defmodule ExSpeedGame.PubSub do
  @moduledoc """
  Light pubsub system based on Registry so that processes can listen to state publishes from
  others.

  Processes must be GenServers and respond to state request.
  """

  @spec subscribe(atom | pid) :: term
  def subscribe(target) when is_atom(target) or is_pid(target) do
    target = if is_atom(target), do: Process.whereis(target), else: target

    {:ok, _} = Registry.register(__MODULE__, target, nil)
    GenServer.call(target, {:esg_pubsub, :get_state})
  end

  @spec publish(any) :: :ok
  def publish(data) do
    Registry.dispatch(__MODULE__, self(), fn entries ->
      for {pid, _} <- entries, do: send(pid, {:esg_pubsub, :pub, data})
    end)
  end

  @spec clear(atom | pid) :: :ok
  def clear(target) when is_atom(target) or is_pid(target) do
    target = if is_atom(target), do: Process.whereis(target), else: target

    :ok = Registry.unregister(__MODULE__, target)
  end
end