#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <stdbool.h>
#include <stdio.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#define G_MAXLONG LONG_MAX
typedef unsigned long gulong;

bool
get_cardinal_list(Screen  *screen,
                  Window   xwindow,
                  Atom     atom,
                  gulong **cardinals,
                  int     *len)
{
  Display *display;
  Atom type;
  int format;
  gulong nitems;
  gulong bytes_after;
  gulong *nums;
  int err, result;

  display = DisplayOfScreen (screen);

  *cardinals = NULL;
  *len = 0;

  type = None;
  result = XGetWindowProperty (display,
			       xwindow,
			       atom,
			       0, G_MAXLONG,
			       False, XA_CARDINAL, &type, &format, &nitems,
			       &bytes_after, (void*)&nums);

  if (type != XA_CARDINAL)
    {
      XFree (nums);
      return false;
    }

  *cardinals = malloc(sizeof(gulong) * nitems); // Need to deallocate!
  memcpy (*cardinals, nums, sizeof (gulong) * nitems);
  *len = nitems;

  XFree (nums);

  return true;
}

void
write_coords(gulong *p_coord, int n_coord)
{
    if (p_coord != NULL) {
        int i;
        for (i = 0; i < n_coord; ++i)
            printf(" %lu", (unsigned long)p_coord[i]);
        printf("\n");
    }
    else {
        printf("NULL\n");
    }
}

Atom get_atom(Display *display, const char *atom_name)
{
    const bool only_if_exists = true;
    return XInternAtom(display, atom_name, only_if_exists);
}

void
print_atom(Display *display, const char *atom_name)
{
    int screen_number = 0;
    Window xroot = RootWindow(display, screen_number);
    Screen *xscreen = ScreenOfDisplay(display, screen_number);
    assert(xscreen);

    gulong *p_coord = NULL;
    int n_coord = 0;
    get_cardinal_list(xscreen,
            xroot,
            get_atom(display, atom_name),
            &p_coord, &n_coord);
    printf(atom_name);
    write_coords(p_coord, n_coord);
    if (p_coord != NULL)
        free(p_coord);
}


int main(int argc, char** argv)
{
    Display *display = XOpenDisplay(":0.0");
    assert(display);

    print_atom(display, "_NET_DESKTOP_GEOMETRY");
    print_atom(display, "_NET_DESKTOP_VIEWPORT");

    int res = XCloseDisplay(display);
    printf("XCloseDisplay returned %d\n", res);

    return res;
}