defmodule PigLatin do
  @doc """
  Given a `phrase`, translate it a word at a time to Pig Latin.
  """

  @vowels ~w(a e i o u)

  @spec translate(phrase :: String.t()) :: String.t()
  def translate(phrase) do
    phrase
    |> String.split()
    |> Enum.map(&String.graphemes/1)
    |> Enum.map(&translate_word/1)
    |> Enum.join(" ")
  end

  @spec translate_word(word :: [String.t()]) :: String.t()
  defp translate_word(["q", "u" | rest]), do: rest ++ ~w(quay)
  defp translate_word(["x", "r" | _rest] = word), do: ay(word)
  defp translate_word(["y", "t" | _rest] = word), do: ay(word)
  defp translate_word([hd | _rest] = word) when hd in @vowels, do: ay(word)
  defp translate_word([hd, x | _rest] = word) when hd in ~w(x y) and x not in @vowels, do: ay(word)
  defp translate_word([hd | rest]), do: translate_word(rest ++ [hd])

  @spec ay(word :: [String.t()]) :: [String.t()]
  defp ay(list), do: list ++ ~w(ay)
end