class MessageBus:
    def __init__(self):
        self.messages = []

    def send(self, sender_id, receiver_id, payload):
        self.messages.append({
            "sender_id": sender_id,
            "receiver_id": receiver_id,
            "payload": payload,
            "timestamp": time.time()
        })

    def receive(self, receiver_id):
        return [m for m in self.messages if m["receiver_id"] == receiver_id]
