baseimage-tutorial-framework/lib/tfw/event_handler_base.py

# Copyright (C) 2018 Avatao.com Innovative Learning Kft.
# All Rights Reserved. See LICENSE file for details.

from abc import ABC, abstractmethod

from tfw.networking import deserialize_tfw_msg
from tfw.networking.event_handlers import ServerConnector


class EventHandlerBase(ABC):
    """
    Abstract base class for all Python based EventHandlers. Useful implementation template
    for other languages.

    Derived classes must implement the handle_event() method
    """
    def __init__(self, key):
        self.server_connector = ServerConnector()
        self.key = key
        self.subscribe(self.key, 'reset')
        self.server_connector.register_callback(self.event_handler_callback)

    def event_handler_callback(self, msg_parts):
        """
        Callback that is invoked when receiving a message.
        This is subscribed in __init__().
        """
        # TODO: fix faulty logic below
        message = deserialize_tfw_msg(*msg_parts)
        response = self.dispatch_handling(message)
        response['key'] = message['key']
        if response is None:
            return
        self.server_connector.send(response)

    def dispatch_handling(self, message):
        if message['key'] != 'reset':
            return self.handle_event(message)
        return self.handle_reset(message)

    @abstractmethod
    def handle_event(self, message):
        """
        Abstract method that implements the handling of messages.

        :param message: the message received
        """
        raise NotImplementedError

    def handle_reset(self, message):
        # pylint: disable=unused-argument,no-self-use
        """
        'reset' events usually receive some sort of special treatment.

        :param message: the message received
        """
        return None

    def subscribe(self, *keys):
        """
        Subscribe this EventHandler to receive events for given keys.
        Note that you can subscribe to the same key several times in which
        case you will need to unsubscribe multiple times in order to stop
        receiving events.
        
        :param keys: list of keys to subscribe to
        """
        for key in keys:
            self.server_connector.subscribe(key)

    def unsubscribe(self, *keys):
        """
        Unsubscribe this eventhandler from the given keys.

        :param keys: list of keys to unsubscribe from
        """
        for key in keys:
            self.server_connector.unsubscribe(key)

    def cleanup(self):
        """
        Perform cleanup actions such as releasing database
        connections and stuff like that.
        """
        pass


class TriggeredEventHandler(EventHandlerBase, ABC):
    # pylint: disable=abstract-method
    """
    Abstract base class for EventHandlers which are only triggered in case
    TFWServer has successfully triggered an FSM step defined in __init__.
    """
    def __init__(self, key, trigger):
        super().__init__(key)
        self.trigger = trigger

    def dispatch_handling(self, message):
        if message.get('trigger') == self.trigger:
            return super().dispatch_handling(message)
        return None