baseimage-tutorial-framework/lib/tfw/components/fsm_managing_event_handler.py

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

from collections import defaultdict

from tfw import BroadcastingEventHandler
from tfw.config.logs import logging

LOG = logging.getLogger(__name__)


class FSMManagingEventHandler(BroadcastingEventHandler):
    def __init__(self, key, fsm_type):
        super().__init__(key)
        self.fsm = fsm_type()
        self.fsm_manager = FSMManager(self.fsm)
        self._fsm_updater = FSMUpdater(self.fsm)

        self.command_handlers = {
            'trigger': self.handle_trigger,
            'update':  self.handle_update
        }

    def handle_event(self, message):
        try:
            data = message['data']
            message['data'] = self.command_handlers[data['command']](data)
            return message
        except KeyError:
            LOG.error('IGNORING MESSAGE: Invalid message received: %s', message)

    def handle_trigger(self, data):
        self.fsm_manager.trigger(data['value'])
        return self.with_fsm_update(data)

    def with_fsm_update(self, data):
        return {
            **data,
            **self._fsm_updater.get_fsm_state_and_transitions()
        }

    def handle_update(self, data):
        return self.with_fsm_update(data)


class FSMManager:
    def __init__(self, fsm):
        self.fsm = fsm
        self.trigger_predicates = defaultdict(list)

    def trigger(self, trigger):
        predicate_results = [
            predicate()
            for predicate in self.trigger_predicates[trigger]
        ]

        # TODO: think about what could we do when this prevents triggering
        if all(predicate_results):
            try:
                self.fsm.trigger(trigger)
            except AttributeError:
                LOG.debug('FSM failed to execute nonexistent trigger: "%s"', trigger)

    def subscribe_predicate(self, trigger, *predicates):
        self.trigger_predicates[trigger].extend(predicates)

    def unsubscribe_predicate(self, trigger, *predicates):
        self.trigger_predicates[trigger] = [
            predicate
            for predicate in self.trigger_predicates[trigger]
            not in predicates
        ]


class FSMUpdater:
    def __init__(self, fsm):
        self.fsm = fsm

    def get_fsm_state_and_transitions(self):
        state = self.fsm.state
        valid_transitions = [
            {'trigger': trigger}
            for trigger in self.fsm.machine.get_triggers(self.fsm.state)
        ]
        return {
            'current_state': state,
            'valid_transitions': valid_transitions
        }