# cn.py - functions for handling Japanese Individual Numbers (IN)
# coding: utf-8
#
# Copyright (C) 2025 Luca Sicurello
#
# 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

"""IN (個人番号, kojin bangō, Japanese Individual Number) 
it often referred to with its nickname マイナンバー (mai nanba-, 
My number).

The Individual Number is assigned to identify citizens 
and residents. The number consists of 12 digits where 
the last digit is a check digit. No personal information
(such as name, gender, date of birth, etc.) is encoded 
in the number.

More information:

 * https://en.wikipedia.org/wiki/Individual_Number
 * https://digitalforensic.jp/2016/03/14/column404/

>>> validate('6214 9832 0257')
'621498320257'
>>> validate('6214 9832 0257')
Traceback (most recent call last):
  ...
InvalidChecksum: ...
>>> format('621498320257')
'6214 9832 0257'
"""


from stdnum.exceptions import *
from stdnum.util import clean, isdigits

def compact(number):
    """Convert the number to the minimal representation. This strips the
    number of any valid separators and removes surrounding whitespace."""
    return clean(number, '- ').strip()

def calc_check_digit(number):
    """Calculate the check digit. The number passed should not have
    the check digit included."""
    weights = (6, 5, 4, 3, 2, 7, 6, 5, 4, 3, 2)
    s = sum(w * int(n) for w, n in zip(weights, number)) % 11
    return '0' if s <= 1 else str(11-s)

def validate(number):
    """Check if the number is valid. This checks the length and check
    digit."""
    number = compact(number)
    if len(number) != 12:
        raise InvalidLength()
    if not isdigits(number):
        raise InvalidFormat()
    if calc_check_digit(number[:-1]) != number[-1]:
        raise InvalidChecksum()
    return number


def is_valid(number):
    """Check if the number is a valid IN."""
    try:
        return bool(validate(number))
    except ValidationError:
        return False


def format(number):
    """Reformat the number to the presentation format found on 
    My Number Cards."""
    number = compact(number)
    return ' '.join(
        (number[0:4], number[4:8], number[8:12]))