Rock Scissors Paper game in Elixir! (remember to wrap this inside a module)

rps.ex

  @weapons ~w(rock scissors paper)a

  def rps(user_choice) when is_binary(user_choice), do: is_valid_choice(String.to_atom(user_choice))
  def rps(user_choice) when is_atom(user_choice), do: is_valid_choice(user_choice)
  def rps(user_choice), do: {:lost, "Invalid type!"}

  defp is_valid_choice(user_choice) when user_choice in @weapons, do: time_to_play(user_choice)
  defp is_valid_choice(user_choice), do: {:lost, "Invalid choice!"}

  defp time_to_play(user_choice) do
    weapons = @weapons
    computer_choice = Enum.random(weapons)

    computer_choice_index = find_weapon_index(weapons, computer_choice)
    user_choice_index = find_weapon_index(weapons, user_choice)

    game_result = cond do
      user_choice_index == computer_choice_index -> :draft
      rem(user_choice_index + 1, 3) == computer_choice_index -> :win
      true -> :lost
    end

    format_result_with_message(%{game_result: game_result, user_choice: user_choice, computer_choice: computer_choice})
  end

  defp find_weapon_index(weapons, choice) do
    Enum.find_index(weapons, & &1 == choice)
  end

  defp format_result_with_message(%{game_result: game_result, user_choice: user_choice, computer_choice: computer_choice}) do
    {game_result, result_message(user_choice, computer_choice)}
  end

  defp result_message(user_choice, computer_choice) do
    "You: #{user_choice}, Computer: #{computer_choice}"
  end