Log entity state changes

link/adapters/present.py

@@ -18,3 +18,23 @@ def update_idle_entities(response: events.IdleEntitiesListed) -> None:
         update(translator.to_primary_key(identifier) for identifier in response.identifiers)
 
     return update_idle_entities
+
+
+def create_state_change_logger(
+    translator: IdentificationTranslator, log: Callable[[str], None]
+) -> Callable[[events.StateChanged], None]:
+    """Create a logger that logs state changes of entities."""
+
+    def log_state_change(state_change: events.StateChanged) -> None:
+        context = {
+            "identifier": translator.to_primary_key(state_change.identifier),
+            "operation": state_change.operation.name,
+            "transition": {
+                "old": state_change.transition.current.__name__,
+                "new": state_change.transition.new.__name__,
+            },
+            "command": state_change.command.name,
+        }
+        log(f"Entity state changed {context}")
+
+    return log_state_change

link/infrastructure/link.py

@@ -1,6 +1,7 @@
 """Contains the link decorator that is used by the user to establish a link."""
 from __future__ import annotations
 
+import logging
 from collections.abc import Callable
 from functools import partial
 from typing import Any, Mapping, Optional
@@ -9,9 +10,9 @@
 from link.adapters.custom_types import PrimaryKey
 from link.adapters.gateway import DJLinkGateway
 from link.adapters.identification import IdentificationTranslator
-from link.adapters.present import create_idle_entities_updater
+from link.adapters.present import create_idle_entities_updater, create_state_change_logger
 from link.domain import commands, events
-from link.service.handlers import delete, list_idle_entities, pull
+from link.service.handlers import delete, list_idle_entities, log_state_change, pull
 from link.service.messagebus import CommandHandlers, EventHandlers, MessageBus
 from link.service.uow import UnitOfWork
 
@@ -46,14 +47,17 @@ def inner(obj: type) -> Any:
         uow = UnitOfWork(gateway)
         source_restriction: IterationCallbackList[PrimaryKey] = IterationCallbackList()
         idle_entities_updater = create_idle_entities_updater(translator, create_content_replacer(source_restriction))
+        logger = logging.getLogger(obj.__name__)
         command_handlers: CommandHandlers = {}
         command_handlers[commands.PullEntities] = partial(pull, uow=uow)
         command_handlers[commands.DeleteEntities] = partial(delete, uow=uow)
         command_handlers[commands.ListIdleEntities] = partial(
             list_idle_entities, uow=uow, output_port=idle_entities_updater
         )
         event_handlers: EventHandlers = {}
-        event_handlers[events.StateChanged] = [lambda event: None]
+        event_handlers[events.StateChanged] = [
+            partial(log_state_change, log=create_state_change_logger(translator, logger.info))
+        ]
         event_handlers[events.InvalidOperationRequested] = [lambda event: None]
         bus = MessageBus(uow, command_handlers, event_handlers)
         controller = DJController(bus, translator)

link/service/handlers.py

@@ -32,3 +32,8 @@ def list_idle_entities(
     with uow:
         idle = uow.link.list_idle_entities()
         output_port(events.IdleEntitiesListed(idle))
+
+
+def log_state_change(event: events.StateChanged, log: Callable[[events.StateChanged], None]) -> None:
+    """Log the state change of an entity."""
+    log(event)