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from abc import ABCMeta, abstractmethod
from datetime import timedelta
import random
class BaseTrigger(metaclass=ABCMeta):
"""Abstract base class that defines the interface that every trigger must implement."""
__slots__ = ()
@abstractmethod
def get_next_fire_time(self, previous_fire_time, now):
"""
Returns the next datetime to fire on, If no such datetime can be calculated, returns
``None``.
:param datetime.datetime previous_fire_time: the previous time the trigger was fired
:param datetime.datetime now: current datetime
"""
def _apply_jitter(self, next_fire_time, jitter, now):
"""
Randomize ``next_fire_time`` by adding or subtracting a random value (the jitter). If the
resulting datetime is in the past, returns the initial ``next_fire_time`` without jitter.
``next_fire_time - jitter <= result <= next_fire_time + jitter``
:param datetime.datetime|None next_fire_time: next fire time without jitter applied. If
``None``, returns ``None``.
:param int|None jitter: maximum number of seconds to add or subtract to
``next_fire_time``. If ``None`` or ``0``, returns ``next_fire_time``
:param datetime.datetime now: current datetime
:return datetime.datetime|None: next fire time with a jitter.
"""
if next_fire_time is None or not jitter:
return next_fire_time
next_fire_time_with_jitter = next_fire_time + timedelta(
seconds=random.uniform(-jitter, jitter))
if next_fire_time_with_jitter < now:
# Next fire time with jitter is in the past.
# Ignore jitter to avoid false misfire.
return next_fire_time
return next_fire_time_with_jitter
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