defmodule Mix.Tasks.Test.Watch do
  use Mix.Task
  use GenServer

  def run(_) do
    Application.start :fs
    GenServer.start_link( __MODULE__, [], name: __MODULE__ )
    :timer.sleep :infinity
  end


  def init(_) do
    :fs.subscribe
    {:ok, []}
  end

  def handle_info({_pid, {:fs, :file_event}, {path, _event}}, _) do
    path = to_string path
    if watching? path do run_tests end
    {:noreply, []}
  end


  defp watching?(path) do
    Regex.match?( ~r/\.exs?\z/i, path )
  end

  defp run_tests do
    # Mix.Tasks.Test.run []
    output = :os.cmd( mix_cmd )
    IO.puts to_string(output)
  end

  defp mix_cmd do
    enable_ansi = "Application.put_env(:elixir, :ansi_enabled, true);"
    set_mix_env = ~S[System.put_env("MIX_ENV", "test");]
    to_char_list  ~s[mix do run -e '#{enable_ansi} #{set_mix_env}', test]
  end
end