class Timer:
    def __init__(self, pubsub, timer_length):
        self.timer_length = timer_length
        self.last_tick = 0
        self.pubsub = pubsub
        self.topic = f"tick {self.timer_length}"
    def tick(self, now):
        if (now - self.last_tick) > self.timer_length:
            self.last_tick = now
            self.pubsub.publish(self.topic, {})