Ruby implementation of the old school Rail Fence Cypher, encrypts and decrypts using 2, 3 or 4 rows.

rail_fence_cypher

class Rail_Fence_Cipher

  def initialize instruction, number, text
    @letter_array = text.split("")
    @text_length = text.length
    @number = number

    case instruction
      when "encrypt"
        encrypt
      when "decrypt"
        decrypt
      else raise "Invalid instruction"
      end
    end

  def encrypt
    case @number
    when 2
      encrypt_2
    when 3
      encrypt_3
    when 4
      encrypt_4
    else
      raise "Not a valid encryption code"
    end
  end

  def encrypt_2
    first, second = [], []
    (0..@text_length).each do |index|
      if index % 2 == 0
        first << @letter_array[index]
      else
        second << @letter_array[index]
      end
    end

    puts (first + second).join("")
  end

  def encrypt_3
    first, second, third = [], [], []
    (0..@text_length).each do |index|
      if index % 4 == 0
        first << @letter_array[index]
      elsif index % 2 == 1
        second << @letter_array[index]
      else
        third << @letter_array[index]
      end
    end
    puts (first + second + third).join("")
  end

  def encrypt_4
    first, second, third, fourth = [], [], [], []
    (0..@text_length).each do |index|
      if index % 6 == 0
        first << @letter_array[index]
      elsif index % 2 == 1 && index % 3 != 0
        second << @letter_array[index]
      elsif index % 2 == 0 && index % 3 !=0
        third << @letter_array[index]
      else
        fourth << @letter_array[index]
      end
    end
    puts (first + second + third + fourth).join("")
  end

  def decrypt
   case @number
    when 2
      decrypt_2
    when 3
      decrypt_3
    when 4
      decrypt_4
    # when 5
    #   decrypt_5
    else
      raise "Not a valid encryption code"
    end
  end

  def decrypt_2
    zipper =  @letter_array.each_slice(@text_length/2).to_a
    puts zipper[0].zip(zipper[1]).flatten.join("")
  end

  def decrypt_3
    zipper = @letter_array.each_slice(@text_length/4).to_a
    puts zipper[0].zip(zipper[3]).flatten.zip(zipper[1] + zipper[2]).flatten.join("")
  end

  def decrypt_4

    zipper = @letter_array.each_slice(@text_length/6).to_a
    first_and_last = zipper[0].zip(zipper[5]).flatten
    space_holders = []

    first_and_last.length.times do
      space_holders << 0
    end

    new_zipper = first_and_last.zip(space_holders).flatten
    middles = (zipper[1] + zipper[2]).zip(zipper[3] + zipper[4])
    middles.each_with_index{|small_array, index| small_array.reverse! if index % 2 == 1}
    middles.flatten!
    solution = new_zipper.zip(middles).flatten
    solution.delete(0)
    puts solution.join("")
  end

end


Rail_Fence_Cipher.new "decrypt", 4, "rclretoiygardimapomeddrm"

Rail_Fence_Cipher.new "encrypt", 4, "redditcomdailyprogrammer"