How to Implement an Outbox Table Poll Publisher in Python

import time
import json
from dataclasses import dataclass, asdict
from datetime import datetime, timedelta

@dataclass
class OutboxRecord:
    id: int
    topic: str
    payload: dict
    created_at: datetime

class OutboxPollPublisher:
    def __init__(self, poll_interval_seconds=1):
        self.poll_interval = poll_interval_seconds
        self.outbox = []
        self.next_id = 1

    def add_outbox_records(self, records):
        """Simulate new rows appearing in the outbox table."""
        self.outbox.extend(records)

    def publish_pending(self):
        """Poll for pending records and 'publish' them (simulate)."""
        published = []
        for record in self.outbox:
            if record.created_at <= datetime.now():
                message = {
                    "event_id": record.id,
                    "topic": record.topic,
                    "payload": record.payload,
                    "published_at": datetime.now().isoformat()
                }
                print(f"PUBLISHED: {json.dumps(message)}")
                published.append(record)
        # Remove published records
        self.outbox = [r for r in self.outbox if r not in published]
        return len(published)

if __name__ == "__main__":
    publisher = OutboxPollPublisher()

    # Simulate records being inserted into the outbox table
    publisher.add_outbox_records([
        OutboxRecord(id=1, topic="order.created", payload={"order_id": "A1"}, created_at=datetime.now() - timedelta(seconds=2)),
        OutboxRecord(id=2, topic="payment.processed", payload={"payment_id": "P99"}, created_at=datetime.now() - timedelta(seconds=1)),
        OutboxRecord(id=3, topic="user.registered", payload={"user_id": 42}, created_at=datetime.now() + timedelta(seconds=5))  # Future — won't publish yet
    ])

    print(f"Polling outbox. Records pending: {len(publisher.outbox)}")
    publisher.publish_pending()
    print(f"After poll, remaining: {len(publisher.outbox)}")