# This software is:
 #
 # Copyright (C) 2004 Salvatore Sanfilippo <antirez at invece dot org>
 #
 # The following terms apply to all files associated with the software
 # unless explicitly disclaimed in individual files.
 #
 # The authors hereby grant permission to use, copy, modify, distribute,
 # and license this software and its documentation for any purpose, provided
 # that existing copyright notices are retained in all copies and that this
 # notice is included verbatim in any distributions. No written agreement,
 # license, or royalty fee is required for any of the authorized uses.
 # Modifications to this software may be copyrighted by their authors
 # and need not follow the licensing terms described here, provided that
 # the new terms are clearly indicated on the first page of each file where
 # they apply.
 # 
 # IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY
 # FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
 # ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY
 # DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 # 
 # THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
 # INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY,
 # FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT.  THIS SOFTWARE
 # IS PROVIDED ON AN "AS IS" BASIS, AND THE AUTHORS AND DISTRIBUTORS HAVE
 # NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
 # MODIFICATIONS.
 # 
 # GOVERNMENT USE: If you are acquiring this software on behalf of the
 # U.S. government, the Government shall have only "Restricted Rights"
 # in the software and related documentation as defined in the Federal 
 # Acquisition Regulations (FARs) in Clause 52.227.19 (c) (2).  If you
 # are acquiring the software on behalf of the Department of Defense, the
 # software shall be classified as "Commercial Computer Software" and the
 # Government shall have only "Restricted Rights" as defined in Clause
 # 252.227-7013 (c) (1) of DFARs.  Notwithstanding the foregoing, the
 # authors grant the U.S. Government and others acting in its behalf
 # permission to use and distribute the software in accordance with the
 # terms specified in this license. 
 
 
 # isbnValidChecksum - Validate ISBN numbers checksum
 #
 # Return 1 if the input ISBN number checksum is ok. Otherwise zero
 # is returned. The algorithm only considers digits for the first 9
 # sums, and a digit or a 'X' or 'x' character for the final ISBN digit.
 # Any other character presents in the input string is ignored.
 #
 # Note that this algorithm works with any 10-digit ISBN, and is
 # not Italian-specific as [isbnAddDashes] is.
 proc isbnValidChecksum isbn {
     set digits 0
     set sum 0
     foreach d [split $isbn {}] {
         if {![string is digit $d]} { ;# Not a digit...
             if {$digits != 9 || ($d ne {x} && $d ne {X})} {
                 # ... Nor a 'x' as last character. Skip it.
                 continue
             }
         }
         incr digits
         if {$d eq {x} || $d eq {X}} {set d 10}
         set sum [expr {$sum+($d*(11-$digits))}]
     }
     if {$digits == 10 && ($sum % 11) == 0} {return 1}
     return 0
 }
 
 # isbnValidChecksum - Add/Fix dashes in Italian ISBN numbers.
 #
 # If the ISBN is not Italian or it appears to be corrputed,
 # the original string is returned unmodified.
 proc isbnAddDashes isbn {
     set orig $isbn
     set isbn [string trim $isbn " \t\r\n"]
     if {[string range $isbn 0 1] ne {88}} {return $orig}
     set isbn [string map {{ } {} {-} {}} $isbn]
     if {[string length $isbn] != 10} {return $orig}
     switch -- [string index $isbn 2] {
         0 - 1 {set idlen 2}
         2 - 3 - 4 - 5 {set idlen 3}
         6 - 7 {set idlen 4}
         8 {
             switch -- [string index $isbn 3] {
                 0 - 1 - 2 - 3 - 4 {set idlen 4}
                 5 - 6 - 7 - 8 - 9 {set idlen 5}
                 default {return $orig}
             }
         }
         9 {set idlen 5}
         default {return $orig}
     }
     set new "88-"
     append new [string range $isbn 2 [expr {$idlen+1}]]-
     append new [string range $isbn [expr {$idlen+2}] end-1]-
     append new [string index $isbn end]
     return $new
 }
 
 # Simple test program
 while 1 {
     set l [gets stdin]
     puts "With dashes fixed (if Italian): [isbnAddDashes $l]"
     puts "Valid checksum? [isbnValidChecksum $l]"
 }

 # Given an ISBN, returns the check digit.
 # Both 10 digit and 13 digit ISBNs are acceptable input.
 # In either case, the ISBN may already contain a check digit,
 # which is ignored if present, or it may be an incomplete
 # ISBN for which the check digit is to be calculated.
 # Internal hyphens and spaces are ignored.
 # If the ISBN is ill-formed returns -1.
 
 proc isbncd {k} {
    set k [string map {- "" " " ""} $k];
    set len [string length $k]
    if {($len < 9) || ($len > 13)} {
        return -1
    }
    set sum 0
    # 13-digit ISBN
    if {$len >= 12} {
        if {$len == 13} {
            set k [string range $k 0 11];# Remove check digit
        }
        if {[regexp {\D} $k]} {return -1};# Ensure that there are only digits
        set kl [split $k ""]
        # Weights are 1, 3, 1, 3, ...
        foreach {a b} $kl {
            incr sum [expr {$a + (3 * $b)}]
        }
        set rem [expr {$sum % 10}]
        if {$rem == 0} {
            return 0
        } else {
            return [expr {10 - $rem}]
        }
    }
    # 10-digit ISBN
    if {$len == 10} {
        set k [string range $k 0 8];# Remove check digit
    }
    if {[regexp {\D} $k]} {return -1};# Ensure that there are only digits
    set kl [split $k ""]
    # Weights are 10, 9, 8, ...
    set weight 10
    foreach d $kl {
        incr sum [expr {$d * $weight}]
        incr weight -1
    }
    set rem [expr {$sum % 11}]
    if {$rem == 0} {
        return 0
    } else {
        set ck [expr {11 - $rem}]
        if {$ck == 10} {
            set ck X
        }
        return $ck
    }
 }