"""AT-specific Form helpers."""
import re

from django.forms import CharField, RegexField, Select, ValidationError
from django.utils.translation import gettext_lazy as _

from .at_states import STATE_CHOICES

re_ssn = re.compile(r'^\d{4} \d{6}')


class ATZipCodeField(RegexField):
    """
    A form field that validates its input is an Austrian postcode.

    Accepts 4 digits (first digit must be greater than 0).
    """

    default_error_messages = {
        'invalid': _('Enter a zip code in the format XXXX.'),
    }

    def __init__(self, **kwargs):
        super().__init__(r'^[1-9]{1}\d{3}$', **kwargs)


class ATStateSelect(Select):
    """A ``Select`` widget that uses a list of AT states as its choices."""

    def __init__(self, attrs=None):
        super().__init__(attrs, choices=STATE_CHOICES)


class ATSocialSecurityNumberField(CharField):
    """
    Austrian Social Security numbers are composed of a 4 digits and 6 digits field.

    The latter represents in most cases the person's birthdate while
    the first 4 digits represent a 3-digits counter and a one-digit checksum.

    The 6-digits field can also differ from the person's birthdate if the
    3-digits counter suffered an overflow.

    This code is based on information available on
    http://de.wikipedia.org/wiki/Sozialversicherungsnummer#.C3.96sterreich
    """

    default_error_messages = {
        'invalid': _('Enter a valid Austrian Social Security Number in XXXX XXXXXX format.'),
    }

    def clean(self, value):
        value = super().clean(value)
        if value in self.empty_values:
            return value
        if not re_ssn.search(value):
            raise ValidationError(self.error_messages['invalid'], code='invalid')
        sqnr, date = value.split(" ")
        sqnr, check = (sqnr[:3], (sqnr[3]))
        if int(sqnr) < 100:
            raise ValidationError(self.error_messages['invalid'], code='invalid')
        res = (int(sqnr[0]) * 3 + int(sqnr[1]) * 7 + int(sqnr[2]) * 9 +
               int(date[0]) * 5 + int(date[1]) * 8 + int(date[2]) * 4 +
               int(date[3]) * 2 + int(date[4]) * 1 + int(date[5]) * 6)
        res = res % 11
        if res != int(check):
            raise ValidationError(self.error_messages['invalid'], code='invalid')
        return '%s%s %s' % (sqnr, check, date)
