first cut of message bus [service_talks_to_messagebus]

hjwp · hjwp · commit 833c3e71ad0a · 2024-03-01T15:01:36.000Z
diff --git a/src/allocation/service_layer/messagebus.py b/src/allocation/service_layer/messagebus.py
@@ -0,0 +1,20 @@
+from typing import List, Dict, Callable, Type
+from allocation.adapters import email
+from allocation.domain import events
+
+
+def handle(event: events.Event):
+    for handler in HANDLERS[type(event)]:
+        handler(event)
+
+
+def send_out_of_stock_notification(event: events.OutOfStock):
+    email.send_mail(
+        "stock@made.com",
+        f"Out of stock for {event.sku}",
+    )
+
+
+HANDLERS = {
+    events.OutOfStock: [send_out_of_stock_notification],
+}  # type: Dict[Type[events.Event], List[Callable]]
diff --git a/src/allocation/service_layer/services.py b/src/allocation/service_layer/services.py
@@ -1,11 +1,13 @@
 from __future__ import annotations
-from typing import Optional
+from typing import Optional, TYPE_CHECKING
 from datetime import date
 
-from allocation.adapters import email
 from allocation.domain import model
 from allocation.domain.model import OrderLine
-from allocation.service_layer import unit_of_work
+from . import messagebus
+
+if TYPE_CHECKING:
+    from . import unit_of_work
 
 
 class InvalidSku(Exception):
@@ -38,6 +40,5 @@ def allocate(
             batchref = product.allocate(line)
             uow.commit()
             return batchref
-        except model.OutOfStock:
-            email.send_mail("stock@made.com", f"Out of stock for {line.sku}")
-            raise
+        finally:
+            messagebus.handle(product.events)
