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

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods);
static void mouse_button_callback(GLFWwindow* window, int button, int action, int mods);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

float r = 0, g = 0, b = 0;

const char *vertexShaderSource =
"#version 400 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 400 core\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
"   FragColor = vec4(0.0f, 0.0f, 1.0f, 1.0f);\n"
"}\n\0";

int main() {
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    
#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // uncomment this statement to fix compilation on OS X
#endif
    
    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", nullptr, nullptr);
    if (window == nullptr) {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    
    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }
    
    // build and compile our shader program
    // ------------------------------------
    // vertex shader
    int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, nullptr);
    glCompileShader(vertexShader);
    // check for shader compile errors
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(vertexShader, 512, nullptr, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    
    // fragment shader
    int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, nullptr);
    glCompileShader(fragmentShader);
    // check for shader compile errors
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(fragmentShader, 512, nullptr, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    
    // link shaders
    int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    // check for linking errors
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, nullptr, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    }
    
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);
    
    // set up vertex data (and buffer(s)) and configure vertex attributes
    // -------------------------

    ///////////////////////////////////////////////////////////////////
    /// rectangle

    float vertices[] = {
       0.5f,  0.5f, 0.0f,  // top right
       0.5f, -0.5f, 0.0f,  // bottom right
       -0.5f, -0.5f, 0.0f,  // bottom left
       -0.5f,  0.5f, 0.0f   // top left
    };
    
    ///////////////////////////////////////////////////////////////////
    /// for EBO index drawing
    
    unsigned int indices[] = {  // note that we start from 0!
       0, 1, 3,  // first Triangle
       1, 2, 3   // second Triangle
    };
    
    ///////////////////////////////////////////////////////////////////

    unsigned int VBO, VAO;
    
    ///////////////////////////////////////////////////////////////////

    unsigned int EBO;
    
    ///////////////////////////////////////////////////////////////////

    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    
    ///////////////////////////////////////////////////////////////////

    glGenBuffers(1, &EBO);
    
    ///////////////////////////////////////////////////////////////////

    // bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
    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);
    
    // note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    
    // You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
    // VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
    glBindVertexArray(0);
    
    
    // uncomment this call to draw in wireframe polygons.
    ///////////////////////////////////////////////////////////////////

    //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    
    ///////////////////////////////////////////////////////////////////
    
    glfwSetKeyCallback(window, key_callback);
    glfwSetMouseButtonCallback(window, mouse_button_callback);
    
    // render loop
    // -----------
    while (!glfwWindowShouldClose(window)) {
        // render
        // ------
        glClearColor(r, g, b, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        
        // draw our first triangle
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
               
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
        
        // glBindVertexArray(0); // no need to unbind it every time
        
        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    
    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);

    glDeleteBuffers(1, &EBO);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window) {
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height) {
    // make sure the viewport matches the new window dimensions; note that width and
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods) {
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
    
    if(glfwGetKey(window, GLFW_KEY_R) == GLFW_PRESS) {
        if(r < 1.0 )
            r += 0.1;
        else
            r = 0.0;
    }
    if(glfwGetKey(window, GLFW_KEY_G) == GLFW_PRESS) {
        if(g < 1.0 )
            g += 0.1;
        else
            g = 0.0;
    }
    if(glfwGetKey(window, GLFW_KEY_B) == GLFW_PRESS) {
        if(b < 1.0 )
            b += 0.1;
        else
            b = 0.0;
    }
}

static void mouse_button_callback(GLFWwindow* window, int button, int action, int mods) {
    if(button == GLFW_MOUSE_BUTTON_LEFT && action == GLFW_PRESS) {
        double xpos, ypos;
        //getting cursor position
        glfwGetCursorPos(window, &xpos, &ypos);
        std::cout << "Cursor Position at (" << xpos << " : " << ypos << "\n";
    }
}