Practice/Amazon/Design a Pub-Sub System for Delivery Drivers

Design a Pub-Sub System for Delivery Drivers

Object Oriented DesignMust

Problem

Design and implement a real-time event distribution system for managing driver notifications. The system allows drivers to subscribe to specific event topics (such as weather alerts, route updates, or order assignments) and receive relevant events as they occur. The system must support dynamic topic subscriptions, event validation through custom rules, and efficient message delivery to potentially tens of thousands of concurrent drivers.

Your implementation should handle driver registration, topic-based subscriptions, event publishing with validation, and the ability to extend the system with custom validation logic without modifying the core code.

Requirements

1. Driver Management: Support registering drivers with unique identifiers and names
2. Topic-Based Subscriptions: Allow drivers to subscribe to and unsubscribe from multiple topics
3. Event Publishing: Publish events to specific topics and deliver them to all subscribed drivers
4. Event Validation: Support adding custom validators that check events before publishing
5. Scalability: Design the system to efficiently handle up to 100,000 active drivers
6. Extensibility: Allow new validators to be added dynamically without changing existing code

Constraints

• Driver IDs must be unique across the system
• A driver can subscribe to multiple topics simultaneously
• Events must pass all registered validators before being published
• The system should handle concurrent operations efficiently
• Each event should contain at least a topic and timestamp
• Failed validation should not crash the system

Examples

Example 1: Basic Event Flow

` system = EventDistributionSystem() driver1 = Driver("D001", "Alice") driver2 = Driver("D002", "Bob")

system.register_driver(driver1) system.register_driver(driver2)

system.subscribe("D001", "weather_alert") system.subscribe("D002", "weather_alert")

event = {"type": "storm", "severity": "high", "timestamp": "2024-01-15T10:00:00"} count = system.publish_event("weather_alert", event)

Output: count = 2 (both drivers receive the event)

`

Example 2: Multiple Topics

` system.subscribe("D001", "traffic_update") system.subscribe("D001", "order_assignment")

event1 = {"type": "congestion", "location": "Highway 101"} system.publish_event("traffic_update", event1)

D001 receives traffic update

event2 = {"type": "new_order", "order_id": "ORD123"} system.publish_event("order_assignment", event2)

D001 receives order assignment

`

Example 3: Event Validation

` class PriorityValidator(EventValidator): def validate(self, event): return "priority" in event and event["priority"] in ["low", "medium", "high"]

system.add_validator(PriorityValidator())

valid_event = {"type": "alert", "priority": "high"} system.publish_event("alerts", valid_event) # Published successfully

invalid_event = {"type": "alert", "priority": "urgent"} system.publish_event("alerts", invalid_event) # Rejected by validator `