Aggregate.ex

defmodule EventSourcing.Aggregate do
  defmacro __using__(_) do
    quote do
      use GenServer
      alias EventSourcing.Event

      def start_link, do: start_link([])

      def start_link(events) do
        GenServer.start_link(__MODULE__, events)
      end

      def init(events) do
        {:ok, apply_events(events)}
      end

      defp apply_events(events) do
        Enum.reduce(events, %{}, &apply_event/2)
      end

      defp apply_event(%Event{name: name, data: data}, state) do
        apply_event(name, data, state)
      end
    end
  end  
end