from django.utils.encoding import smart_str, smart_unicode

def ssn_check_digit(value):

    "Calculate Italian social security number check digit."

    ssn_even_chars = {

        '0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8,

        '9': 9, 'A': 0, 'B': 1, 'C': 2, 'D': 3, 'E': 4, 'F': 5, 'G': 6, 'H': 7,

        'I': 8, 'J': 9, 'K': 10, 'L': 11, 'M': 12, 'N': 13, 'O': 14, 'P': 15,

        'Q': 16, 'R': 17, 'S': 18, 'T': 19, 'U': 20, 'V': 21, 'W': 22, 'X': 23,

        'Y': 24, 'Z': 25

    }

    ssn_odd_chars = {

        '0': 1, '1': 0, '2': 5, '3': 7, '4': 9, '5': 13, '6': 15, '7': 17, '8':

        19, '9': 21, 'A': 1, 'B': 0, 'C': 5, 'D': 7, 'E': 9, 'F': 13, 'G': 15,

        'H': 17, 'I': 19, 'J': 21, 'K': 2, 'L': 4, 'M': 18, 'N': 20, 'O': 11,

        'P': 3, 'Q': 6, 'R': 8, 'S': 12, 'T': 14, 'U': 16, 'V': 10, 'W': 22,

        'X': 25, 'Y': 24, 'Z': 23

    }

    # Chars from 'A' to 'Z'

    ssn_check_digits = [chr(x) for x in range(65, 91)]

    ssn = value.upper()

    total = 0

    for i in range(0, 15):

        try:

            if i % 2 == 0:

                total += ssn_odd_chars[ssn[i]]

            else:

                total += ssn_even_chars[ssn[i]]

        except KeyError:

            msg = "Character '%(char)s' is not allowed." % {'char': ssn[i]}

            raise ValueError(msg)

    return ssn_check_digits[total % 26]

def vat_number_check_digit(vat_number):

    "Calculate Italian VAT number check digit."

    normalized_vat_number = smart_str(vat_number).zfill(10)

    total = 0

    for i in range(0, 10, 2):

        total += int(normalized_vat_number[i])

    for i in range(1, 11, 2):

        quotient , remainder = divmod(int(normalized_vat_number[i]) * 2, 10)

        total += quotient + remainder

    return smart_unicode((10 - total % 10) % 10)