top-secret

elixir/top-secret/lib/top_secret.ex

@@ -0,0 +1,35 @@
+defmodule TopSecret do
+  def to_ast(string), do: Code.string_to_quoted!(string)
+
+  def decode_secret_message_part({is_function?, _, arguments} = ast, acc)
+      when is_function? in [:defp, :def] do
+    {ast, [get_letters(arguments) | acc]}
+  end
+
+  def decode_secret_message_part(ast, acc), do: {ast, acc}
+
+  defp get_letters([{:when, _, arguments} | _]), do: get_letters(arguments)
+
+  defp get_letters([{name, _, arguments} | _]) when is_list(arguments),
+    do: letters_from_name_and_arguments(name, arguments)
+
+  defp get_letters([{name, _, arguments} | _]) when is_atom(arguments),
+    do: letters_from_name_and_arguments(name, [])
+
+  defp letters_from_name_and_arguments(name, arguments) do
+    name
+    |> Atom.to_string()
+    |> String.slice(0, length(arguments))
+  end
+
+  def decode_secret_message(string) do
+    {_ast, result} =
+      string
+      |> to_ast()
+      |> Macro.prewalk([], &decode_secret_message_part/2)
+
+    result
+    |> Enum.reverse()
+    |> Enum.join()
+  end
+end