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