Implement frontend state recovery backend (partial)

lib/tfw/networking/server/tfw_server.py

@@ -1,10 +1,13 @@
 # Copyright (C) 2018 Avatao.com Innovative Learning Kft.
 # All Rights Reserved. See LICENSE file for details.
 
+from abc import ABC, abstractmethod
+
 from tornado.web import Application
 
 from tfw.networking.event_handlers import ServerUplinkConnector
 from tfw.networking.server import EventHandlerConnector
+from tfw.networking import MessageSender
 from tfw.config.logs import logging
 from .zmq_websocket_proxy import ZMQWebSocketProxy
 
@@ -24,10 +27,13 @@ class TFWServer:
         self.application = Application([(
             r'/ws', ZMQWebSocketProxy,{
                 'event_handler_connector': self._event_handler_connector,
-                'message_handlers': [self.handle_trigger]
+                'message_handlers': [self.handle_trigger, self.handle_recover],
+                'frontend_message_handlers': [self.save_frontend_messages]
             })]
         )
 
+        self._frontend_messages = FrontendMessageStorage()
+
     def handle_trigger(self, message):
         if 'trigger' in message:
             LOG.debug('Executing handler for trigger "%s"', message.get('trigger', ''))
@@ -39,5 +45,43 @@ class TFWServer:
                 }
             })
 
+    def handle_recover(self, message):
+        if message['key'] == 'recover':
+            self._frontend_messages.replay_messages(self._uplink_connector)
+
+    def save_frontend_messages(self, message):
+        self._frontend_messages.save_message(message)
+
     def listen(self, port):
         self.application.listen(port)
+
+
+class MessageStorage(ABC):
+    def __init__(self):
+        self.saved_messages = []
+
+    def save_message(self, message):
+        if self.filter_message(message):
+            self.saved_messages.extend(self.transform_message(message))
+
+    @abstractmethod
+    def filter_message(self, message):
+        raise NotImplementedError
+
+    def transform_message(self, message):
+        yield message
+
+
+class FrontendMessageStorage(MessageStorage):
+    def filter_message(self, message):
+        return message['key'] in ('message', 'dashboard', 'queueMessages')
+
+    def transform_message(self, message):
+        if message['key'] == 'queueMessages':
+            yield from MessageSender.generate_messages_from_queue(message)
+        else:
+            yield message
+
+    def replay_messages(self, connector):
+        for message in self.saved_messages:
+            connector.send(message)