////////////////////////////////////////////////////////////
// Headers
////////////////////////////////////////////////////////////
#include <SFML/Window.hpp>

#include <X11/Xlib.h>
#define GLAD_GL_IMPLEMENTATION
#include <gl.h>

#include <array>
#include <iostream>

#include <cmath>
#include <cstdlib>

////////////////////////////////////////////////////////////
/// Initialize OpenGL states into the specified view
///
/// \param Window Target window to initialize
///
/// \return True if operation was successful, false otherwise
///
////////////////////////////////////////////////////////////
[[nodiscard]] bool initialize(sf::Window& window)
{
    // Activate the window
    if (!window.setActive())
    {
        std::cerr << "Failed to set the window as active" << std::endl;
        return false;
    }

    // Setup OpenGL states
    // Set color and depth clear value

#ifdef SFML_OPENGL_ES
    glClearDepthf(1.f);
#else
    glClearDepth(1.f);
#endif

    glClearColor(0.f, 0.5f, 0.5f, 0.f);

    // Enable Z-buffer read and write
    glEnable(GL_DEPTH_TEST);
    glDepthMask(GL_TRUE);

    // Setup a perspective projection
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    const float extent = std::tan(sf::degrees(45).asRadians());

#ifdef SFML_OPENGL_ES
    glFrustumf(-extent, extent, -extent, extent, 1.0f, 500.0f);
#else
    glFrustum(-extent, extent, -extent, extent, 1.0f, 500.0f);
#endif

    // Enable position and texture coordinates vertex components
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_COLOR_ARRAY);

    return true;
}

////////////////////////////////////////////////////////////
/// Draw the OpenGL scene (a rotating cube) into
/// the specified view
///
/// \param window      Target window for rendering
/// \param elapsedTime Time elapsed since the last draw
///
/// \return True if operation was successful, false otherwise
///
////////////////////////////////////////////////////////////
[[nodiscard]] bool draw(sf::Window& window, float elapsedTime)
{
    // Activate the window
    if (!window.setActive())
    {
        std::cerr << "Failed to set the window as active" << std::endl;
        return false;
    }

    // Clear color and depth buffers
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // Apply some transformations
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(0.f, 0.f, -200.f);
    glRotatef(elapsedTime * 10.f, 1.f, 0.f, 0.f);
    glRotatef(elapsedTime * 6.f, 0.f, 1.f, 0.f);
    glRotatef(elapsedTime * 18.f, 0.f, 0.f, 1.f);

    // Define a 3D cube (6 faces made of 2 triangles composed by 3 vertices)
    // clang-format off
    constexpr std::array<GLfloat, 216> cube =
    {
        // positions    // colors
        -50, -50, -50,  1, 1, 0,
        -50,  50, -50,  1, 1, 0,
        -50, -50,  50,  1, 1, 0,
        -50, -50,  50,  1, 1, 0,
        -50,  50, -50,  1, 1, 0,
        -50,  50,  50,  1, 1, 0,

         50, -50, -50,  1, 1, 0,
         50,  50, -50,  1, 1, 0,
         50, -50,  50,  1, 1, 0,
         50, -50,  50,  1, 1, 0,
         50,  50, -50,  1, 1, 0,
         50,  50,  50,  1, 1, 0,

        -50, -50, -50,  1, 0, 1,
         50, -50, -50,  1, 0, 1,
        -50, -50,  50,  1, 0, 1,
        -50, -50,  50,  1, 0, 1,
         50, -50, -50,  1, 0, 1,
         50, -50,  50,  1, 0, 1,

        -50,  50, -50,  1, 0, 1,
         50,  50, -50,  1, 0, 1,
        -50,  50,  50,  1, 0, 1,
        -50,  50,  50,  1, 0, 1,
         50,  50, -50,  1, 0, 1,
         50,  50,  50,  1, 0, 1,

        -50, -50, -50,  0, 1, 1,
         50, -50, -50,  0, 1, 1,
        -50,  50, -50,  0, 1, 1,
        -50,  50, -50,  0, 1, 1,
         50, -50, -50,  0, 1, 1,
         50,  50, -50,  0, 1, 1,

        -50, -50,  50,  0, 1, 1,
         50, -50,  50,  0, 1, 1,
        -50,  50,  50,  0, 1, 1,
        -50,  50,  50,  0, 1, 1,
         50, -50,  50,  0, 1, 1,
         50,  50,  50,  0, 1, 1
    };
    // clang-format on

    // Draw the cube
    glVertexPointer(3, GL_FLOAT, 6 * sizeof(GLfloat), cube.data());
    glColorPointer(3, GL_FLOAT, 6 * sizeof(GLfloat), cube.data() + 3);
    glDrawArrays(GL_TRIANGLES, 0, 36);

    return true;
}


////////////////////////////////////////////////////////////
/// Entry point of application
///
/// \return Error code
///
////////////////////////////////////////////////////////////
int main()
{
    // Open a connection with the X server
    Display* display = XOpenDisplay(nullptr);
    if (!display)
        return EXIT_FAILURE;

    // Get the default screen
    const int screen = DefaultScreen(display);

    // Let's create the main window
    XSetWindowAttributes attributes;
    attributes.background_pixel = BlackPixel(display, screen);
    attributes.event_mask       = KeyPressMask;
    const Window window         = XCreateWindow(display,
                                        RootWindow(display, screen),
                                        0,
                                        0,
                                        650,
                                        330,
                                        0,
                                        DefaultDepth(display, screen),
                                        InputOutput,
                                        DefaultVisual(display, screen),
                                        CWBackPixel | CWEventMask,
                                        &attributes);
    if (!window)
        return EXIT_FAILURE;

    // Set the window's name
    XStoreName(display, window, "SFML Window");

    // Let's create the windows which will serve as containers for our SFML views
    const Window view1 = XCreateWindow(display,
                                       window,
                                       10,
                                       10,
                                       310,
                                       310,
                                       0,
                                       DefaultDepth(display, screen),
                                       InputOutput,
                                       DefaultVisual(display, screen),
                                       0,
                                       nullptr);
    const Window view2 = XCreateWindow(display,
                                       window,
                                       330,
                                       10,
                                       310,
                                       310,
                                       0,
                                       DefaultDepth(display, screen),
                                       InputOutput,
                                       DefaultVisual(display, screen),
                                       0,
                                       nullptr);

    // Show our windows
    XMapWindow(display, window);
    XFlush(display);

    // Create our SFML views
    sf::Window sfmlView1(view1);
    sf::Window sfmlView2(view2);

    // Create a clock for measuring elapsed time
    const sf::Clock clock;

    // Load OpenGL or OpenGL ES entry points using glad
    if (!sfmlView1.setActive())
    {
        std::cerr << "Failed to set view 1 as active" << std::endl;
        return EXIT_FAILURE;
    }

#ifdef SFML_OPENGL_ES
    gladLoadGLES1(sf::Context::getFunction);
#else
    gladLoadGL(sf::Context::getFunction);
#endif

    // Initialize our views
    if (!initialize(sfmlView1))
    {
        std::cerr << "Failed to initialize view 1" << std::endl;
        return EXIT_FAILURE;
    }

    if (!initialize(sfmlView2))
    {
        std::cerr << "Failed to initialize view 2" << std::endl;
        return EXIT_FAILURE;
    }

    // Start the event loop
    bool running = true;
    while (running)
    {
        while (XPending(display))
        {
            // Get the next pending event
            XEvent event;
            XNextEvent(display, &event);

            // Process it
            switch (event.type)
            {
                // Any key is pressed: quit
                case KeyPress:
                    running = false;
                    break;
            }
        }

        // Draw something into our views
        if (!draw(sfmlView1, clock.getElapsedTime().asSeconds()))
        {
            std::cerr << "Failed to draw on view 1" << std::endl;
            return EXIT_FAILURE;
        }

        if (!draw(sfmlView2, clock.getElapsedTime().asSeconds() * 0.3f))
        {
            std::cerr << "Failed to draw on view 2" << std::endl;
            return EXIT_FAILURE;
        }

        // Display the views on screen
        sfmlView1.display();
        sfmlView2.display();
    }

    // Close our SFML views before destroying the underlying window
    sfmlView1.close();
    sfmlView2.close();

    // Destroy the window
    XDestroyWindow(display, window);

    // Close the display
    XCloseDisplay(display);
}
