"Implementation of tzinfo classes for use with datetime.datetime."

import time

from datetime import timedelta, tzinfo

from django.utils.encoding import smart_unicode, smart_str, DEFAULT_LOCALE_ENCODING

class FixedOffset(tzinfo):

    "Fixed offset in minutes east from UTC."

    def __init__(self, offset):

        if isinstance(offset, timedelta):

            self.__offset = offset

            offset = self.__offset.seconds // 60

        else:

            self.__offset = timedelta(minutes=offset)

        sign = offset < 0 and '-' or '+'

        self.__name = u"%s%02d%02d" % (sign, abs(offset) / 60., abs(offset) % 60)

    def __repr__(self):

        return self.__name

    def utcoffset(self, dt):

        return self.__offset

    def tzname(self, dt):

        return self.__name

    def dst(self, dt):

        return timedelta(0)

class LocalTimezone(tzinfo):

    "Proxy timezone information from time module."

    def __init__(self, dt):

        tzinfo.__init__(self)

        self._tzname = self.tzname(dt)

    def __repr__(self):

        return smart_str(self._tzname)

    def utcoffset(self, dt):

        if self._isdst(dt):

            return timedelta(seconds=-time.altzone)

        else:

            return timedelta(seconds=-time.timezone)

    def dst(self, dt):

        if self._isdst(dt):

            return timedelta(seconds=-time.altzone) - timedelta(seconds=-time.timezone)

        else:

            return timedelta(0)

    def tzname(self, dt):

        try:

            return smart_unicode(time.tzname[self._isdst(dt)],

                                 DEFAULT_LOCALE_ENCODING)

        except UnicodeDecodeError:

            return None

    def _isdst(self, dt):

        tt = (dt.year, dt.month, dt.day, dt.hour, dt.minute, dt.second, dt.weekday(), 0, -1)

        try:

            stamp = time.mktime(tt)

        except (OverflowError, ValueError):

            # 32 bit systems can't handle dates after Jan 2038, and certain

            # systems can't handle dates before ~1901-12-01:

            #

            # >>> time.mktime((1900, 1, 13, 0, 0, 0, 0, 0, 0))

            # OverflowError: mktime argument out of range

            # >>> time.mktime((1850, 1, 13, 0, 0, 0, 0, 0, 0))

            # ValueError: year out of range

            #

            # In this case, we fake the date, because we only care about the

            # DST flag.

            tt = (2037,) + tt[1:]

            stamp = time.mktime(tt)

        tt = time.localtime(stamp)

        return tt.tm_isdst > 0