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

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>

using namespace std;

static string ParseShader(const string filePath)
{
    ifstream stream(filePath);

    string line;
    stringstream ss;

    while (getline(stream, line))
    {
        ss << line << "\n";
    }

    return ss.str();
}

static unsigned int CompileShader(unsigned int type, const string &source)
{
    unsigned int id = glCreateShader(type);
    const char *src = source.c_str();

    glShaderSource(id, 1, &src, nullptr);
    glCompileShader(id);

    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);

    if (result == GL_FALSE)
    {
        int lenght;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &lenght);

        char *message = (char *)malloc(lenght + sizeof(char));

        glGetShaderInfoLog(id, lenght, &lenght, message);

        cout << "Failed to compile " << (type == GL_VERTEX_SHADER ? "vertex" : "fragment") << " shader!" << endl;
        cout << message << endl;

        glDeleteShader(id);

        return 0;
    }

    return id;
}

static unsigned int CreateShader(const string &vertexShader, const string &fragmentShader)
{
    unsigned int program = glCreateProgram();

    unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);

    glAttachShader(program, vs);
    glAttachShader(program, fs);

    glLinkProgram(program);
    glValidateProgram(program);

    glDeleteShader(vs);
    glDeleteShader(fs);

    return program;
}

int main()
{
    GLFWwindow *window;

    /* Initialize the library */
    if (!glfwInit())
        return -1;

    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(1280, 720, "Hello World", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    /* Make the window's context current */
    glfwMakeContextCurrent(window);

    if (glewInit() != GLEW_OK)
    {
        cout << "Error!" << endl;
    }

    cout << glGetString(GL_VERSION) << endl;

    float positions[6] = {
        -0.5f, -0.5f,
        0.0f, 0.5f,
        0.5f, -0.5f};

    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), positions, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
    glEnableVertexAttribArray(0);

    string vertexShader = ParseShader("Shaders/Vertex.glsl");
    cout << "VERTEX:" << endl;
    cout << vertexShader << endl;

    string fragmentShader = ParseShader("Shaders/Fragment.glsl");
    cout << "FRAGMENT:" << endl;
    cout << fragmentShader << endl;

    unsigned int shader = CreateShader(vertexShader, fragmentShader);

    glUseProgram(shader);

    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    {
        /* Render here */
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES, 0, 3);

        /* Swap front and back buffers */
        glfwSwapBuffers(window);

        /* Poll for and process events */
        glfwPollEvents();
    }

    glDeleteProgram(shader);

    glfwTerminate();

    return 0;
}