Add framework and apiserver

[pti/o2.git] / src / o2ims / service / messagebus.py

diff --git a/src/o2ims/service/messagebus.py b/src/o2ims/service/messagebus.py
new file mode 100644 (file)
index 0000000..bff45ab
--- /dev/null
+++ b/src/o2ims/service/messagebus.py
@@ -0,0 +1,69 @@
+# Copyright (C) 2021 Wind River Systems, Inc.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+# pylint: disable=broad-except, attribute-defined-outside-init
+from __future__ import annotations
+import logging
+from typing import Callable, Dict, List, Union, Type, TYPE_CHECKING
+from o2ims.domain import commands, events
+
+if TYPE_CHECKING:
+    from . import unit_of_work
+
+logger = logging.getLogger(__name__)
+
+Message = Union[commands.Command, events.Event]
+
+
+class MessageBus:
+    def __init__(
+        self,
+        uow: unit_of_work.AbstractUnitOfWork,
+        event_handlers: Dict[Type[events.Event], List[Callable]],
+        command_handlers: Dict[Type[commands.Command], Callable],
+    ):
+        self.uow = uow
+        self.event_handlers = event_handlers
+        self.command_handlers = command_handlers
+
+    def handle(self, message: Message):
+        self.queue = [message]
+        while self.queue:
+            message = self.queue.pop(0)
+            if isinstance(message, events.Event):
+                self.handle_event(message)
+            elif isinstance(message, commands.Command):
+                self.handle_command(message)
+            else:
+                raise Exception(f"{message} was not an Event or Command")
+
+    def handle_event(self, event: events.Event):
+        for handler in self.event_handlers[type(event)]:
+            try:
+                logger.debug("handling event %s with handler %s", event, handler)
+                handler(event)
+                self.queue.extend(self.uow.collect_new_events())
+            except Exception:
+                logger.exception("Exception handling event %s", event)
+                continue
+
+    def handle_command(self, command: commands.Command):
+        logger.debug("handling command %s", command)
+        try:
+            handler = self.command_handlers[type(command)]
+            handler(command)
+            self.queue.extend(self.uow.collect_new_events())
+        except Exception:
+            logger.exception("Exception handling command %s", command)
+            raise