"""

DE-specific Form helpers

"""

from django.forms import ValidationError

from django.forms.fields import Field, RegexField, Select, EMPTY_VALUES

from django.utils.translation import ugettext_lazy as _

import re

id_re = re.compile(r"^(?P<residence>\d{10})(?P<origin>\w{1,3})[-\ ]?(?P<birthday>\d{7})[-\ ]?(?P<validity>\d{7})[-\ ]?(?P<checksum>\d{1})$")

class DEZipCodeField(RegexField):

    default_error_messages = {

        'invalid': _('Enter a zip code in the format XXXXX.'),

    }

    def __init__(self, *args, **kwargs):

        super(DEZipCodeField, self).__init__(r'^\d{5}$',

            max_length=None, min_length=None, *args, **kwargs)

class DEStateSelect(Select):

    """

    A Select widget that uses a list of DE states as its choices.

    """

    def __init__(self, attrs=None):

        from de_states import STATE_CHOICES

        super(DEStateSelect, self).__init__(attrs, choices=STATE_CHOICES)

class DEIdentityCardNumberField(Field):

    """

    A German identity card number.

    Checks the following rules to determine whether the number is valid:

        * Conforms to the XXXXXXXXXXX-XXXXXXX-XXXXXXX-X format.

        * No group consists entirely of zeroes.

        * Included checksums match calculated checksums

    Algorithm is documented at http://de.wikipedia.org/wiki/Personalausweis

    """

    default_error_messages = {

        'invalid': _('Enter a valid German identity card number in XXXXXXXXXXX-XXXXXXX-XXXXXXX-X format.'),

    }

    def has_valid_checksum(self, number):

        given_number, given_checksum = number[:-1], number[-1]

        calculated_checksum = 0

        fragment = ""

        parameter = 7

        for i in range(len(given_number)):

            fragment = str(int(given_number[i]) * parameter)

            if fragment.isalnum():

                calculated_checksum += int(fragment[-1])

            if parameter == 1:

                parameter = 7

            elif parameter == 3:

                parameter = 1

            elif parameter ==7:

                parameter = 3

        return str(calculated_checksum)[-1] == given_checksum

    def clean(self, value):

        super(DEIdentityCardNumberField, self).clean(value)

        if value in EMPTY_VALUES:

            return u''

        match = re.match(id_re, value)

        if not match:

            raise ValidationError(self.error_messages['invalid'])

        gd = match.groupdict()

        residence, origin = gd['residence'], gd['origin']

        birthday, validity, checksum = gd['birthday'], gd['validity'], gd['checksum']

        if residence == '0000000000' or birthday == '0000000' or validity == '0000000':

            raise ValidationError(self.error_messages['invalid'])

        all_digits = u"%s%s%s%s" % (residence, birthday, validity, checksum)

        if not self.has_valid_checksum(residence) or not self.has_valid_checksum(birthday) or \

            not self.has_valid_checksum(validity) or not self.has_valid_checksum(all_digits):

                raise ValidationError(self.error_messages['invalid'])

        return u'%s%s-%s-%s-%s' % (residence, origin, birthday, validity, checksum)