Mock NATS queue group load balancing in Python

import random
import time
from collections import defaultdict


class MockQueueGroup:
    """Mock a NATS queue group: each message is delivered to exactly one subscriber."""

    def __init__(self, subscribers):
        self.subscribers = subscribers

    def publish(self, message):
        receiver = random.choice(self.subscribers)
        time.sleep(0.01)  # simulate processing time
        return receiver

    def run_demo(self, messages, message_label="Task"):
        deliveries = defaultdict(int)
        for idx, msg in enumerate(messages, start=1):
            worker = self.publish(msg)
            deliveries[worker] += 1
            print(f"{message_label} #{idx} -> {worker} handled: {msg}")

        print("\nDelivery distribution after load balancing:")
        total = len(messages)
        for worker in self.subscribers:
            count = deliveries[worker]
            percent = (count / total) * 100
            print(f"{worker}: {count} messages ({percent:.1f}%)")


if __name__ == "__main__":
    workers = ["worker-A", "worker-B", "worker-C"]
    tasks = list(range(1, 21))  # 20 tasks to load balance
    queue_group = MockQueueGroup(workers)
    queue_group.run_demo(tasks)