// gcc -o wm_take_focus wm_take_focus.c -lX11

#include <X11/Xlib.h>
#include <X11/Xutil.h>

#include <stdio.h>

Display *display;
int screen_num;
Window root;
Atom XA_WM_TAKE_FOCUS;

Window create_window(char * name, Window parent, int x, int y, int width, int height) 
{
    XSizeHints sh;
    XWMHints wmh;
    Window win = XCreateSimpleWindow(display, parent, x, y, width, height,
                                     2, // border width
                                     BlackPixel(display, screen_num),
                                     WhitePixel(display, screen_num));                 
    XStoreName(display, win, name);
    XSelectInput(display, win, FocusChangeMask | ButtonPressMask  | ButtonReleaseMask );
    
    sh.width = width;
    sh.height = height;
    sh.x = x;
    sh.y = y;
    sh.flags = USPosition | USSize;
    XSetWMNormalHints(display, win, &sh);

    wmh.input = False;
    wmh.flags = InputHint;
    XSetWMHints(display, win, &wmh);

    Atom protocols[1];
    protocols[0] = XA_WM_TAKE_FOCUS = XInternAtom (display, "WM_TAKE_FOCUS", True);
    XSetWMProtocols (display, win, protocols, 1);

    return win;
}

int main(int argc, char **argv)
{
    Window window, win;
    XEvent ev;

    char *display_name = NULL;
    if ((display = XOpenDisplay(display_name)) == NULL)
    {
        fprintf(stderr, "Couldn't open %s\n", XDisplayName(display_name));
        return -1;
    }
    screen_num = DefaultScreen(display);
    root = RootWindow(display, screen_num);

    window = create_window("TestFrame", root, 100, 100, 200, 100);

    XMapWindow(display, window);

    XFlush(display);
    XSync(display, False);

    while (1)
    {
        XNextEvent(display, &ev);

        int i = 0;
        for (i = 0; i < 2; i++) {

            win = ev.xany.window;
            if (win == window) {

                fprintf(stderr, "event on frame %i: ", i);

                switch(ev.xany.type) {

                case ClientMessage:
                    fprintf(stderr, "ClientMessage\n");
                    if (ev.xclient.data.l[0] == XA_WM_TAKE_FOCUS) {
                        fprintf(stderr, "  WM_TAKE_FOCUS\n");
                        XSetInputFocus(display, win, RevertToPointerRoot, CurrentTime);
                    }
                    break;
                case FocusIn:
                    fprintf(stderr, "FocusIn\n");
                    break;
                case FocusOut:
                    fprintf(stderr, "FocusOut\n");
                    break;
                default:
                    fprintf(stderr, "%d\n", ev.xany.type);
                }
            }
        }
    }
    return 0;
}