Build a Notification DispatcherStep 5 of 5

Broadcast Fan-Out

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Step 5: Broadcast Fan-Out

Real alerts rarely target one channel, an outage should hit email and SMS and push at once. Because every notifier shares the same send shape and the factory builds any of them on demand, fan-out is a short loop over the single-channel path you already have.

Add broadcast to NotificationService:

  • broadcast(channels, message) builds one notifier per channel via the factory, sends the same message on each, and returns the list of send results in the order the channels were given

Reuse notify from Step 4 rather than re-deriving it. An empty channel list should return an empty list.

Hints
Starter code
class Notifier:
    def send(self, message):
        raise NotImplementedError


class EmailNotifier(Notifier):
    def send(self, message):
        return {"channel": "email", "message": message}


class SmsNotifier(Notifier):
    def send(self, message):
        return {"channel": "sms", "message": message}


class PushNotifier(Notifier):
    def send(self, message):
        return {"channel": "push", "message": message}


def notifier_for(channel):
    if channel == "email":
        return EmailNotifier()
    if channel == "sms":
        return SmsNotifier()
    if channel == "push":
        return PushNotifier()
    raise ValueError("unknown channel: " + str(channel))


class NotifierFactory:
    def __init__(self):
        self._registry = {}

    def register(self, channel, cls):
        self._registry[channel] = cls

    def create(self, channel):
        if channel not in self._registry:
            raise ValueError("unknown channel: " + str(channel))
        return self._registry[channel]()


class NotificationService:
    def __init__(self, factory):
        self._factory = factory

    def notify(self, channel, message):
        notifier = self._factory.create(channel)
        return notifier.send(message)

    def broadcast(self, channels, message):
        """Send message on each channel; return the list of send results."""
        # TODO: return [self.notify(c, message) for c in channels]
        pass
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