using System;
using System.Collections.Generic;
using System.Numerics;
using AcDream.Core.Meshing;
using AcDream.Core.Terrain;
using AcDream.Core.World;
using Chorizite.OpenGLSDLBackend.Lib;
using Silk.NET.OpenGL;

namespace AcDream.App.Rendering.Wb;

/// <summary>
/// Draws entities using WB's <see cref="ObjectRenderData"/> (VAO/VBO per GfxObj,
/// per-batch IBO) with acdream's <see cref="TextureCache"/> for texture resolution
/// and <see cref="AcSurfaceMetadataTable"/> for translucency classification.
///
/// <para>
/// <b>Atlas-tier</b> entities (<c>ServerGuid == 0</c>): mesh data comes from WB's
/// <see cref="ObjectMeshManager"/> via <see cref="WbMeshAdapter.TryGetRenderData"/>.
/// Textures resolve through <see cref="TextureCache.GetOrUpload"/> using the batch's
/// <c>SurfaceId</c>.
/// </para>
///
/// <para>
/// <b>Per-instance-tier</b> entities (<c>ServerGuid != 0</c>): mesh data also from
/// WB, but textures resolve through <see cref="TextureCache"/> with palette and
/// surface overrides applied. Part overrides and hidden-parts from
/// <see cref="AnimatedEntityState"/> control which GfxObj renders per part.
/// </para>
///
/// <para>
/// <b>GL strategy:</b> per-entity single-instance drawing. Each draw call uploads
/// one model matrix to the instance VBO, binds WB's VAO (with instance attribute
/// slots patched on first use), binds the batch's IBO, and calls DrawElements with
/// instance count 1. True instancing grouping deferred to N.6.
/// </para>
///
/// <para>
/// <b>Shader:</b> reuses <c>mesh_instanced</c> (vert locations 0-2 = Position/
/// Normal/UV from WB's <c>VertexPositionNormalTexture</c>; locations 3-6 = instance
/// matrix from our VBO). WB's 32-byte vertex stride is compatible.
/// </para>
/// </summary>
public sealed unsafe class WbDrawDispatcher : IDisposable
{
    private readonly GL _gl;
    private readonly Shader _shader;
    private readonly TextureCache _textures;
    private readonly WbMeshAdapter _meshAdapter;
    private readonly EntitySpawnAdapter _entitySpawnAdapter;

    private readonly uint _instanceVbo;
    private readonly float[] _matrixBuf = new float[16];
    private readonly HashSet<uint> _patchedVaos = new();

    private bool _disposed;

    public WbDrawDispatcher(
        GL gl,
        Shader shader,
        TextureCache textures,
        WbMeshAdapter meshAdapter,
        EntitySpawnAdapter entitySpawnAdapter)
    {
        ArgumentNullException.ThrowIfNull(gl);
        ArgumentNullException.ThrowIfNull(shader);
        ArgumentNullException.ThrowIfNull(textures);
        ArgumentNullException.ThrowIfNull(meshAdapter);
        ArgumentNullException.ThrowIfNull(entitySpawnAdapter);

        _gl = gl;
        _shader = shader;
        _textures = textures;
        _meshAdapter = meshAdapter;
        _entitySpawnAdapter = entitySpawnAdapter;

        _instanceVbo = _gl.GenBuffer();
        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, _instanceVbo);
        _gl.BufferData(BufferTargetARB.ArrayBuffer, 64, null, BufferUsageARB.DynamicDraw);
    }

    public static Matrix4x4 ComposePartWorldMatrix(
        Matrix4x4 entityWorld,
        Matrix4x4 animOverride,
        Matrix4x4 restPose)
        => restPose * animOverride * entityWorld;

    public void Draw(
        ICamera camera,
        IEnumerable<(uint LandblockId, Vector3 AabbMin, Vector3 AabbMax, IReadOnlyList<WorldEntity> Entities)> landblockEntries,
        FrustumPlanes? frustum = null,
        uint? neverCullLandblockId = null,
        HashSet<uint>? visibleCellIds = null,
        HashSet<uint>? animatedEntityIds = null)
    {
        _shader.Use();
        var vp = camera.View * camera.Projection;
        _shader.SetMatrix4("uViewProjection", vp);

        var metaTable = _meshAdapter.MetadataTable;

        // Collect visible entities into opaque and translucent lists for two-pass rendering.
        // We walk entities once and classify each (entity, meshRef, batch) triple.
        var opaqueDraws = new List<DrawItem>();
        var translucentDraws = new List<DrawItem>();

        foreach (var entry in landblockEntries)
        {
            bool landblockVisible = frustum is null
                || entry.LandblockId == neverCullLandblockId
                || FrustumCuller.IsAabbVisible(frustum.Value, entry.AabbMin, entry.AabbMax);

            if (!landblockVisible && (animatedEntityIds is null || animatedEntityIds.Count == 0))
                continue;

            foreach (var entity in entry.Entities)
            {
                if (entity.MeshRefs.Count == 0) continue;

                bool isAnimated = animatedEntityIds?.Contains(entity.Id) == true;
                if (!landblockVisible && !isAnimated) continue;

                if (entity.ParentCellId.HasValue && visibleCellIds is not null
                    && !visibleCellIds.Contains(entity.ParentCellId.Value))
                    continue;

                var entityWorld =
                    Matrix4x4.CreateFromQuaternion(entity.Rotation) *
                    Matrix4x4.CreateTranslation(entity.Position);

                bool isPerInstance = entity.ServerGuid != 0;
                AnimatedEntityState? animState = isPerInstance
                    ? _entitySpawnAdapter.GetState(entity.ServerGuid)
                    : null;

                for (int partIdx = 0; partIdx < entity.MeshRefs.Count; partIdx++)
                {
                    if (animState is not null && animState.IsPartHidden(partIdx))
                        continue;

                    var meshRef = entity.MeshRefs[partIdx];

                    ulong gfxObjId = meshRef.GfxObjId;
                    if (animState is not null)
                        gfxObjId = animState.ResolvePartGfxObj(partIdx, gfxObjId);

                    var renderData = _meshAdapter.TryGetRenderData(gfxObjId);
                    if (renderData is null) continue;

                    // For Setup objects, WB stores sub-parts in SetupParts. For
                    // single GfxObjs, SetupParts is empty and the render data
                    // itself contains the batches.
                    if (renderData.IsSetup && renderData.SetupParts.Count > 0)
                    {
                        foreach (var (partGfxObjId, partTransform) in renderData.SetupParts)
                        {
                            var partData = _meshAdapter.TryGetRenderData(partGfxObjId);
                            if (partData is null) continue;

                            var model = ComposePartWorldMatrix(
                                entityWorld, meshRef.PartTransform, partTransform);

                            ClassifyBatches(partData, partGfxObjId, model,
                                entity, meshRef, metaTable, opaqueDraws, translucentDraws);
                        }
                    }
                    else
                    {
                        var model = meshRef.PartTransform * entityWorld;

                        ClassifyBatches(renderData, gfxObjId, model,
                            entity, meshRef, metaTable, opaqueDraws, translucentDraws);
                    }
                }
            }
        }

        // ── Pass 1: Opaque + ClipMap ─────────────────────────────────────────
        if (string.Equals(Environment.GetEnvironmentVariable("ACDREAM_NO_CULL"), "1", StringComparison.Ordinal))
            _gl.Disable(EnableCap.CullFace);

        foreach (var item in opaqueDraws)
        {
            _shader.SetInt("uTranslucencyKind", (int)item.Translucency);
            UploadMatrixAndDraw(item);
        }

        // ── Pass 2: Translucent ──────────────────────────────────────────────
        _gl.Enable(EnableCap.Blend);
        _gl.DepthMask(false);

        if (string.Equals(Environment.GetEnvironmentVariable("ACDREAM_NO_CULL"), "1", StringComparison.Ordinal))
        {
            _gl.Disable(EnableCap.CullFace);
        }
        else
        {
            _gl.Enable(EnableCap.CullFace);
            _gl.CullFace(TriangleFace.Back);
            _gl.FrontFace(FrontFaceDirection.Ccw);
        }

        foreach (var item in translucentDraws)
        {
            switch (item.Translucency)
            {
                case TranslucencyKind.Additive:
                    _gl.BlendFunc(BlendingFactor.SrcAlpha, BlendingFactor.One);
                    break;
                case TranslucencyKind.InvAlpha:
                    _gl.BlendFunc(BlendingFactor.OneMinusSrcAlpha, BlendingFactor.SrcAlpha);
                    break;
                default:
                    _gl.BlendFunc(BlendingFactor.SrcAlpha, BlendingFactor.OneMinusSrcAlpha);
                    break;
            }

            _shader.SetInt("uTranslucencyKind", (int)item.Translucency);
            UploadMatrixAndDraw(item);
        }

        _gl.DepthMask(true);
        _gl.Disable(EnableCap.Blend);
        _gl.Disable(EnableCap.CullFace);
        _gl.BindVertexArray(0);
    }

    private void ClassifyBatches(
        ObjectRenderData renderData,
        ulong gfxObjId,
        Matrix4x4 model,
        WorldEntity entity,
        MeshRef meshRef,
        AcSurfaceMetadataTable metaTable,
        List<DrawItem> opaqueDraws,
        List<DrawItem> translucentDraws)
    {
        for (int batchIdx = 0; batchIdx < renderData.Batches.Count; batchIdx++)
        {
            var batch = renderData.Batches[batchIdx];

            TranslucencyKind translucency;
            if (metaTable.TryLookup(gfxObjId, batchIdx, out var meta))
            {
                translucency = meta.Translucency;
            }
            else
            {
                // Fallback: derive from WB batch flags.
                translucency = batch.IsAdditive ? TranslucencyKind.Additive
                    : batch.IsTransparent ? TranslucencyKind.AlphaBlend
                    : TranslucencyKind.Opaque;
            }

            uint texHandle = ResolveTexture(entity, meshRef, batch);
            if (texHandle == 0) continue;

            var item = new DrawItem
            {
                Vao = renderData.VAO,
                Ibo = batch.IBO,
                IndexCount = batch.IndexCount,
                Model = model,
                TextureHandle = texHandle,
                Translucency = translucency,
            };

            if (translucency == TranslucencyKind.Opaque || translucency == TranslucencyKind.ClipMap)
                opaqueDraws.Add(item);
            else
                translucentDraws.Add(item);
        }
    }

    private uint ResolveTexture(WorldEntity entity, MeshRef meshRef, ObjectRenderBatch batch)
    {
        uint surfaceId = batch.SurfaceId;
        if (surfaceId == 0) return 0;

        uint overrideOrigTex = 0;
        bool hasOrigTexOverride = meshRef.SurfaceOverrides is not null
            && meshRef.SurfaceOverrides.TryGetValue(surfaceId, out overrideOrigTex);
        uint? origTexOverride = hasOrigTexOverride ? overrideOrigTex : (uint?)null;

        if (entity.PaletteOverride is not null)
        {
            return _textures.GetOrUploadWithPaletteOverride(
                surfaceId, origTexOverride, entity.PaletteOverride);
        }
        else if (hasOrigTexOverride)
        {
            return _textures.GetOrUploadWithOrigTextureOverride(surfaceId, overrideOrigTex);
        }
        else
        {
            return _textures.GetOrUpload(surfaceId);
        }
    }

    private void EnsureInstanceAttribs(uint vao)
    {
        if (!_patchedVaos.Add(vao)) return;

        _gl.BindVertexArray(vao);
        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, _instanceVbo);
        for (uint row = 0; row < 4; row++)
        {
            uint loc = 3 + row;
            _gl.EnableVertexAttribArray(loc);
            _gl.VertexAttribPointer(loc, 4, VertexAttribPointerType.Float, false, 64, (void*)(row * 16));
            _gl.VertexAttribDivisor(loc, 1);
        }
    }

    private void UploadMatrixAndDraw(in DrawItem item)
    {
        WriteMatrix(_matrixBuf, 0, item.Model);

        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, _instanceVbo);
        fixed (float* p = _matrixBuf)
            _gl.BufferSubData(BufferTargetARB.ArrayBuffer, 0, 64, p);

        EnsureInstanceAttribs(item.Vao);
        _gl.BindVertexArray(item.Vao);

        // Re-point instance attributes to offset 0 (single matrix).
        _gl.BindBuffer(BufferTargetARB.ArrayBuffer, _instanceVbo);
        for (uint row = 0; row < 4; row++)
            _gl.VertexAttribPointer(3 + row, 4, VertexAttribPointerType.Float, false, 64, (void*)(row * 16));

        _gl.ActiveTexture(TextureUnit.Texture0);
        _gl.BindTexture(TextureTarget.Texture2D, item.TextureHandle);

        _gl.BindBuffer(BufferTargetARB.ElementArrayBuffer, item.Ibo);
        _gl.DrawElementsInstanced(PrimitiveType.Triangles,
            (uint)item.IndexCount, DrawElementsType.UnsignedShort,
            (void*)0, 1);
    }

    private static void WriteMatrix(float[] buf, int offset, in Matrix4x4 m)
    {
        buf[offset + 0]  = m.M11; buf[offset + 1]  = m.M12; buf[offset + 2]  = m.M13; buf[offset + 3]  = m.M14;
        buf[offset + 4]  = m.M21; buf[offset + 5]  = m.M22; buf[offset + 6]  = m.M23; buf[offset + 7]  = m.M24;
        buf[offset + 8]  = m.M31; buf[offset + 9]  = m.M32; buf[offset + 10] = m.M33; buf[offset + 11] = m.M34;
        buf[offset + 12] = m.M41; buf[offset + 13] = m.M42; buf[offset + 14] = m.M43; buf[offset + 15] = m.M44;
    }

    public void Dispose()
    {
        if (_disposed) return;
        _disposed = true;
        _gl.DeleteBuffer(_instanceVbo);
    }

    private struct DrawItem
    {
        public uint Vao;
        public uint Ibo;
        public int IndexCount;
        public Matrix4x4 Model;
        public uint TextureHandle;
        public TranslucencyKind Translucency;
    }
}