#ifndef MODEL_H
#define MODEL_H

#include <glad/glad.h> 

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

#include <stb_image.cpp>

#include <assimp/Importer.hpp>
#include <assimp/scene.h>
#include <assimp/postprocess.h>

#include "shader.h"

#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <map>
#include <vector>

using namespace std;






//--------------------------mesh------------------------------
#define MAX_BONE_INFLUENCE 4

struct Vertex {
	// position
	glm::vec3 Position;
	// normal
	glm::vec3 Normal;
	// texCoords
	glm::vec2 TexCoords;
	// tangent
	glm::vec3 Tangent;
	// bitangent
	glm::vec3 Bitangent;
	//bone indexes which will influence this vertex
	int m_BoneIDs[MAX_BONE_INFLUENCE];
	//weights from each bone
	float m_Weights[MAX_BONE_INFLUENCE];
};

struct Texture {
	unsigned int id;
	string type;
	string path;
};

class Mesh {
public:
	// mesh Data
	vector<Vertex>       vertices;
	vector<unsigned int> indices;
	vector<Texture>      textures;
	unsigned int VAO;

	// constructor
	Mesh(vector<Vertex> vertices, vector<unsigned int> indices, vector<Texture> textures) {
		this->vertices = vertices;
		this->indices = indices;
		this->textures = textures;

		// now that we have all the required data, set the vertex buffers and its attribute pointers.
		setupMesh();
	}

	// render the mesh
	void Draw(Shader &shader) {
		// bind appropriate textures
		unsigned int diffuseNr = 1;
		unsigned int specularNr = 1;
		unsigned int normalNr = 1;
		unsigned int heightNr = 1;
		for (unsigned int i = 0; i < textures.size(); i++) {
			glActiveTexture(GL_TEXTURE0 + i); // active proper texture unit before binding
			// retrieve texture number (the N in diffuse_textureN)
			string number;
			string name = textures[i].type;
			if (name == "texture_diffuse")
				number = to_string(diffuseNr++);
			else if (name == "texture_specular")
				number = to_string(specularNr++); // transfer unsigned int to string
			else if (name == "texture_normal")
				number = to_string(normalNr++); // transfer unsigned int to string
			else if (name == "texture_height")
				number = to_string(heightNr++); // transfer unsigned int to string

			// now set the sampler to the correct texture unit
			glUniform1i(glGetUniformLocation(shader.ID, (name + number).c_str()), i);
			// and finally bind the texture
			glBindTexture(GL_TEXTURE_2D, textures[i].id);
		}

		// draw mesh
		glBindVertexArray(VAO);
		glDrawElements(GL_TRIANGLES, static_cast<unsigned int>(indices.size()), GL_UNSIGNED_INT, 0);
		glBindVertexArray(0);

		// always good practice to set everything back to defaults once configured.
		glActiveTexture(GL_TEXTURE0);
	}

private:
	// render data 
	unsigned int VBO, EBO;

	// initializes all the buffer objects/arrays
	void setupMesh() {
		// create buffers/arrays
		glGenVertexArrays(1, &VAO);
		glGenBuffers(1, &VBO);
		glGenBuffers(1, &EBO);

		glBindVertexArray(VAO);
		// load data into vertex buffers
		glBindBuffer(GL_ARRAY_BUFFER, VBO);
		// A great thing about structs is that their memory layout is sequential for all its items.
		// The effect is that we can simply pass a pointer to the struct and it translates perfectly to a glm::vec3/2 array which
		// again translates to 3/2 floats which translates to a byte array.
		glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(Vertex), &vertices[0], GL_STATIC_DRAW);

		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
		glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(unsigned int), &indices[0], GL_STATIC_DRAW);

		// set the vertex attribute pointers
		// vertex Positions
		glEnableVertexAttribArray(0);
		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)0);
		// vertex normals
		glEnableVertexAttribArray(1);
		glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, Normal));
		// vertex texture coords
		glEnableVertexAttribArray(2);
		glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, TexCoords));
		// vertex tangent
		glEnableVertexAttribArray(3);
		glVertexAttribPointer(3, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, Tangent));
		// vertex bitangent
		glEnableVertexAttribArray(4);
		glVertexAttribPointer(4, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, Bitangent));
		// ids
		glEnableVertexAttribArray(5);
		glVertexAttribIPointer(5, 4, GL_INT, sizeof(Vertex), (void*)offsetof(Vertex, m_BoneIDs));

		// weights
		glEnableVertexAttribArray(6);
		glVertexAttribPointer(6, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)offsetof(Vertex, m_Weights));
		glBindVertexArray(0);
	}
};






//--------------------------model------------------------------

unsigned int TextureFromFile(const char *path, const string &directory, bool gamma = false) {
	string filename = string(path);
	filename = directory + '\\' + filename;

	unsigned int textureID;
	glGenTextures(1, &textureID);

	int width, height, nrComponents;
	unsigned char *data = stbi_load(filename.c_str(), &width, &height, &nrComponents, 0);
	if (data) {
		GLenum format;
		if (nrComponents == 1)format = GL_RED;
		else if (nrComponents == 3)format = GL_RGB;
		else if (nrComponents == 4)format = GL_RGBA;

		glBindTexture(GL_TEXTURE_2D, textureID);
		glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 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);
	}
	else {
		cout << "Texture failed to load at path: " << filename << endl;
		stbi_image_free(data);
	}

	return textureID;
}

class Model {
public:
	// model data
	struct TEX {
		Texture tex;
		bool real;
	};
	map<string, TEX> textures_loaded;	// stores all the textures loaded so far, optimization to make sure textures aren't loaded more than once.
	vector<Mesh>    meshes;
	string directory;
	bool gammaCorrection;

	bool real;

	// constructor, expects a filepath to a 3D model.
	Model(string const &path, bool gamma = false) : gammaCorrection(gamma) {
		loadModel(path);
	}
	Model() {
		real = 0;
	}

	// draws the model, and thus all its meshes
	void Draw(Shader &shader) {
		EnableBlend(0);

		for (unsigned int i = 0; i < meshes.size(); i++) {
			meshes[i].Draw(shader);
		}

		EnableBlend(1);
	}

private:
	// loads a model with supported ASSIMP extensions from file and stores the resulting meshes in the meshes vector.
	void loadModel(string const &path) {
		// read file via ASSIMP
		Assimp::Importer importer;
		const aiScene* scene = importer.ReadFile(path, aiProcess_Triangulate | aiProcess_GenSmoothNormals | aiProcess_FlipUVs | aiProcess_CalcTangentSpace);
		// check for errors
		if (!scene || scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE || !scene->mRootNode) { // if is Not Zero
			cout << "ERROR::ASSIMP:: " << importer.GetErrorString() << endl;
			return;
		}
		// retrieve the directory path of the filepath
		directory = path.substr(0, path.find_last_of('\\'));

		// process ASSIMP's root node recursively
		processNode(scene->mRootNode, scene);

		real = 1;
	}

	// processes a node in a recursive fashion. Processes each individual mesh located at the node and repeats this process on its children nodes (if any).
	void processNode(aiNode *node, const aiScene *scene) {
		// process each mesh located at the current node
		for (unsigned int i = 0; i < node->mNumMeshes; i++) {
			// the node object only contains indices to index the actual objects in the scene. 
			// the scene contains all the data, node is just to keep stuff organized (like relations between nodes).
			aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];
			meshes.push_back(processMesh(mesh, scene));
		}
		// after we've processed all of the meshes (if any) we then recursively process each of the children nodes
		for (unsigned int i = 0; i < node->mNumChildren; i++) {
			processNode(node->mChildren[i], scene);
		}
	}

	Mesh processMesh(aiMesh *mesh, const aiScene *scene) {
		// data to fill
		vector<Vertex> vertices;
		vector<unsigned int> indices;
		vector<Texture> textures;

		// walk through each of the mesh's vertices
		for (unsigned int i = 0; i < mesh->mNumVertices; i++) {
			Vertex vertex;
			glm::vec3 vector; // we declare a placeholder vector since assimp uses its own vector class that doesn't directly convert to glm's vec3 class so we transfer the data to this placeholder glm::vec3 first.
			// positions
			vector.x = mesh->mVertices[i].x;
			vector.y = mesh->mVertices[i].y;
			vector.z = mesh->mVertices[i].z;
			vertex.Position = vector;
			// normals
			if (mesh->HasNormals()) {
				vector.x = mesh->mNormals[i].x;
				vector.y = mesh->mNormals[i].y;
				vector.z = mesh->mNormals[i].z;
				vertex.Normal = vector;
			}
			// texture coordinates
			if (mesh->mTextureCoords[0]) { // does the mesh contain texture coordinates?
				glm::vec2 vec;
				// a vertex can contain up to 8 different texture coordinates. We thus make the assumption that we won't 
				// use models where a vertex can have multiple texture coordinates so we always take the first set (0).
				vec.x = mesh->mTextureCoords[0][i].x;
				vec.y = mesh->mTextureCoords[0][i].y;
				vertex.TexCoords = vec;
				// tangent
				vector.x = mesh->mTangents[i].x;
				vector.y = mesh->mTangents[i].y;
				vector.z = mesh->mTangents[i].z;
				vertex.Tangent = vector;
				// bitangent
				vector.x = mesh->mBitangents[i].x;
				vector.y = mesh->mBitangents[i].y;
				vector.z = mesh->mBitangents[i].z;
				vertex.Bitangent = vector;
			}
			else {
				vertex.TexCoords = glm::vec2(0.0f, 0.0f);
			}

			vertices.push_back(vertex);
		}
		// now wak through each of the mesh's faces (a face is a mesh its triangle) and retrieve the corresponding vertex indices.
		for (unsigned int i = 0; i < mesh->mNumFaces; ++i) {
			aiFace face = mesh->mFaces[i];
			// retrieve all indices of the face and store them in the indices vector
			for (unsigned int j = 0; j < face.mNumIndices; ++j)
				indices.push_back(face.mIndices[j]);
		}
		// process materials
		aiMaterial* material = scene->mMaterials[mesh->mMaterialIndex];
		// we assume a convention for sampler names in the shaders. Each diffuse texture should be named
		// as 'texture_diffuseN' where N is a sequential number ranging from 1 to MAX_SAMPLER_NUMBER. 
		// Same applies to other texture as the following list summarizes:
		// diffuse: texture_diffuseN
		// specular: texture_specularN
		// normal: texture_normalN

		// 1. diffuse maps
		vector<Texture> diffuseMaps = loadMaterialTextures(material, aiTextureType_DIFFUSE, "texture_diffuse");
		textures.insert(textures.end(), diffuseMaps.begin(), diffuseMaps.end());
		// 2. specular maps
		vector<Texture> specularMaps = loadMaterialTextures(material, aiTextureType_SPECULAR, "texture_specular");
		textures.insert(textures.end(), specularMaps.begin(), specularMaps.end());
		// 3. normal maps
		std::vector<Texture> normalMaps = loadMaterialTextures(material, aiTextureType_HEIGHT, "texture_normal");
		textures.insert(textures.end(), normalMaps.begin(), normalMaps.end());
		// 4. height maps
		std::vector<Texture> heightMaps = loadMaterialTextures(material, aiTextureType_AMBIENT, "texture_height");
		textures.insert(textures.end(), heightMaps.begin(), heightMaps.end());

		// return a mesh object created from the extracted mesh data
		return Mesh(vertices, indices, textures);
	}

	// checks all material textures of a given type and loads the textures if they're not loaded yet.
	// the required info is returned as a Texture struct.
	vector<Texture> loadMaterialTextures(aiMaterial *mat, aiTextureType type, string typeName) {
		vector<Texture> textures;
		for (unsigned int i = 0; i < mat->GetTextureCount(type); ++i) {
			aiString str;
			mat->GetTexture(type, i, &str);
			if (textures_loaded[str.C_Str()].real) {
				textures.push_back(textures_loaded[str.C_Str()].tex);
			}
			else {   // if texture hasn't been loaded already, load it
				Texture texture;
				texture.id = TextureFromFile(str.C_Str(), this->directory);
				texture.type = typeName;
				texture.path = str.C_Str();
				textures.push_back(texture);
				textures_loaded[texture.path.data()] = { texture,1 };  // store it as texture loaded for entire model, to ensure we won't unnecessary load duplicate textures.
			}
		}
		return textures;
	}
};


#endif