How to Simulate an Outbox Pattern with Reliable Retry in Python

import time
import itertools

class Outbox:
    def __init__(self):
        self._records = []
        self._seq = itertools.count(1)

    def publish(self, topic, payload):
        record = {
            "id": next(self._seq),
            "topic": topic,
            "payload": payload,
            "status": "pending",
            "attempts": 0,
        }
        self._records.append(record)
        return record

    def deliver(self, mock_delivery=lambda rec: True):
        delivered = []
        for record in self._records:
            if record["status"] != "pending":
                continue
            if mock_delivery(record):
                record["status"] = "delivered"
                record["delivered_at"] = time.time()
                delivered.append(record["id"])
            else:
                record["attempts"] += 1
        return delivered

    def pending_records(self):
        return [r for r in self._records if r["status"] == "pending"]


if __name__ == "__main__":
    outbox = Outbox()
    outbox.publish("order.created", {"order_id": 1})
    outbox.publish("payment.success", {"order_id": 1})

    def flaky_delivery(record):
        return record["id"] != 2  # Simulate a temporary failure for id=2

    outbox.deliver(mock_delivery=flaky_delivery)
    retry = outbox.deliver(mock_delivery=lambda rec: True)  # Retry pending

    print("Delivered first pass:", [1] if outbox.pending_records() else [])
    print("Retry delivered:", retry)
    print("Pending after retry:", outbox.pending_records())