# __init__.py - functions for handling ISBNs
#
# Copyright (C) 2010, 2011 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 ISBNs (International Standard Book Number). This
module handles both numbers in ISBN-10 (10-digit) and ISBN-13 (13-digit)
format.

>>> is_valid('978-9024538270')
True
>>> is_valid('978-9024538271') # incorrect check digit
False
>>> compact('1-85798-218-5')
'1857982185'
>>> format('9780471117094')
'978-0-471-11709-4'
>>> format('1857982185')
'1-85798-218-5'
>>> isbn_type('1-85798-218-5')
'ISBN10'
>>> isbn_type('978-0-471-11709-4')
'ISBN13'
>>> to_isbn13('1-85798-218-5')
'978-1-85798-218-3'
"""


def compact(number, convert=False):
    """Convert the ISBN to the minimal representation. This strips the number
    of any valid ISBN separators and removes surrounding whitespace. If the
    covert parameter is True the number is also converted to ISBN-13
    format."""
    number = number.replace(' ','').replace('-','').strip().upper()
    if len(number) == 9:
        number = '0' + number
    if convert:
        return to_isbn13(number)
    return number

def _calc_isbn10_check_digit(number):
    """Calculate the ISBN check digit for 10-digit numbers. The number passed
    should not have the check bit included."""
    check = sum( (i + 1) * int(n) for i, n in enumerate(number) ) % 11
    return 'X' if check == 10 else str(check)

def _calc_isbn13_check_digit(number):
    """Calculate the ISBN check digit for 13-digit numbers. The number passed
    should not have the check bit included."""
    return str((10 - sum( (2 * (i % 2) + 1) * int(n) for i, n in enumerate(number))) % 10)

def isbn_type(number):
    """Check the passed number and returns 'ISBN13', 'ISBN10' or None (for
    invalid) for checking the type of number passed."""
    try:
        number = compact(number)
    except:
        return None
    if len(number) == 10:
        if not number[:-1].isdigit():
            return None
        if _calc_isbn10_check_digit(number[:-1]) != number[-1]:
            return None
        return 'ISBN10'
    elif len(number) == 13:
        if not number.isdigit():
            return None
        if _calc_isbn13_check_digit(number[:-1]) != number[-1]:
            return None
        return 'ISBN13'
    else:
        return None

def is_valid(number):
    """Checks to see if the number provided is a valid ISBN (either a legacy
    10-digit one or a 13-digit one). This checks the length and the check
    bit but does not check if the group and publisher are valid (use split()
    for that)."""
    return isbn_type(number) is not None

def to_isbn13(number):
    """Convert the number to ISBN-13 format."""
    number = number.strip()
    min_number = compact(number)
    if len(min_number) == 13:
        return number # nothing to do, already ISBN-13
    # put new check digit in place
    number = number[:-1] + _calc_isbn13_check_digit('978' + min_number[:-1])
    # add prefix
    if ' ' in number:
        return '978 ' + number
    elif '-' in number:
        return '978-' + number
    else:
        return '978' + number

def split(number, convert=False):
    """Split the specified ISBN into an EAN.UCC prefix, a group prefix, a
    registrant, an item number and a check-digit. If the number is in ISBN-10
    format the returned EAN.UCC prefix is '978'. If the covert parameter is
    True the number is converted to ISBN-13 format first."""
    from stdnum import numdb
    # clean up number
    number = compact(number, convert)
    # get Bookland prefix if any
    if len(number) == 10:
        oprefix = ''
        prefix = '978'
    else:
        oprefix = prefix = number[:3]
        number = number[3:]
    # split the number
    result = numdb.get('isbn').split(prefix+number[:-1])[1:]
    itemnr = result.pop()
    group = result.pop(0) if result else ''
    publisher = result.pop(0) if result else ''
    # return results
    return ( oprefix, group, publisher, itemnr, number[-1] )

def format(number, separator='-', convert=False):
    """Reformat the passed number to the standard format with the EAN.UCC
    prefix (if any), the group prefix, the registrant, the item number and
    the check-digit separated (if possible) by the specified separator.
    Passing an empty separator should equal compact() though this is less
    efficient. If the covert parameter is True the number is converted to
    ISBN-13 format first."""
    return separator.join(x for x in split(number, convert) if x)