from __future__ import absolute_import, unicode_literals

import datetime

timezonenames = {
    'ut': 0, 'gmt': 0, 'z': 0,
    'adt': -3, 'ast': -4, 'at': -4,
    'edt': -4, 'est': -5, 'et': -5,
    'cdt': -5, 'cst': -6, 'ct': -6,
    'mdt': -6, 'mst': -7, 'mt': -7,
    'pdt': -7, 'pst': -8, 'pt': -8,
    'a': -1, 'n': 1,
    'm': -12, 'y': 12,
}
# W3 date and time format parser
# http://www.w3.org/TR/NOTE-datetime
# Also supports MSSQL-style datetimes as defined at:
# http://msdn.microsoft.com/en-us/library/ms186724.aspx
# (basically, allow a space as a date/time/timezone separator)
def _parse_date_w3dtf(datestr):
    if not datestr.strip():
        return None
    parts = datestr.lower().split('t')
    if len(parts) == 1:
        # This may be a date only, or may be an MSSQL-style date
        parts = parts[0].split()
        if len(parts) == 1:
            # Treat this as a date only
            parts.append('00:00:00z')
    elif len(parts) > 2:
        return None
    date = parts[0].split('-', 2)
    if not date or len(date[0]) != 4:
        return None
    # Ensure that `date` has 3 elements. Using '1' sets the default
    # month to January and the default day to the 1st of the month.
    date.extend(['1'] * (3 - len(date)))
    try:
        year, month, day = [int(i) for i in date]
    except ValueError:
        # `date` may have more than 3 elements or may contain
        # non-integer strings.
        return None
    if parts[1].endswith('z'):
        parts[1] = parts[1][:-1]
        parts.append('z')
    # Append the numeric timezone offset, if any, to parts.
    # If this is an MSSQL-style date then parts[2] already contains
    # the timezone information, so `append()` will not affect it.
    # Add 1 to each value so that if `find()` returns -1 it will be
    # treated as False.
    loc = parts[1].find('-') + 1 or parts[1].find('+') + 1 or len(parts[1]) + 1
    loc = loc - 1
    parts.append(parts[1][loc:])
    parts[1] = parts[1][:loc]
    time = parts[1].split(':', 2)
    # Ensure that time has 3 elements. Using '0' means that the
    # minutes and seconds, if missing, will default to 0.
    time.extend(['0'] * (3 - len(time)))
    tzhour = 0
    tzmin = 0
    if parts[2][:1] in ('-', '+'):
        try:
            tzhour = int(parts[2][1:3])
            tzmin = int(parts[2][4:])
        except ValueError:
            return None
        if parts[2].startswith('-'):
            tzhour = tzhour * -1
            tzmin = tzmin * -1
    else:
        tzhour = timezonenames.get(parts[2], 0)
    try:
        hour, minute, second = [int(float(i)) for i in time]
    except ValueError:
        return None
    # Create the datetime object and timezone delta objects
    try:
        stamp = datetime.datetime(year, month, day, hour, minute, second)
    except ValueError:
        return None
    delta = datetime.timedelta(0, 0, 0, 0, tzmin, tzhour)
    # Return the date and timestamp in a UTC 9-tuple
    try:
        return (stamp - delta).utctimetuple()
    except (OverflowError, ValueError):
        # IronPython throws ValueErrors instead of OverflowErrors
        return None
