old_contents: import logging
  import time
  
  from mopidy.exceptions import MpdNotImplemented
  from mopidy.models import Playlist
  
  logger = logging.getLogger('backends.base')
  
  class BaseBackend(object):
      current_playlist = None
      library = None
      playback = None
      stored_playlists = None
      uri_handlers = []
  
  class BaseCurrentPlaylistController(object):
      def __init__(self, backend):
          self.backend = backend
  
  class BasePlaybackController(object):
      PAUSED = 'paused'
      PLAYING = 'playing'
      STOPPED = 'stopped'
      
      def __init__(self, backend):
          self.backend = backend
          self.state = self.STOPPED
          self.current_track = None
          self.playlist_position = None
  
      def play(self, id=None, position=None):
          raise NotImplementedError
  
      def next(self):
          raise NotImplementedError
  
new_contents: import logging
  import time
  
  from mopidy.exceptions import MpdNotImplemented
  from mopidy.models import Playlist
  
  logger = logging.getLogger('backends.base')
  
  class BaseBackend(object):
      current_playlist = None
      library = None
      playback = None
      stored_playlists = None
      uri_handlers = []
  
  class BaseCurrentPlaylistController(object):
      def __init__(self, backend):
          self.backend = backend
  
      def add(self, track, at_position=None):
          raise NotImplementedError
  
  class BasePlaybackController(object):
      PAUSED = 'paused'
      PLAYING = 'playing'
      STOPPED = 'stopped'
      
      def __init__(self, backend):
          self.backend = backend
          self.state = self.STOPPED
          self.current_track = None
          self.playlist_position = None
  
      def play(self, id=None, position=None):
          raise NotImplementedError
  
      def next(self):
          raise NotImplementedError
  
subject: Add add method to BaseCurrentPlaylistController