# Date/time manipulation

import datetime

import dateutil.tz

import strings

import time

utc = dateutil.tz.tzutc()

local = dateutil.tz.tzlocal()

def naive2utc(datetime_):

    assert datetime_.tzinfo == None

    return datetime_.replace(tzinfo=utc)

def aware2local(datetime_): return datetime_.astimezone(local)

def from_timestamp(utc_timestamp):

    return naive2utc(datetime.datetime.utcfromtimestamp(utc_timestamp))

def timestamp(datetime_):

    datetime_ = aware2local(datetime_)

    return int(time.mktime(datetime_.timetuple())) + datetime_.microsecond/1e6

epoch = from_timestamp(0)

def total_seconds(timedelta_): return timestamp(epoch + timedelta_)

def now(): return datetime.datetime.now(utc)

def strftime(format, datetime_):

    '''datetime.strftime() can't handle years before 1900'''

    return (datetime_.replace(year=epoch.year, day=1).strftime(format

        .replace('%Y', '%%Y')

        .replace('%d', '%%d')

        )

        .replace('%Y', '%04d' % datetime_.year)

        .replace('%d', '%02d' % datetime_.day)

        )

def strtotime(str_, default=epoch):

    import dateutil.parser

    return dateutil.parser.parse(str_, default=default)

def could_be_year(str_): return str_.isdigit() and len(str_) == 4

def could_be_day(str_): return str_.isdigit() and len(str_) <= 2

def parse_date_range(str_, range_sep='-', part_sep=' '):

    str_ = strings.single_space(str_)

    # range_sep might be used as date part separator instead

    if str_.find(part_sep) < 0: return (str_, None)

    start, sep, end = str_.partition(range_sep)

    if sep == '': return (str_, None) # not a range

    start = start.split(part_sep)

    end = end.split(part_sep)

    # Has form M D1-D2 or M D1-D2 Y (not M1 Y1-M2 Y2 or M1 D1-M2 D2)

    if len(start) == 2 and (len(end) == 1 or (

            len(end) == 2 and could_be_day(start[-1]) and could_be_day(end[0])

            and could_be_year(end[-1])

        )):

        end.insert(0, start[0]) # make end fully specified

    ct_diff = len(end) - len(start)

    # Has form D1-D2 M Y, M1 D1-M2 D2 Y, M1-M2 Y, etc.

    if ct_diff > 0: start += end[-ct_diff:] # make start fully specified

    # Other forms are invalid and will be left as-is

    return (start, end)