#include <err.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <unistd.h>
#include <X11/Xatom.h>
#include <X11/Xlib.h>

/* configuration */
#define ARGV "xterm", "xterm", "-e", "u", "/usr/local/bin/ksh", "-w", fifo
#define MAX_CMD 1000
#define MAX_LOOK 1000

/* state */
Atom pidatom;
Display *display;

/* print on stderr and exit */
#define die(...) do { fprintf(stderr, __VA_ARGS__); exit(1); } while (0)

/* find window associated with pid */
Window
findwindow(unsigned int pid, Window w)
{
	Atom type;
	int format;
	unsigned char *pidprop;
	unsigned int i, nchildren;
	unsigned long nitems, bytes_after;
	Window *children, _root, parent;

	pidprop = 0;
	if (XGetWindowProperty(display, w, pidatom, 0, 1, False, XA_CARDINAL,
		&type, &format, &nitems, &bytes_after, &pidprop) == Success
	&& pidprop && pid == *((unsigned long *)pidprop))
		return w;

	if (XQueryTree(display, w, &_root, &parent, &children, &nchildren))
		for (i = 0; i < nchildren; i++) {
			w = findwindow(pid, children[i]);
			if (w) return w;
		}
	return 0;
}

/* copy cwd and rewrite /home/ */
char *
cwdcpy(char *path)
{
	char *user, *r;
	int len;

	r = strdup(path);
        if (strncmp(path, "/home/", sizeof("/home/")-1) == 0) {
		user = getenv("USER");
		len = strlen(user);
                r += sizeof("/home")-1;
                if (strncmp(r + 1, user, len) == 0)
                        r += len;
                r[0] = '~';
        }
	return r;
}

int
main()
{
	char *cwd, *cmd, *line, *fifo;
	FILE *fifofp;
	int i;
	pid_t child;
	size_t size;
	ssize_t len;
	Window w;

	if ((display = XOpenDisplay(0)) == NULL)
		die("could not open display\n");

	if (mkdir("/var/tmp/tterm", 0700) == -1 && errno != EEXIST)
		err(1, "mkdir");

	/* build fifo path */
	if ((fifo = malloc(40*sizeof(char))) == NULL)
		err(1, "malloc");
	sprintf(fifo, "/var/tmp/tterm/%d", getpid());

	/* create fifo */
	unlink(fifo);
	if (mkfifo(fifo, 0600) == -1)
		err(1, "mkfifo");

	/* retrieve atom for _NET_WM_PID */
	pidatom = XInternAtom(display, "_NET_WM_PID", 0);
	if (pidatom == None) die("no _NET_WM_PID atom found\n");

	/* use ISO8859-1 encoding to speed up xterm start */
	setenv("LC_ALL", "en_US.ISO8859-1", 1);

	/* start terminal */
	if ((child = vfork()) == 0) {
		execlp(ARGV, NULL);
		err(1, "execvp");
	}

	/* find window belonging to child */
	for (i = 0; !w && i < MAX_LOOK; i++)
		w = findwindow(child, XDefaultRootWindow(display));
	if (!w)
		die("could not find window\n");

	/* read from fifo */
	if ((fifofp = fopen(fifo, "r")) == NULL)
		err(1, "fopen");
	if ((cmd = malloc(MAX_CMD*sizeof(char))) == NULL)
		err(1, "malloc");

	line = NULL;
	size = 0;

	/* get first line and unlink fifo */
	if ((len = getline(&line, &size, fifofp)) == -1) goto end;
	unlink(fifo);
	goto loop;

	/* process line and update title */
	while ((len = getline(&line, &size, fifofp)) != -1) {
loop:		if (strncmp(line, "cwd", 3) == 0) {
			line[len-1] = 0;
			line += 3;
			cwd = cwdcpy(line);
			XStoreName(display, w, cwd);
			XFlush(display);
		} else if (strncmp(line, "cmd", 3) == 0) {
			line[len-1] = 0; len -= 1;
			line += 3; len -= 3;
			for (i = len-1; i > 0 && line[i] == ' '; i--)
				line[i] = 0; /* strip space */
			snprintf(cmd, MAX_CMD, "%s (%s)", line, cwd);
			XStoreName(display, w, cmd);
			XFlush(display);
		} else {
			XStoreName(display, w, cwd);
			XFlush(display);
		}
	}

end:	XCloseDisplay(display);
}