#define TINYOBJLOADER_IMPLEMENTATION
#include "tiny_obj_loader.h"
#include "../Components/ModelComponent.h" // For definitions of SubMesh and Vertex
#include "AssetManager.h"
#include <iostream>
#include <fstream>
#include <sstream>
#include <glm/glm.hpp>
#include "stb_image.h"

// Get the singleton instance.
AssetManager& AssetManager::Get() {
    static AssetManager instance;
    return instance;
}

bool AssetManager::LoadModel(const std::string &filepath, ModelAsset &outAsset) {
    // Check if the model is already cached.
    auto it = modelCache.find(filepath);
    if (it != modelCache.end()) {
        outAsset = it->second;
        return true;
    }

    std::cout << "[Info] AssetManager: Loading Model '" << filepath << "'" << std::endl;
    ModelAsset asset;
    asset.modelPath = filepath;

    tinyobj::attrib_t attrib;
    std::vector<tinyobj::shape_t> shapes;
    std::vector<tinyobj::material_t> materials;
    std::string warn, err;

    // Get the base directory for the OBJ file.
    std::string baseDir = "";
    size_t lastSlash = filepath.find_last_of("/\\");
    if (lastSlash != std::string::npos) {
        baseDir = filepath.substr(0, lastSlash + 1);
    }

    bool ret = tinyobj::LoadObj(&attrib, &shapes, &materials, &warn, &err, filepath.c_str(), baseDir.c_str());
    if (!warn.empty()) {
        std::cout << "[Warning] " << warn << std::endl;
    }
    if (!err.empty()) {
        std::cerr << "[Error] " << err << std::endl;
    }
    if (!ret) {
        std::cerr << "[Error] Failed to load/parse OBJ file: " << filepath << std::endl;
        return false;
    }

    // Process each shape.
    for (size_t s = 0; s < shapes.size(); s++) {
        // Use a map to group faces by material ID.
        std::map<int, SubMesh> submeshMap;
        size_t index_offset = 0;
        for (size_t f = 0; f < shapes[s].mesh.num_face_vertices.size(); f++) {
            int fv = shapes[s].mesh.num_face_vertices[f];
            int matID = -1;
            if (shapes[s].mesh.material_ids.size() > f)
                matID = shapes[s].mesh.material_ids[f];
            if (submeshMap.find(matID) == submeshMap.end())
                submeshMap[matID] = SubMesh();
            
            SubMesh &currentMesh = submeshMap[matID];
            for (size_t v = 0; v < fv; v++) {
                tinyobj::index_t idx = shapes[s].mesh.indices[index_offset + v];
                Vertex vertex;
                // Position.
                vertex.Position = glm::vec3(
                    attrib.vertices[3 * idx.vertex_index + 0],
                    attrib.vertices[3 * idx.vertex_index + 1],
                    attrib.vertices[3 * idx.vertex_index + 2]
                );
                // Normal.
                if (idx.normal_index >= 0 && 3 * idx.normal_index + 2 < attrib.normals.size()) {
                    vertex.Normal = glm::vec3(
                        attrib.normals[3 * idx.normal_index + 0],
                        attrib.normals[3 * idx.normal_index + 1],
                        attrib.normals[3 * idx.normal_index + 2]
                    );
                } else {
                    vertex.Normal = glm::vec3(0.0f);
                }
                // Texture Coordinates.
                if (idx.texcoord_index >= 0 && 2 * idx.texcoord_index + 1 < attrib.texcoords.size()) {
                    vertex.TexCoords = glm::vec2(
                        attrib.texcoords[2 * idx.texcoord_index + 0],
                        attrib.texcoords[2 * idx.texcoord_index + 1]
                    );
                } else {
                    vertex.TexCoords = glm::vec2(0.0f);
                }
                // Tangent (not provided).
                vertex.Tangent = glm::vec3(0.0f);
                
                // Add vertex and index.
                currentMesh.vertices.push_back(vertex);
                currentMesh.indices.push_back(static_cast<GLuint>(currentMesh.vertices.size() - 1));
            }
            index_offset += fv;
        }

        // Process each submesh for this shape.
        for (auto &pair : submeshMap) {
            int matID = pair.first;
            SubMesh &subMesh = pair.second;
            if (matID >= 0 && matID < static_cast<int>(materials.size())) {
                tinyobj::material_t mat = materials[matID];
                subMesh.diffuseColor = glm::vec3(mat.diffuse[0], mat.diffuse[1], mat.diffuse[2]);
                subMesh.specularColor = glm::vec3(mat.specular[0], mat.specular[1], mat.specular[2]);
                subMesh.shininess = mat.shininess;
                if (!mat.diffuse_texname.empty()) {
                    std::string texturePath = baseDir + mat.diffuse_texname;
                    // Load and cache the texture.
                    LoadTexture(texturePath, subMesh.diffuseTexture);
                }
            }
            // Note: OpenGL buffers (VAO, VBO, EBO) are not created here.
            asset.meshes.push_back(subMesh);
        }
    }

    std::cout << "[Done] AssetManager: Loaded Model '" << filepath << "'" << std::endl;
    modelCache[filepath] = asset;
    outAsset = asset;
    return true;
}

bool AssetManager::LoadTexture(const std::string &filepath, GLuint &textureID) {
    // Check if texture is already cached.
    auto it = textureCache.find(filepath);
    if (it != textureCache.end()) {
        textureID = it->second;
        return true;
    }

    int w, h, channels;
    unsigned char* data = stbi_load(filepath.c_str(), &w, &h, &channels, 0);
    if (!data) {
        std::cerr << "[Error] AssetManager: Failed to load texture: " << filepath << std::endl;
        return false;
    }

    glGenTextures(1, &textureID);
    glBindTexture(GL_TEXTURE_2D, textureID);
    GLenum format = (channels == 3) ? GL_RGB : GL_RGBA;
    glTexImage2D(GL_TEXTURE_2D, 0, format, w, h, 0, format, GL_UNSIGNED_BYTE, data);
    glGenerateMipmap(GL_TEXTURE_2D);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    stbi_image_free(data);

    textureCache[filepath] = textureID;
    return true;
}

void AssetManager::Clear() {
    modelCache.clear();
    // Optionally delete textures from OpenGL context.
    for (auto &pair : textureCache) {
        glDeleteTextures(1, &pair.second);
    }
    textureCache.clear();
}