#include <glad/glad.h>
#include <iostream>
#include <GLFW/glfw3.h>

const char *vertexShaderSource = "#version 330 core\n"
    "layout (location = 0) in vec3 aPos;\n"
    "void main()\n"
    "{\n"
    "   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
    "}\0";

const char *fragmentShaderSource = "#version 330 core\n"
    "out vec4 FragColor;\n"
    "\n"
    "void main()\n"
    "{\n"
    "    FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
    "}\0";

void framebuffer_size_callback(GLFWwindow* window, int width, int height);

void processInput(GLFWwindow *window);

int main()
{
	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	
	GLFWwindow* window = glfwCreateWindow(
						800, 
						600, 
						"My OpenGL project", 
						NULL, 
						NULL
					     );
	if (window == NULL) {
		std::cout << "Failed to create GLFW window" << std::endl;
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);

	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
		std::cout << "Failed to initialize GLAD" << std::endl;
		return -1;
	}    

	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
	
	// вершины фигуры
	float vertices[] = {
    		-0.5f, -0.5f, 0.0f,
    		 0.5f, -0.5f, 0.0f,
    		 0.5f,  0.5f, 0.0f,
		-0.5f,  0.5f, 0.0f
	};  
	unsigned int indices[] = {
		0, 1, 2, // первый треугольник
		2, 3, 0  // второй треугольник
	};


	// ШЕЙДЕРЫ
	unsigned int vertexShader;
	vertexShader = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
	glCompileShader(vertexShader);

	unsigned int fragmentShader;
	fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
	glCompileShader(fragmentShader);
	
	int  success, success_vertex, success_fragment;
	char infoLog[512];
	glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success_vertex);
	glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success_fragment);

	// проверка компиляции шейдеров
	if (!success_vertex) {
		glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
		std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" 
			  << infoLog << std::endl;
	} else if (!success_fragment) {
		glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
		std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" 
			  << infoLog << std::endl;
	}

	// линкуем шейдеры к программному объекту
	unsigned int shaderProgram;
	shaderProgram = glCreateProgram();

	glAttachShader(shaderProgram, vertexShader);
	glAttachShader(shaderProgram, fragmentShader);
	glLinkProgram(shaderProgram);

	glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
	if (!success) {
		glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
		std::cout << "ERROR::PROGRAM::LINKING_FAILED\n" << infoLog 
			  << std::endl;
	}

	glDeleteShader(vertexShader);
	glDeleteShader(fragmentShader);

	
	// ИНИЦИАЛИЗАЦИЯ VAO
	unsigned int VBO, VAO, EBO;
	glGenVertexArrays(1, &VAO);
	glGenBuffers(1, &VBO);
	glGenBuffers(1, &EBO);
	glBindVertexArray(VAO);

	glBindBuffer(GL_ARRAY_BUFFER, VBO);
	glBufferData(
			GL_ARRAY_BUFFER, 
			sizeof(vertices), 
			vertices, 
			GL_STATIC_DRAW
		    );

	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
	glBufferData(
			GL_ELEMENT_ARRAY_BUFFER, 
			sizeof(indices), 
			indices,
			GL_STATIC_DRAW
		    );

	glVertexAttribPointer(
				0, 
				3, 
				GL_FLOAT, 
				GL_FALSE, 
				3 * sizeof(float), 
				(void*)0
			     );
	glEnableVertexAttribArray(0);

	glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
	while (!glfwWindowShouldClose(window)) {
		processInput(window);

		glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);
		
		glUseProgram(shaderProgram);
		glBindVertexArray(VAO);
		/* glDrawArrays(GL_TRIANGLES, 0, 3); */
		glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
		/* glBindVertexArray(0); */

		glfwSwapBuffers(window);
		glfwPollEvents();
	}

	glfwTerminate();

	return 0;
}

void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    glViewport(0, 0, width, height);
}

void processInput(GLFWwindow *window)
{
	if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
		glfwSetWindowShouldClose(window, true);
}