cronlike.py

from datetime import datetime
from collections import namedtuple

ANY = '*'


class JobTime(namedtuple('JobTime', ['minute', 'hour',
                                     'day_of_month',
                                     'month', 'day_of_week'])):
    _field_to_datetime = [('month', 'month'),
                          ('day_of_month', 'day'),
                          ('hour', 'hour'),
                          ('minute', 'minute')]

                          # 'day_of_week': 'weekday'}

    @classmethod
    def fromlist(cls, spec):
        return cls(*[slot if slot == ANY else int(slot) for slot in spec])

    def to_datetime(self):
        now = datetime.now()
        args = [now.year]
        items = self._asdict()
        for field, name in self._field_to_datetime:
            item = items[field]
            if item == ANY:
                item = getattr(now, name)
            args.append(item)
        dt = datetime(*args)

        if self.day_of_week != ANY and self.day_of_month != ANY:
            if self.day_of_week != dt.weekday:
                raise ValueError("%r won't run this year!" % self)
        elif self.day_of_week != ANY and self.day_of_month == ANY:
            difference = self.day_of_week - dt.weekday()
            offset = (7 + difference) % 7
            return dt.replace(day=dt.day + offset)
        else:
            return dt


def parse(spec):
    parts = spec.split(None, 5)
    if len(parts) != 6:
        raise ValueError
    time_spec, command = parts[:5], parts[5:]
    return JobTime.fromlist(time_spec)