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This diagram shows how events trigger notifications that are queued and processed by delivery handlers respecting user preferences.
### Before: No notification system, direct calls class OrderService: def place_order(self, user, order): # process order self.send_email(user.email, "Order placed") def send_email(self, email, message): # direct email sending print(f"Sending email to {email}: {message}") ### After: Using Notification System from enum import Enum class Channel(Enum): EMAIL = 'email' SMS = 'sms' class Notification: def __init__(self, user_id, message, channel): self.user_id = user_id self.message = message self.channel = channel class NotificationQueue: def __init__(self): self.queue = [] def enqueue(self, notification): self.queue.append(notification) def dequeue(self): if self.queue: return self.queue.pop(0) return None class NotificationService: def __init__(self, queue, user_prefs): self.queue = queue self.user_prefs = user_prefs def notify(self, user_id, message): prefs = self.user_prefs.get(user_id, [Channel.EMAIL]) for channel in prefs: notification = Notification(user_id, message, channel) self.queue.enqueue(notification) def process_notifications(self): notification = self.queue.dequeue() while notification: self.send(notification) notification = self.queue.dequeue() def send(self, notification): print(f"Sending {notification.channel.value} to user {notification.user_id}: {notification.message}") class OrderService: def __init__(self, notification_service): self.notification_service = notification_service def place_order(self, user_id, order): # process order self.notification_service.notify(user_id, "Your order has been placed.") # Usage user_prefs = {1: [Channel.EMAIL, Channel.SMS], 2: [Channel.EMAIL]} queue = NotificationQueue() notif_service = NotificationService(queue, user_prefs) order_service = OrderService(notif_service) order_service.place_order(1, "Order123") notif_service.process_notifications()