Module: StdNum::ISBN

Extended by:
Helpers
Defined in:
lib/library_stdnums.rb

Overview

Validate, convert, and normalize ISBNs (10-digit or 13-digit)

Constant Summary

Constants included from Helpers

Helpers::STDNUMPAT

Class Method Summary (collapse)

Methods included from Helpers

extractNumber, reduce_to_basics

Class Method Details

+ (Array<String,String>?) allNormalizedValues(isbn)

Return an array of the ISBN13 and ISBN10 (in that order) for the passed in value. You'll only get one value back if it's a 13-digit ISBN that can't be converted to an ISBN10. it can't be recognized.

Examples:

Get the normalized values and index them (if valid) or original value (if not)

norms = StdNum::ISBN.allNormalizedValues(rawisbn)
doc['isbn'] = norms ? norms : [rawisbn]

Parameters:

  • isbn (String) —

    The original ISBN, in 10-character or 13-digit format

Returns:

  • (Array<String,String>, nil) —

    Either the (one or two) normalized ISBNs, or nil if



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# File 'lib/library_stdnums.rb', line 151

def self.allNormalizedValues isbn
  isbn = reduce_to_basics isbn, [10,13]
  return [] unless isbn
  case isbn.size
  when 10
    return [self.convert_to_13(isbn), isbn]
  when 13
    return [isbn, self.convert_to_10(isbn)].compact
  end
end

+ (String?) checkdigit(isbn, preprocessed = false)

Compute check digits for 10 or 13-digit ISBNs. See algorithm at en.wikipedia.org/wiki/International_Standard_Book_Number

Parameters:

  • isbn (String) —

    The ISBN (we'll try to clean it up if possible)

  • preprocessed (Boolean) (defaults to: false) —

    Set to true if the ISBN has already been through reduce_to_basics

Returns:

  • (String, nil) —

    the one-character checkdigit, or nil if it's not an ISBN string



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# File 'lib/library_stdnums.rb', line 57

def self.checkdigit isbn, preprocessed = false
  isbn = reduce_to_basics isbn, [10,13] unless preprocessed
  return nil unless isbn

  checkdigit = 0
  if isbn.size == 10
    digits = isbn[0..8].split(//).map {|i| i.to_i}
    (1..9).each do |i|
      checkdigit += digits[i-1] * i
    end
    checkdigit = checkdigit % 11
    return 'X' if checkdigit == 10
    return checkdigit.to_s
  else # size == 13
    checkdigit = 0
    digits = isbn[0..11].split(//).map {|i| i.to_i}
    6.times do
      checkdigit += digits.shift
      checkdigit += digits.shift * 3
    end
    check = 10 - (checkdigit % 10)
    check = 0 if check == 10
    return check.to_s
  end
end

+ (String) convert_to_10(isbn)

Convert to 10 if it's 13 digits and the first three digits are 978. Pass through anything 10-digits, and return nil for everything else.

Parameters:

  • isbn (String) —

    The ISBN (we'll try to clean it up if possible)

Returns:

  • (String) —

    The converted 10-character ISBN, nil if something looks wrong, or whatever was passed in if it already looked like a 10-digit ISBN



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# File 'lib/library_stdnums.rb', line 128

def self.convert_to_10 isbn
  isbn = reduce_to_basics isbn, [10,13]

  # Already 10 digits? Just return
  return isbn if isbn.size == 10
  
  # Can't be converted to ISBN-10? Bail
  return nil unless isbn[0..2] == '978'
  
  prefix = isbn[3..11]
  return prefix + self.checkdigit(prefix + '0')
end

+ (String?) convert_to_13(isbn)

To convert to an ISBN13, throw a '978' on the front and compute the checkdigit We leave 13-digit numbers alone, figuring they're already ok. NO CHECKSUM CHECK IS DONE FOR 13-DIGIT ISBNS! and return nil on anything that's not the right length

Parameters:

  • isbn (String) —

    The ISBN (we'll try to clean it up if possible)

Returns:

  • (String, nil) —

    The converted 13-character ISBN, nil if something looks wrong, or whatever was passed in if it already looked like a 13-digit ISBN



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# File 'lib/library_stdnums.rb', line 115

def self.convert_to_13 isbn
  isbn = reduce_to_basics isbn, [10,13]
  return nil unless isbn
  return isbn if isbn.size == 13
  prefix = '978' + isbn[0..8]
  return prefix + self.checkdigit(prefix + '0', true)
end

+ (String?) normalize(rawisbn)

For an ISBN normalizing it is the same as converting to ISBN 13 and making sure it's valid

Parameters:

  • isbn (String) —

    The ISBN to normalize

Returns:

  • (String, nil) —

    the normalized (to 13 digit) ISBN, or nil on failure



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# File 'lib/library_stdnums.rb', line 100

def self.normalize rawisbn
  isbn = convert_to_13 rawisbn
  if isbn and valid?(isbn, true)
    return isbn
  else
    return nil
  end
end

+ (Boolean) valid?(isbn, preprocessed = false)

Check to see if the checkdigit is correct

Parameters:

  • isbn (String) —

    The ISBN (we'll try to clean it up if possible)

  • preprocessed (Boolean) (defaults to: false) —

    Set to true if the ISBN has already been through reduce_to_basics

Returns:

  • (Boolean) —

    Whether or not the checkdigit is correct



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# File 'lib/library_stdnums.rb', line 87

def self.valid? isbn, preprocessed = false
  return nil if isbn.nil?
  isbn = reduce_to_basics(isbn, [10,13]) unless preprocessed
  return false unless isbn
  return false unless isbn[-1..-1] == self.checkdigit(isbn, true)
  return true
end