#!/usr/local/bin/python
"""Watch an Aspen website to make sure it stays up.

Only works on *NIX.

"""
import commands
import os
import sys
import syslog
import time
import traceback

from aspen.daemon import Daemon


# Configure logging.
# ==================

syslog.openlog('aspen.monitord')


# Get the root of the website we are tracking.
# ============================================

try:
    root = sys.argv[1]
except IndexError:
    print >> sys.stderr, "please tell us the website root"
    raise SystemExit(1)
root = os.path.realpath(root)
if not os.path.isdir(root):
    print >> sys.stderr, "couldn't find %s" % root
    raise SystemExit(1)


# Daemonize
# =========
# We keep our own pidfile around, but just use kill if you want to stop us.

_pidfile = os.path.join(root, '__', 'var', 'aspen.monitord.pid')
daemon = Daemon(stdout='/dev/null', stderr='/dev/null', pidfile=_pidfile)
daemon.start()
syslog.syslog(syslog.LOG_NOTICE, "daemon now tracking %s" % root)


# Keep it up.
# ===========

class Restart(SystemExit):
    """Propagate a termination of the monitored process.
    """


def check(pidfile):
    """Given the path to a pidfile, return None or raise Restart.
    """

    # Locate the pidfile.
    # ===================
    
    if not os.path.isfile(pidfile):
        syslog.syslog(syslog.LOG_NOTICE, "missing pidfile: %s" % pidfile)
        raise Restart


    # Parse and validate the pid.
    # ===========================
    
    pid = open(pidfile).read()
    if not pid:
        syslog.syslog(syslog.LOG_NOTICE, "empty pidfile: %s" % pidfile)
        raise Restart
    elif not pid.isdigit(): # catches mangled or missing pid
        syslog.syslog( syslog.LOG_NOTICE
                     , "mangled pid (%s) in pidfile: %s" % ( pid
                                                           , pidfile
                                                            )
                      )
        raise Restart


    # Look for the process.
    # =====================

    raw = commands.getoutput('ps -p%s' % pid) # portable?!
    nlines = raw.count('\n') + 1

    if nlines == 1:                                 # not running
        #  PID  TT  STAT      TIME COMMAND
        syslog.syslog( syslog.LOG_NOTICE
                     , "dead pid (%s) in pidfile: %s" % (pid, pidfile)
                      )
        raise Restart
    elif nlines == 2:                               # running
        #  PID  TT  STAT      TIME COMMAND
        #  45489  ??  S      0:02.42 /usr/local/bin/python /usr/local/bi...
        pass


# Main loop
# =========

pidfile = os.path.join(root, '__', 'var', 'aspen.pid')

while 1:
    try:
        try:
            check(pidfile)
        except Restart:

            # Benefit of the doubt
            # ====================
            # Give any existing aspen instance a chance to fix its pidfile 
            # before assuming it is dead and restarting. If we start another 
            # instance when there is already one running then ours will thrash
            # trying to bind to the port, which will already be in use.

            time.sleep(2)
            check(pidfile)


    except Restart: 
        
        # Syslog the error and then restart the sucker.
        # =============================================

        syslog.syslog(syslog.LOG_EMERG, "restarting %s" % root)
        if os.path.isfile(pidfile):
            os.remove(pidfile)
        os.system("aspen start --root=%s" % root)
        time.sleep(20) # give it time to restart

    except: 
        
        # Syslog the traceback.
        # =====================

        syslog.syslog(syslog.LOG_EMERG, traceback.format_exc())
        time.sleep(5)

    else:

        # Wait a second.
        # ==============

        time.sleep(1)