crypto

# ruby 2.6.3
#
class Crypto


  def initialize(method, string, count)
    @method = method
    @string = string
    @count = count
  end

  def call
    return @string if @string.nil? || @string.empty? || @count <= 0

    case @method
    when 'encrypt'
      p encrypt
    when 'decrypt'
      p decrypt
    else
      raise ArgumentError.new("Method must be in %w[encrypt decrypt]")
    end
  end

  private

  def encrypt
    result = @string
    @count.times do |_|
      odd = ''
      even = ''
      result.split('').each_with_index do |letter, index|
        index.even? ? odd << letter : even << letter
      end
      result = odd + even
    end
    result
  end

  def decrypt
    length = @string.length.even? ? @string.length / 2 : @string.length / 2 + 1
    result = @string
    @count.times do |_|
      odd = result[0...length]
      even = result[length..]
      result = ''
      length.times do |index|
        result << odd[index] << even[index]
      end
    end
    result
  end
end

Crypto.new("encrypt", "abcdefghij", 1).call
Crypto.new("decrypt", "acegibdfhj", 1).call


Crypto.new("encrypt", "abcdefghij", 2).call
Crypto.new("decrypt", "aeidhcgbfj", 2).call

Crypto.new("encrypt", "abcdefghij", 3).call
Crypto.new("decrypt", "aihgfedcbj", 3).call