Implement a retry queue with visibility timeout in Python

import time
from collections import deque


class SimpleQueue:
    def __init__(self, visibility_timeout=2):
        self.queue = deque()
        self.in_flight = {}
        self.visibility_timeout = visibility_timeout

    def send(self, message):
        self.queue.append(message)

    def receive(self):
        if self.queue:
            message = self.queue.popleft()
            self.in_flight[message] = time.time() + self.visibility_timeout
            return message
        return None

    def delete(self, message):
        if message in self.in_flight:
            del self.in_flight[message]

    def retry_after_timeout(self):
        current_time = time.time()
        expired = [
            msg for msg, deadline in self.in_flight.items() if deadline <= current_time
        ]
        for msg in expired:
            del self.in_flight[msg]
            self.queue.appendleft(msg)
        return expired


if __name__ == "__main__":
    queue = SimpleQueue(visibility_timeout=1)
    queue.send("task-1")
    queue.send("task-2")

    print("First receive:", queue.receive())
    time.sleep(1.2)
    requeued = queue.retry_after_timeout()
    print("Requeued after timeout:", requeued)
    print("Next receive:", queue.receive())
    queue.delete("task-1")
    print("Queue size:", len(queue.queue))