# 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

"""Module for handling Slovenian ID za DDV (Davčna številka, Davek na
dodano vrednost, VAT) numbers.

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]