exercise.ex

defmodule Test do
  @proto_version "1.0"

  def process_options(opts) do
    ["-proto", @proto_version] ++ log_opt ++ process_input_options(opts)
  end

  defp log_opt do
    case :application.get_env(:porcelain, :goon_driver_log) do
      :undefined -> []
      {:ok, val} -> ["-log", val]
    end
  end

  defp process_input_options(opts) do
    Enum.reduce(opts, [], &(process_option(&1) ++ &2))
  end

  defp process_option({:in, true}), do: ["-in"]
  defp process_option({:err, :out}), do: ["-err", "out"]
  defp process_option({:err, :err}), do: ["-err", "err"]
  defp process_option({:dir, dir}), do: ["-dir", "dir"]
  defp process_option(_), do: []
end

Test.process_options(in: true, err: :out, dir: "dir")