gistfile1.rb

def split_isbn
  return if isbn.nil?
  x = 4
  case isbn[0..2].to_i
  when  0..19, 100..109 then x = 2
  when 20..69, 110..139 then x = 3
  when 70..84, 140..154 then x = 4
  when 85..89, 155..185 then x = 5
  when 90..95, 187..198 then x = 6
  when 95..99           then x = 7
  when 186, 199
    case isbn[1..4].to_i
    when 8600..8697             then x = 5
    when 8698..8699, 9900..9989 then x = 6
    when 9990..9999             then x = 7
    end
  else
    # Non-English
    return
  end
  isbn = "#{isbn[0]}-#{isbn[1..x]}-#{isbn[(x+1)..8]}-#{isbn[9]}"
end