#include <stdio.h>
#include <stdlib.h>
#include <err.h>
#include <sys/queue.h>

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

struct win {
	Window w_win;
	TAILQ_ENTRY(win) w_list;
};

Display *display;
Window win, rootwindow;
int screen, width, height, numwins;
TAILQ_HEAD(winhead, win);
struct winhead winhead;

void
reorganize(void)
{
	XWindowChanges changes;
	struct win *w;
	int i;

	i = 0;
	TAILQ_FOREACH(w, &winhead, w_list) {
		changes.x = width / numwins * i;
		changes.y = 0;
		changes.width = width / numwins;
		changes.height = height;
		XConfigureWindow(display, w->w_win, CWX | CWY | CWWidth |
		    CWHeight, &changes);
		i++;
	}
}

int
main(void)
{
	XEvent ev;

	display = XOpenDisplay(":1");
	if (!display)
		errx(1, "XOpenDisplay");
	screen = DefaultScreen(display);
	width = XDisplayWidth(display, screen);
	height = XDisplayHeight(display, screen);
	rootwindow = RootWindow(display, screen);

	printf("Display with %dx%d\n", width, height);

	if (XSelectInput(display, rootwindow, EnterWindowMask |
	    LeaveWindowMask | SubstructureNotifyMask) == BadWindow)
		errx(1, "XSelectInput");

	numwins = 0;
	while (1) {
		struct win *win, *w, *tmp;

		XNextEvent(display, &ev);
		switch (ev.type) {
		case MapNotify:
			numwins++;

			win = malloc(sizeof(*win));
			win->w_win = ev.xconfigure.window;
			TAILQ_INSERT_HEAD(&winhead, win, w_list);

			reorganize();
			break;
		case UnmapNotify:
			numwins--;
			TAILQ_FOREACH_SAFE(w, &winhead, w_list, tmp) {
				if (w->w_win == ev.xconfigure.window) {
					TAILQ_REMOVE(&winhead, w, w_list);
					break;
				}
			}
			reorganize();
			break;
		default:
			printf("got event %d!\n", ev.type);
		}
	}

	return (0);
}