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41 lines
1.4 KiB
Python
41 lines
1.4 KiB
Python
"""Cron math for the ``schedule`` trigger: validate + advance ``next_fire_at``."""
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from __future__ import annotations
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from datetime import UTC, datetime
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from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
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from croniter import CroniterBadCronError, croniter
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class InvalidCronError(ValueError):
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"""Raised when a cron expression or timezone fails validation."""
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def validate_cron(cron: str, timezone: str) -> None:
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"""Raise ``InvalidCronError`` if cron or timezone are unusable."""
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try:
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ZoneInfo(timezone)
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except ZoneInfoNotFoundError as exc:
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raise InvalidCronError(f"unknown timezone {timezone!r}") from exc
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try:
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croniter(cron)
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except (CroniterBadCronError, ValueError) as exc:
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raise InvalidCronError(f"invalid cron {cron!r}: {exc}") from exc
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def compute_next_fire_at(cron: str, timezone: str, *, after: datetime) -> datetime:
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"""Return the next moment matching ``cron`` in ``timezone`` strictly after ``after``.
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The result is normalized to UTC for storage. ``after`` is converted into the
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given timezone before evaluation so DST and IANA rules apply correctly.
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"""
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tz = ZoneInfo(timezone)
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base = (
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after.astimezone(tz)
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if after.tzinfo
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else after.replace(tzinfo=UTC).astimezone(tz)
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)
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nxt: datetime = croniter(cron, base).get_next(datetime)
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return nxt.astimezone(UTC)
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