from datetime import datetime, timedelta

from tzlocal import get_localzone
import six

from apscheduler.triggers.base import BaseTrigger
from apscheduler.triggers.cron.fields import BaseField, WeekField, DayOfMonthField, DayOfWeekField, DEFAULT_VALUES
from apscheduler.util import datetime_ceil, convert_to_datetime, datetime_repr, astimezone


class CronTrigger(BaseTrigger):
    """
    Triggers when current time matches all specified time constraints, similarly to how the UNIX cron scheduler works.

    :param int|str year: 4-digit year
    :param int|str month: month (1-12)
    :param int|str day: day of the (1-31)
    :param int|str week: ISO week (1-53)
    :param int|str day_of_week: number or name of weekday (0-6 or mon,tue,wed,thu,fri,sat,sun)
    :param int|str hour: hour (0-23)
    :param int|str minute: minute (0-59)
    :param int|str second: second (0-59)
    :param datetime|str start_date: earliest possible date/time to trigger on (inclusive)
    :param datetime|str end_date: latest possible date/time to trigger on (inclusive)
    :param datetime.tzinfo|str timezone: time zone to use for the date/time calculations
                                         (defaults to scheduler timezone)

    .. note:: The first weekday is always **monday**.
    """

    FIELD_NAMES = ('year', 'month', 'day', 'week', 'day_of_week', 'hour', 'minute', 'second')
    FIELDS_MAP = {
        'year': BaseField,
        'month': BaseField,
        'week': WeekField,
        'day': DayOfMonthField,
        'day_of_week': DayOfWeekField,
        'hour': BaseField,
        'minute': BaseField,
        'second': BaseField
    }

    __slots__ = 'timezone', 'start_date', 'end_date', 'fields'

    def __init__(self, year=None, month=None, day=None, week=None, day_of_week=None, hour=None, minute=None,
                 second=None, start_date=None, end_date=None, timezone=None):
        if timezone:
            self.timezone = astimezone(timezone)
        elif start_date and start_date.tzinfo:
            self.timezone = start_date.tzinfo
        elif end_date and end_date.tzinfo:
            self.timezone = end_date.tzinfo
        else:
            self.timezone = get_localzone()

        self.start_date = convert_to_datetime(start_date, self.timezone, 'start_date')
        self.end_date = convert_to_datetime(end_date, self.timezone, 'end_date')

        values = dict((key, value) for (key, value) in six.iteritems(locals())
                      if key in self.FIELD_NAMES and value is not None)
        self.fields = []
        assign_defaults = False
        for field_name in self.FIELD_NAMES:
            if field_name in values:
                exprs = values.pop(field_name)
                is_default = False
                assign_defaults = not values
            elif assign_defaults:
                exprs = DEFAULT_VALUES[field_name]
                is_default = True
            else:
                exprs = '*'
                is_default = True

            field_class = self.FIELDS_MAP[field_name]
            field = field_class(field_name, exprs, is_default)
            self.fields.append(field)

    def _increment_field_value(self, dateval, fieldnum):
        """
        Increments the designated field and resets all less significant fields to their minimum values.

        :type dateval: datetime
        :type fieldnum: int
        :return: a tuple containing the new date, and the number of the field that was actually incremented
        :rtype: tuple
        """

        values = {}
        i = 0
        while i < len(self.fields):
            field = self.fields[i]
            if not field.REAL:
                if i == fieldnum:
                    fieldnum -= 1
                    i -= 1
                else:
                    i += 1
                continue

            if i < fieldnum:
                values[field.name] = field.get_value(dateval)
                i += 1
            elif i > fieldnum:
                values[field.name] = field.get_min(dateval)
                i += 1
            else:
                value = field.get_value(dateval)
                maxval = field.get_max(dateval)
                if value == maxval:
                    fieldnum -= 1
                    i -= 1
                else:
                    values[field.name] = value + 1
                    i += 1

        difference = datetime(**values) - dateval.replace(tzinfo=None)
        return self.timezone.normalize(dateval + difference), fieldnum

    def _set_field_value(self, dateval, fieldnum, new_value):
        values = {}
        for i, field in enumerate(self.fields):
            if field.REAL:
                if i < fieldnum:
                    values[field.name] = field.get_value(dateval)
                elif i > fieldnum:
                    values[field.name] = field.get_min(dateval)
                else:
                    values[field.name] = new_value

        difference = datetime(**values) - dateval.replace(tzinfo=None)
        return self.timezone.normalize(dateval + difference)

    def get_next_fire_time(self, previous_fire_time, now):
        if previous_fire_time:
            start_date = max(now, previous_fire_time + timedelta(microseconds=1))
        else:
            start_date = max(now, self.start_date) if self.start_date else now

        fieldnum = 0
        next_date = datetime_ceil(start_date).astimezone(self.timezone)
        while 0 <= fieldnum < len(self.fields):
            field = self.fields[fieldnum]
            curr_value = field.get_value(next_date)
            next_value = field.get_next_value(next_date)

            if next_value is None:
                # No valid value was found
                next_date, fieldnum = self._increment_field_value(next_date, fieldnum - 1)
            elif next_value > curr_value:
                # A valid, but higher than the starting value, was found
                if field.REAL:
                    next_date = self._set_field_value(next_date, fieldnum, next_value)
                    fieldnum += 1
                else:
                    next_date, fieldnum = self._increment_field_value(next_date, fieldnum)
            else:
                # A valid value was found, no changes necessary
                fieldnum += 1

            # Return if the date has rolled past the end date
            if self.end_date and next_date > self.end_date:
                return None

        if fieldnum >= 0:
            return next_date

    def __str__(self):
        options = ["%s='%s'" % (f.name, f) for f in self.fields if not f.is_default]
        return 'cron[%s]' % (', '.join(options))

    def __repr__(self):
        options = ["%s='%s'" % (f.name, f) for f in self.fields if not f.is_default]
        if self.start_date:
            options.append("start_date='%s'" % datetime_repr(self.start_date))
        return '<%s (%s)>' % (self.__class__.__name__, ', '.join(options))
