#include <X11/Xatom.h>
#include <X11/Xlib.h>
#include <errno.h>
#include <error.h>		/* GNU */
#include <stdio.h>
#include <stdlib.h>

#define MAX_PASTE 8192

Window make_input_window(Display *dpy)
{
    return XCreateWindow(dpy, DefaultRootWindow(dpy),
			 0, 0, 1, 1,
			 0, 0,
			 InputOnly, CopyFromParent,
			 0, 0);
}

size_t print_clipboard_contents(Display *dpy)
{
    XEvent e;
    Window w = make_input_window(dpy); /* TODO: check w */
    XConvertSelection(dpy, XA_PRIMARY, XA_STRING, XA_STRING,
		      w, CurrentTime);
    do
	XNextEvent(dpy, &e);
    while (e.type != SelectionNotify);
    if (e.xselection.property != XA_STRING)
	return 0;
    {
	Atom actual_type_return;
	int actual_format_return;
	unsigned long nitems_return;
	unsigned long bytes_after_return;
	unsigned char *prop_return;
	int i;

	for (i=0; i<2; ++i) {
	    if (XGetWindowProperty(dpy, w, XA_STRING, 0,
				   i == 0 ? 0 : bytes_after_return,
				   False, AnyPropertyType,
				   &actual_type_return,
				   &actual_format_return,
				   &nitems_return,
				   &bytes_after_return,
				   &prop_return) != Success)
		return 0;
	    if (i == 0 && bytes_after_return <= 0)
		return 0;
	}
	return fwrite(prop_return, /* this is just leaked */
		      actual_format_return / 8,
		      nitems_return,
		      stdout);
    }
}
    
void set_clipboard_contents(Display *dpy, unsigned char *s, size_t len)
{
    Window w = make_input_window(dpy); /* TODO: check w */
    XSetSelectionOwner(dpy, XA_PRIMARY, w, CurrentTime);
    for (;;) {
	XEvent e, respond;
	XNextEvent(dpy, &e);
	if (e.type == SelectionClear)
	    break;
	if (e.type != SelectionRequest)
	    continue;
#define req e.xselectionrequest
#define rex respond.xselection
	rex.type = SelectionNotify;
	rex.display = req.display;
	rex.requestor = req.requestor;
	rex.selection = req.selection;
	rex.target = req.target;
	rex.time = req.time;
	if (req.target == XA_STRING)
	{
	    XChangeProperty(dpy, req.requestor,
			    req.property != None ? req.property : req.target,
			    XA_STRING, 8, PropModeReplace,
			    s, len);
	    rex.property = req.property;
	} else
	    rex.property = None;
	XSendEvent(dpy, req.requestor, 0, 0, &respond);
#undef req
#undef rex
    }
}

int main(int argc, char **argv)
{
    Display *dpy;

    if (argc > 2 || argc == 2 && strcmp(argv[1], "-paste"))
	error(1, 0, "Usage: xcopy [-paste]");
    
    if ((dpy =  XOpenDisplay(NULL)) == NULL)
	error(2, 0, "Could not connect to X server");

    if (argc == 2)		/* -paste */
	print_clipboard_contents(dpy);
    else {
	char buf[MAX_PASTE];
	size_t n = fread(buf, 1, MAX_PASTE, stdin);

	if (ferror(stdin))
	    error(3, errno, "fread()");
	set_clipboard_contents(dpy, buf, n);
    }
    XCloseDisplay(dpy);
    return 0;
}