DegradeMode == 2;
        }
        catch
        {
            return false;
        }
    }

    private static float FallbackParticleExtent(float value)
        => value > 1e-4f ? Math.Clamp(value, 1e-4f, 10_000f) : 1f;

    private static Quaternion ParticleOrientation(AcDream.Core.Vfx.ParticleEmitter em, Particle p)
    {
        Quaternion orientation = (em.Desc.Flags & EmitterFlags.AttachLocal) != 0
            ? em.AnchorRot
            : p.SpawnRotation;

        if (em.Desc.Type is AcDream.Core.Vfx.ParticleType.ParabolicLVGAGR
            or AcDream.Core.Vfx.ParticleType.ParabolicLVLALR
            or AcDream.Core.Vfx.ParticleType.ParabolicGVGAGR)
        {
            Vector3 angular = p.C * p.Age;
            float radians = angular.Length();
            if (radians > 1e-6f)
                orientation = Quaternion.Normalize(orientation * Quaternion.CreateFromAxisAngle(angular / radians, radians));
        }

        return orientation;
    }

    public void Dispose()
    {
        _particles.EmitterDied -= OnEmitterDied;
        _meshReferences?.Dispose();

        _gl.DeleteBuffer(_quadVbo);
        _gl.DeleteBuffer(_quadEbo);
        _gl.DeleteBuffer(_instanceVbo);
        _gl.DeleteBuffer(_meshInstanceVbo);
        _gl.DeleteVertexArray(_quadVao);
        _gl.DeleteVertexArray(_meshVao);
        _shader.Dispose();
        _meshShader?.Dispose();
    }

    private readonly record struct ParticleGfxInfo(
        uint TextureHandle,
        Vector2 Size,
        Vector3 AxisX,
        Vector3 AxisY,
        Vector3 CenterOffset,
        bool IsBillboard,
        bool Additive,
        bool HasMaterial)
    {
        public static ParticleGfxInfo Default { get; } =
            Billboard(0u, Vector2.One, Vector3.Zero, additive: false, hasMaterial: false);

        public static ParticleGfxInfo Billboard(
            uint textureHandle,
            Vector2 size,
            Vector3 centerOffset,
            bool additive,
            bool hasMaterial) =>
            new(textureHandle, size, Vector3.UnitX, Vector3.UnitY, centerOffset, true, additive, hasMaterial);
    }
}