chronoscope/lib/chronoscope_web/client_activator.ex

defmodule ChronoscopeWeb.ClientActivator do
  use GenServer

  require Logger

  alias Chronoscope.NTS
  alias Chronoscope.NTS.Parse
  alias ChronoscopeWeb.Endpoint

  @topic Application.compile_env(:chronoscope, :nts_topic)
  @nts_file Application.compile_env(:chronoscope, :nts_file)

  def start_link(_) do
    GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
  end

  @impl true
  def init(_) do
    Endpoint.subscribe(@topic)

    {:ok, %{nts_servers: nts_servers() |> tap(&start_clients/1)}}
  end

  @impl true
  def handle_info(%{topic: @topic, event: "initializing", payload: server}, state) do
    if server in state.nts_servers do
      Logger.info("activating #{inspect(server)}")
      NTS.auto_refresh(server)
    end

    {:noreply, state}
  end

  @impl true
  def handle_info(%{topic: @topic, event: "cancel-auto-refresh", payload: server}, state) do
    if server in state.nts_servers do
      Logger.info("#{inspect(server)} was deactivated")
    end

    {:noreply, state}
  end

  @impl true
  def handle_info(_, state) do
    {:noreply, state}
  end

  @impl true
  def handle_call(:get_nts_servers, _from, state) do
    {:reply, state.nts_servers, state}
  end

  defp start_clients(servers) do
    Enum.each(servers, &NTS.start_client/1)
  end

  defp nts_servers() do
    File.touch(Application.app_dir(:chronoscope, @nts_file))

    Application.app_dir(:chronoscope, @nts_file)
    |> File.stream!()
    |> Stream.map(&String.trim/1)
    |> Stream.filter(&(&1 != ""))
    |> Stream.map(&Parse.parse_nts_server/1)
    |> Enum.to_list()
  end
end