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

// glm math
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

#include <iostream>
#include <fstream>
#include <sstream>
#include <stdio.h>
#include <stdlib.h>

#define VERTEX_FILE "./shaders/vertex.glsl"
#define FRAGMENT_FILE "./shaders/fragment.glsl"
#define COMPUTE_FILE "./shaders/compute.glsl"

const float SCR_WIDTH = 1200.0f;
const float SCR_HEIGHT = 1200.0f;

// Shader loader helper
std::string loadShaderSource(const std::string& filepath) {
    std::ifstream file(filepath);
    if (!file.is_open()) {
        std::cerr << "Failed to open shader file: " << filepath << std::endl;
        return "";
    }
    std::stringstream buffer;

    std::cout << "Loaded " << filepath << " successfully!\n";

    buffer << file.rdbuf();
    return buffer.str();
}

GLuint compileShader(GLenum type, const std::string& source) {
    GLuint shader = glCreateShader(type);
    const char* src = source.c_str();
    glShaderSource(shader, 1, &src, nullptr);
    glCompileShader(shader);

    int success;
    glGetShaderiv(shader, GL_COMPILE_STATUS, &success);
    if (!success) {
        char infoLog[512];
        glGetShaderInfoLog(shader, 512, nullptr, infoLog);
        std::cerr << "Shader compilation failed:\n" << infoLog << std::endl;
        exit(10);
    }
    return shader;
}

GLuint createShaderProgram(const std::string& vertexPath, const std::string& fragmentPath) {
    std::string vertexSrc = loadShaderSource(vertexPath);
    std::string fragmentSrc = loadShaderSource(fragmentPath);

    GLuint vertexShader = compileShader(GL_VERTEX_SHADER, vertexSrc);
    GLuint fragmentShader = compileShader(GL_FRAGMENT_SHADER, fragmentSrc);

    GLuint program = glCreateProgram();
    glAttachShader(program, vertexShader);
    glAttachShader(program, fragmentShader);
    glLinkProgram(program);

    int success;
    glGetProgramiv(program, GL_LINK_STATUS, &success);
    if (!success) {
        char infoLog[512];
        glGetProgramInfoLog(program, 512, nullptr, infoLog);
        std::cerr << "Shader linking failed:\n" << infoLog << std::endl;
        exit(11);
    }

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);
    return program;
}

GLuint createComputeProgram(const std::string& computePath) {
    std::string computeSrc = loadShaderSource(computePath);
    GLuint computeShader = compileShader(GL_COMPUTE_SHADER, computeSrc);

    GLuint program = glCreateProgram();
    glAttachShader(program, computeShader);
    glLinkProgram(program);

    int success;
    glGetProgramiv(program, GL_LINK_STATUS, &success);
    if (!success) {
        char infoLog[512];
        glGetProgramInfoLog(program, 512, nullptr, infoLog);
        std::cerr << "Compute shader linking failed:\n" << infoLog << std::endl;;
    }

    glDeleteShader(computeShader);
    return program;
}

int main() {
    // Initialize GLFW
    if (!glfwInit()) return -1;

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 1);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // REQUIRED on macOS
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_SAMPLES, 16); // 16x MSAA

    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "OpenGL Template", nullptr, nullptr);
    if (!window) {
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);

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

    glViewport(0, 0, (int)SCR_WIDTH, (int)SCR_HEIGHT);

    //DEBUG
    std::cout << "OpenGL Version: " << glGetString(GL_VERSION) << std::endl;

    // ERROR: macOS does not support compute shaders in OpenGL < 4.3.
    // GLuint computeProgram = createComputeProgram(COMPUTE_FILE);

    // ----- Vertex Data -----
    // Cube
    // Positions
    float vertices[] = {
        // positions
        -1.0f, -1.0f, 0.0f,
         1.0f, -1.0f, 0.0f,
         1.0f,  1.0f, 0.0f,
        -1.0f,  1.0f, 0.0f
    };

    unsigned int indices[] = {
        0, 1, 2,
        2, 3, 0
    };

    GLuint VAO, VBO, 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);

    // position - VERTEX SHADER
    glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,3*sizeof(float),(void*)0);
    glEnableVertexAttribArray(0);

    // color - FRAGMENT SHADER
    glVertexAttribPointer(1,3,GL_FLOAT,GL_FALSE,3*sizeof(float),(void*)(3*sizeof(float)));
    glEnableVertexAttribArray(1);

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

    // Load shaders
    GLuint shaderProgram = createShaderProgram(VERTEX_FILE, FRAGMENT_FILE);

    // Check if shader program was created successfully
    if (shaderProgram == 0) {
        std::cerr << "Failed to create shader programs.\n";
        return -1;
    }

    // Caulculate model, view, projection matrices
    glm::mat4 model = glm::mat4(1.0f);
    glm::mat4 view = glm::translate(glm::mat4(1.0f), glm::vec3(0.0f, 0.0f, -1.0f));
    glm::mat4 projection = glm::perspective(glm::radians(45.0f), SCR_WIDTH/SCR_HEIGHT, 0.1f, 100.0f);

    GLuint modelLoc = glGetUniformLocation(shaderProgram, "model");
    GLuint viewLoc = glGetUniformLocation(shaderProgram, "view");
    GLuint projLoc = glGetUniformLocation(shaderProgram, "projection");

    glUseProgram(shaderProgram);
    glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
    glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
    glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));


    GLint resLoc = glGetUniformLocation(shaderProgram, "u_resolution");
    glUniform2f(resLoc, SCR_WIDTH, SCR_HEIGHT); // hardcode for now

    GLint timeLoc = glGetUniformLocation(shaderProgram, "u_time");
    GLint directionLoc = glGetUniformLocation(shaderProgram, "u_direction");
    GLint oscilationLoc = glGetUniformLocation(shaderProgram, "u_oscilator");

    glEnable(GL_MULTISAMPLE);

    float oscillation = 5.0f;
    // Render loop
    while (!glfwWindowShouldClose(window)) {
        static float direction = 1.0f;
        static int frameCount = 0;
        static unsigned char invert = 0;
        float timeValue = (float)glfwGetTime();


        // Input
        glfwPollEvents();

        if (frameCount++ % 24 == 0) {
            if (oscillation > 40) invert = 1;

            if (oscillation < 5) invert = 0;

            if (invert) oscillation -= 0.001;
            else oscillation += 0.001;

            // Debug
            std::cout << "Oscillation: " << oscillation << "\t";
            std::cout << "Invert: " << invert << std::endl;

            direction = rand() % 50; // change direction every 300 frames
        }

        glUniform1f(timeLoc, timeValue);
        glUniform1f(directionLoc, direction);
        glUniform1f(oscilationLoc, oscillation);


        glClearColor(0.01f, 0.01f, 0.01f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glBindVertexArray(VAO);
        glDrawElements(GL_TRIANGLES,6,GL_UNSIGNED_INT,0);

        glUseProgram(shaderProgram);

        // Move WASD
        if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
            view = glm::translate(view, glm::vec3(0.0f, 0.01f, 0.0f));
        if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
            view = glm::translate(view, glm::vec3(0.0f, -0.01f, 0.0f));
        if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
            view = glm::translate(view, glm::vec3(-0.01f, 0.0f, 0.0f));
        if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
            view = glm::translate(view, glm::vec3(0.01f, 0.0f, 0.0f));

        // QE rotate
        if (glfwGetKey(window, GLFW_KEY_Q) == GLFW_PRESS)
            view = glm::rotate(view, glm::radians(1.0f), glm::vec3(0.0f, 0.0f, 1.0f));
        if (glfwGetKey(window, GLFW_KEY_E) == GLFW_PRESS)
            view = glm::rotate(view, glm::radians(-1.0f), glm::vec3(0.0f, 0.0f, 1.0f));

        glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
        glfwSwapBuffers(window);
    }

    glDeleteVertexArrays(1,&VAO);
    glDeleteBuffers(1,&VBO);
    glDeleteBuffers(1,&EBO);
    glDeleteProgram(shaderProgram);

    glfwDestroyWindow(window);
    glfwTerminate();
    return 0;
}