base_converter.rb

class Base
  def initialize(alphabets)
    @alphabets = alphabets
  end

  def base
    @alphabets.length
  end

  def to_decimal(number)
    number.chars.reverse.each_with_index.inject(0) do |decimal, (digit, position)|
      coiefficient = @alphabets.index(digit)
      decimal + coiefficient * base**position
    end
  end

  def from_decimal(number)
    hash = map_coificients(number)

    hash.keys.max.downto(0).each_with_object('') do |position, output|
      output << hash[position].to_s
    end
  end

  private

  def map_coificients(number)
    current_number = number
    hash = Hash.new(zero)

    until current_number == 0
      position = Math.log(current_number, base).floor
      coiefficient = current_number / base**position
      hash[position] = @alphabets[coiefficient]
      current_number -= coiefficient * base**position
    end
    hash
  end

  def zero
    @alphabets[0]
  end
end

class BaseConverter
  def initialize(source_alphabets, target_alphabets)
    @source = Base.new source_alphabets
    @target = Base.new target_alphabets
  end

  def convert(number)
    @target.from_decimal @source.to_decimal number
  end

  def self.convert(input, source_alphabets, target_alphabets)
    new(source_alphabets, target_alphabets).convert input
  end
end