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

#include <stdio.h>

static int
min(int a, int b)
{
	return a < b ? a : b;
}

static int
absd(int x)
{
	return x < 0 ? -x : x;
}

static int
window_under_pointer(Display *dpy, Window root, Window *win)
{
	Window rootret, childret;
	int rootx, rooty, winx, winy;
	unsigned int mask;

	if (!XQueryPointer(dpy, root, &rootret, &childret,
	    &rootx, &rooty, &winx, &winy, &mask))
	    return 0;
	if (childret == None)
	    return 0;
	*win = childret;
	return 1;
}

static int
window_geometry_on_root(Display *dpy, Window root, Window win,
    int *x, int *y, int *w, int *h)
{
	XWindowAttributes attr;
	Window child;
	int tx, ty;

	if (!XGetWindowAttributes(dpy, win, &attr))
	    return 0;
	if (attr.map_state != IsViewable)
	    return 0;
	if (!XTranslateCoordinates(dpy, win, root, 0, 0, &tx, &ty, &child))
	    return 0;
	*x = tx;
	*y = ty;
	*w = attr.width;
	*h = attr.height;
	return 1;
}

int
main(void)
{
	Display *dpy;
	Window root;
	Cursor cursor;
	GC gc;
	XGCValues gcv;
	XEvent ev;
	Window win;
	int selecting;
	int dragdrawn;
	int hoverdrawn;
	int sx, sy, ex, ey;
	int dragx, dragy, dragw, dragh;
	int hoverx, hovery, hoverw, hoverh;
	int done;

	if ((dpy = XOpenDisplay(NULL)) == NULL) {
	    fprintf(stderr, "failed to open X display\n");
	    return 1;
	}
	root = DefaultRootWindow(dpy);
	cursor = XCreateFontCursor(dpy, XC_crosshair);

	if (XGrabPointer(dpy, root, False,
	    ButtonPressMask | ButtonReleaseMask | PointerMotionMask,
	    GrabModeAsync, GrabModeAsync, None, cursor, CurrentTime) != GrabSuccess) {
	    fprintf(stderr, "failed to grab pointer\n");
	    XCloseDisplay(dpy);
	    return 1;
	}

	gcv.function = GXinvert;
	gcv.subwindow_mode = IncludeInferiors;
	gcv.line_width = 1;
	gcv.foreground = WhitePixel(dpy, DefaultScreen(dpy));
	gc = XCreateGC(dpy, root,
	    GCFunction | GCSubwindowMode | GCLineWidth | GCForeground, &gcv);

	selecting = 0;
	dragdrawn = 0;
	hoverdrawn = 0;
	sx = sy = ex = ey = 0;
	dragx = dragy = dragw = dragh = 0;
	hoverx = hovery = hoverw = hoverh = 0;
	done = 0;

	while (!done) {
	    XNextEvent(dpy, &ev);

	    if (ev.type == ButtonPress) {
	        if (ev.xbutton.button != Button1) {
	            done = 1;
	            break;
	        }

	        if (hoverdrawn) {
	            XDrawRectangle(dpy, root, gc,
	                hoverx, hovery, (unsigned int)hoverw, (unsigned int)hoverh);
	            XFlush(dpy);
	            hoverdrawn = 0;
	        }

	        selecting = 1;
	        sx = ev.xbutton.x_root;
	        sy = ev.xbutton.y_root;
	        ex = sx;
	        ey = sy;
	    } else if (ev.type == MotionNotify) {
	        while (XCheckTypedEvent(dpy, MotionNotify, &ev))
	            continue;

	        if (selecting) {
	            int x, y, w, h;

	            if (dragdrawn)
	                XDrawRectangle(dpy, root, gc,
	                    dragx, dragy, (unsigned int)dragw, (unsigned int)dragh);

	            ex = ev.xmotion.x_root;
	            ey = ev.xmotion.y_root;
	            x = min(sx, ex);
	            y = min(sy, ey);
	            w = absd(ex - sx);
	            h = absd(ey - sy);
	            XDrawRectangle(dpy, root, gc, x, y, (unsigned int)w, (unsigned int)h);
	            XFlush(dpy);

	            dragx = x;
	            dragy = y;
	            dragw = w;
	            dragh = h;
	            dragdrawn = 1;
	        } else {
	            int wx, wy, ww, wh;
	            int have;

	            have = 0;
	            if (window_under_pointer(dpy, root, &win))
	                have = window_geometry_on_root(dpy, root, win, &wx, &wy, &ww, &wh);

	            if (have) {
	                if (hoverdrawn &&
	                    hoverx == wx && hovery == wy && hoverw == ww && hoverh == wh)
	                    continue;

	                if (hoverdrawn)
	                    XDrawRectangle(dpy, root, gc,
	                        hoverx, hovery,
	                        (unsigned int)hoverw, (unsigned int)hoverh);
	                XDrawRectangle(dpy, root, gc,
	                    wx, wy, (unsigned int)ww, (unsigned int)wh);
	                XFlush(dpy);

	                hoverx = wx;
	                hovery = wy;
	                hoverw = ww;
	                hoverh = wh;
	                hoverdrawn = 1;
	            } else if (hoverdrawn) {
	                XDrawRectangle(dpy, root, gc,
	                    hoverx, hovery, (unsigned int)hoverw, (unsigned int)hoverh);
	                XFlush(dpy);
	                hoverdrawn = 0;
	            }
	        }
	    } else if (ev.type == ButtonRelease && selecting && ev.xbutton.button == Button1) {
	        int outx, outy, outw, outh;

	        if (dragdrawn) {
	            XDrawRectangle(dpy, root, gc,
	                dragx, dragy, (unsigned int)dragw, (unsigned int)dragh);
	            XFlush(dpy);
	            dragdrawn = 0;
	        }

	        ex = ev.xbutton.x_root;
	        ey = ev.xbutton.y_root;
	        outx = min(sx, ex);
	        outy = min(sy, ey);
	        outw = absd(ex - sx);
	        outh = absd(ey - sy);

	        if (outw == 0 || outh == 0) {
	            if (window_under_pointer(dpy, root, &win))
	                window_geometry_on_root(dpy, root, win,
	                    &outx, &outy, &outw, &outh);
	        }

	        printf("%dx%d+%d+%d\n", outw, outh, outx, outy);
	        fflush(stdout);
	        done = 1;
	    }
	}

	if (hoverdrawn) {
	    XDrawRectangle(dpy, root, gc,
	        hoverx, hovery, (unsigned int)hoverw, (unsigned int)hoverh);
	    XFlush(dpy);
	}

	XFreeGC(dpy, gc);
	XUngrabPointer(dpy, CurrentTime);
	XFreeCursor(dpy, cursor);
	XCloseDisplay(dpy);
	return 0;
}