add notifier

notifier.py

@@ -0,0 +1,44 @@
+from typing import TypedDict
+
+import json
+import pika
+from pika.adapters.blocking_connection import BlockingChannel
+from pika.spec import Basic
+
+conn = pika.BlockingConnection(pika.ConnectionParameters("localhost"))
+ch = conn.channel()
+
+ch.basic_qos(prefetch_count=1)
+
+# hover over on_messae_callback
+# the docs specify signature
+
+
+class OrderMessage(TypedDict):
+    order_id: int
+    user_id: str
+    amount: float
+    should_fail: bool
+    retry_count: int
+
+
+def on_order_processed(channel: BlockingChannel, method: Basic.Deliver, properties, body):
+    order: OrderMessage = json.loads(body)
+    print(f"processed order: {order["order_id"]}")
+    channel.basic_ack(delivery_tag=method.delivery_tag)
+
+
+def on_order_failed(channel: BlockingChannel, method: Basic.Deliver, properties, body):
+    order: OrderMessage = json.loads(body)
+    print(f"failed after retries: {order["order_id"]}")
+    channel.basic_ack(delivery_tag=method.delivery_tag)
+
+
+ch.basic_consume(queue="orders.processed.q",
+                 on_message_callback=on_order_processed, auto_ack=False)
+ch.basic_consume(queue="orders.failed.q",
+                 on_message_callback=on_order_failed, auto_ack=False)
+
+# easy to forget
+print("[notifier] waiting on messages")
+ch.start_consuming()