/*
Crafter®.Asset
Copyright (C) 2026 Catcrafts®
catcrafts.net

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License version 3.0 as published by the Free Software Foundation;

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
*/

export module Crafter.Asset:Mesh;
import :Compression;
import Crafter.Math;
import std;
namespace fs = std::filesystem;

export namespace Crafter {
    struct __attribute__((packed)) VertexNormalTangentUVPacked {
        Vector<float, 3, 4> normal;
        Vector<float, 3, 4> tangent;
        Vector<float, 2, 4> uv;
    };

    struct VertexNormalTangentUV {
        Vector<float, 3, 0> normal;
        Vector<float, 3, 0> tangent;
        Vector<float, 2, 0> uv;
    };

    // GDeflate-compressed counterpart of MeshAsset<T>::Save output. Three
    // regions: [vertex, index, data]. dataCount==0 leaves the data region
    // empty (zero compressedSize/decompressedSize). dataStride records sizeof(T)
    // at compress time so consumers can validate.
    struct CompressedMeshAsset {
        std::uint32_t vertexCount = 0;
        std::uint32_t indexCount = 0;
        std::uint32_t dataCount = 0;
        std::uint32_t dataStride = 0;
        Compression::CompressedBlob blob;
    };

    namespace MeshAssetFormat {
        inline constexpr char magic[4] = {'C', 'G', 'D', 'M'};
        inline constexpr std::uint32_t version = 1;
    }

    inline CompressedMeshAsset LoadCompressedMesh(fs::path path) {
        std::ifstream file(path, std::ios::binary);
        char magic[4];
        file.read(magic, 4);
        if (std::memcmp(magic, MeshAssetFormat::magic, 4) != 0) {
            throw std::runtime_error("LoadCompressedMesh: bad magic on " + path.string());
        }
        std::uint32_t version = 0;
        file.read(reinterpret_cast<char*>(&version), sizeof(version));
        if (version != MeshAssetFormat::version) {
            throw std::runtime_error("LoadCompressedMesh: unsupported version on " + path.string());
        }
        CompressedMeshAsset out;
        file.read(reinterpret_cast<char*>(&out.vertexCount), sizeof(out.vertexCount));
        file.read(reinterpret_cast<char*>(&out.indexCount), sizeof(out.indexCount));
        file.read(reinterpret_cast<char*>(&out.dataCount), sizeof(out.dataCount));
        file.read(reinterpret_cast<char*>(&out.dataStride), sizeof(out.dataStride));
        out.blob = Compression::ReadBlob(file);
        return out;
    }

    template <typename T>
    struct MeshAsset {
        std::vector<Vector<float, 3, 3>> vertexes;
        std::vector<std::uint32_t> indexes;
        std::vector<T> datas;

        void Save(fs::path path) {
            std::ofstream file(path, std::ios::binary);

            std::uint32_t vertexCount = vertexes.size();
            std::uint32_t indexCount = indexes.size();
            std::uint32_t dataCount = datas.size();

            file.write(reinterpret_cast<char*>(&vertexCount), sizeof(vertexCount));
            file.write(reinterpret_cast<char*>(&indexCount), sizeof(indexCount));
            file.write(reinterpret_cast<char*>(&dataCount), sizeof(dataCount));

            file.write(reinterpret_cast<char*>(vertexes.data()), vertexCount * sizeof(Vector<float, 3, 3>));
            file.write(reinterpret_cast<char*>(indexes.data()), indexCount * sizeof(std::uint32_t));
            file.write(reinterpret_cast<char*>(datas.data()), dataCount * sizeof(T));
        }

        void SaveCompressed(fs::path path) const {
            std::array<std::span<const std::byte>, 3> streams = {
                std::as_bytes(std::span(vertexes)),
                std::as_bytes(std::span(indexes)),
                std::as_bytes(std::span(datas)),
            };
            Compression::CompressedBlob blob = Compression::CompressStreams(streams);

            std::ofstream file(path, std::ios::binary);
            file.write(MeshAssetFormat::magic, 4);
            std::uint32_t version = MeshAssetFormat::version;
            std::uint32_t vc = static_cast<std::uint32_t>(vertexes.size());
            std::uint32_t ic = static_cast<std::uint32_t>(indexes.size());
            std::uint32_t dc = static_cast<std::uint32_t>(datas.size());
            std::uint32_t stride = static_cast<std::uint32_t>(sizeof(T));
            file.write(reinterpret_cast<const char*>(&version), sizeof(version));
            file.write(reinterpret_cast<const char*>(&vc), sizeof(vc));
            file.write(reinterpret_cast<const char*>(&ic), sizeof(ic));
            file.write(reinterpret_cast<const char*>(&dc), sizeof(dc));
            file.write(reinterpret_cast<const char*>(&stride), sizeof(stride));
            Compression::WriteBlob(file, blob);
        }

        static MeshAsset<T> Load(fs::path path) {
            MeshAsset<T> mesh;
            
            std::ifstream file(path, std::ios::binary);

            std::uint32_t vertexCount = 0;
            std::uint32_t indexCount  = 0;
            std::uint32_t dataCount   = 0;

            file.read(reinterpret_cast<char*>(&vertexCount), sizeof(vertexCount));
            file.read(reinterpret_cast<char*>(&indexCount),  sizeof(indexCount));
            file.read(reinterpret_cast<char*>(&dataCount),   sizeof(dataCount));

            mesh.vertexes.resize(vertexCount);
            mesh.indexes.resize(indexCount);
            mesh.datas.resize(dataCount);

            file.read(reinterpret_cast<char*>(mesh.vertexes.data()), vertexCount * sizeof(Vector<float, 3, 3>));
            file.read(reinterpret_cast<char*>(mesh.indexes.data()), indexCount * sizeof(std::uint32_t));
            file.read(reinterpret_cast<char*>(mesh.datas.data()), dataCount * sizeof(T));

            return mesh;
        }

        static MeshAsset<T> LoadOBJ(fs::path path) requires (std::same_as<T, VertexNormalTangentUVPacked> || std::same_as<T, VertexNormalTangentUV>) {
            std::ifstream file(path);

            MeshAsset<T> mesh;
                
            std::string line;
        
            std::vector<Vector<float, 3, 0>> positions;
            std::vector<Vector<float, 3, 0>> normals;
            std::vector<Vector<float, 2, 0>> uvs;
        
            while (std::getline(file, line)) {
                if (line.substr(0, 2) == "vt") {
                    std::istringstream iss(line.substr(3));
                    Vector<float,2, 0> uv;
                    iss >> uv.x >> uv.y;
                    uvs.push_back(uv);
                } else if (line.substr(0, 2) == "vn") {
                    std::istringstream iss(line.substr(3));
                    Vector<float, 3, 0> normal;
                    iss >> normal.x >> normal.y >> normal.z;
                    normals.push_back(normal);
                } else if (line.substr(0, 1) == "v") {
                    std::istringstream iss(line.substr(2));
                    Vector<float,3, 3> position;
                    iss >> position.x >> position.y >> position.z;
                    positions.push_back(position);
                } else if (line.substr(0, 1) == "f") {
                    std::istringstream iss(line.substr(2));
                    std::string vertexGroup;

                    while (iss >> vertexGroup) {
                        std::istringstream vss(vertexGroup);
                        std::string vIndex, vtIndex, vnIndex;

                        std::getline(vss, vIndex, '/');
                        std::getline(vss, vtIndex, '/');
                        std::getline(vss, vnIndex, '/');

                        Vector<float, 3, 0> v  = positions[std::stoi(vIndex) - 1];
                        Vector<float, 2, 0> vt = uvs[std::stoi(vtIndex) - 1];
                        Vector<float, 3, 0> vn = normals[std::stoi(vnIndex) - 1];

                        for (std::uint32_t i = 0; i < mesh.datas.size(); i++) {
                            if (mesh.datas[i].normal == vn && mesh.datas[i].uv == vt && mesh.vertexes[i] == v) {

                                mesh.indexes.push_back(i);
                                goto skip;
                            }
                        }

                        mesh.indexes.push_back(mesh.datas.size());
                        mesh.datas.push_back({vn, {0,0,0}, vt});
                        mesh.vertexes.push_back(v);
                        skip:;
                    }
                }
            }

            // Accumulate face normals and tangents
            for (std::uint32_t i = 0; i < mesh.indexes.size(); i += 3)
            {
                std::uint32_t i0 = mesh.indexes[i];
                std::uint32_t i1 = mesh.indexes[i + 1];
                std::uint32_t i2 = mesh.indexes[i + 2];

                // Edges of the triangle
                Vector<float, 3, 0> edge1 = mesh.vertexes[i1] - mesh.vertexes[i0];
                Vector<float, 3, 0> edge2 = mesh.vertexes[i2] - mesh.vertexes[i0];

                // Texture coordinate deltas
                Vector<float, 2, 0> deltaUV1 = mesh.datas[i1].uv - mesh.datas[i0].uv;
                Vector<float, 2, 0> deltaUV2 = mesh.datas[i2].uv - mesh.datas[i0].uv;

                // Tangent calculation
                float f = 1.0f / (deltaUV1.x * deltaUV2.y - deltaUV1.y * deltaUV2.x);
                Vector<float, 3, 0> tangent;
                tangent.x = f * (deltaUV2.y * edge1.x - deltaUV1.y * edge2.x);
                tangent.y = f * (deltaUV2.y * edge1.y - deltaUV1.y * edge2.y);
                tangent.z = f * (deltaUV2.y * edge1.z - deltaUV1.y * edge2.z);

                // Normalize tangent
                tangent.Normalize();

                // Accumulate normals and tangents for each vertex
                mesh.datas[i0].tangent += tangent;
                mesh.datas[i1].tangent += tangent;
                mesh.datas[i2].tangent += tangent;
            }

            // Normalize vertex normals and tangents
            for (T& v : mesh.datas) {
                v.tangent.Normalize();
            }

            return mesh;
        }
    };

    template <>
    struct MeshAsset<void> {
        std::vector<Vector<float, 3, 3>> vertexes;
        std::vector<std::uint32_t> indexes;
        void Save(fs::path path) {
            std::ofstream file(path, std::ios::binary);

            std::uint32_t vertexCount = vertexes.size();
            std::uint32_t indexCount = indexes.size();

            file.write(reinterpret_cast<char*>(&vertexCount), sizeof(vertexCount));
            file.write(reinterpret_cast<char*>(&indexCount), sizeof(indexCount));

            file.write(reinterpret_cast<char*>(vertexes.data()), vertexCount * sizeof(Vector<float, 3, 3>));
            file.write(reinterpret_cast<char*>(indexes.data()), indexCount * sizeof(std::uint32_t));
        }

        void SaveCompressed(fs::path path) const {
            // Three regions to keep file format identical to the templated
            // variant; the data region is empty (skipped on the GPU path).
            std::array<std::span<const std::byte>, 3> streams = {
                std::as_bytes(std::span(vertexes)),
                std::as_bytes(std::span(indexes)),
                std::span<const std::byte>{},
            };
            Compression::CompressedBlob blob = Compression::CompressStreams(streams);

            std::ofstream file(path, std::ios::binary);
            file.write(MeshAssetFormat::magic, 4);
            std::uint32_t version = MeshAssetFormat::version;
            std::uint32_t vc = static_cast<std::uint32_t>(vertexes.size());
            std::uint32_t ic = static_cast<std::uint32_t>(indexes.size());
            std::uint32_t dc = 0;
            std::uint32_t stride = 0;
            file.write(reinterpret_cast<const char*>(&version), sizeof(version));
            file.write(reinterpret_cast<const char*>(&vc), sizeof(vc));
            file.write(reinterpret_cast<const char*>(&ic), sizeof(ic));
            file.write(reinterpret_cast<const char*>(&dc), sizeof(dc));
            file.write(reinterpret_cast<const char*>(&stride), sizeof(stride));
            Compression::WriteBlob(file, blob);
        }

        static MeshAsset<void> Load(fs::path path) {
            MeshAsset<void> mesh;
            
            std::ifstream file(path, std::ios::binary);

            std::uint32_t vertexCount = 0;
            std::uint32_t indexCount  = 0;

            file.read(reinterpret_cast<char*>(&vertexCount), sizeof(vertexCount));
            file.read(reinterpret_cast<char*>(&indexCount),  sizeof(indexCount));

            mesh.vertexes.resize(vertexCount);
            mesh.indexes.resize(indexCount);

            file.read(reinterpret_cast<char*>(mesh.vertexes.data()), vertexCount * sizeof(Vector<float, 3, 3>));
            file.read(reinterpret_cast<char*>(mesh.indexes.data()), indexCount * sizeof(std::uint32_t));

            return mesh;
        }
        static MeshAsset<void> LoadOBJ(fs::path path) {
            std::ifstream file(path);

            MeshAsset<void> mesh;
                
            std::string line;
        
            while (std::getline(file, line)) {
                if (line.rfind("v ", 0) == 0) {
                    std::istringstream iss(line.substr(2));
                    Vector<float,3, 3> position;
                    iss >> position.x >> position.y >> position.z;
                    mesh.vertexes.push_back(position);
                } else if (line.rfind("f ", 0) == 0) {
                    std::istringstream iss(line.substr(2));
                    std::string vertexGroup;

                    while (iss >> vertexGroup) {
                        mesh.indexes.push_back(std::stoi(vertexGroup) - 1);
                    }
                }
            }

            return mesh;
        }
    };
}