dsl.ex

defmodule MessageRouter.DSL do
  alias MessageRouter.Route
  alias MessageRouter.QueueHandler
  alias MessageRouter.Supervisor

  defmacro __using__(_args) do
    quote do
      import MessageRouter.DSL

      Module.register_attribute(__MODULE__, :routes, accumulate: true)
      Module.register_attribute(__MODULE__, :queue_handlers, accumulate: true)

      def routes do
        @routes |> Enum.group_by(&(&1.queue))
      end

      def queue_handlers do
        @queue_handlers
      end
    end
  end

  defmacro route(options) do
    key = Keyword.fetch!(options, :key)
    queue = Keyword.fetch!(options, :to)
    route = %Route{key: key, queue: queue}

    quote do
      Module.put_attribute __MODULE__, :routes, unquote(Macro.escape(route))
    end
  end

  defmacro handle(options) do
    queue = Keyword.fetch!(options, :queue)
    handler = Keyword.fetch!(options, :with)
    queue_handler = %QueueHandler{queue: queue, handler: handler}

    quote do
      @queue_handlers unquote(Macro.escape(queue_handler))
    end
  end
end

dsl_test.exs

defmodule MessageRouter.DSLTest do
  use ExUnit.Case, async: true

  defmodule Router do
    use MessageRouter.DSL

    route(key: "source.event", to: "destination.event")
    route(key: "other_source.event", to: "destination.event")

    handle(queue: "destination.queue", with: Handler)
  end

  test ".routes" do
    # Should be a map of queue name to routes
    assert Router.routes == %{}
  end

  test ".queue_handlers" do
    # Should be a list of handlers
    assert Router.queue_handlers == []
  end
end