"""

Kuwait-specific Form helpers

"""

import re

from datetime import date

from django.core.validators import EMPTY_VALUES

from django.forms import ValidationError

from django.forms.fields import Field, RegexField

from django.utils.translation import gettext as _

id_re = re.compile(r'^(?P<initial>\d{1})(?P<yy>\d\d)(?P<mm>\d\d)(?P<dd>\d\d)(?P<mid>\d{4})(?P<checksum>\d{1})')

class KWCivilIDNumberField(Field):

    """

    Kuwaiti Civil ID numbers are 12 digits, second to seventh digits

    represents the person's birthdate.

    Checks the following rules to determine the validty of the number:

        * The number consist of 12 digits.

        * The birthdate of the person is a valid date.

        * The calculated checksum equals to the last digit of the Civil ID.

    """

    default_error_messages = {

        'invalid': _('Enter a valid Kuwaiti Civil ID number'),

    }

    def has_valid_checksum(self, value):

        weight = (2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2)

        calculated_checksum = 0

        for i in range(11):

            calculated_checksum += int(value[i]) * weight[i]

        remainder = calculated_checksum % 11

        checkdigit = 11 - remainder

        if checkdigit != int(value[11]):

            return False

        return True

    def clean(self, value):

        super(KWCivilIDNumberField, self).clean(value)

        if value in EMPTY_VALUES:

            return u''

        if not re.match(r'^\d{12}$', value):

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

        match = re.match(id_re, value)

        if not match:

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

        gd = match.groupdict()

        try:

            d = date(int(gd['yy']), int(gd['mm']), int(gd['dd']))

        except ValueError:

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

        if not self.has_valid_checksum(value):

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

        return value