text: # @license
  # Copyright 2017 Google Inc.
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #      http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  from __future__ import absolute_import
  
  from . import server, url_state, viewer_base
  
  
  class _ViewerHelper(object):
      """Mixin for implementing viewers based on the built-in server."""
  
      def __init__(self):
          super(_ViewerHelper, self).__init__()
          server.register_viewer(self)
  
      def defer_callback(self, callback, *args, **kwargs):
          server.defer_callback(callback, *args, **kwargs)
  
      def __repr__(self):
          return self.get_viewer_url()
  
      def _repr_html_(self):
          return '<a href="%s" target="_blank">Viewer</a>' % self.get_viewer_url()
  
      def get_viewer_url(self):
          raise NotImplementedError
  
  
  class Viewer(viewer_base.ViewerBase, _ViewerHelper):
      def __init__(self):
          super(Viewer, self).__init__()
          server.register_viewer(self)
  
      def get_viewer_url(self):
          return '%s/v/%s/' % (server.get_server_url(), self.token)
  
  
  class UnsynchronizedViewer(viewer_base.UnsynchronizedViewerBase, _ViewerHelper):
      def __init__(self):
          super(UnsynchronizedViewer, self).__init__()
          server.register_viewer(self)
  
      def get_viewer_url(self):
          return url_state.to_url(self.raw_state, '%s/v/%s/' % (server.get_server_url(), self.token))
  