"""

Chile specific form helpers.

"""

from django.forms import ValidationError

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

from django.utils.translation import ugettext_lazy as _

from django.utils.encoding import smart_unicode

class CLRegionSelect(Select):

    """

    A Select widget that uses a list of Chilean Regions (Regiones)

    as its choices.

    """

    def __init__(self, attrs=None):

        from cl_regions import REGION_CHOICES

        super(CLRegionSelect, self).__init__(attrs, choices=REGION_CHOICES)

class CLRutField(RegexField):

    """

    Chilean "Rol Unico Tributario" (RUT) field. This is the Chilean national

    identification number.

    Samples for testing are available from

    https://palena.sii.cl/cvc/dte/ee_empresas_emisoras.html

    """

    default_error_messages = {

        'invalid': _('Enter a valid Chilean RUT.'),

        'strict': _('Enter a valid Chilean RUT. The format is XX.XXX.XXX-X.'),

        'checksum': _('The Chilean RUT is not valid.'),

    }

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

        if 'strict' in kwargs:

            del kwargs['strict']

            super(CLRutField, self).__init__(r'^(\d{1,2}\.)?\d{3}\.\d{3}-[\dkK]$',

                error_message=self.default_error_messages['strict'], *args, **kwargs)

        else:

            # In non-strict mode, accept RUTs that validate but do not exist in

            # the real world.

            super(CLRutField, self).__init__(r'^[\d\.]{1,11}-?[\dkK]$', *args, **kwargs)

    def clean(self, value):

        """

        Check and clean the Chilean RUT.

        """

        super(CLRutField, self).clean(value)

        if value in EMPTY_VALUES:

            return u''

        rut, verificador = self._canonify(value)

        if self._algorithm(rut) == verificador:

            return self._format(rut, verificador)

        else:

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

    def _algorithm(self, rut):

        """

        Takes RUT in pure canonical form, calculates the verifier digit.

        """

        suma  = 0

        multi = 2

        for r in rut[::-1]:

            suma  += int(r) * multi

            multi += 1

            if multi == 8:

                multi = 2

        return u'0123456789K0'[11 - suma % 11]

    def _canonify(self, rut):

        """

        Turns the RUT into one normalized format. Returns a (rut, verifier)

        tuple.

        """

        rut = smart_unicode(rut).replace(' ', '').replace('.', '').replace('-', '')

        return rut[:-1], rut[-1]

    def _format(self, code, verifier=None):

        """

        Formats the RUT from canonical form to the common string representation.

        If verifier=None, then the last digit in 'code' is the verifier.

        """

        if verifier is None:

            verifier = code[-1]

            code = code[:-1]

        while len(code) > 3 and '.' not in code[:3]:

            pos = code.find('.')

            if pos == -1:

                new_dot = -3

            else:

                new_dot = pos - 3

            code = code[:new_dot] + '.' + code[new_dot:]

        return u'%s-%s' % (code, verifier)