Code for step 6

lib/elixir_popularity/application.ex

@@ -27,7 +27,8 @@ defmodule ElixirPopularity.Application do
              }
            ]},
         restart: :transient
-      }
+      },
+      ElixirPopularity.HackernewsIdProcessor
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html

lib/hackernews_id_processor.ex

@@ -0,0 +1,64 @@
+defmodule ElixirPopularity.HackernewsIdProcessor do
+  use Broadway
+
+  alias Broadway.Message
+  alias ElixirPopularity.{HackernewsApi, RMQPublisher}
+
+  def start_link(_opts) do
+    Broadway.start_link(__MODULE__,
+      name: __MODULE__,
+      producers: [
+        default: [
+          module:
+            {BroadwayRabbitMQ.Producer,
+             queue: RMQPublisher.item_id_queue_name(),
+             connection: [
+               username: "rabbitmq",
+               password: "rabbitmq"
+             ]},
+          stages: 1
+        ]
+      ],
+      processors: [
+        default: [
+          stages: 100
+        ]
+      ],
+      batchers: [
+        default: [
+          batch_size: 10,
+          batch_timeout: 10_000,
+          stages: 2
+        ]
+      ]
+    )
+  end
+
+  @impl true
+  def handle_message(_processor, message, _context) do
+    Message.update_data(message, fn hn_id ->
+      {hn_id, HackernewsApi.get_hn_item(hn_id)}
+    end)
+  end
+
+  @impl true
+  def handle_batch(_batcher, messages, _batch_info, _context) do
+    encoded_payload =
+      messages
+      |> Enum.reject(fn
+        %Message{data: {_id, :error}} -> true
+        _ -> false
+      end)
+      |> Enum.map(fn %Message{data: {id, item}} ->
+        %{
+          id: id,
+          item: Map.from_struct(item)
+        }
+      end)
+      |> Jason.encode!()
+
+    RMQPublisher.publish_hn_items(encoded_payload)
+
+    messages
+  end
+end