/**
 * Example on how to output GStreamer video on SDL windows.
 *
 * GStreamer and other players can output to some X11 Window, even if this
 * window belongs to another program/application/process.
 *
 * One X11 Window is not necessarily a top level window as shown by
 * window managers, rather it's a rectangular area where you can draw.
 * Often toolkits use windows to draw components, like a Button, so you
 * can use its Window ID and play video there.
 *
 * Using this feature with SDL may not work as expected, since a SDL
 * window is just one X11 window, so you cannot output to just part of
 * the window.
 *
 * In order to output to a subpart of a SDL screen, you need to create
 * a X11 window and attach it to SDL's X11 window, then you use its id
 * with the GStreamer X Overlay interface (gst_x_overlay_set_xwindow_id()).
 *
 * Basic X11/Xlib types:
 *  - Display: structure with connection to X11 server, we use SDL's.
 *  - Window: and integer that identifies an window on some display.
 *
 * Basic X11/Xlib programming:
 *  - X11 is a client/server protocol and Xlib is the C implementation.
 *  - Xlib is asynchronous, you should wait for events.
 *  - Xlib needs XFlush() to send events to server, otherwise it will stay
 *    on client.
 *
 * We get Display and Window from SDL_SysWMinfo, and to use Display without
 * messing up SDL, we need to lock it during operation.
 *
 *
 * BUILDING
 * ========
 *
 * gcc -lX11 $(pkg-config --libs --cflags gstreamer-0.10) -lgstinterfaces-0.10 $(sdl-config --libs --cflags) sdl-gstreamer.c -o sdl-gstreamer
 *
 *
 * REFERENCES
 * ==========
 *
 *  - http://tronche.com/gui/x/xlib/
 *  - http://users.actcom.co.il/~choo/lupg/tutorials/xlib-programming/xlib-programming.html
 *
 *
 * LICENSE
 * =======
 *
 * GNU-LGPL - GNU Lesser General Public License.
 *
 *
 * AUTHOR
 * ======
 *
 * Gustavo Sverzut Barbieri <barbieri@gmail.com>
 *
 */

#include <X11/Xlib.h>
#include <SDL/SDL.h>
#include <SDL/SDL_syswm.h>

#include <gst/gst.h>
#include <gst/interfaces/xoverlay.h>

#include <stdio.h>

Window
create_x11_subwindow (Display *dpy,
                      Window parent,
                      int x,
                      int y,
                      int width,
                      int height)
{
  Window win;
  int black;

  if (!dpy)
    return 0;

  black = BlackPixel (dpy, DefaultScreen (dpy));
  win = XCreateSimpleWindow (dpy, parent, x, y, width, height,
                             0, black, black);

  if (!win)
    return 0;

  if (!XSelectInput (dpy, win, StructureNotifyMask))
    return 0;

  if (!XMapWindow (dpy, win))
    return 0;

  while (1) {
    XEvent e;
    XNextEvent (dpy, &e);
    if (e.type == MapNotify && e.xmap.window == win)
      break;
  }

  XSelectInput (dpy, win, NoEventMask);

  return win;
}

int
init_sdl (void)
{
  if (SDL_Init (SDL_INIT_VIDEO) < 0) {
    fprintf (stderr, "Failed to init SDL: %s\n", SDL_GetError ());
    return 0;
  }
  atexit (SDL_Quit);

  if (SDL_SetVideoMode (800, 600, 0, SDL_ASYNCBLIT | SDL_HWSURFACE) == NULL) {
    fprintf (stderr, "Failed to init Video: %s\n", SDL_GetError ());
    return 0;
  }

  return 1;
}

SDL_SysWMinfo
get_sdl_wm_info (void)
{
  SDL_SysWMinfo sdl_info;

  memset (&sdl_info, 0, sizeof (sdl_info));

  SDL_VERSION (&sdl_info.version);
  if (SDL_GetWMInfo (&sdl_info) <= 0 ||
      sdl_info.subsystem != SDL_SYSWM_X11) {
    fprintf (stderr, "This is not X11\n");

    memset (&sdl_info, 0, sizeof (sdl_info));
    return sdl_info;
  }

  return sdl_info;
}

GstElement *
create_gst_playbin (void)
{
  GstElement *playbin, *videosink, *audiosink;

  playbin = gst_element_factory_make ("playbin", "playbin");
  videosink = gst_element_factory_make ("xvimagesink", "videosink");
  audiosink = gst_element_factory_make ("alsasink", "audiosink");

  g_object_set (videosink,
                "force-aspect-ratio", TRUE,
                NULL);

  g_object_set (playbin,
                "audio-sink", audiosink,
                "video-sink", videosink,
                NULL);

  return playbin;
}

Window
set_gst_sdl_video_overlay (GstElement *pipeline,
                           int x,
                           int y,
                           int width,
                           int height)
{
  GstElement *videosink;
  SDL_SysWMinfo sdl_info;
  Window play_win;

  sdl_info = get_sdl_wm_info ();
  if (!sdl_info.version.major)
    return 0;

  g_object_get (pipeline, "video-sink", &videosink, NULL);

  if (videosink && GST_IS_X_OVERLAY (videosink)) {
    sdl_info.info.x11.lock_func ();

    play_win = create_x11_subwindow (sdl_info.info.x11.display,
                                     sdl_info.info.x11.window,
                                     x, y, width, height);
    sdl_info.info.x11.unlock_func ();

    gst_x_overlay_set_xwindow_id (GST_X_OVERLAY (videosink), play_win);
  } else
    play_win = 0;

  g_object_unref (videosink);

  return play_win;
}

void
main_loop (void)
{
  SDL_Surface *screen;
  Uint32 color;
  unsigned c_shift, run;

  fprintf (stderr, "Type 'q' or Escape to exit\n");

  screen = SDL_GetVideoSurface ();
  run = 1;
  color = 0x000000;
  c_shift = 1;
  while (run) {
    SDL_Event event;

    while (SDL_PollEvent (&event)) {
      switch (event.type) {
      case SDL_QUIT:
        run = 0;
        break;

      case SDL_KEYDOWN:
        switch (event.key.keysym.sym) {
        case SDLK_q:
        case SDLK_ESCAPE:
          run = 0;
          break;
        default:
          break;
        }
        break;

      default:
        break;
      }
    }

    SDL_FillRect (screen, NULL, color);
    SDL_Flip (screen);
    color |= 0x1 << c_shift;
    c_shift ++;

    if (c_shift >= 32) {
      c_shift = 0;
      color = 0;
    }

    SDL_Delay (20);
  }
}

int
main(int argc,
     char *argv[])
{
  GstElement *playbin;

  if (argc < 2) {
    fprintf (stderr, "Usage:\n\t%s <uri>\n\n", argv[0]);
    return -1;
  }

  if (!init_sdl ())
    return -1;

  gst_init (&argc, &argv);

  playbin = create_gst_playbin ();
  if (!set_gst_sdl_video_overlay (playbin, 20, 20, 760, 560))
    fprintf (stderr, "Not using Window overlay.\n");

  g_object_set (playbin, "uri", argv[1], NULL);
  gst_element_set_state (playbin, GST_STATE_PLAYING);

  main_loop ();

  gst_element_set_state (playbin, GST_STATE_NULL);
  gst_object_unref (playbin);

  return 0;
}