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

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

const unsigned int SCR_WIDTH = 1280;
const unsigned int SCR_HEIGHT = 720;

//顶点着色器代码
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";

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

float vertices[] = 
{
    -0.5f, -0.5f, 0.0f, //左
     0.5f, -0.5f, 0.0f, //右
     0.0f,  0.5f, 0.0f  //上
};

float rectVertices[] = 
{
     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,
    0, 2, 3
};

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(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

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

    //创建\编译我们的着色器程序
    //定点着色器
    int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);

    //片元着色器
    int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);

    //链接着色器
    int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    //别忘了释放着色器
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    unsigned int VBO, VAO;
    glGenVertexArrays(1, &VAO);
    glBindVertexArray(VAO);

    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(rectVertices), rectVertices, GL_STATIC_DRAW);

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

    unsigned int EBO;
    glGenBuffers(1, &EBO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    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_TRIANGLE_FAN, 0, 3);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

        glfwSwapBuffers(window);
        glfwPollEvents();

    }

    glDeleteBuffers(1, &VBO);
    glfwTerminate();
    
    return 0;
}

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

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