MailNotifier.php

<?php

class MailNotifier implements Notifier {
  
  public function notify (Notification $n, Closure $next) {
    
    Mail::send(); // ... whatever
    
    return $next($n);
  }
  
}

PushNotifier.php

<?php

class PusherNotifier implements Notifier {
  
  public function notify (Notification $n, Closure $next) {
    
    Pusher::push($n->recepient()->getOption('pusher.id'), $n->getPayload());
    
    return $next($n);
  }
  
}

SomeEventListener.php

<?php

// in an event listener for when a chat reply goes out

foreach ($chatroom->users() as $user) {
  if ($user != $event->author()) { // prevet message author from getting it
    $user->notify(new ChatReplyNotification($event->message(), $event->author())); // just a DTO
  }
}

User.php

<?php

class User {
  
  public function notify (Notification $n) {
    $notifier = NotifierFactory::buildStack($this->getNotificationOptions()); // builds the notification stack
    $notifier->notify($n);
  }
  
}