class BaseConverter
  class DecodeError < StandardError
  end

  def initialize(base = 16, digits = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
    @digits  = digits.split(//)
    @rdigits = Hash.new
    @digits.each_with_index {|d,i| @rdigits[d] = i}
    @base = if base == 0 or not base
      @digits.size
    else
      base
    end
  end

  def encode(int)
    sign = ''
    str  = ''

    return @digits[0] if int == 0

    raise ArgumentError, "Negative values not supported" if int < 0

    while int > 0
      rem = int % @base
      str = @digits[rem] + str
      int = ((int - rem) / @base)
    end

    str
  end

  def decode(str)
    begin
      int = 0

      str.each_byte do |b|
        int = (int * @base) + @rdigits.fetch(b.chr)
      end

      int
    rescue IndexError
      raise DecodeError
    end
  end
end