#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include "glad/glad.h"
#include <GLFW/glfw3.h>

int SCREEN_WIDTH = 1024;
int SCREEN_HEIGHT = 768;

void checkCode(int code, char* errorMsg) {
    if (code < 0) {
        fprintf(stderr, "Application Error %i: %s\n", code, errorMsg);
        exit(1);
    }
}

void* checkPtr(void *ptr, char* errorMsg) {
    if (ptr == NULL) {
        fprintf(stderr, "Application Error: %s\n", errorMsg);
        exit(1);
    }
    return ptr;
}

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

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

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

unsigned int compileVertShader() {
    unsigned int vertexShader;
    vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertSrc, NULL);
    glCompileShader(vertexShader);
    int success;
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    checkCode(success, "Failed to compile vertex shader");
    return vertexShader;
}

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

unsigned int compileFragShader() {
    unsigned int fragmentShader;
    fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragSrc, NULL);
    glCompileShader(fragmentShader);
    int success;
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    checkCode(success, "Failed to compile fragment shader");
    return fragmentShader;
}

int main(void) {
    glfwInit();

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow* window =
        checkPtr(glfwCreateWindow(SCREEN_WIDTH, SCREEN_HEIGHT, "Learn OpenGL", NULL, NULL),
                 "Error creating GLFW window");
    if (window == NULL) glfwTerminate();

    glfwMakeContextCurrent(window);

    checkCode(gladLoadGLLoader((GLADloadproc)glfwGetProcAddress), "Error initializing GLAD");

    glViewport(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);

    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    unsigned int vertexShader = compileVertShader();
    unsigned int fragmentShader = compileFragShader();
    unsigned int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    int success = 0;
    glGetShaderiv(shaderProgram, GL_LINK_STATUS, &success);
    checkCode(success, "Failed to link shader program");

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);  

    float vertices[] = {
        -0.5f, -0.5f, 0.0f,
        0.5f, -0.5f, 0.0f,
        0.0f,  0.5f, 0.0f
    };  

    unsigned int VBO, VAO;
    glGenVertexArrays(1, &VAO); 
    glGenBuffers(1, &VBO); 
    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0); 

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0); 

    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);

        glfwSwapBuffers(window);
        glfwPollEvents();  
    }

    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteProgram(shaderProgram);
    glfwTerminate();
    return 0;
}