'''Base classes and helpers for building zone specific tzinfo classes'''

from datetime import datetime, timedelta, tzinfo
from bisect import bisect_right
try:
    set
except NameError:
    from sets import Set as set

import pytz
from pytz.exceptions import AmbiguousTimeError, NonExistentTimeError

__all__ = []

_timedelta_cache = {}


def memorized_timedelta(seconds):
    '''Create only one instance of each distinct timedelta'''
    try:
        return _timedelta_cache[seconds]
    except KeyError:
        delta = timedelta(seconds=seconds)
        _timedelta_cache[seconds] = delta
        return delta

_epoch = datetime.utcfromtimestamp(0)
_datetime_cache = {0: _epoch}


def memorized_datetime(seconds):
    '''Create only one instance of each distinct datetime'''
    try:
        return _datetime_cache[seconds]
    except KeyError:
        # NB. We can't just do datetime.utcfromtimestamp(seconds) as this
        # fails with negative values under Windows (Bug #90096)
        dt = _epoch + timedelta(seconds=seconds)
        _datetime_cache[seconds] = dt
        return dt

_ttinfo_cache = {}


def memorized_ttinfo(*args):
    '''Create only one instance of each distinct tuple'''
    try:
        return _ttinfo_cache[args]
    except KeyError:
        ttinfo = (
            memorized_timedelta(args[0]),
            memorized_timedelta(args[1]),
            args[2]
        )
        _ttinfo_cache[args] = ttinfo
        return ttinfo

_notime = memorized_timedelta(0)


def _to_seconds(td):
    '''Convert a timedelta to seconds'''
    return td.seconds + td.days * 24 * 60 * 60


class BaseTzInfo(tzinfo):
    # Overridden in subclass
    _utcoffset = None
    _tzname = None
    zone = None

    def __str__(self):
        return self.zone


class StaticTzInfo(BaseTzInfo):
    '''A timezone that has a constant offset from UTC

    These timezones are rare, as most locations have changed their
    offset at some point in their history
    '''
    def fromutc(self, dt):
        '''See datetime.tzinfo.fromutc'''
        if dt.tzinfo is not None and dt.tzinfo is not self:
            raise ValueError('fromutc: dt.tzinfo is not self')
        return (dt + self._utcoffset).replace(tzinfo=self)

    def utcoffset(self, dt, is_dst=None):
        '''See datetime.tzinfo.utcoffset

        is_dst is ignored for StaticTzInfo, and exists only to
        retain compatibility with DstTzInfo.
        '''
        return self._utcoffset

    def dst(self, dt, is_dst=None):
        '''See datetime.tzinfo.dst

        is_dst is ignored for StaticTzInfo, and exists only to
        retain compatibility with DstTzInfo.
        '''
        return _notime

    def tzname(self, dt, is_dst=None):
        '''See datetime.tzinfo.tzname

        is_dst is ignored for StaticTzInfo, and exists only to
        retain compatibility with DstTzInfo.
        '''
        return self._tzname

    def localize(self, dt, is_dst=False):
        '''Convert naive time to local time'''
        if dt.tzinfo is not None:
            raise ValueError('Not naive datetime (tzinfo is already set)')
        return dt.replace(tzinfo=self)

    def normalize(self, dt, is_dst=False):
        '''Correct the timezone information on the given datetime.

        This is normally a no-op, as StaticTzInfo timezones never have
        ambiguous cases to correct:

        >>> from pytz import timezone
        >>> gmt = timezone('GMT')
        >>> isinstance(gmt, StaticTzInfo)
        True
        >>> dt = datetime(2011, 5, 8, 1, 2, 3, tzinfo=gmt)
        >>> gmt.normalize(dt) is dt
        True

        The supported method of converting between timezones is to use
        datetime.astimezone(). Currently normalize() also works:

        >>> la = timezone('America/Los_Angeles')
        >>> dt = la.localize(datetime(2011, 5, 7, 1, 2, 3))
        >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
        >>> gmt.normalize(dt).strftime(fmt)
        '2011-05-07 08:02:03 GMT (+0000)'
        '''
        if dt.tzinfo is self:
            return dt
        if dt.tzinfo is None:
            raise ValueError('Naive time - no tzinfo set')
        return dt.astimezone(self)

    def __repr__(self):
        return '<StaticTzInfo %r>' % (self.zone,)

    def __reduce__(self):
        # Special pickle to zone remains a singleton and to cope with
        # database changes.
        return pytz._p, (self.zone,)


class DstTzInfo(BaseTzInfo):
    '''A timezone that has a variable offset from UTC

    The offset might change if daylight saving time comes into effect,
    or at a point in history when the region decides to change their
    timezone definition.
    '''
    # Overridden in subclass

    # Sorted list of DST transition times, UTC
    _utc_transition_times = None

    # [(utcoffset, dstoffset, tzname)] corresponding to
    # _utc_transition_times entries
    _transition_info = None

    zone = None

    # Set in __init__

    _tzinfos = None
    _dst = None  # DST offset

    def __init__(self, _inf=None, _tzinfos=None):
        if _inf:
            self._tzinfos = _tzinfos
            self._utcoffset, self._dst, self._tzname = _inf
        else:
            _tzinfos = {}
            self._tzinfos = _tzinfos
            self._utcoffset, self._dst, self._tzname = (
                self._transition_info[0])
            _tzinfos[self._transition_info[0]] = self
            for inf in self._transition_info[1:]:
                if inf not in _tzinfos:
                    _tzinfos[inf] = self.__class__(inf, _tzinfos)

    def fromutc(self, dt):
        '''See datetime.tzinfo.fromutc'''
        if (dt.tzinfo is not None and
                getattr(dt.tzinfo, '_tzinfos', None) is not self._tzinfos):
            raise ValueError('fromutc: dt.tzinfo is not self')
        dt = dt.replace(tzinfo=None)
        idx = max(0, bisect_right(self._utc_transition_times, dt) - 1)
        inf = self._transition_info[idx]
        return (dt + inf[0]).replace(tzinfo=self._tzinfos[inf])

    def normalize(self, dt):
        '''Correct the timezone information on the given datetime

        If date arithmetic crosses DST boundaries, the tzinfo
        is not magically adjusted. This method normalizes the
        tzinfo to the correct one.

        To test, first we need to do some setup

        >>> from pytz import timezone
        >>> utc = timezone('UTC')
        >>> eastern = timezone('US/Eastern')
        >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'

        We next create a datetime right on an end-of-DST transition point,
        the instant when the wallclocks are wound back one hour.

        >>> utc_dt = datetime(2002, 10, 27, 6, 0, 0, tzinfo=utc)
        >>> loc_dt = utc_dt.astimezone(eastern)
        >>> loc_dt.strftime(fmt)
        '2002-10-27 01:00:00 EST (-0500)'

        Now, if we subtract a few minutes from it, note that the timezone
        information has not changed.

        >>> before = loc_dt - timedelta(minutes=10)
        >>> before.strftime(fmt)
        '2002-10-27 00:50:00 EST (-0500)'

        But we can fix that by calling the normalize method

        >>> before = eastern.normalize(before)
        >>> before.strftime(fmt)
        '2002-10-27 01:50:00 EDT (-0400)'

        The supported method of converting between timezones is to use
        datetime.astimezone(). Currently, normalize() also works:

        >>> th = timezone('Asia/Bangkok')
        >>> am = timezone('Europe/Amsterdam')
        >>> dt = th.localize(datetime(2011, 5, 7, 1, 2, 3))
        >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
        >>> am.normalize(dt).strftime(fmt)
        '2011-05-06 20:02:03 CEST (+0200)'
        '''
        if dt.tzinfo is None:
            raise ValueError('Naive time - no tzinfo set')

        # Convert dt in localtime to UTC
        offset = dt.tzinfo._utcoffset
        dt = dt.replace(tzinfo=None)
        dt = dt - offset
        # convert it back, and return it
        return self.fromutc(dt)

    def localize(self, dt, is_dst=False):
        '''Convert naive time to local time.

        This method should be used to construct localtimes, rather
        than passing a tzinfo argument to a datetime constructor.

        is_dst is used to determine the correct timezone in the ambigous
        period at the end of daylight saving time.

        >>> from pytz import timezone
        >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
        >>> amdam = timezone('Europe/Amsterdam')
        >>> dt  = datetime(2004, 10, 31, 2, 0, 0)
        >>> loc_dt1 = amdam.localize(dt, is_dst=True)
        >>> loc_dt2 = amdam.localize(dt, is_dst=False)
        >>> loc_dt1.strftime(fmt)
        '2004-10-31 02:00:00 CEST (+0200)'
        >>> loc_dt2.strftime(fmt)
        '2004-10-31 02:00:00 CET (+0100)'
        >>> str(loc_dt2 - loc_dt1)
        '1:00:00'

        Use is_dst=None to raise an AmbiguousTimeError for ambiguous
        times at the end of daylight saving time

        >>> try:
        ...     loc_dt1 = amdam.localize(dt, is_dst=None)
        ... except AmbiguousTimeError:
        ...     print('Ambiguous')
        Ambiguous

        is_dst defaults to False

        >>> amdam.localize(dt) == amdam.localize(dt, False)
        True

        is_dst is also used to determine the correct timezone in the
        wallclock times jumped over at the start of daylight saving time.

        >>> pacific = timezone('US/Pacific')
        >>> dt = datetime(2008, 3, 9, 2, 0, 0)
        >>> ploc_dt1 = pacific.localize(dt, is_dst=True)
        >>> ploc_dt2 = pacific.localize(dt, is_dst=False)
        >>> ploc_dt1.strftime(fmt)
        '2008-03-09 02:00:00 PDT (-0700)'
        >>> ploc_dt2.strftime(fmt)
        '2008-03-09 02:00:00 PST (-0800)'
        >>> str(ploc_dt2 - ploc_dt1)
        '1:00:00'

        Use is_dst=None to raise a NonExistentTimeError for these skipped
        times.

        >>> try:
        ...     loc_dt1 = pacific.localize(dt, is_dst=None)
        ... except NonExistentTimeError:
        ...     print('Non-existent')
        Non-existent
        '''
        if dt.tzinfo is not None:
            raise ValueError('Not naive datetime (tzinfo is already set)')

        # Find the two best possibilities.
        possible_loc_dt = set()
        for delta in [timedelta(days=-1), timedelta(days=1)]:
            loc_dt = dt + delta
            idx = max(0, bisect_right(
                self._utc_transition_times, loc_dt) - 1)
            inf = self._transition_info[idx]
            tzinfo = self._tzinfos[inf]
            loc_dt = tzinfo.normalize(dt.replace(tzinfo=tzinfo))
            if loc_dt.replace(tzinfo=None) == dt:
                possible_loc_dt.add(loc_dt)

        if len(possible_loc_dt) == 1:
            return possible_loc_dt.pop()

        # If there are no possibly correct timezones, we are attempting
        # to convert a time that never happened - the time period jumped
        # during the start-of-DST transition period.
        if len(possible_loc_dt) == 0:
            # If we refuse to guess, raise an exception.
            if is_dst is None:
                raise NonExistentTimeError(dt)

            # If we are forcing the pre-DST side of the DST transition, we
            # obtain the correct timezone by winding the clock forward a few
            # hours.