snapcast

defmodule Snapcast.LocalClient do
  @moduledoc """
  Supervises a local `snapclient` process connected to the embedded Snap server.

  The Homebrew/macOS snapclient daemon mode wants a system pid directory, so the
  client is run in the foreground as an Erlang port. If the process exits, this
  GenServer starts it again after a short delay.
  """

  use GenServer

  require Logger

  @restart_ms 2_000

  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end

  @impl true
  def init(_opts) do
    Process.flag(:trap_exit, true)

    {:ok, %{port: nil}, {:continue, :start_snapclient}}
  end

  @impl true
  def handle_continue(:start_snapclient, state) do
    {:noreply, start_snapclient(state)}
  end

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

  def handle_info({port, {:exit_status, status}}, %{port: port} = state) do
    Logger.warning("local snapclient exited with status #{inspect(status)}; restarting")
    schedule_restart()
    {:noreply, %{state | port: nil}}
  end

  def handle_info({port, {:data, data}}, %{port: port} = state) do
    log_snapclient_output(data)
    {:noreply, state}
  end

  def handle_info(_msg, state), do: {:noreply, state}

  @impl true
  def terminate(_reason, %{port: port}) when is_port(port) do
    Port.close(port)
    :ok
  rescue
    _error -> :ok
  end

  def terminate(_reason, _state), do: :ok

  defp start_snapclient(%{port: port} = state) when is_port(port), do: state

  defp start_snapclient(state) do
    case Snapcast.snapclient_path() do
      path when is_binary(path) ->
        args = snapclient_args()

        stop_stale_snapclients(path, args)
        Logger.info("starting local snapclient: #{path} #{Enum.join(args, " ")}")

        port =
          Port.open({:spawn_executable, path}, [
            :binary,
            :exit_status,
            :stderr_to_stdout,
            args: args
          ])

        %{state | port: port}

      _missing ->
        Logger.warning("local snapclient is enabled but no snapclient executable was found")
        schedule_restart()
        state
    end
  end

  defp snapclient_args do
    [
      "--hostID",
      Snapcast.local_client_id(),
      "--logsink",
      "stdout",
      "--logfilter",
      Snapcast.local_client_logfilter(),
      Snapcast.local_client_url()
    ]
  end

  defp stop_stale_snapclients(path, args) do
    with ps when is_binary(ps) <- System.find_executable("ps"),
         kill when is_binary(kill) <- System.find_executable("kill"),
         {output, 0} <- System.cmd(ps, ["-axo", "pid=,command="]) do
      output
      |> String.split("\n", trim: true)
      |> Enum.flat_map(&stale_snapclient_pid(&1, path, args))
      |> Enum.each(fn pid ->
        Logger.info("stopping stale local snapclient pid #{pid}")
        System.cmd(kill, ["-TERM", pid])
      end)
    else
      _missing_or_failed -> :ok
    end
  end

  defp stale_snapclient_pid(line, path, args) do
    case Regex.run(~r/^\s*(\d+)\s+(.+)$/, line) do
      [_, pid, command] ->
        if stale_snapclient_command?(command, path, args), do: [pid], else: []

      _no_match ->
        []
    end
  end

  defp stale_snapclient_command?(command, path, args) do
    String.starts_with?(command, path) and
      Enum.all?(args, &String.contains?(command, &1))
  end

  defp schedule_restart, do: Process.send_after(self(), :restart_snapclient, @restart_ms)

  defp log_snapclient_output(data) do
    data
    |> to_string()
    |> String.split(["\r", "\n"], trim: true)
    |> Enum.each(&Logger.debug("snapclient: #{&1}"))
  end
end