# 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=' '):
    default = (str_, None)
    # range_sep might be used as date part separator instead
    if str_.find(part_sep) < 0: return default
    
    start, sep, end = str_.partition(range_sep)
    if sep == '': return default # not a range
    start, end = (strings.single_space(d).split(part_sep) for d in (start, end))
    
    # 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 tuple(part_sep.join(d) for d in (start, end))