The user-readable huge number encoder that corrects misreadings

numcode.rb

# encoding: utf-8

##
# The arbitrary-length positive integers to human readable form codec (serials, links and like).
# The idea is to avoid misreading/misinterpetation of symbols. For example,
# the letter 0 o and O, ir I and 1, often looks very likely. The numcode
# takes care of it using clearly distinctive characters for both English and Russian
# charset and corrects potential errors
#
# Numcode uses set 21 characters common to Russian and English to encode positive decimal
# integer numbers of arbitrary size. Characters and digits are chosen in a way
# to reduce the risk oh misreading it (ABEKMHOPCTYX123456789). Resulting word
# can be separated by '-' (default) or any of ' =./:' to ease reading.
#
class Numcode

  class Error < StandardError; end

  @@digits = ["ABEKMHOPCTYX123456789","АВЕКМНОРСТУХI", "АВЕКМН0"]

  def self.encode x, delimiter='-'
    value = x.to_i
    raise Error, "Should be integer number: #{x}" if x != value
    res = ''
    digs = @@digits[0]
    n = -1
    begin
      res << delimiter if (n += 1) > 1 &&  n % 5 == 0
      value,r = value.divmod(21)
      res << digs[r]
    end while value > 0
    res
  end

  # Correct key, substitute alike characters (0 for O) including
  # language (Rusian/English) misunderstanging and decode value
  def self.decode str
    value = 0
    k = 1
    str.upcase.each_char do |c|
      next if '-=./: '.include? c
      n = nil
      @@digits.each { |set|
        n = set.index(c)
        break if n
      }
      raise Error, "Bad characted in numcode #{str.inspect}" unless n
      value += n * k
      k *= 21
    end
    value
  end

  def self.test
    77134.times { |i|
      x = decode(encode(i))
      raise "#{i} -> #{x}" unless x == i
    }
  end

  ## Create random Numcode of len characters not including
  # separators
  def self.random len=15, delimiter = '-'
    dd = @@digits[0]
    n = -1
    res = ''
    while (len-=1) >= 0
      res << delimiter if (n += 1) > 1 &&  n % 5 == 0
      res << dd[rand 21]
    end
    res
  end


  def self.guid
    random_code 15, '-'
  end
end

class Numeric
  def to_numcode delimiter='-'
    Numcode.encode(self,delimiter)
  end
end

class String
  def decode_numcode
    Numcode.decode self
  end
end