import re

import datetime

def id_number_checksum(gd):

    """

    Calculates a Swedish ID number checksum, using the

    "Luhn"-algoritm

    """

    n = s = 0

    for c in (gd['year'] + gd['month'] + gd['day'] + gd['serial']):

        tmp = ((n % 2) and 1 or 2) * int(c)

        if tmp > 9:

            tmp = sum([int(i) for i in str(tmp)])

        s += tmp

        n += 1

    if (s % 10) == 0:

        return 0

    return (((s / 10) + 1) * 10) - s

def validate_id_birthday(gd, fix_coordination_number_day=True):

    """

    Validates the birth_day and returns the datetime.date object for

    the birth_day.

    If the date is an invalid birth day, a ValueError will be raised.

    """

    today = datetime.date.today()

    day = int(gd['day'])

    if fix_coordination_number_day and day > 60:

        day -= 60

    if gd['century'] is None:

        # The century was not specified, and need to be calculated from todays date

        current_year = today.year

        year = int(today.strftime('%Y')) - int(today.strftime('%y')) + int(gd['year'])

        if ('%s%s%02d' % (gd['year'], gd['month'], day)) > today.strftime('%y%m%d'):

            year -= 100

        # If the person is older than 100 years

        if gd['sign'] == '+':

            year -= 100

    else:

        year = int(gd['century'] + gd['year'])

        # Make sure the year is valid

        # There are no swedish personal identity numbers where year < 1800

        if year < 1800:

            raise ValueError

    # ValueError will be raise for invalid dates

    birth_day = datetime.date(year, int(gd['month']), day)

    # birth_day must not be in the future

    if birth_day > today:

        raise ValueError

    return birth_day

def format_personal_id_number(birth_day, gd):

    # birth_day.strftime cannot be used, since it does not support dates < 1900

    return unicode(str(birth_day.year) + gd['month'] + gd['day'] + gd['serial'] + gd['checksum'])

def format_organisation_number(gd):

    if gd['century'] is None:

        century = ''

    else:

        century = gd['century']

    return unicode(century + gd['year'] + gd['month'] + gd['day'] + gd['serial'] + gd['checksum'])

def valid_organisation(gd):

    return gd['century'] in (None, 16) and \

        int(gd['month']) >= 20 and \

        gd['sign'] in (None, '-') and \

        gd['year'][0] in ('2', '5', '7', '8', '9') # group identifier