# dic.py - functions for handling Czech 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

"""DIČ (Daňové identifikační číslo, Czech VAT number).

The number is an 8, 9 or 10 digit code that includes a check digit and is
used to uniquely identify taxpayers for VAT (DPH in Czech). The number can
refer to legal entities (8 digit numbers), individuals with a RČ (the 9 or
10 digit Czech birth number) or individuals without a RČ (9 digit numbers
that begin with a 6).

>>> compact('CZ 25123891')
'25123891'
>>> is_valid('25123891')  # legal entity
True
>>> is_valid('25123890')  # incorrect check digit
False
>>> is_valid('7103192745')  # RČ
True
>>> is_valid('640903926')  # special case
True
"""

from stdnum.cz import rc
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('CZ'):
        number = number[2:]
    return number


def calc_check_digit_legal(number):
    """Calculate the check digit for 8 digit legal entities. The number
    passed should not have the check digit included."""
    check = (11 - sum((8 - i) * int(n) for i, n in enumerate(number))) % 11
    return str((check or 1) % 10)


def calc_check_digit_special(number):
    """Calculate the check digit for special cases. The number passed
    should not have the first and last digits included."""
    check = (11 - sum((8 - i) * int(n) for i, n in enumerate(number))) % 11
    return str(9 - check % 10)


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
    if not number.isdigit():
        return False
    if len(number) == 8 and not number.startswith('9'):
        # legal entities
        return calc_check_digit_legal(number[:-1]) == number[-1]
    if len(number) == 9 and number.startswith('6'):
        # special cases (skip first digit in calculation)
        return calc_check_digit_special(number[1:-1]) == number[-1]
    if len(number) in (9, 10):
        # 9 or 10 digit individual
        return rc.is_valid(number)
    return False