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path: root/wallace/module_invitationpolicy.py
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# -*- coding: utf-8 -*-
# Copyright 2014 Kolab Systems AG (http://www.kolabsys.com)
#
# Thomas Bruederli (Kolab Systems) <bruederli@kolabsys.com>
#
# 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 3 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, see <http://www.gnu.org/licenses/>.
#

import datetime
import os
import tempfile
import time
from urlparse import urlparse
import urllib
import hashlib

from email import message_from_string
from email.parser import Parser
from email.utils import formataddr
from email.utils import getaddresses

import modules

import pykolab
import kolabformat

from pykolab import utils
from pykolab.auth import Auth
from pykolab.conf import Conf
from pykolab.imap import IMAP
from pykolab.xml import to_dt
from pykolab.xml import event_from_message
from pykolab.xml import participant_status_label
from pykolab.itip import events_from_message
from pykolab.itip import check_event_conflict
from pykolab.itip import send_reply
from pykolab.translate import _

# define some contstants used in the code below
COND_IF_AVAILABLE  = 32
COND_IF_CONFLICT   = 64
COND_TENTATIVE     = 128
COND_NOTIFY        = 256
ACT_MANUAL         = 1
ACT_ACCEPT         = 2
ACT_DELEGATE       = 4
ACT_REJECT         = 8
ACT_UPDATE         = 16
ACT_TENTATIVE                = ACT_ACCEPT + COND_TENTATIVE
ACT_ACCEPT_IF_NO_CONFLICT    = ACT_ACCEPT + COND_IF_AVAILABLE
ACT_TENTATIVE_IF_NO_CONFLICT = ACT_ACCEPT + COND_TENTATIVE + COND_IF_AVAILABLE
ACT_DELEGATE_IF_CONFLICT     = ACT_DELEGATE + COND_IF_CONFLICT
ACT_REJECT_IF_CONFLICT       = ACT_REJECT + COND_IF_CONFLICT
ACT_UPDATE_AND_NOTIFY        = ACT_UPDATE + COND_NOTIFY
ACT_SAVE_TO_CALENDAR         = 512

FOLDER_TYPE_ANNOTATION = '/vendor/kolab/folder-type'

MESSAGE_PROCESSED = 1
MESSAGE_FORWARD   = 2

policy_name_map = {
    'ACT_MANUAL':                   ACT_MANUAL,
    'ACT_ACCEPT':                   ACT_ACCEPT,
    'ACT_ACCEPT_IF_NO_CONFLICT':    ACT_ACCEPT_IF_NO_CONFLICT,
    'ACT_TENTATIVE':                ACT_TENTATIVE,
    'ACT_TENTATIVE_IF_NO_CONFLICT': ACT_TENTATIVE_IF_NO_CONFLICT,
    'ACT_DELEGATE':                 ACT_DELEGATE,
    'ACT_DELEGATE_IF_CONFLICT':     ACT_DELEGATE_IF_CONFLICT,
    'ACT_REJECT':                   ACT_REJECT,
    'ACT_REJECT_IF_CONFLICT':       ACT_REJECT_IF_CONFLICT,
    'ACT_UPDATE':                   ACT_UPDATE,
    'ACT_UPDATE_AND_NOTIFY':        ACT_UPDATE_AND_NOTIFY,
    'ACT_SAVE_TO_CALENDAR':         ACT_SAVE_TO_CALENDAR
}

policy_value_map = dict([(v, k) for (k, v) in policy_name_map.iteritems()])

log = pykolab.getLogger('pykolab.wallace')
conf = pykolab.getConf()

mybasepath = '/var/spool/pykolab/wallace/invitationpolicy/'

auth = None
imap = None
write_locks = []

def __init__():
    modules.register('invitationpolicy', execute, description=description())

def accept(filepath):
    new_filepath = os.path.join(
        mybasepath,
        'ACCEPT',
        os.path.basename(filepath)
    )

    cleanup()
    os.rename(filepath, new_filepath)
    filepath = new_filepath
    exec('modules.cb_action_ACCEPT(%r, %r)' % ('invitationpolicy',filepath))

def reject(filepath):
    new_filepath = os.path.join(
        mybasepath,
        'REJECT',
        os.path.basename(filepath)
    )

    os.rename(filepath, new_filepath)
    filepath = new_filepath
    exec('modules.cb_action_REJECT(%r, %r)' % ('invitationpolicy',filepath))

def description():
    return """Invitation policy execution module."""

def cleanup():
    global auth, imap, write_locks

    log.debug("cleanup(): %r, %r" % (auth, imap), level=9)

    auth.disconnect()
    del auth

    # Disconnect IMAP or we lock the mailbox almost constantly
    imap.disconnect()
    del imap

    # remove remaining write locks
    for key in write_locks:
        remove_write_lock(key, False)

def execute(*args, **kw):
    global auth, imap

    # (re)set language to default
    pykolab.translate.setUserLanguage(conf.get('kolab','default_locale'))

    if not os.path.isdir(mybasepath):
        os.makedirs(mybasepath)

    for stage in ['incoming', 'ACCEPT', 'REJECT', 'HOLD', 'DEFER', 'locks']:
        if not os.path.isdir(os.path.join(mybasepath, stage)):
            os.makedirs(os.path.join(mybasepath, stage))

    log.debug(_("Invitation policy called for %r, %r") % (args, kw), level=9)

    auth = Auth()
    imap = IMAP()

    filepath = args[0]

    # ignore calls on lock files
    if '/locks/' in filepath or kw.has_key('stage') and kw['stage'] == 'locks':
        return False

    log.debug("Invitation policy executing for %r, %r" % (filepath, '/locks/' in filepath), level=8)

    if kw.has_key('stage'):
        log.debug(_("Issuing callback after processing to stage %s") % (kw['stage']), level=8)

        log.debug(_("Testing cb_action_%s()") % (kw['stage']), level=8)
        if hasattr(modules, 'cb_action_%s' % (kw['stage'])):
            log.debug(_("Attempting to execute cb_action_%s()") % (kw['stage']), level=8)

            exec(
                'modules.cb_action_%s(%r, %r)' % (
                    kw['stage'],
                    'invitationpolicy',
                    filepath
                )
            )

            return filepath
    else:
        # Move to incoming
        new_filepath = os.path.join(
            mybasepath,
            'incoming',
            os.path.basename(filepath)
        )

        if not filepath == new_filepath:
            log.debug("Renaming %r to %r" % (filepath, new_filepath))
            os.rename(filepath, new_filepath)
            filepath = new_filepath

    # parse full message
    message = Parser().parse(open(filepath, 'r'))

    recipients = [address for displayname,address in getaddresses(message.get_all('X-Kolab-To'))]
    sender_email = [address for displayname,address in getaddresses(message.get_all('X-Kolab-From'))][0]

    any_itips = False
    recipient_email = None
    recipient_user_dn = None

    # An iTip message may contain multiple events. Later on, test if the message
    # is an iTip message by checking the length of this list.
    try:
        itip_events = events_from_message(message, ['REQUEST', 'REPLY', 'CANCEL'])
    except Exception, e:
        log.error(_("Failed to parse iTip events from message: %r" % (e)))
        itip_events = []

    if not len(itip_events) > 0:
        log.info(_("Message is not an iTip message or does not contain any (valid) iTip events."))

    else:
        any_itips = True
        log.debug(_("iTip events attached to this message contain the following information: %r") % (itip_events), level=9)

    # See if any iTip actually allocates a user.
    if any_itips and len([x['uid'] for x in itip_events if x.has_key('attendees') or x.has_key('organizer')]) > 0:
        auth.connect()

        for recipient in recipients:
            recipient_user_dn = user_dn_from_email_address(recipient)
            if recipient_user_dn:
                recipient_email = recipient
                break

    if not any_itips:
        log.debug(_("No itips, no users, pass along %r") % (filepath), level=5)
        return filepath
    elif recipient_email is None:
        log.debug(_("iTips, but no users, pass along %r") % (filepath), level=5)
        return filepath

    # we're looking at the first itip event object
    itip_event = itip_events[0]

    # for replies, the organizer is the recipient
    if itip_event['method'] == 'REPLY':
        user_attendees = [itip_event['organizer']] if str(itip_event['organizer']).split(':')[-1] == recipient_email else []

    else:
        # Limit the attendees to the one that is actually invited with the current message.
        attendees = [str(a).split(':')[-1] for a in (itip_event['attendees'] if itip_event.has_key('attendees') else [])]
        user_attendees = [a for a in attendees if a == recipient_email]

        if itip_event.has_key('organizer'):
            sender_email = itip_event['xml'].get_organizer().email()

    # abort if no attendee matches the envelope recipient
    if len(user_attendees) == 0:
        log.info(_("No user attendee matching envelope recipient %s, skip message") % (recipient_email))
        return filepath

    receiving_user = auth.get_entry_attributes(None, recipient_user_dn, ['*'])
    log.debug(_("Receiving user: %r") % (receiving_user), level=8)

    # change gettext language to the preferredlanguage setting of the receiving user
    if receiving_user.has_key('preferredlanguage'):
        pykolab.translate.setUserLanguage(receiving_user['preferredlanguage'])

    # find user's kolabInvitationPolicy settings and the matching policy values
    policies = get_matching_invitation_policies(receiving_user, sender_email)

    # select a processing function according to the iTip request method
    method_processing_map = {
        'REQUEST': process_itip_request,
        'REPLY':   process_itip_reply,
        'CANCEL':  process_itip_cancel
    }

    done = None
    if method_processing_map.has_key(itip_event['method']):
        processor_func = method_processing_map[itip_event['method']]

        # connect as cyrus-admin
        imap.connect()

        for policy in policies:
            log.debug(_("Apply invitation policy %r for sender %r") % (policy_value_map[policy], sender_email), level=8)
            done = processor_func(itip_event, policy, recipient_email, sender_email, receiving_user)

            # matching policy found
            if done is not None:
                break

            # remove possible write lock from this iteration
            remove_write_lock(get_lock_key(receiving_user, itip_event['uid']))

    else:
        log.debug(_("Ignoring '%s' iTip method") % (itip_event['method']), level=8)

    # message has been processed by the module, remove it
    if done == MESSAGE_PROCESSED:
        log.debug(_("iTip message %r consumed by the invitationpolicy module") % (message.get('Message-ID')), level=5)
        os.unlink(filepath)
        cleanup()
        return None

    # accept message into the destination inbox
    accept(filepath)


def process_itip_request(itip_event, policy, recipient_email, sender_email, receiving_user):
    """
        Process an iTip REQUEST message according to the given policy
    """

    # if invitation policy is set to MANUAL, pass message along
    if policy & ACT_MANUAL:
        log.info(_("Pass invitation for manual processing"))
        return MESSAGE_FORWARD

    try:
        receiving_attendee = itip_event['xml'].get_attendee_by_email(recipient_email)
        log.debug(_("Receiving Attendee: %r") % (receiving_attendee), level=9)
    except Exception, e:
        log.error("Could not find envelope attendee: %r" % (e))
        return MESSAGE_FORWARD

    # process request to participating attendees with RSVP=TRUE or PARTSTAT=NEEDS-ACTION
    nonpart = receiving_attendee.get_role() == kolabformat.NonParticipant
    partstat = receiving_attendee.get_participant_status()
    save_event = not nonpart or not partstat == kolabformat.PartNeedsAction
    rsvp = receiving_attendee.get_rsvp()
    scheduling_required = rsvp or partstat == kolabformat.PartNeedsAction
    respond_with = receiving_attendee.get_participant_status(True)
    condition_fulfilled = True

    # find existing event in user's calendar
    existing = find_existing_event(itip_event['uid'], receiving_user, True)

    # compare sequence number to determine a (re-)scheduling request
    if existing is not None:
        log.debug(_("Existing event: %r") % (existing), level=9)
        scheduling_required = itip_event['sequence'] > 0 and itip_event['sequence'] > existing.get_sequence()
        save_event = True

    # if scheduling: check availability
    if scheduling_required:
        if policy & (COND_IF_AVAILABLE | COND_IF_CONFLICT):
            condition_fulfilled = check_availability(itip_event, receiving_user)
        if policy & COND_IF_CONFLICT:
            condition_fulfilled = not condition_fulfilled

        log.debug(_("Precondition for event %r fulfilled: %r") % (itip_event['uid'], condition_fulfilled), level=5)

        respond_with = None
        if policy & ACT_ACCEPT and condition_fulfilled:
            respond_with = 'TENTATIVE' if policy & COND_TENTATIVE else 'ACCEPTED'

        elif policy & ACT_REJECT and condition_fulfilled:
            respond_with = 'DECLINED'
            # TODO: only save declined invitation when a certain config option is set?

        elif policy & ACT_DELEGATE and condition_fulfilled:
            # TODO: delegate (but to whom?)
            return None

    # if RSVP, send an iTip REPLY
    if rsvp or scheduling_required:
        # set attendee's CN from LDAP record if yet missing
        if not receiving_attendee.get_name() and receiving_user.has_key('cn'):
            receiving_attendee.set_name(receiving_user['cn'])

        # send iTip reply
        if respond_with is not None:
            receiving_attendee.set_participant_status(respond_with)
            send_reply(recipient_email, itip_event, invitation_response_text(),
                subject=_('"%(summary)s" has been %(status)s'))

        elif policy & ACT_SAVE_TO_CALENDAR:
            # copy the invitation into the user's calendar with PARTSTAT=NEEDS-ACTION
            itip_event['xml'].set_attendee_participant_status(receiving_attendee, 'NEEDS-ACTION')
            save_event = True

        else:
            # policy doesn't match, pass on to next one
            return None

    else:
        log.debug(_("No RSVP for recipient %r requested") % (receiving_user['mail']), level=8)
        # TODO: only update if policy & ACT_UPDATE ?

    if save_event:
        targetfolder = None

        if existing:
            # delete old version from IMAP
            targetfolder = existing._imap_folder
            delete_event(existing)

        if not nonpart or existing:
            # save new copy from iTip
            if store_event(itip_event['xml'], receiving_user, targetfolder):
                return MESSAGE_PROCESSED

    return None


def process_itip_reply(itip_event, policy, recipient_email, sender_email, receiving_user):
    """
        Process an iTip REPLY message according to the given policy
    """

    # if invitation policy is set to MANUAL, pass message along
    if policy & ACT_MANUAL:
        log.info(_("Pass reply for manual processing"))
        return MESSAGE_FORWARD

    # auto-update is enabled for this user
    if policy & ACT_UPDATE:
        try:
            sender_attendee = itip_event['xml'].get_attendee_by_email(sender_email)
            log.debug(_("Sender Attendee: %r") % (sender_attendee), level=9)
        except Exception, e:
            log.error("Could not find envelope sender attendee: %r" % (e))
            return MESSAGE_FORWARD

        # find existing event in user's calendar
        # TODO: set/check lock to avoid concurrent wallace processes trying to update the same event simultaneously
        existing = find_existing_event(itip_event['uid'], receiving_user, True)

        if existing:
            # compare sequence number to avoid outdated replies?
            if not itip_event['sequence'] == existing.get_sequence():
                log.info(_("The iTip reply sequence (%r) doesn't match the referred event version (%r). Forwarding to Inbox.") % (
                    itip_event['sequence'], existing.get_sequence()
                ))
                remove_write_lock(existing._lock_key)
                return MESSAGE_FORWARD

            log.debug(_("Auto-updating event %r on iTip REPLY") % (existing.uid), level=8)
            try:
                existing.set_attendee_participant_status(sender_email, sender_attendee.get_participant_status(), rsvp=False)
            except Exception, e:
                log.error("Could not find corresponding attende in organizer's event: %r" % (e))

                # TODO: accept new participant if ACT_ACCEPT ?
                remove_write_lock(existing._lock_key)
                return MESSAGE_FORWARD

            # update the organizer's copy of the event
            if update_event(existing, receiving_user):
                if policy & COND_NOTIFY:
                    send_reply_notification(existing, receiving_user)

                # update all other attendee's copies
                if conf.get('wallace','invitationpolicy_autoupdate_other_attendees_on_reply'):
                    propagate_changes_to_attendees_calendars(existing)

                return MESSAGE_PROCESSED

        else:
            log.error(_("The event referred by this reply was not found in the user's calendars. Forwarding to Inbox."))
            return MESSAGE_FORWARD

    return None


def process_itip_cancel(itip_event, policy, recipient_email, sender_email, receiving_user):
    """
        Process an iTip CANCEL message according to the given policy
    """

    # if invitation policy is set to MANUAL, pass message along
    if policy & ACT_MANUAL:
        log.info(_("Pass cancellation for manual processing"))
        return MESSAGE_FORWARD

    # auto-update the local copy with STATUS=CANCELLED
    if policy & ACT_UPDATE:
        # find existing event in user's calendar
        existing = find_existing_event(itip_event['uid'], receiving_user, True)

        if existing:
            existing.set_status('CANCELLED')
            existing.set_transparency(True)
            if update_event(existing, receiving_user):
                # TODO: send cancellation notification if policy & ACT_UPDATE_AND_NOTIFY: ?
                return MESSAGE_PROCESSED

        else:
            log.error(_("The event referred by this reply was not found in the user's calendars. Forwarding to Inbox."))
            return MESSAGE_FORWARD

    return None


def user_dn_from_email_address(email_address):
    """
        Resolves the given email address to a Kolab user entity
    """
    global auth

    if not auth:
        auth = Auth()
        auth.connect()

    # return cached value
    if user_dn_from_email_address.cache.has_key(email_address):
        return user_dn_from_email_address.cache[email_address]

    local_domains = auth.list_domains()

    if not local_domains == None:
        local_domains = list(set(local_domains.keys()))

    if not email_address.split('@')[1] in local_domains:
        user_dn_from_email_address.cache[email_address] = None
        return None

    log.debug(_("Checking if email address %r belongs to a local user") % (email_address), level=8)

    user_dn = auth.find_user_dn(email_address, True)

    if isinstance(user_dn, basestring):
        log.debug(_("User DN: %r") % (user_dn), level=8)
    else:
        log.debug(_("No user record(s) found for %r") % (email_address), level=9)

    # remember this lookup
    user_dn_from_email_address.cache[email_address] = user_dn

    return user_dn

user_dn_from_email_address.cache = {}


def get_matching_invitation_policies(receiving_user, sender_email):
    # get user's kolabInvitationPolicy settings
    policies = receiving_user['kolabinvitationpolicy'] if receiving_user.has_key('kolabinvitationpolicy') else []
    if policies and not isinstance(policies, list):
        policies = [policies]

    if len(policies) == 0:
        policies = conf.get_list('wallace', 'kolab_invitation_policy')

    # match policies agains the given sender_email
    matches = []
    for p in policies:
        if ':' in p:
            (value, domain) = p.split(':')
        else:
            value = p
            domain = ''

        if domain == '' or domain == '*' or str(sender_email).endswith(domain):
            value = value.upper()
            if policy_name_map.has_key(value):
                matches.append(policy_name_map[value])

    # add manual as default action
    if len(matches) == 0:
        matches.append(ACT_MANUAL)

    return matches


def imap_proxy_auth(user_rec):
    """
        
    """
    global imap

    mail_attribute = conf.get('cyrus-sasl', 'result_attribute')
    if mail_attribute == None:
        mail_attribute = 'mail'

    mail_attribute = mail_attribute.lower()

    if not user_rec.has_key(mail_attribute):
        log.error(_("User record doesn't have the mailbox attribute %r set" % (mail_attribute)))
        return False

    # do IMAP prox auth with the given user
    backend = conf.get('kolab', 'imap_backend')
    admin_login = conf.get(backend, 'admin_login')
    admin_password = conf.get(backend, 'admin_password')

    try:
        imap.disconnect()
        imap.connect(login=False)
        imap.login_plain(admin_login, admin_password, user_rec[mail_attribute])
    except Exception, errmsg:
        log.error(_("IMAP proxy authentication failed: %r") % (errmsg))
        return False

    return True


def list_user_calendars(user_rec):
    """
        Get a list of the given user's private calendar folders
    """
    global imap

    # return cached list
    if user_rec.has_key('_calendar_folders'):
        return user_rec['_calendar_folders'];

    calendars = []

    if not imap_proxy_auth(user_rec):
        return calendars

    folders = imap.list_folders('*')
    log.debug(_("List calendar folders for user %r: %r") % (user_rec['mail'], folders), level=8)

    (ns_personal, ns_other, ns_shared) = imap.namespaces()

    if isinstance(ns_shared, list):
        ns_shared = ns_shared[0]
    if isinstance(ns_other, list):
        ns_other = ns_other[0]

    for folder in folders:
        # exclude shared and other user's namespace
        # TODO: list shared folders the user has write privileges ?
        if folder.startswith(ns_other) or folder.startswith(ns_shared):
            continue;

        metadata = imap.get_metadata(folder)
        log.debug(_("IMAP metadata for %r: %r") % (folder, metadata), level=9)
        if metadata.has_key(folder) and ( \
            metadata[folder].has_key('/shared' + FOLDER_TYPE_ANNOTATION) and metadata[folder]['/shared' + FOLDER_TYPE_ANNOTATION].startswith('event') \
            or metadata[folder].has_key('/private' + FOLDER_TYPE_ANNOTATION) and metadata[folder]['/private' + FOLDER_TYPE_ANNOTATION].startswith('event')):
            calendars.append(folder)

            # store default calendar folder in user record
            if metadata[folder].has_key('/private' + FOLDER_TYPE_ANNOTATION) and metadata[folder]['/private' + FOLDER_TYPE_ANNOTATION].endswith('.default'):
                user_rec['_default_calendar'] = folder

    # cache with user record
    user_rec['_calendar_folders'] = calendars

    return calendars


def find_existing_event(uid, user_rec, lock=False):
    """
        Search user's calendar folders for the given event (by UID)
    """
    global imap

    lock_key = None

    if lock:
        lock_key = get_lock_key(user_rec, uid)
        set_write_lock(lock_key)

    event = None
    for folder in list_user_calendars(user_rec):
        log.debug(_("Searching folder %r for event %r") % (folder, uid), level=8)
        imap.imap.m.select(imap.folder_utf7(folder))

        typ, data = imap.imap.m.search(None, '(UNDELETED HEADER SUBJECT "%s")' % (uid))
        for num in reversed(data[0].split()):
            typ, data = imap.imap.m.fetch(num, '(RFC822)')

            try:
                event = event_from_message(message_from_string(data[0][1]))
                setattr(event, '_imap_folder', folder)
                setattr(event, '_lock_key', lock_key)
            except Exception, e:
                log.error(_("Failed to parse event from message %s/%s: %r") % (folder, num, e))
                continue

            if event and event.uid == uid:
                return event

    if lock_key is not None:
        remove_write_lock(lock_key)

    return event


def check_availability(itip_event, receiving_user):
    """
        For the receiving user, determine if the event in question is in conflict.
    """

    start = time.time()
    num_messages = 0
    conflict = False

    # return previously detected conflict
    if itip_event.has_key('_conflicts'):
        return not itip_event['_conflicts']

    for folder in list_user_calendars(receiving_user):
        log.debug(_("Listing events from folder %r") % (folder), level=8)
        imap.imap.m.select(imap.folder_utf7(folder))

        typ, data = imap.imap.m.search(None, '(UNDELETED HEADER X-Kolab-Type "application/x-vnd.kolab.event")')
        num_messages += len(data[0].split())

        for num in reversed(data[0].split()):
            event = None
            typ, data = imap.imap.m.fetch(num, '(RFC822)')

            try:
                event = event_from_message(message_from_string(data[0][1]))
            except Exception, e:
                log.error(_("Failed to parse event from message %s/%s: %r") % (folder, num, e))
                continue

            if event and event.uid:
                conflict = check_event_conflict(event, itip_event)
                if conflict:
                    log.info(_("Existing event %r conflicts with invitation %r") % (event.uid, itip_event['uid']))
                    break

        if conflict:
            break

    end = time.time()
    log.debug(_("start: %r, end: %r, total: %r, messages: %d") % (start, end, (end-start), num_messages), level=9)

    # remember the result of this check for further iterations
    itip_event['_conflicts'] = conflict

    return not conflict


def set_write_lock(key, wait=True):
    """
        Set a write-lock for the given key and wait if such a lock already exists
    """
    if not os.path.isdir(mybasepath):
        os.makedirs(mybasepath)
    if not os.path.isdir(os.path.join(mybasepath, 'locks')):
        os.makedirs(os.path.join(mybasepath, 'locks'))

    file = os.path.join(mybasepath, 'locks', key + '.lock')
    locked = os.path.getmtime(file) if os.path.isfile(file) else 0
    expired = time.time() - 300

    # wait if file lock is in place
    while locked and locked > expired:
        if not wait:
            return False

        log.debug(_("%r is locked, waiting...") % (key), level=9)
        time.sleep(0.5)
        locked = os.path.getmtime(file) if os.path.isfile(file) else 0

    # touch the file
    if os.path.isfile(file):
        os.utime(file, None)
    else:
        open(file, 'w').close()

    # register active lock
    write_locks.append(key)

    return True


def remove_write_lock(key, update=True):
    """
        Remove the lock file for the given key
    """
    global write_locks

    if key is not None:
        file = os.path.join(mybasepath, 'locks', key + '.lock')
        if os.path.isfile(file):
            os.remove(file)
            if update:
                write_locks = [k for k in write_locks if not k == key]


def get_lock_key(user, uid):
    return hashlib.md5("%s/%s" % (user['mail'], uid)).hexdigest()


def update_event(event, user_rec):
    """
        Update the given event in IMAP (i.e. delete + append)
    """
    success = False

    if hasattr(event, '_imap_folder'):
        delete_event(event)
        success = store_event(event, user_rec, event._imap_folder)

        # remove write lock for this event
        if hasattr(event, '_lock_key') and event._lock_key is not None:
            remove_write_lock(event._lock_key)

    return success


def store_event(event, user_rec, targetfolder=None):
    """
        Append the given event object to the user's default calendar
    """

    # find default calendar folder to save event to
    if targetfolder is None:
        targetfolder = list_user_calendars(user_rec)[0]
        if user_rec.has_key('_default_calendar'):
            targetfolder = user_rec['_default_calendar']

    if not targetfolder:
        log.error(_("Failed to save event: no calendar folder found for user %r") % (user_rec['mail']))
        return Fasle

    log.debug(_("Save event %r to user calendar %r") % (event.uid, targetfolder), level=8)

    try:
        imap.imap.m.select(imap.folder_utf7(targetfolder))
        result = imap.imap.m.append(
            imap.folder_utf7(targetfolder),
            None,
            None,
            event.to_message().as_string()
        )
        return result

    except Exception, e:
        log.error(_("Failed to save event to user calendar at %r: %r") % (
            targetfolder, e
        ))

    return False


def delete_event(existing):
    """
        Removes the IMAP object with the given UID from a user's calendar folder
    """
    targetfolder = existing._imap_folder
    imap.imap.m.select(imap.folder_utf7(targetfolder))

    typ, data = imap.imap.m.search(None, '(HEADER SUBJECT "%s")' % existing.uid)

    log.debug(_("Delete event %r in %r: %r") % (
        existing.uid, targetfolder, data
    ), level=8)

    for num in data[0].split():
        imap.imap.m.store(num, '+FLAGS', '\\Deleted')

    imap.imap.m.expunge()


def send_reply_notification(event, receiving_user):
    """
        Send a (consolidated) notification about the current participant status to organizer
    """
    global auth

    import smtplib
    from email.MIMEText import MIMEText
    from email.Utils import formatdate

    log.debug(_("Compose participation status summary for event %r to user %r") % (
        event.uid, receiving_user['mail']
    ), level=8)

    organizer = event.get_organizer()
    orgemail = organizer.email()
    orgname = organizer.name()

    auto_replies_expected = 0
    auto_replies_received = 0
    partstats = { 'ACCEPTED':[], 'TENTATIVE':[], 'DECLINED':[], 'DELEGATED':[], 'PENDING':[] }
    for attendee in event.get_attendees():
        parstat = attendee.get_participant_status(True)
        if partstats.has_key(parstat):
            partstats[parstat].append(attendee.get_displayname())
        else:
            partstats['PENDING'].append(attendee.get_displayname())

        # look-up kolabinvitationpolicy for this attendee
        if attendee.get_cutype() == kolabformat.CutypeResource:
            resource_dns = auth.find_resource(attendee.get_email())
            if isinstance(resource_dns, list):
                attendee_dn = resource_dns[0] if len(resource_dns) > 0 else None
            else:
                attendee_dn = resource_dns
        else:
            attendee_dn = user_dn_from_email_address(attendee.get_email())

        if attendee_dn:
            attendee_rec = auth.get_entry_attributes(None, attendee_dn, ['kolabinvitationpolicy'])
            if is_auto_reply(attendee_rec, orgemail):
                auto_replies_expected += 1
                if not parstat == 'NEEDS-ACTION':
                    auto_replies_received += 1

    # skip notification until we got replies from all automatically responding attendees
    if auto_replies_received < auto_replies_expected:
        log.debug(_("Waiting for more automated replies (got %d of %d); skipping notification") % (
            auto_replies_received, auto_replies_expected
        ), level=8)
        return

    roundup = ''
    for status,attendees in partstats.iteritems():
        if len(attendees) > 0:
            roundup += "\n" + participant_status_label(status) + ":\n" + "\n".join(attendees) + "\n"

    message_text = """
        The event '%(summary)s' at %(start)s has been updated in your calendar.
        %(roundup)s
    """ % {
        'summary': event.get_summary(),
        'start': event.get_start().strftime('%Y-%m-%d %H:%M %Z'),
        'roundup': roundup
    }

    # compose mime message
    msg = MIMEText(utils.stripped_message(message_text))

    msg['To'] = receiving_user['mail']
    msg['Date'] = formatdate(localtime=True)
    msg['Subject'] = _('"%s" has been updated') % (event.get_summary())
    msg['From'] = '"%s" <%s>' % (orgname, orgemail) if orgname else orgemail

    smtp = smtplib.SMTP("localhost", 10027)

    if conf.debuglevel > 8:
        smtp.set_debuglevel(True)

    try:
        smtp.sendmail(orgemail, receiving_user['mail'], msg.as_string())
    except Exception, e:
        log.error(_("SMTP sendmail error: %r") % (e))

    smtp.quit()


def is_auto_reply(user, sender_email):
    accept_available = False
    accept_conflicts = False
    for policy in get_matching_invitation_policies(user, sender_email):
        if policy & (ACT_ACCEPT | ACT_REJECT | ACT_DELEGATE):
            if check_policy_condition(policy, True):
                accept_available = True
            if check_policy_condition(policy, False):
                accept_conflicts = True

        # we have both cases covered by a policy
        if accept_available and accept_conflicts:
            return True

        # manual action reached
        if policy & (ACT_MANUAL | ACT_SAVE_TO_CALENDAR):
            return False

    return False


def check_policy_condition(policy, available):
    condition_fulfilled = True
    if policy & (COND_IF_AVAILABLE | COND_IF_CONFLICT):
        condition_fulfilled = available
    if policy & COND_IF_CONFLICT:
        condition_fulfilled = not condition_fulfilled
    return condition_fulfilled


def propagate_changes_to_attendees_calendars(event):
    """
        Find and update copies of this event in all attendee's calendars
    """
    for attendee in event.get_attendees():
        attendee_user_dn = user_dn_from_email_address(attendee.get_email())
        if attendee_user_dn:
            attendee_user = auth.get_entry_attributes(None, attendee_user_dn, ['*'])
            attendee_event = find_existing_event(event.uid, attendee_user, True)  # does IMAP authenticate
            if attendee_event:
                try:
                    attendee_entry = attendee_event.get_attendee_by_email(attendee_user['mail'])
                except:
                    attendee_entry = None

                # copy all attendees from master event (covers additions and removals)
                new_attendees = kolabformat.vectorattendee();
                for a in event.get_attendees():
                    # keep my own entry intact
                    if attendee_entry is not None and attendee_entry.get_email() == a.get_email():
                        new_attendees.append(attendee_entry)
                    else:
                        new_attendees.append(a)

                attendee_event.event.setAttendees(new_attendees)

                success = update_event(attendee_event, attendee_user)
                log.debug(_("Updated %s's copy of %r: %r") % (attendee_user['mail'], event.uid, success), level=8)

            else:
                log.debug(_("Attendee %s's copy of %r not found") % (attendee_user['mail'], event.uid), level=8)

        else:
            log.debug(_("Attendee %r not found in LDAP") % (attendee.get_email()), level=8)


def invitation_response_text():
    return _("""
        %(name)s has %(status)s your invitation for %(summary)s.

        *** This is an automated response sent by the Kolab Invitation system ***
    """)