defmodule CaesarCipher do
  @moduledoc """
  Documentation for `CaesarCipher`.
  """

  @caesar_map ~w/A B C D E F G H I J K L M N O P Q R S T U V W X Y Z/
  @alphabet_lenght 26

    @doc """
    This function encrypt a string with the salt specified.

    ## Examples Encrypt
      iex> CaesarCipher.encrypt("HELLO WORLD", 2) 
      "JGNNQ YQTNF"

  """
  def encrypt(word, salt) do
    run(String.split(String.upcase(word), ""), salt, :+, [])
  end

  @doc """
    This function decrypt a string with the salt specified.

    ## Examples Decrypt
      iex> CaesarCipher.decrypt("JGNNQ YQTNF", 2) 
      "HELLO WORLD"
  """
  def decrypt(word, salt) do
    run(String.split(String.upcase(word), ""), salt, :-, [])
  end

  defp convertToString([""], _, _, result) do
    List.to_string(result)
  end

  defp run([h | t], salt, operator, result) do
    index = Enum.find_index(@caesar_map, fn n -> n == h end)

    replacement =
      if index do
        adjustment = apply(Kernel, operator, [index, salt])
        Enum.at(@caesar_map, rem(adjustment, @alphabet_lenght))
      else
        h
      end

      if t ==  [""] do
        convertToString(t, salt, operator, result ++ [replacement])
      else
        run(t, salt, operator, result ++ [replacement])
      end
  end
end