event_bus.ex

defmodule DeviceHandler.EventBus do
  def new(opts) do
    Registry.start_link(opts)
  end

  def child_spec([]) do
    child_spec name: __MODULE__,
      keys: :duplicate
  end

  def child_spec(opts) do
    %{
      id: __MODULE__,
      start: {__MODULE__, :new, [opts]},
      type: :supervisor,
    }
  end

  def subscribe(registry, message, serial \\ :all) do
    Registry.register(registry, message, serial)
  end

  def update(hub), do: update(__MODULE__, hub)
  def update(registry, hub) do
    serial = hub.serial
    Registry.dispatch(registry, :update, fn(subscribers) ->
      for {pid, intrest} <- subscribers, interested?(intrest, serial), do: brodcast({:update, hub}, pid)
    end)
  end

  def remove(hub), do: remove(__MODULE__, hub)
  def remove(registry, serial) do
    Registry.dispatch(registry, :remove, fn(subscribers) ->
      for {pid, intrest} <- subscribers, interested?(intrest, serial), do: brodcast({:remove, serial}, pid)
    end)
  end

  defp interested?(:all, _), do: true
  defp interested?(intrest, serial), do: intrest == serial

  defp brodcast(event, pid), do: send(pid, {:event, event})
end