defmodule Caesar_cipher do
  defp set_map(map, range, key) do
    org = Enum.map(range, &List.to_string [&1])
    {a, b} = Enum.split(org, key)
    Enum.zip(org, b ++ a) |> Enum.into(map)
  end

  def encode(text, key) do
    map = Map.new |> set_map(?a..?z, key) |> set_map(?A..?Z, key)
    String.graphemes(text) |> Enum.map_join(fn c -> Map.get(map, c, c) end)
  end
end

text = "The five boxing wizards jump quickly"
key = 3
IO.puts "Original:  #{text}"
IO.puts "Encrypted: #{enc = Caesar_cipher.encode(text, key)}"
IO.puts "Decrypted: #{Caesar_cipher.encode(enc, -key)}"