using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using UniGLTF;
using Unity.Collections;
using UnityEngine;

namespace UniVRM10
{
    /// <summary>
    /// 座標系を変換した Model により、Mesh, Node, BindMatrices を更新する。
    /// 
    /// * gltf.images の参照する bufferView
    /// * gltf.meshes の参照する index, VERTEX, MorphTarget の accessor, bufferView
    /// * gltf.nodes の参照する skin の inverseBindMatrices 向けの accessor, bufferView
    /// 
    /// を詰め込みなすことで bin を再構築する
    /// </summary>
    class MeshUpdater
    {
        GltfData _data;
        ArrayByteBuffer _buffer;
        List<glTFBufferView> _bufferViews = new List<glTFBufferView>();
        List<glTFAccessor> _accessors = new List<glTFAccessor>();

        MeshUpdater(GltfData data)
        {
            _data = data;
            _buffer = new ArrayByteBuffer(new byte[data.Bin.Length]);
        }

        /// <summary>
        /// data を model で更新する
        /// </summary>
        /// <param name="data">更新前のオリジナル</param>
        /// <param name="model">座標系の変換などの操作済み</param>
        /// <returns></returns>
        public static (glTF, ArraySegment<byte>) Execute(GltfData data, VrmLib.Model model)
        {
            return new MeshUpdater(data).Update(model);
        }

        int AddBuffer(NativeArray<byte> bytes, glBufferTarget target)
        {
            var bufferView = _buffer.Extend(bytes, target);
            var index = _bufferViews.Count;
            _bufferViews.Add(bufferView);

            // padding for 4byte alignment
            var mod = bytes.Length % 4;
            if (mod != 0)
            {
                _buffer.Extend(new ArraySegment<byte>(new byte[4 - mod]));
            }

            return index;
        }

        static (float[], float[]) GetMinMax(NativeArray<Vector3> v)
        {
            var minX = float.PositiveInfinity;
            var minY = float.PositiveInfinity;
            var minZ = float.PositiveInfinity;
            var maxX = float.NegativeInfinity;
            var maxY = float.NegativeInfinity;
            var maxZ = float.NegativeInfinity;
            for (int i = 0; i < v.Length; ++i)
            {
                if (v[i].x < minX) minX = v[i].x;
                if (v[i].y < minY) minY = v[i].y;
                if (v[i].z < minZ) minZ = v[i].z;
                if (v[i].x > maxX) maxX = v[i].x;
                if (v[i].y > maxY) maxY = v[i].y;
                if (v[i].z > maxZ) maxZ = v[i].z;
            }
            return (new float[] { minX, minY, minZ }, new float[] { maxX, maxY, maxZ });
        }

        int AddAccessor<T>(NativeArray<T> span, glBufferTarget target, bool minMaxBounds) where T : struct
        {
            var bufferViewIndex = AddBuffer(span.Reinterpret<byte>(Marshal.SizeOf<T>()), target);
            var accessor = new glTFAccessor
            {
                bufferView = bufferViewIndex,
                count = span.Length,
                byteOffset = 0,
                componentType = glTFExtensions.GetComponentType<T>(),
                type = glTFExtensions.GetAccessorType<T>(),
            };
            if (minMaxBounds)
            {
                if (span is NativeArray<Vector3> positions)
                {
                    var (min, max) = GetMinMax(positions);
                    accessor.min = min;
                    accessor.max = max;
                }
            }
            var index = _accessors.Count;
            _accessors.Add(accessor);
            return index;
        }

        int? AddAccessor<T>(BufferAccessor buffer, glBufferTarget target, bool minMaxBounds) where T : struct
        {
            if (buffer == null)
            {
                return default;
            }
            return AddAccessor(buffer.GetSpan<T>(), target, minMaxBounds);
        }

        struct MorphAccessor
        {
            public int? Position;
            public int? Normal;
        };

        /// <summary>
        /// bufferView, accessor を push することで bin を再構築する
        /// </summary>
        /// <param name="model">meshの右手左手変換結果</param>
        /// <returns></returns>
        (glTF, ArraySegment<byte>) Update(VrmLib.Model model)
        {
            var gltf = _data.GLTF;

            // copy images
            foreach (var image in gltf.images)
            {
                var bytes = _data.GetBytesFromBufferView(image.bufferView);
                image.bufferView = AddBuffer(bytes, default);
            }

            // copy mesh
            if (model.MeshGroups.All(x => x.Meshes.Count == 1))
            {
                UpdateSharedVertexBuffer(model);
            }
            else
            {
                UpdateDividedVertexBuffer(model);
            }

            // update nodes and remove unused skin
            var skins = gltf.skins.ToArray();
            gltf.skins.Clear();
            foreach (var (gltfNode, node) in Enumerable.Zip(gltf.nodes, model.Nodes, (l, r) => (l, r)))
            {
                gltfNode.translation = node.LocalTranslation.ToFloat3();
                gltfNode.rotation = node.LocalRotation.ToFloat4();
                gltfNode.scale = node.LocalScaling.ToFloat3();

                if (gltfNode.mesh >= 0)
                {
                    if (gltfNode.skin >= 0)
                    {
                        //
                        // mesh with skin
                        // only this case, skin is enable
                        // [SkinnedMeshRenderer]
                        //
                        var gltfSkin = skins[gltfNode.skin];
                        // get or create
                        var skinIndex = gltf.skins.IndexOf(gltfSkin);
                        if (skinIndex == -1)
                        {
                            skinIndex = gltf.skins.Count;
                            gltfSkin.inverseBindMatrices = AddAccessor(node.MeshGroup.Skin.InverseMatrices.GetSpan<Matrix4x4>(), default, false);
                            gltf.skins.Add(gltfSkin);
                        }
                        else
                        {
                            // multi nodes sharing a same skin may be error ?
                            // edge case.
                        }
                        // update
                        gltfNode.skin = skinIndex;
                    }
                    else
                    {
                        //
                        // mesh without skin
                        // [MeshRenderer]
                        //
                    }
                }
                else
                {
                    if (gltfNode.skin >= 0)
                    {
                        //
                        // no mesh but skin
                        // fix error
                        //
                        gltfNode.skin = -1;
                    }
                    else
                    {
                        //
                        // no mesh no skin
                        //
                    }
                }
            }

            // replace
            gltf.buffers[0].byteLength = _buffer.Bytes.Count;
            gltf.bufferViews = _bufferViews;
            gltf.accessors = _accessors;

            return (gltf, _buffer.Bytes);

        }

        /// <summary>
        /// model はひとつのノードに複数の mesh をぶら下げることができる(meshGroup)
        /// gltf.meshes[i].primitives[j] <-> model.meshGroups[i].meshes[0].submeshes[j]
        /// </summary>
        void UpdateSharedVertexBuffer(VrmLib.Model model)
        {
            var gltf = _data.GLTF;

            // gltfMeshes[i] <=> MeshGroups[i].Meshes[0] ( MeshGroups[i].Meshes.Count == 1 )
            foreach (var (gltfMesh, mesh) in Enumerable.Zip(gltf.meshes, model.MeshGroups, (l, r) => (l, r.Meshes[0])))
            {
                NativeArray<uint> indices;
                switch (mesh.IndexBuffer.Stride)
                {
                    case 1:
                        {
                            // byte
                            var byte_indices = mesh.IndexBuffer.GetSpan<byte>();
                            indices = _data.NativeArrayManager.Convert(byte_indices, (byte x) => (uint)x);
                            break;
                        }

                    case 2:
                        {
                            // ushort
                            var ushort_indices = mesh.IndexBuffer.GetSpan<ushort>();
                            indices = _data.NativeArrayManager.Convert(ushort_indices, (ushort x) => (uint)x);
                            break;
                        }

                    case 4:
                        {
                            // uint
                            indices = mesh.IndexBuffer.GetSpan<uint>();
                            break;
                        }

                    default:
                        throw new NotImplementedException();
                }
                var position = AddAccessor<Vector3>(mesh.VertexBuffer.Positions, glBufferTarget.ARRAY_BUFFER, true);
                var normal = AddAccessor<Vector3>(mesh.VertexBuffer.Normals, glBufferTarget.ARRAY_BUFFER, false);
                var uv = AddAccessor<Vector2>(mesh.VertexBuffer.TexCoords, glBufferTarget.ARRAY_BUFFER, false);
                var weights = AddAccessor<Vector4>(mesh.VertexBuffer.Weights, glBufferTarget.ARRAY_BUFFER, false);
                var joints = AddAccessor<UShort4>(mesh.VertexBuffer.Joints, glBufferTarget.ARRAY_BUFFER, false);
                var color = AddAccessor<Vector4>(mesh.VertexBuffer.Colors, glBufferTarget.ARRAY_BUFFER, false);

                var morphTargets = new MorphAccessor[] { };
                if (mesh.MorphTargets != null)
                {
                    morphTargets = mesh.MorphTargets.Select(x => new MorphAccessor
                    {
                        Position = AddAccessor<Vector3>(x.VertexBuffer.Positions, glBufferTarget.ARRAY_BUFFER, true),
                        Normal = AddAccessor<Vector3>(x.VertexBuffer.Normals, glBufferTarget.ARRAY_BUFFER, false),
                    }).ToArray();
                }

                // gltfPrim[j] <=> mesh.Submeshes[j]
                foreach (var (gltfPrim, submesh) in Enumerable.Zip(gltfMesh.primitives, mesh.Submeshes, (l, r) => (l, r)))
                {
                    var subIndices = indices.GetSubArray(submesh.Offset, submesh.DrawCount);
                    gltfPrim.indices = AddAccessor(subIndices, glBufferTarget.ELEMENT_ARRAY_BUFFER, false);
                    gltfPrim.attributes.POSITION = position.Value;
                    gltfPrim.attributes.NORMAL = normal.GetValueOrDefault(-1); // たぶん、ありえる
                    gltfPrim.attributes.TANGENT = -1;
                    gltfPrim.attributes.COLOR_0 = color.GetValueOrDefault(-1);
                    gltfPrim.attributes.TEXCOORD_0 = uv.GetValueOrDefault(-1); // ありえる？
                    gltfPrim.attributes.TEXCOORD_1 = -1;
                    gltfPrim.attributes.WEIGHTS_0 = weights.GetValueOrDefault(-1);
                    gltfPrim.attributes.JOINTS_0 = joints.GetValueOrDefault(-1);
                    foreach (var (gltfMorph, morph) in Enumerable.Zip(gltfPrim.targets, morphTargets, (l, r) => (l, r)))
                    {
                        gltfMorph.POSITION = morph.Position.GetValueOrDefault(-1);
                        gltfMorph.NORMAL = morph.Normal.GetValueOrDefault(-1);
                        gltfMorph.TANGENT = -1;
                    }
                }
            }
        }

        /// <summary>
        /// model はひとつのノードに複数の mesh をぶら下げることができる(meshGroup)
        /// gltf.meshes[i].primitives[j] <-> model.meshGroups[i].meshes[j].submeshes[0]
        /// </summary>
        void UpdateDividedVertexBuffer(VrmLib.Model model)
        {
            var gltf = _data.GLTF;

            // gltfMesh[i] <=> meshGroups[i]
            foreach (var (gltfMesh, meshGroup) in Enumerable.Zip(gltf.meshes, model.MeshGroups, (l, r) => (l, r)))
            {
                // gltfPrimitives[j] <=> meshGroup.Meshes[j] (meshGroup.Meshes[j].Submeshes.Count==1)
                foreach (var (gltfPrim, mesh) in Enumerable.Zip(gltfMesh.primitives, meshGroup.Meshes, (l, r) => (l, r)))
                {
                    NativeArray<uint> indices;
                    switch (mesh.IndexBuffer.Stride)
                    {
                        case 1:
                            {
                                // byte
                                var byte_indices = mesh.IndexBuffer.GetSpan<byte>();
                                indices = _data.NativeArrayManager.Convert(byte_indices, (byte x) => (uint)x);
                                break;
                            }

                        case 2:
                            {
                                // ushort
                                var ushort_indices = mesh.IndexBuffer.GetSpan<ushort>();
                                indices = _data.NativeArrayManager.Convert(ushort_indices, (ushort x) => (uint)x);
                                break;
                            }

                        case 4:
                            {
                                // uint
                                indices = mesh.IndexBuffer.GetSpan<uint>();
                                break;
                            }

                        default:
                            throw new NotImplementedException();
                    }

                    var position = AddAccessor<Vector3>(mesh.VertexBuffer.Positions, glBufferTarget.ARRAY_BUFFER, true);
                    var normal = AddAccessor<Vector3>(mesh.VertexBuffer.Normals, glBufferTarget.ARRAY_BUFFER, false);
                    var uv = AddAccessor<Vector2>(mesh.VertexBuffer.TexCoords, glBufferTarget.ARRAY_BUFFER, false);
                    var weights = AddAccessor<Vector4>(mesh.VertexBuffer.Weights, glBufferTarget.ARRAY_BUFFER, false);
                    var joints = AddAccessor<UShort4>(mesh.VertexBuffer.Joints, glBufferTarget.ARRAY_BUFFER, false);
                    var color = AddAccessor<Vector4>(mesh.VertexBuffer.Colors, glBufferTarget.ARRAY_BUFFER, false);

                    var morphTargets = new MorphAccessor[] { };
                    if (mesh.MorphTargets != null)
                    {
                        morphTargets = mesh.MorphTargets.Select(x => new MorphAccessor
                        {
                            Position = AddAccessor<Vector3>(x.VertexBuffer.Positions, glBufferTarget.ARRAY_BUFFER, true),
                            Normal = AddAccessor<Vector3>(x.VertexBuffer.Normals, glBufferTarget.ARRAY_BUFFER, false),
                        }).ToArray();
                    }

                    gltfPrim.indices = AddAccessor(indices, glBufferTarget.ELEMENT_ARRAY_BUFFER, false);
                    gltfPrim.attributes.POSITION = position.Value;
                    gltfPrim.attributes.NORMAL = normal.GetValueOrDefault(-1); // たぶん、ありえる
                    gltfPrim.attributes.TANGENT = -1;
                    gltfPrim.attributes.COLOR_0 = color.GetValueOrDefault(-1);
                    gltfPrim.attributes.TEXCOORD_0 = uv.GetValueOrDefault(-1); // ありえる？
                    gltfPrim.attributes.TEXCOORD_1 = -1;
                    gltfPrim.attributes.WEIGHTS_0 = weights.GetValueOrDefault(-1);
                    gltfPrim.attributes.JOINTS_0 = joints.GetValueOrDefault(-1);
                    foreach (var (gltfMorph, morph) in Enumerable.Zip(gltfPrim.targets, morphTargets, (l, r) => (l, r)))
                    {
                        gltfMorph.POSITION = morph.Position.GetValueOrDefault(-1);
                        gltfMorph.NORMAL = morph.Normal.GetValueOrDefault(-1);
                        gltfMorph.TANGENT = -1;
                    }
                }
            }
        }
    }
}