# ddv.py - functions for handling Slovenian VAT numbers
# coding: utf-8
#
# Copyright (C) 2012 Arthur de Jong
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301 USA

"""ID za DDV (Davčna številka, Slovenian VAT number).

The DDV number (Davčna številka) is used for VAT (DDV, Davek na dodano
vrednost) purposes and consist of 8 digits of which the last is a check
digit.

>>> compact('SI 5022 3054')
'50223054'
>>> is_valid('SI 50223054')
True
>>> is_valid('SI 50223055')  # invalid check digits
False
"""

from stdnum.util import clean


def compact(number):
    """Convert the number to the minimal representation. This strips the
    number of any valid separators and removes surrounding whitespace."""
    number = clean(number, ' -').upper().strip()
    if number.startswith('SI'):
        number = number[2:]
    return number


def calc_check_digit(number):
    """Calculate the check digit. The number passed should not have the
    check digit included."""
    check = (11 - sum((8 - i) * int(n) for i, n in enumerate(number)) % 11)
    # this results in a two-digit check digit for 11 which should be wrong
    return '0' if check == 10 else str(check)


def is_valid(number):
    """Checks to see if the number provided is a valid VAT number. This
    checks the length, formatting and check digit."""
    try:
        number = compact(number)
    except:
        return False
    return number.isdigit() and len(number) == 8 and number[0] != '0' and \
           calc_check_digit(number[:-1]) == number[-1]