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from __future__ import absolute_import

import re

from datetime import datetime, timedelta
from dateutil.relativedelta import relativedelta

from .utils.timeutils import (timedelta_seconds, weekday,
                              remaining, humanize_seconds)


class ParseException(Exception):
    """Raised by :class:`crontab_parser` when input can't be parsed."""


def _is_iterable(obj):
    try:
        iter(obj)
    except TypeError:
        return False
    return True


class schedule(object):
    relative = False

    def __init__(self, run_every=None, relative=False):
        self.run_every = run_every
        self.relative = relative

    def remaining_estimate(self, last_run_at):
        """Returns when the periodic task should run next as a timedelta."""
        return remaining(last_run_at, self.run_every, relative=self.relative)

    def is_due(self, last_run_at):
        """Returns tuple of two items `(is_due, next_time_to_run)`,
where next time to run is in seconds.

e.g.

* `(True, 20)`, means the task should be run now, and the next
time to run is in 20 seconds.

* `(False, 12)`, means the task should be run in 12 seconds.

You can override this to decide the interval at runtime,
but keep in mind the value of :setting:`CELERYBEAT_MAX_LOOP_INTERVAL`,
which decides the maximum number of seconds celerybeat can sleep
between re-checking the periodic task intervals. So if you
dynamically change the next run at value, and the max interval is
set to 5 minutes, it will take 5 minutes for the change to take
effect, so you may consider lowering the value of
:setting:`CELERYBEAT_MAX_LOOP_INTERVAL` if responsiveness is of
importance to you.

"""
        rem_delta = self.remaining_estimate(last_run_at)
        rem = timedelta_seconds(rem_delta)
        if rem == 0:
            return True, timedelta_seconds(self.run_every)
        return False, rem

    def __repr__(self):
        return "<freq: %s>" % (
                    humanize_seconds(timedelta_seconds(self.run_every)), )

    def __eq__(self, other):
        if isinstance(other, schedule):
            return self.run_every == other.run_every
        return self.run_every == other


class crontab_parser(object):
    """Parser for crontab expressions. Any expression of the form 'groups'
(see BNF grammar below) is accepted and expanded to a set of numbers.
These numbers represent the units of time that the crontab needs to
run on::

digit :: '0'..'9'
dow :: 'a'..'z'
number :: digit+ | dow+
steps :: number
range :: number ( '-' number ) ?
numspec :: '*' | range
expr :: numspec ( '/' steps ) ?
groups :: expr ( ',' expr ) *

The parser is a general purpose one, useful for parsing hours, minutes and
day_of_week expressions. Example usage::

>>> minutes = crontab_parser(60).parse("*/15")
[0, 15, 30, 45]
>>> hours = crontab_parser(24).parse("*/4")
[0, 4, 8, 12, 16, 20]
>>> day_of_week = crontab_parser(7).parse("*")
[0, 1, 2, 3, 4, 5, 6]

"""
    ParseException = ParseException

    _range = r'(\w+?)-(\w+)'
    _steps = r'/(\w+)?'
    _star = r'\*'

    def __init__(self, max_=60):
        self.max_ = max_
        self.pats = (
                (re.compile(self._range + self._steps), self._range_steps),
                (re.compile(self._range), self._expand_range),
                (re.compile(self._star + self._steps), self._star_steps),
                (re.compile('^' + self._star + '$'), self._expand_star))

    def parse(self, spec):
        acc = set()
        for part in spec.split(','):
            if not part:
                raise self.ParseException("empty part")
            acc |= set(self._parse_part(part))
        return acc

    def _parse_part(self, part):
        for regex, handler in self.pats:
            m = regex.match(part)
            if m:
                return handler(m.groups())
        return self._expand_range((part, ))

    def _expand_range(self, toks):
        fr = self._expand_number(toks[0])
        if len(toks) > 1:
            to = self._expand_number(toks[1])
            return range(fr, min(to + 1, self.max_ + 1))
        return [fr]

    def _range_steps(self, toks):
        if len(toks) != 3 or not toks[2]:
            raise self.ParseException("empty filter")
        return self._filter_steps(self._expand_range(toks[:2]), int(toks[2]))

    def _star_steps(self, toks):
        if not toks or not toks[0]:
            raise self.ParseException("empty filter")
        return self._filter_steps(self._expand_star(), int(toks[0]))

    def _filter_steps(self, numbers, steps):
        return [n for n in numbers if n % steps == 0]

    def _expand_star(self, *args):
        return range(self.max_)

    def _expand_number(self, s):
        if isinstance(s, basestring) and s[0] == '-':
            raise self.ParseException("negative numbers not supported")
        try:
            i = int(s)
        except ValueError:
            try:
                i = weekday(s)
            except KeyError:
                raise ValueError("Invalid weekday literal '%s'." % s)
        return i


class crontab(schedule):
    """A crontab can be used as the `run_every` value of a
:class:`PeriodicTask` to add cron-like scheduling.

Like a :manpage:`cron` job, you can specify units of time of when
you would like the task to execute. It is a reasonably complete
implementation of cron's features, so it should provide a fair
degree of scheduling needs.

You can specify a minute, an hour, and/or a day of the week in any
of the following formats:

.. attribute:: minute

- A (list of) integers from 0-59 that represent the minutes of
an hour of when execution should occur; or
- A string representing a crontab pattern. This may get pretty
advanced, like `minute="*/15"` (for every quarter) or
`minute="1,13,30-45,50-59/2"`.

.. attribute:: hour

- A (list of) integers from 0-23 that represent the hours of
a day of when execution should occur; or
- A string representing a crontab pattern. This may get pretty
advanced, like `hour="*/3"` (for every three hours) or
`hour="0,8-17/2"` (at midnight, and every two hours during
office hours).

.. attribute:: day_of_week

- A (list of) integers from 0-6, where Sunday = 0 and Saturday =
6, that represent the days of a week that execution should
occur.
- A string representing a crontab pattern. This may get pretty
advanced, like `day_of_week="mon-fri"` (for weekdays only).
(Beware that `day_of_week="*/2"` does not literally mean
"every two days", but "every day that is divisible by two"!)

"""

    @staticmethod
    def _expand_cronspec(cronspec, max_):
        """Takes the given cronspec argument in one of the forms::

int (like 7)
basestring (like '3-5,*/15', '*', or 'monday')
set (like set([0,15,30,45]))
list (like [8-17])

And convert it to an (expanded) set representing all time unit
values on which the crontab triggers. Only in case of the base
type being 'basestring', parsing occurs. (It is fast and
happens only once for each crontab instance, so there is no
significant performance overhead involved.)

For the other base types, merely Python type conversions happen.

The argument `max_` is needed to determine the expansion of '*'.

"""
        if isinstance(cronspec, int):
            result = set([cronspec])
        elif isinstance(cronspec, basestring):
            result = crontab_parser(max_).parse(cronspec)
        elif isinstance(cronspec, set):
            result = cronspec
        elif _is_iterable(cronspec):
            result = set(cronspec)
        else:
            raise TypeError(
                    "Argument cronspec needs to be of any of the "
                    "following types: int, basestring, or an iterable type. "
                    "'%s' was given." % type(cronspec))

        # assure the result does not exceed the max
        for number in result:
            if number >= max_:
                raise ValueError(
                        "Invalid crontab pattern. Valid "
                        "range is 0-%d. '%d' was found." % (max_ - 1, number))

        return result

    def __init__(self, minute='*', hour='*', day_of_week='*',
            nowfun=datetime.utcnow):
        self._orig_minute = minute
        self._orig_hour = hour
        self._orig_day_of_week = day_of_week
        self.hour = self._expand_cronspec(hour, 24)
        self.minute = self._expand_cronspec(minute, 60)
        self.day_of_week = self._expand_cronspec(day_of_week, 7)
        self.nowfun = nowfun

    def __repr__(self):
        return "<crontab: %s %s %s (m/h/d)>" % (self._orig_minute or "*",
                                                self._orig_hour or "*",
                                                self._orig_day_of_week or "*")

    def __reduce__(self):
        return (self.__class__, (self._orig_minute,
                                 self._orig_hour,
                                 self._orig_day_of_week), None)

    def remaining_estimate(self, last_run_at):
        """Returns when the periodic task should run next as a timedelta."""
        weekday = last_run_at.isoweekday()
        weekday = 0 if weekday == 7 else weekday # Sunday is day 0, not day 7.

        execute_this_hour = (weekday in self.day_of_week and
                                last_run_at.hour in self.hour and
                                    last_run_at.minute < max(self.minute))

        if execute_this_hour:
            next_minute = min(minute for minute in self.minute
                                        if minute > last_run_at.minute)
            delta = relativedelta(minute=next_minute,
                                  second=0,
                                  microsecond=0)
        else:
            next_minute = min(self.minute)
            execute_today = (weekday in self.day_of_week and
                                 last_run_at.hour < max(self.hour))

            if execute_today:
                next_hour = min(hour for hour in self.hour
                                        if hour > last_run_at.hour)
                delta = relativedelta(hour=next_hour,
                                      minute=next_minute,
                                      second=0,
                                      microsecond=0)
            else:
                next_hour = min(self.hour)
                next_day = min([day for day in self.day_of_week
                                    if day > weekday] or
                               self.day_of_week)
                add_week = next_day == weekday

                delta = relativedelta(weeks=add_week and 1 or 0,
                                      weekday=(next_day - 1) % 7,
                                      hour=next_hour,
                                      minute=next_minute,
                                      second=0,
                                      microsecond=0)

        return remaining(last_run_at, delta, now=self.nowfun())

    def is_due(self, last_run_at):
        """Returns tuple of two items `(is_due, next_time_to_run)`,
where next time to run is in seconds.

See :meth:`celery.schedules.schedule.is_due` for more information.

"""
        rem_delta = self.remaining_estimate(last_run_at)
        rem = timedelta_seconds(rem_delta)
        due = rem == 0
        if due:
            rem_delta = self.remaining_estimate(last_run_at=self.nowfun())
            rem = timedelta_seconds(rem_delta)
        return due, rem

    def __eq__(self, other):
        if isinstance(other, crontab):
            return (other.day_of_week == self.day_of_week and
                    other.hour == self.hour and
                    other.minute == self.minute)
        return other is self


def maybe_schedule(s, relative=False):
    if isinstance(s, int):
        s = timedelta(seconds=s)
    if isinstance(s, timedelta):
        return schedule(s, relative)
    return s
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