// GLEW
#define GLEW_STATIC
#include <GL/glew.h>

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

// GL includes
#include "Shader.h"

// GLM Mathemtics
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

// Properties
GLuint screenWidth = 800, screenHeight = 600;

// Function prototypes
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);


// The MAIN function, from here we start our application and run the Game loop
int main()
{
    // Init GLFW
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

    GLFWwindow* window = glfwCreateWindow(screenWidth, screenHeight, "LearnOpenGL", nullptr, nullptr); // Windowed
    glfwMakeContextCurrent(window);

    // Set the required callback functions
    glfwSetKeyCallback(window, key_callback);

    // Initialize GLEW to setup the OpenGL Function pointers
    glewExperimental = GL_TRUE;
    glewInit();

    // Define the viewport dimensions
    glViewport(0, 0, screenWidth, screenHeight);

    // Setup and compile our shader(s)
    Shader shader("shaders/instancing.vs", "shaders/instancing.frag");

    // Generate a list of 100 quad locations/translation-vectors
    glm::vec2 translations[100];
    int index = 0;
    GLfloat offset = 0.1f;
    for(GLint y = -10; y < 10; y += 2)
    {
        for(GLint x = -10; x < 10; x += 2)
        {
            glm::vec2 translation;
            translation.x = (GLfloat)x / 10.0f + offset;
            translation.y = (GLfloat)y / 10.0f + offset;
            translations[index++] = translation;
        }
    }

    // Store instance data in an array buffer
    GLuint instanceVBO;
    glGenBuffers(1, &instanceVBO);
    glBindBuffer(GL_ARRAY_BUFFER, instanceVBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(glm::vec2) * 100, &translations[0], GL_STATIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    // Generate quad VAO
    GLfloat quadVertices[] = {
        // Positions   // Colors
        -0.05f,  0.05f,  1.0f, 0.0f, 0.0f,
         0.05f, -0.05f,  0.0f, 1.0f, 0.0f,
        -0.05f, -0.05f,  0.0f, 0.0f, 1.0f,

        -0.05f,  0.05f,  1.0f, 0.0f, 0.0f,
         0.05f, -0.05f,  0.0f, 1.0f, 0.0f,   
         0.05f,  0.05f,  0.0f, 1.0f, 1.0f		    		
    };
    GLuint quadVAO, quadVBO;
    glGenVertexArrays(1, &quadVAO);
    glGenBuffers(1, &quadVBO);
    glBindVertexArray(quadVAO);
    glBindBuffer(GL_ARRAY_BUFFER, quadVBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(quadVertices), quadVertices, GL_STATIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)(2 * sizeof(GLfloat)));
    // Also set instance data
    glEnableVertexAttribArray(2);
    glBindBuffer(GL_ARRAY_BUFFER, instanceVBO);
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(GLfloat), (GLvoid*)0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);	
    glVertexAttribDivisor(2, 1); // Tell OpenGL this is an instanced vertex attribute.
    glBindVertexArray(0);
    

    // Game loop
    while(!glfwWindowShouldClose(window))
    {
        // Check and call events
        glfwPollEvents();

        // Clear buffers
        glClearColor(0.03f, 0.03f, 0.03f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // Draw 100 instanced quads
        shader.Use();
        glBindVertexArray(quadVAO);
        glDrawArraysInstanced(GL_TRIANGLES, 0, 6, 100); // 100 triangles of 6 vertices each
        glBindVertexArray(0);
        
        // Swap the buffers
        glfwSwapBuffers(window);
    }

    glfwTerminate();
    return 0;
}

// Is called whenever a key is pressed/released via GLFW
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{
    if(key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, GL_TRUE);
}