caesar_cipher.rb

class CaesarCipherizer

  def initialize(distance = nil)
    @distance = distance.to_i
  end

  def encrypt(text)
    text.tr(alphabet, cipher)
  end

  def decrypt(text)
    text.tr(cipher, alphabet)
  end

  private
  attr_reader :distance

  def alphabet
    Alphabet.to_s
  end

  def cipher
    CaesarCipher.new(distance: distance).to_s
  end
end

class CaesarCipher

  def initialize(distance: 0)
    raise ArgumentError unless distance.is_a? Integer
    @distance = distance
  end

  def to_s
    Alphabet.to_a.rotate(distance).join
  end

  private
  attr_reader :distance
end

module Alphabet
  def self.to_a
    [*('a'..'z'), *('A'..'Z')]
  end

  def self.to_s
    to_a.join
  end
end

#~-~-~-~#

require 'minitest/autorun'

describe 'CaesarCipherizer' do
  subject { CaesarCipherizer.new(distance) }
  let(:distance) { nil }

  describe "#encrypt" do
    describe "with no distance specified" do

      it "should return the original string" do
        assert_equal "Hello", subject.encrypt("Hello")
        assert_equal "Testing", subject.encrypt("Testing")
      end
    end

    describe "with a distance of 1 specified" do
      let(:distance) { 1 }

      it "should return the correct string" do
        assert_equal "Ifmmp", subject.encrypt("Hello")
        assert_equal "Uftujoh", subject.encrypt("Testing")
      end
    end

    describe "with a distance of 5 specified" do
      let(:distance) { 5 }

      it "should return the correct string" do
        assert_equal "Mjqqt", subject.encrypt("Hello")
        assert_equal "doCDsxq", subject.encrypt("Yjxynsl")
      end
    end
  end

  describe '.distance' do
    describe "with no distance specified" do

      it "should be inaccessible" do
        assert_raises(NoMethodError) { subject.distance }
      end
    end

    describe "with a distance of 1 specified" do
      let(:distance) { 1 }

      it "should still be totallyl inaccessible" do
        assert_raises(NoMethodError) { subject.distance }
      end
    end
  end
end

describe 'CaesarCipher' do
  subject { CaesarCipher.new(distance: distance) }

  let(:distance) { nil }

  it "should be not give away its distance" do
    assert_raises(ArgumentError) { subject.distance }
  end

  describe "#to_s" do
    describe "with a hil input" do
      it "should repeat back the alphabet" do
        assert_equal "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ", CaesarCipher.new.to_s
      end
    end

    it "should not give away its distance" do
      assert_raises(NoMethodError) { CaesarCipher.new.distance }
    end

    describe "with a 0 input" do
      let(:distance) { 0 }
      it "should repeat back the alphabet" do
        assert_equal "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ", subject.to_s
      end

      it "should not give away its distance" do
        assert_raises(NoMethodError) { subject.distance }
      end
    end

    describe "with a 1 input" do
      let(:distance) { 1 }
      it "should repeat back the alphabet shifted one across" do
        assert_equal "bcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZa", subject.to_s
      end

      it "should not give away its distance" do
        assert_raises(NoMethodError) { subject.distance }
      end
    end
  end
end