Simple in-process pub/sub event bus.

In production replace with Phoenix.PubSub, Broadway, or a message broker.

Usage

DDD.EventBus.subscribe(MyApp.Events.OrderPlaced, MyApp.Handlers.SendEmail)
DDD.EventBus.publish(event)

defmodule MyApp.Handlers.SendEmail do
  def handle(%MyApp.Events.OrderPlaced{} = event) do
    MyApp.Mailer.send_confirmation(event.customer_id)
  end
end