defmodule EightBallChip do
    @answers [
    "It is certain",
    "It is decidedly so",
    "Without a doubt",
    "Yes, definitely",
    "You may rely on it",
    "As I see it, yes",
    "Most likely",
    "Outlook good",
    "Yes",
    "Signs point to yes",
    "Reply hazy try again",
    "Ask again later",
    "Better not tell you now",
    "Cannot predict now",
    "Concentrate and ask again",
    "Don't count on it",
    "My reply is no",
    "My sources say no",
    "Outlook not so good",
    "Very doubtful"
  ]

  def ask(question) do
      EightBallChip.QuestionValidator.validate!(question)
      @answers |> Enum.shuffle |> List.first
  end

end


  defmodule EightBallChip.QuestionValidator do
      @validation_regex ~r/\?$/

      def validate!(question) when is_binary(question) do
          unless String.strip(question) =~ @validation_regex, do: throw_validation_error
      end

      def validate!(question) do
          throw_validation_error
      end

      defp throw_validation_error do
          throw "Question must be a string, ending with a question mark."
      end
  end