text: from __future__ import annotations
  
  from datetime import date, datetime, time, timedelta, tzinfo
  from typing import Any, Optional
  
  import attr
  
  from ..abc import Trigger
  from ..marshalling import marshal_date, marshal_timezone, unmarshal_date, unmarshal_timezone
  from ..util import timezone_repr
  from ..validators import as_date, as_timezone, require_state_version
  
  
  @attr.define(kw_only=True)
  class CalendarIntervalTrigger(Trigger):
      """
      Runs the task on specified calendar-based intervals always at the same exact time of day.
  
      When calculating the next date, the ``years`` and ``months`` parameters are first added to the
      previous date while keeping the day of the month constant. This is repeated until the resulting
      date is valid. After that, the ``weeks`` and ``days`` parameters are added to that date.
      Finally, the date is combined with the given time (hour, minute, second) to form the final
      datetime.
  
      This means that if the ``days`` or ``weeks`` parameters are not used, the task will always be
      executed on the same day of the month at the same wall clock time, assuming the date and time
      are valid.
  
      If the resulting datetime is invalid due to a daylight saving forward shift, the date is
      discarded and the process moves on to the next date. If instead the datetime is ambiguous due
      to a backward DST shift, the earlier of the two resulting datetimes is used.
  
      If no previous run time is specified when requesting a new run time (like when starting for the
      first time or resuming after being paused), ``start_date`` is used as a reference and the next
      valid datetime equal to or later than the current time will be returned. Otherwise, the next
      valid datetime starting from the previous run time is returned, even if it's in the past.
  
      .. warning:: Be wary of setting a start date near the end of the month (29. – 31.) if you have
          ``months`` specified in your interval, as this will skip the months where those days do not
          exist. Likewise, setting the start date on the leap day (February 29th) and having
          ``years`` defined may cause some years to be skipped.
  
          Users are also discouraged from  using a time inside the target timezone's DST switching
          period (typically around 2 am) since a date could either be skipped or repeated due to the
          specified wall clock time either occurring twice or not at all.
  
      :param years: number of years to wait
      :param months: number of months to wait
      :param weeks: number of weeks to wait
      :param days: number of days to wait
      :param hour: hour to run the task at
      :param minute: minute to run the task at
      :param second: second to run the task at
      :param start_date: first date to trigger on (defaults to current date if omitted)
      :param end_date: latest possible date to trigger on
      :param timezone: time zone to use for calculating the next fire time
      """
  
      years: int = 0
      months: int = 0
      weeks: int = 0
      days: int = 0
      hour: int = 0
      minute: int = 0
      second: int = 0
      start_date: date = attr.field(converter=as_date, factory=date.today)
      end_date: date | None = attr.field(converter=as_date, default=None)
      timezone: tzinfo = attr.field(converter=as_timezone, default='local')
      _time: time = attr.field(init=False, eq=False)
      _last_fire_date: Optional[date] = attr.field(init=False, eq=False, default=None)
  
      def __attrs_post_init__(self) -> None:
          self._time = time(self.hour, self.minute, self.second, tzinfo=self.timezone)
  
          if self.years == self.months == self.weeks == self.days == 0:
              raise ValueError('interval must be at least 1 day long')
  
          if self.start_date and self.end_date and self.start_date > self.end_date:
              raise ValueError('end_date cannot be earlier than start_date')
  
      def next(self) -> Optional[datetime]:
          previous_date: date = self._last_fire_date
          while True:
              if previous_date:
                  year, month = previous_date.year, previous_date.month
                  while True:
                      month += self.months
                      year += self.years + (month - 1) // 12
                      month = (month - 1) % 12 + 1
                      try:
                          next_date = date(year, month, previous_date.day)
                      except ValueError:
                          pass  # Nonexistent date
                      else:
                          next_date += timedelta(self.days + self.weeks * 7)
                          break
              else:
                  next_date = self.start_date
  
              # Don't return any date past end_date
              if self.end_date and next_date > self.end_date:
                  return None
  
              # Combine the date with the designated time and normalize the result
              timestamp = datetime.combine(next_date, self._time).timestamp()
              next_time = datetime.fromtimestamp(timestamp, self.timezone)
  
              # Check if the time is off due to normalization and a forward DST shift
              if next_time.time() != self._time:
                  previous_date = next_time.date()
              else:
                  self._last_fire_date = next_date
                  return next_time
  
      def __getstate__(self) -> dict[str, Any]:
          return {
              'version': 1,
              'interval': [self.years, self.months, self.weeks, self.days],
              'time': [self._time.hour, self._time.minute, self._time.second],
              'start_date': marshal_date(self.start_date),
              'end_date': marshal_date(self.end_date),
              'timezone': marshal_timezone(self.timezone),
              'last_fire_date': marshal_date(self._last_fire_date)
          }
  
      def __setstate__(self, state: dict[str, Any]) -> None:
          require_state_version(self, state, 1)
          self.years, self.months, self.weeks, self.days = state['interval']
          self.start_date = unmarshal_date(state['start_date'])
          self.end_date = unmarshal_date(state['end_date'])
          self.timezone = unmarshal_timezone(state['timezone'])
          self._time = time(*state['time'], tzinfo=self.timezone)
          self._last_fire_date = unmarshal_date(state['last_fire_date'])
  
      def __repr__(self) -> str:
          fields = []
          for field in 'years', 'months', 'weeks', 'days':
              value = getattr(self, field)
              if value > 0:
                  fields.append(f'{field}={value}')
  
          fields.append(f'time={self._time.isoformat()!r}')
          fields.append(f"start_date='{self.start_date}'")
          if self.end_date:
              fields.append(f"end_date='{self.end_date}'")
  
          fields.append(f'timezone={timezone_repr(self.timezone)!r}')
          return f'{self.__class__.__name__}({", ".join(fields)})'
  