# iva.py - functions for handling Italian VAT numbers
#
# Copyright (C) 2012, 2013 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

"""Partita IVA (Italian VAT number).

The Partita IVA (Imposta sul valore aggiunto) consists of 11 digits. The
first 7 digits are a company identifier, the next 3 refer to the province
of residence and the last is a check digit.

The fiscal code for individuals is not accepted as valid code for
intracommunity VAT related operations so it is ignored here.

>>> validate('IT 00743110157')
'00743110157'
>>> validate('00743110158')  # invalid check digit
Traceback (most recent call last):
    ...
InvalidChecksum: ...
"""

from stdnum import luhn
from stdnum.exceptions import *
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('IT'):
        number = number[2:]
    return number


def validate(number):
    """Checks to see if the number provided is a valid VAT number. This checks
    the length, formatting and check digit."""
    number = compact(number)
    if not number.isdigit() or int(number[0:7]) == 0:
        raise InvalidFormat()
    if len(number) != 11:
        raise InvalidLength()
    # check the province of residence
    if not('001' <= number[7:10] <= '100') and \
            number[7:10] not in ('120', '121', '888', '999'):
        raise InvalidComponent()
    luhn.validate(number)
    return number


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:
        return bool(validate(number))
    except ValidationError:
        return False
