Generic Cell Rate Algorithm example

gcra.py

class RateLimit:
    def __init__(self, count: int, period: timedelta) -> None:
        self.count = count
        self.period = period

    @property
    def inverse(self) -> float:
        return self.period.total_seconds() / self.count


class Store:

    def get_tat(self, key: str) -> datetime:
        # This should return a previous tat for the key or the current time.
        pass
        
    def set_tat(self, key: str, tat: datetime) -> None:
        pass

    def update(self, key: str, limit: RateLimit) -> bool:
        now = datetime.utcnow()
        tat = max(self.get_tat(key), now)
        separation = (tat - now).total_seconds() 
        max_interval = limit.period.total_seconds() - limit.inverse
        if separation > max_interval:
            reject = True
        else:
            reject = False
            new_tat = max(tat, now) + timedelta(seconds=limit.inverse)
            self.set_tat(key, new_tat)
        return reject