#!/usr/bin/python
"""getty replacement for Debathena

Debathena clusters only allow logins through X, in order to avoid a
user logging into a tty, then switching away from that tty, and
walking away from their session.

This replacement for getty clears the screen, and offers to switch the
user back to their session if they press any key.
"""


import curses
import getopt
import os
import pwd
import subprocess
import sys
import time

import dbus


CK_NAME = 'org.freedesktop.ConsoleKit'
CK_MANAGER_PATH = '/org/freedesktop/ConsoleKit/Manager'
CK_MANAGER_IFACE = 'org.freedesktop.ConsoleKit.Manager'
CK_SESSION_IFACE = 'org.freedesktop.ConsoleKit.Session'
KIOSK_USER = None


def find_tty(args):
    """Find the tty in a set of getty arguments.

    Given the command line arguments one might pass to getty, find and
    return the argument that is the tty to use.

    find_tty uses the getopt option specifier and tty identifying
    logic from util-linux 2.13.1.1.

    Note that all other arguments will be ignored, making this getty
    useless for gettys that are not on normal ttys.
    """
    opts, args = getopt.getopt(args, '8I:LH:f:hil:mt:wUn')

    # Accept both "tty baudrate" and "baudrate tty"
    if '0' <= args[0][0] <= '9':
        return args[1]
    else:
        return args[0]


def activate_session():
    """Seek out and activate what should be the current session.

    Using ConsoleKit, activate_session first looks to see if there is
    an active kiosk-mode browsing session, and if so, switches to
    that. Otherwise, it picks the first local session it can find and
    assumes that's the user's session.

    With the exception of the kiosk-mode session, it should be
    impossible to have more than one session running simultaneously,
    so blindly using the first session shouldn't be a problem.
    """
    global KIOSK_USER
    if KIOSK_USER is None:
        try:
            KIOSK_USER = pwd.getpwnam('kiosk@mit').pw_uid
        except KeyError:
            # There is no kiosk user
            KIOSK_USER = False

    bus = dbus.SystemBus()
    manager = dbus.Interface(bus.get_object(CK_NAME, CK_MANAGER_PATH),
                             CK_MANAGER_IFACE)

    session = None
    if KIOSK_USER:
        # We'll prefer kiosk sessions if they exist
        sessions = manager.GetSessionsForUnixUser(KIOSK_USER)
    if not sessions:
        # But if not, we'll take any graphical session that identifies
        # as local
        sessions = manager.GetSessions()

    for s in sessions:
        session = dbus.Interface(bus.get_object(CK_NAME, s),
                                 CK_SESSION_IFACE)
        if session.IsLocal() and session.GetX11Display():
               break
        else:
            session = None

    if session:
        session.Activate()
    else:
        vt = None

        # Look for a kiosk-mode session that we missed
        try:
            vt = open('/var/run/athena-kiosk-vt').read().strip()
        except IOError, e:
            pass

        # Look for any X session
        if not vt:
            p = subprocess.Popen(['pgrep', '-x', 'Xorg'],
                                 stdout=subprocess.PIPE)
            pid, _ = p.communicate()
            pid = pid.splitlines()[0]

            if pid:
                p = subprocess.Popen(['ps', '-otty=', pid],
                                     stdout=subprocess.PIPE)
                tty, _ = p.communicate()
                tty = tty.splitlines()[0]

                if tty.startswith('tty'):
                    vt = tty[len('tty'):]

        if vt:
            subprocess.call(['chvt', vt])


def main():
    tty_name = find_tty(sys.argv[1:])
    tty = open(os.path.join('/dev', tty_name), 'a+')
    # We want to set TERM for a tty, not for whatever TERM was set to
    # on getty's controlling terminal.
    curses.setupterm("linux", tty.fileno())

    CLEAR = curses.tigetstr('clear')

    while True:
        tty.write(CLEAR)
        tty.write('Please press Enter to return to your session\n')
        tty.readline()

        activate_session()

        tty.write("If you are seeing this message, it was not possible to return you to\n")
        tty.write("your session automatically, Try pressing Ctrl-Alt-F7, Ctrl-Alt-F8 or\n")
        tty.write("Ctrl-Alt-F9. If that does not work, reboot the computer by pressing\n")
        tty.write("Ctrl-Alt-Delete.\n")

        time.sleep(10)


if __name__ == '__main__':
    main()