Base54

base54.rb

module Base54
  L = %w{0 1 2 3 4 5 6 7 8 9
         A B C D E F G H K L
         M N P Q R T U V W X
         Y a b c d e f g h i
         j k m n p q r s t u
         v w x z}

  WHITESPACE = [' ', '-', '_', '.', '+']

  EVIL = {
    'l' => '1',
    'I' => '1',
    'J' => '1',
    'S' => '5',
    'O' => '0',
    'o' => '0',
    'Z' => 'Y',
    'y' => 'z',
  }

  def self.encode54(int, delimiter: '-', group_size: nil)
    l = []
    r = int.to_i
    while r > 0
      l.unshift(L[r % 54])
      r = r / 54
    end
    # debugger
    if group_size && group_size > 0
      raise "illegal delimiter `#{delimiter}`" unless WHITESPACE.member?(delimiter)
      n = (l.length-1) / group_size
      d = (l.length - (n-1) * group_size) / 2
      n.times do |i|
        l.insert(d + (group_size+1)*i, delimiter)
      end
    end
    l.join('')
  end

  def self.decode54(str)
    r = 0
    str.each_char do |c|
      j = L.index(c) || L.index(EVIL[c])
      next if !j && WHITESPACE.member(c)
      raise "illegal character `#{c}`" unless j
      r = (r*54) + j
    end
    r
  end

  class << self
    alias_method :encode, :encode54
    alias_method :enc, :encode54
    alias_method :decode, :decode54
    alias_method :dec, :decode54
  end
end