#!/usr/bin/python
#

# Copyright (C) 2006, 2007 Google Inc.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.


"""Tool to restart erronously downed virtual machines.

This program and set of classes implement a watchdog to restart
virtual machines in a Ganeti cluster that have crashed or been killed
by a node reboot.  Run from cron or similar.
"""


LOGFILE = '/var/log/ganeti/watcher.log'
MAXTRIES = 5
BAD_STATES = ['stopped']
HELPLESS_STATES = ['(node down)']
NOTICE = 'NOTICE'
ERROR = 'ERROR'

import os
import sys
import time
import fcntl
import errno
from optparse import OptionParser


from ganeti import utils
from ganeti import constants


class Error(Exception):
  """Generic custom error class."""
  pass


def Indent(s, prefix='| '):
  """Indent a piece of text with a given prefix before each line.

  Args:
    s: The string to indent
    prefix: The string to prepend each line.
  """
  return "%s%s\n" % (prefix, ('\n' + prefix).join(s.splitlines()))


def DoCmd(cmd):
  """Run a shell command.

  Args:
    cmd: the command to run.

  Raises CommandError with verbose commentary on error.
  """
  res = utils.RunCmd(cmd)

  if res.failed:
    raise Error("Command %s failed:\n%s\nstdout:\n%sstderr:\n%s" %
                (repr(cmd),
                 Indent(res.fail_reason),
                 Indent(res.stdout),
                 Indent(res.stderr)))

  return res


class RestarterState(object):
  """Interface to a state file recording restart attempts.

  Methods:
    Open(): open, lock, read and parse the file.
            Raises StandardError on lock contention.

    NumberOfAttempts(name): returns the number of times in succession
                            a restart has been attempted of the named instance.

    RecordAttempt(name, when): records one restart attempt of name at
                               time in when.

    Remove(name): remove record given by name, if exists.

    Save(name): saves all records to file, releases lock and closes file.
  """
  def __init__(self):
    # The two-step dance below is necessary to allow both opening existing
    # file read/write and creating if not existing.  Vanilla open will truncate
    # an existing file -or- allow creating if not existing.
    f = os.open(constants.WATCHER_STATEFILE, os.O_RDWR | os.O_CREAT)
    f = os.fdopen(f, 'w+')

    try:
      fcntl.flock(f.fileno(), fcntl.LOCK_EX|fcntl.LOCK_NB)
    except IOError, x:
      if x.errno == errno.EAGAIN:
        raise StandardError('State file already locked')
      raise

    self.statefile = f
    self.inst_map = {}

    for line in f:
      name, when, count = line.rstrip().split(':')

      when = int(when)
      count = int(count)

      self.inst_map[name] = (when, count)

  def NumberOfAttempts(self, instance):
    """Returns number of previous restart attempts.

    Args:
      instance - the instance to look up.
    """
    assert self.statefile

    if instance.name in self.inst_map:
      return self.inst_map[instance.name][1]

    return 0

  def RecordAttempt(self, instance):
    """Record a restart attempt.

    Args:
      instance - the instance being restarted
    """
    assert self.statefile

    when = time.time()

    self.inst_map[instance.name] = (when, 1 + self.NumberOfAttempts(instance))

  def Remove(self, instance):
    """Update state to reflect that a machine is running, i.e. remove record

    Args:
      instance - the instance to remove from books

    This method removes the record for a named instance
    """
    assert self.statefile

    if instance.name in self.inst_map:
      del self.inst_map[instance.name]

  def Save(self):
    """Save records to file, then unlock and close file.
    """
    assert self.statefile

    self.statefile.seek(0)
    self.statefile.truncate()

    for name in self.inst_map:
      print >> self.statefile, "%s:%d:%d" % ((name,) + self.inst_map[name])

    fcntl.flock(self.statefile.fileno(), fcntl.LOCK_UN)

    self.statefile.close()
    self.statefile = None


class Instance(object):
  """Abstraction for a Virtual Machine instance.

  Methods:
    Restart(): issue a command to restart the represented machine.
  """
  def __init__(self, name, state):
    self.name = name
    self.state = state

  def Restart(self):
    DoCmd(['gnt-instance', 'startup', '--lock-retries=15', self.name])


class InstanceList(object):
  """The set of Virtual Machine instances on a cluster.
  """
  cmd = ['gnt-instance', 'list', '--lock-retries=15',
         '-o', 'name,admin_state,oper_state', '--no-headers', '--separator=:']

  def __init__(self):
    res = DoCmd(self.cmd)

    lines = res.stdout.splitlines()

    self.instances = []
    for line in lines:
      fields = [fld.strip() for fld in line.split(':')]

      if len(fields) != 3:
        continue
      if fields[1] == "no": #no autostart, we don't care about this instance
        continue
      name, status = fields[0], fields[2]

      self.instances.append(Instance(name, status))

  def __iter__(self):
    return self.instances.__iter__()


class Message(object):
  """Encapsulation of a notice or error message.
  """
  def __init__(self, level, msg):
    self.level = level
    self.msg = msg
    self.when = time.time()

  def __str__(self):
    return self.level + ' ' + time.ctime(self.when) + '\n' + Indent(self.msg)


class Restarter(object):
  """Encapsulate the logic for restarting erronously halted virtual machines.

  The calling program should periodically instantiate me and call Run().
  This will traverse the list of instances, and make up to MAXTRIES attempts
  to restart machines that are down.
  """
  def __init__(self):
    self.instances = InstanceList()
    self.messages = []

  def Run(self):
    """Make a pass over the list of instances, restarting downed ones.
    """
    notepad = RestarterState()

    for instance in self.instances:
      if instance.state in BAD_STATES:
        n = notepad.NumberOfAttempts(instance)

        if n > MAXTRIES:
          # stay quiet.
          continue
        elif n < MAXTRIES:
          last = " (Attempt #%d)" % (n + 1)
        else:
          notepad.RecordAttempt(instance)
          self.messages.append(Message(ERROR, "Could not restart %s for %d"
                                       " times, giving up..." %
                                       (instance.name, MAXTRIES)))
          continue
        try:
          self.messages.append(Message(NOTICE,
                                       "Restarting %s%s." %
                                       (instance.name, last)))
          instance.Restart()
        except Error, x:
          self.messages.append(Message(ERROR, str(x)))

        notepad.RecordAttempt(instance)
      elif instance.state in HELPLESS_STATES:
        if notepad.NumberOfAttempts(instance):
          notepad.Remove(instance)
      else:
        if notepad.NumberOfAttempts(instance):
          notepad.Remove(instance)
          msg = Message(NOTICE,
                        "Restart of %s succeeded." % instance.name)
          self.messages.append(msg)

    notepad.Save()

  def WriteReport(self, logfile):
    """
    Log all messages to file.

    Args:
      logfile: file object open for writing (the log file)
    """
    for msg in self.messages:
      print >> logfile, str(msg)


def ParseOptions():
  """Parse the command line options.

  Returns:
    (options, args) as from OptionParser.parse_args()

  """
  parser = OptionParser(description="Ganeti cluster watcher",
                        usage="%prog [-d]",
                        version="%%prog (ganeti) %s" %
                        constants.RELEASE_VERSION)

  parser.add_option("-d", "--debug", dest="debug",
                    help="Don't redirect messages to the log file",
                    default=False, action="store_true")
  options, args = parser.parse_args()
  return options, args


def main():
  """Main function.

  """
  options, args = ParseOptions()

  if not options.debug:
    sys.stderr = sys.stdout = open(LOGFILE, 'a')

  try:
    restarter = Restarter()
    restarter.Run()
    restarter.WriteReport(sys.stdout)
  except Error, err:
    print err

if __name__ == '__main__':
  main()