#include "obj_loader.h"
#include <fstream>
#include <sstream>
#include <stdexcept>
#include <map>
#include <filesystem>

std::vector<Triangle> ObjLoader::load_obj(const std::string& obj_filepath, 
                                         Renderer& renderer)
{
    std::vector<Triangle> triangles;
    std::vector<Vec3> vertices;
    std::vector<Vec2> uvs;
    std::vector<Vec3> normals;
    std::map<std::string, Texture> material_textures; // Maps material names to textures
    std::string current_material;
    std::string mtl_filepath;

    // Helper to parse MTL file
    auto parse_mtl = [&](const std::string& mtl_path) {
        std::ifstream mtl_file(mtl_path);
        if (!mtl_file.is_open()) {
            // Silently skip if MTL file cannot be opened
            return;
        }

        std::string line, current_mtl;
        while (std::getline(mtl_file, line)) {
            std::istringstream iss(line);
            std::string token;
            iss >> token;

            if (token == "newmtl") {
                iss >> current_mtl;
            }
            else if (token == "map_Kd") {
                std::string texture_path;
                std::getline(iss, texture_path);
                texture_path.erase(0, texture_path.find_first_not_of(" \t"));
                
                // Construct full texture path relative to MTL directory
                std::filesystem::path mtl_dir = std::filesystem::path(mtl_path).parent_path();
                std::filesystem::path tex_path = mtl_dir / texture_path;
                
                try {
                    material_textures[current_mtl] = renderer.load_texture(tex_path.string());
                } catch (const std::exception& e) {
                    // Fallback to default texture (id=0) if loading fails
                    material_textures[current_mtl] = Texture(0, 0, 0);
                }
            }
        }
        mtl_file.close();
    };

    // Open and parse OBJ file
    std::ifstream obj_file(obj_filepath);
    if (!obj_file.is_open()) {
        throw std::runtime_error("Failed to open OBJ file: " + obj_filepath);
    }

    std::filesystem::path obj_dir = std::filesystem::path(obj_filepath).parent_path();

    std::string line;
    while (std::getline(obj_file, line)) {
        std::istringstream iss(line);
        std::string token;
        iss >> token;

        if (token == "v") {
            float x, y, z;
            iss >> x >> y >> z;
            vertices.emplace_back(x, y, z);
        }
        else if (token == "vt") {
            float u, v;
            iss >> u >> v;
            uvs.emplace_back(u, v);
        }
        else if (token == "vn") {
            float x, y, z;
            iss >> x >> y >> z;
            normals.emplace_back(x, y, z);
        }
        else if (token == "f") {
            std::vector<std::tuple<int, int, int>> face_vertices; // v/vt/vn indices
            std::string vertex;
            while (iss >> vertex) {
                int v_idx = 0, vt_idx = 0, vn_idx = 0;
                std::sscanf(vertex.c_str(), "%d/%d/%d", &v_idx, &vt_idx, &vn_idx);
                face_vertices.emplace_back(v_idx - 1, vt_idx - 1, vn_idx - 1); // Convert to 0-based
            }

            // Triangulate if necessary (e.g., for quads)
            for (size_t i = 1; i < face_vertices.size() - 1; ++i) {
                Triangle tri;
                auto [v0, vt0, vn0] = face_vertices[0];
                auto [v1, vt1, vn1] = face_vertices[i];
                auto [v2, vt2, vn2] = face_vertices[i + 1];

                // Assign vertices
                tri.v0 = vertices[v0];
                tri.v1 = vertices[v1];
                tri.v2 = vertices[v2];

                // Assign UVs (use default if not specified)
                tri.uv0 = vt0 >= 0 && vt0 < uvs.size() ? uvs[vt0] : Vec2(0, 0);
                tri.uv1 = vt1 >= 0 && vt1 < uvs.size() ? uvs[vt1] : Vec2(0, 0);
                tri.uv2 = vt2 >= 0 && vt2 < uvs.size() ? uvs[vt2] : Vec2(0, 0);

                // Assign default color
                tri.color = Color(255, 255, 255);

                // Assign texture based on current material
                tri.texture = material_textures.count(current_material) ? 
                             material_textures[current_material] : Texture(0, 0, 0);

                triangles.push_back(tri);
            }
        }
        else if (token == "mtllib") {
            std::string mtl_name;
            iss >> mtl_name;
            mtl_filepath = (obj_dir / mtl_name).string();
            parse_mtl(mtl_filepath);
        }
        else if (token == "usemtl") {
            iss >> current_material;
        }
    }

    obj_file.close();
    return triangles;
}