defmodule Extreme.System.NodeMonitor do
  require Logger

  def start_link do
    {:ok,
     spawn_link(fn ->
       :global_group.monitor_nodes(true)
       Process.register(self(), __MODULE__)
       monitor()
     end)}
  end

  def monitor do
    receive do
      {:nodeup, node} ->
        Logger.info("NodeMonitor: #{node} joined")

      {:nodedown, node} ->
        Logger.warn("NodeMonitor: #{node} left")
        check_cluster()
    end

    monitor()
  end

  defp check_cluster do
    unless in_cluster?(),
      # Node.stop
      do: Logger.error("There's no lighthouse in this cluster. We should restart!")
  end

  defp in_cluster?,
    do:
      Node.list()
      |> Enum.any?(fn node -> node |> to_string |> String.starts_with?("lighthouse") end)
end