text: #!/usr/bin/python3
  
  import argparse
  import base64
  import configparser
  import http.client
  import os
  import re
  import ssl
  import subprocess
  import sys
  import textwrap
  import xml.etree.ElementTree as etree
  
  
  def msgfmt(msg, prefix=''):
      lines = []
      for line in msg.splitlines():
          lines += textwrap.wrap(line, 80 - len(prefix))
      return '\n'.join([prefix + line for line in lines])
  
  
  def warn(msg):
      print(msgfmt(msg, "warning: "))
  
  
  def die(msg):
      sys.exit(msgfmt(msg, "error: "))
  
  
  def die_atnode(msg, node):
      if debug:
          msg += '\n\n'
          msg += 'The error occurred while processing the following XML node:\n'
          msg += etree.tostring(node).decode('utf-8')
      die(msg)
  
  
  def calcurse_wipe():
      if verbose:
          print('Removing all local calcurse objects...')
      if dry_run:
          return
      subprocess.call([calcurse, '-F', '--filter-hash=XXX'])
  
  
  def calcurse_import(icaldata):
      p = subprocess.Popen([calcurse, '-i', '-', '--dump-imported', '-q',
                            '--format-recur-apt=%(hash)\\n',
                            '--format-event=%(hash)\\n',
                            '--format-recur-event=%(hash)\\n',
                            '--format-todo=%(hash)\\n'],
                           stdin=subprocess.PIPE, stdout=subprocess.PIPE)
      return p.communicate(icaldata.encode('utf-8'))[0].decode('utf-8').rstrip()
  
  
  def calcurse_export(objhash):
      p = subprocess.Popen([calcurse, '-x', 'ical', '--export-uid',
                            '--filter-hash=' + objhash], stdout=subprocess.PIPE)
      return p.communicate()[0].decode('utf-8').rstrip()
  
  
  def calcurse_hashset():
      p = subprocess.Popen([calcurse, '-G', '--format-apt=%(hash)\\n',
                            '--format-recur-apt=%(hash)\\n',
                            '--format-event=%(hash)\\n',
                            '--format-recur-event=%(hash)\\n',
                            '--format-todo=%(hash)\\n'], stdout=subprocess.PIPE)
      return set(p.communicate()[0].decode('utf-8').rstrip().splitlines())
  
  
  def calcurse_remove(objhash):
      subprocess.call([calcurse, '-F', '--filter-hash=!' + objhash])
  
  
  def calcurse_version():
      p = subprocess.Popen([calcurse, '--version'], stdout=subprocess.PIPE)
      m = re.match(r'calcurse ([0-9]+)\.([0-9]+)\.([0-9]+)(?:-([0-9]+)-)?',
                   p.communicate()[0].decode('utf-8'))
      if not m:
          return None
      return tuple([int(group) for group in m.groups(0)])
  
  
  def get_auth_headers():
      if not username or not password:
          return {}
      user_password = ('{}:{}'.format(username, password)).encode('ascii')
      user_password = base64.b64encode(user_password).decode('ascii')
      headers = {'Authorization': 'Basic {}'.format(user_password)}
      return headers
  
  
  def remote_query(conn, cmd, path, additional_headers, body):
      headers = custom_headers.copy()
      headers.update(get_auth_headers())
      if cmd == 'PUT':
          headers['Content-Type'] = 'text/calendar; charset=utf-8'
      else:
          headers['Content-Type'] = 'application/xml; charset=utf-8'
      headers.update(additional_headers)
  
      if debug:
          print("> {} {}".format(cmd, path))
          print("> Headers: " + repr(headers))
          if body:
              for line in body.splitlines():
                  print("> " + line)
          print()
  
      if isinstance(body, str):
          body = body.encode('utf-8')
  
      conn.request(cmd, path, headers=headers, body=body)
  
      resp = conn.getresponse()
  
      if not resp:
          return (None, None)
  
      headers = resp.getheaders()
      body = resp.read().decode('utf-8')
  
      if debug:
          print("< Headers: " + repr(headers))
          for line in body.splitlines():
              print("< " + line)
          print()
  
      if resp.status - (resp.status % 100) != 200:
          die(("The server at {} replied with HTTP status code {} ({}) " +
               "while trying to access {}.").format(hostname, resp.status,
                                                    resp.reason, path))
  
      return (headers, body)
  
  
  def get_etags(conn, hrefs=[]):
      if len(hrefs) > 0:
          body = ('<?xml version="1.0" encoding="utf-8" ?>'
                  '<C:calendar-multiget xmlns:D="DAV:" '
                  '                     xmlns:C="urn:ietf:params:xml:ns:caldav">'
                  '<D:prop><D:getetag /></D:prop>')
          for href in hrefs:
              body += '<D:href>{}</D:href>'.format(href)
          body += '</C:calendar-multiget>'
      else:
          body = ('<?xml version="1.0" encoding="utf-8" ?>'
                  '<C:calendar-query xmlns:D="DAV:" '
                  '                  xmlns:C="urn:ietf:params:xml:ns:caldav">'
                  '<D:prop><D:getetag /></D:prop>'
                  '<C:filter><C:comp-filter name="VCALENDAR" /></C:filter>'
                  '</C:calendar-query>')
      headers, body = remote_query(conn, "REPORT", path, {}, body)
      if not headers:
          return {}
      root = etree.fromstring(body)
  
      etagdict = {}
      for node in root.findall(".//D:response", namespaces=nsmap):
          etagnode = node.find("./D:propstat/D:prop/D:getetag", namespaces=nsmap)
          if etagnode is None:
              die_atnode('Missing ETag.', node)
          etag = etagnode.text.strip('"')
  
          hrefnode = node.find("./D:href", namespaces=nsmap)
          if hrefnode is None:
              die_atnode('Missing href.', node)
          href = hrefnode.text
  
          etagdict[href] = etag
  
      return etagdict
  
  
  def remote_wipe(conn):
      if verbose:
          print('Removing all objects from the CalDAV server...')
      if dry_run:
          return
  
      remote_query(conn, "DELETE", path, {}, None)
  
  
  def get_syncdb(fn):
      if not os.path.exists(fn):
          return {}
  
      if verbose:
          print('Loading synchronization database from ' + fn + '...')
  
      syncdb = {}
      with open(fn, 'r') as f:
          for line in f.readlines():
              href, etag, objhash = line.rstrip().split(' ')
              syncdb[href] = (etag, objhash)
  
      return syncdb
  
  
  def save_syncdb(fn, syncdb):
      if verbose:
          print('Saving synchronization database to ' + fn + '...')
      if dry_run:
          return
  
      with open(fn, 'w') as f:
          for href, (etag, objhash) in syncdb.items():
              print("{} {} {}".format(href, etag, objhash), file=f)
  
  
  def push_object(conn, objhash):
      href = path + objhash + ".ics"
      body = calcurse_export(objhash)
      headers, body = remote_query(conn, "PUT", href, {}, body)
  
      if not headers:
          return None
  
      etag = None
      headerdict = dict((key.lower(), value) for key, value in headers)
      if 'etag' in headerdict:
          etag = headerdict['etag']
      while not etag:
          etagdict = get_etags(conn, [href])
          if etagdict:
              etag = next(iter(etagdict.values()))
      etag = etag.strip('"')
  
      return (href, etag)
  
  
  def remove_remote_object(conn, etag, href):
      headers = {'If-Match': '"' + etag + '"'}
      remote_query(conn, "DELETE", href, headers, None)
  
  
  def push_objects(conn, syncdb, etagdict):
      objhashes = calcurse_hashset()
      new = objhashes - set([entry[1] for entry in syncdb.values()])
      gone = set([entry[1] for entry in syncdb.values()]) - objhashes
  
      added = deleted = 0
  
      # Copy new objects to the server.
      for objhash in new:
          if verbose:
              print("Pushing new object {} to the server.".format(objhash))
          if dry_run:
              continue
  
          href, etag = push_object(conn, objhash)
          syncdb[href] = (etag, objhash)
          added += 1
  
      # Remove locally deleted objects from the server.
      for objhash in gone:
          queue = []
          for href, entry in syncdb.items():
              if entry[1] == objhash:
                  queue.append(href)
  
          for href in queue:
              etag = syncdb[href][0]
  
              if etagdict[href] != etag:
                  warn(('{} was deleted locally but modified in the CalDAV '
                        'calendar. Keeping the modified version on the server. '
                        'Run the script again to import the modified '
                        'object.').format(objhash))
                  syncdb.pop(href, None)
                  continue
  
              if verbose:
                  print("Removing remote object {} ({}).".format(etag, href))
              if dry_run:
                  continue
  
              remove_remote_object(conn, etag, href)
              syncdb.pop(href, None)
              deleted += 1
  
      return (added, deleted)
  
  
  def pull_objects(conn, syncdb, etagdict):
      missing = set()
      modified = set()
      for href in set(etagdict.keys()):
          if href not in syncdb:
              missing.add(href)
          elif etagdict[href] != syncdb[href][0]:
              modified.add(href)
      orphan = set(syncdb.keys()) - set(etagdict.keys())
  
      # Download and import new objects from the server.
      body = ('<?xml version="1.0" encoding="utf-8" ?>'
              '<C:calendar-multiget xmlns:D="DAV:" '
              '                     xmlns:C="urn:ietf:params:xml:ns:caldav">'
              '<D:prop><D:getetag /><C:calendar-data /></D:prop>')
      for href in (missing | modified):
          body += '<D:href>{}</D:href>'.format(href)
      body += '</C:calendar-multiget>'
      headers, body = remote_query(conn, "REPORT", path, {}, body)
  
      root = etree.fromstring(body)
  
      added = deleted = 0
  
      for node in root.findall(".//D:response", namespaces=nsmap):
          hrefnode = node.find("./D:href", namespaces=nsmap)
          if hrefnode is None:
              die_atnode('Missing href.', node)
          href = hrefnode.text
  
          etagnode = node.find("./D:propstat/D:prop/D:getetag", namespaces=nsmap)
          if etagnode is None:
              die_atnode('Missing ETag.', node)
          etag = etagnode.text.strip('"')
  
          cdatanode = node.find("./D:propstat/D:prop/C:calendar-data",
                                namespaces=nsmap)
          if cdatanode is None:
              die_atnode('Missing calendar data.', node)
          cdata = cdatanode.text
  
          if href in modified:
              if verbose:
                  print("Replacing object {}.".format(etag))
              if dry_run:
                  continue
              objhash = syncdb[href][1]
              calcurse_remove(objhash)
          else:
              if verbose:
                  print("Importing new object {}.".format(etag))
              if dry_run:
                  continue
  
          objhash = calcurse_import(cdata)
          syncdb[href] = (etag, objhash)
          added += 1
  
      # Delete objects that no longer exist on the server.
      for href in orphan:
          etag, objhash = syncdb[href]
  
          if verbose:
              print("Removing local object {}.".format(objhash))
          if dry_run:
              continue
  
          calcurse_remove(objhash)
          syncdb.pop(href, None)
          deleted += 1
  
      return (added, deleted)
  
  
  def run_hook(name):
      hook_path = hookdir + '/' + name
      if not os.path.exists(hook_path):
          return
      subprocess.call(hook_path, shell=True)
  
  
  # Initialize the XML namespace map.
  nsmap = {"D": "DAV:", "C": "urn:ietf:params:xml:ns:caldav"}
  
  # Initialize default values.
  configfn = os.path.expanduser("~/.calcurse/caldav/config")
  lockfn = os.path.expanduser("~/.calcurse/caldav/lock")
  syncdbfn = os.path.expanduser("~/.calcurse/caldav/sync.db")
  hookdir = os.path.expanduser("~/.calcurse/caldav/hooks/")
  
  # Parse command line arguments.
  parser = argparse.ArgumentParser('calcurse-caldav')
  parser.add_argument('--init', action='store', dest='init', default=None,
                      choices=['keep-remote', 'keep-local', 'two-way'],
                      help='initialize the sync database')
  parser.add_argument('--config', action='store', dest='configfn',
                      default=configfn,
                      help='path to the calcurse-caldav configuration')
  parser.add_argument('--lockfile', action='store', dest='lockfn',
                      default=lockfn,
                      help='path to the calcurse-caldav lock file')
  parser.add_argument('--syncdb', action='store', dest='syncdbfn',
                      default=syncdbfn,
                      help='path to the calcurse-caldav sync DB')
  parser.add_argument('--hookdir', action='store', dest='hookdir',
                      default=hookdir,
                      help='path to the calcurse-caldav hooks directory')
  parser.add_argument('-v', '--verbose', action='store_true', dest='verbose',
                      default=False,
                      help='print status messages to stdout')
  parser.add_argument('--debug', action='store_true', dest='debug',
                      default=False, help='print debug messages to stdout')
  args = parser.parse_args()
  
  init = args.init is not None
  configfn = args.configfn
  lockfn = args.lockfn
  syncdbfn = args.syncdbfn
  hookdir = args.hookdir
  verbose = args.verbose
  debug = args.debug
  
  # Read configuration.
  config = configparser.RawConfigParser()
  if verbose:
      print('Loading configuration from ' + configfn + '...')
  try:
      config.readfp(open(configfn))
  except FileNotFoundError as e:
      die('Configuration file not found: {}'.format(configfn))
  
  hostname = config.get('General', 'HostName')
  path = '/' + config.get('General', 'Path').strip('/') + '/'
  
  if config.has_option('General', 'InsecureSSL'):
      insecure_ssl = config.getboolean('General', 'InsecureSSL')
  else:
      insecure_ssl = False
  
  if config.has_option('General', 'Binary'):
      calcurse = config.get('General', 'Binary')
  else:
      calcurse = 'calcurse'
  
  if config.has_option('General', 'DryRun'):
      dry_run = config.getboolean('General', 'DryRun')
  else:
      dry_run = True
  
  if not verbose and config.has_option('General', 'Verbose'):
      verbose = config.getboolean('General', 'Verbose')
  
  if not debug and config.has_option('General', 'Debug'):
      debug = config.getboolean('General', 'Debug')
  
  if config.has_option('Auth', 'UserName'):
      username = config.get('Auth', 'UserName')
  else:
      username = None
  
  if config.has_option('Auth', 'Password'):
      password = config.get('Auth', 'Password')
  else:
      password = None
  
  if config.has_section('CustomHeaders'):
      custom_headers = dict(config.items('CustomHeaders'))
  else:
      custom_headers = {}
  
  # Show disclaimer when performing a dry run.
  if dry_run:
      warn(('Dry run; nothing is imported/exported. Add "DryRun = No" to the '
            '[General] section in the configuration file to enable '
            'synchronization.'))
  
  # Check whether the specified calcurse binary is executable and compatible.
  ver = calcurse_version()
  if ver is None:
      die('Invalid calcurse binary. Make sure that the file specified in ' +
          'the configuration is a valid and up-to-date calcurse binary.')
  elif ver < (4, 0, 0, 96):
      die('Incompatible calcurse binary detected. Version >=4.1.0 is required ' +
          'to synchronize with CalDAV servers.')
  
  # Run the pre-sync hook.
  run_hook('pre-sync')
  
  # Create lock file.
  if os.path.exists(lockfn):
      die('Leftover lock file detected. If there is no other synchronization ' +
          'instance running, please remove the lock file manually and try ' +
          'again.')
  open(lockfn, 'w')
  
  try:
      # Connect to the server via HTTPs.
      if verbose:
          print('Connecting to ' + hostname + '...')
      if insecure_ssl:
          try:
              context = ssl._create_unverified_context()
              conn = http.client.HTTPSConnection(hostname, context=context)
          except AttributeError:
              # Python versions prior to 3.4.3 do not support
              # ssl._create_unverified_context(). However, these versions do not
              # seem to verify certificates by default so we can simply fall back
              # to http.client.HTTPSConnection().
              conn = http.client.HTTPSConnection(hostname)
      else:
          conn = http.client.HTTPSConnection(hostname)
  
      if init:
          # In initialization mode, start with an empty synchronization database.
          if args.init == 'keep-remote':
              calcurse_wipe()
          elif args.init == 'keep-local':
              remote_wipe(conn)
          syncdb = {}
      else:
          # Read the synchronization database.
          syncdb = get_syncdb(syncdbfn)
  
          if not syncdb:
              die('Sync database not found or empty. Please initialize the ' +
                  'database first.\n\nSupported initialization modes are:\n' +
                  '  --init=keep-remote Remove all local calcurse items\n' +
                  '  --init=keep-local  Remove all remote objects\n' +
                  '  --init=two-way     Copy local items to the server and vice versa')
  
      # Query the server and build a dictionary that maps ETags to paths on the
      # server.
      etagdict = get_etags(conn)
  
      # Retrieve new objects from the server, delete local items that no longer
      # exist on the server.
      local_new, local_del = pull_objects(conn, syncdb, etagdict)
  
      # Push new objects to the server, remove items from the server if they no
      # longer exist locally.
      remote_new, remote_del = push_objects(conn, syncdb, etagdict)
  
      # Write the synchronization database.
      save_syncdb(syncdbfn, syncdb)
  
      # Close the HTTPs connection.
      conn.close()
  finally:
      # Remove lock file.
      os.remove(lockfn)
  
  # Run the post-sync hook.
  run_hook('post-sync')
  
  # Print a summary to stdout.
  print("{} items imported, {} items removed locally.".
        format(local_new, local_del))
  print("{} items exported, {} items removed from the server.".
        format(remote_new, remote_del))
  