Replace interface singleton class with cached functions

src/blueapi/service/interface.py

@@ -1,16 +1,14 @@
+import logging
 from collections.abc import Mapping
+from functools import lru_cache
 from typing import Any
 
 from blueapi.config import ApplicationConfig
 from blueapi.core.context import BlueskyContext
 from blueapi.core.event import EventStream
 from blueapi.messaging.base import MessagingTemplate
 from blueapi.messaging.stomptemplate import StompMessagingTemplate
-from blueapi.service.model import (
-    DeviceModel,
-    PlanModel,
-    WorkerTask,
-)
+from blueapi.service.model import DeviceModel, PlanModel, WorkerTask
 from blueapi.worker.event import TaskStatusEnum, WorkerState
 from blueapi.worker.reworker import TaskWorker
 from blueapi.worker.task import Task
@@ -20,61 +18,77 @@
 context and worker"""
 
 
-class InitialisationException(Exception):
-    pass
+_CONFIG: ApplicationConfig = ApplicationConfig()
 
 
-class _Singleton:
-    context: BlueskyContext
-    worker: Worker
-    messaging_template: MessagingTemplate | None = None
-    initialized = False
+def config() -> ApplicationConfig:
+    return _CONFIG
 
 
-def start_worker(
-    config: ApplicationConfig,
-    bluesky_context: BlueskyContext | None = None,
-    worker: TaskWorker | None = None,
-) -> None:
-    """Creates and starts a worker with supplied config"""
-    if _Singleton.initialized:
-        raise InitialisationException(
-            "Worker is already running. To reload call stop first"
-        )
-    if bluesky_context is None:
-        _Singleton.context = BlueskyContext()
-        _Singleton.context.with_config(config.env)
-    else:
-        _Singleton.context = bluesky_context
+def set_config(new_config: ApplicationConfig):
+    global _CONFIG
 
-    if worker is None:
-        _Singleton.worker = TaskWorker(
-            _Singleton.context,
-            broadcast_statuses=config.env.events.broadcast_status_events,
-        )
-    else:
-        _Singleton.worker = worker
-    if config.stomp is not None:
-        _Singleton.messaging_template = StompMessagingTemplate.autoconfigured(
-            config.stomp
-        )
+    _CONFIG = new_config
 
-    # Start worker and setup events
-    _Singleton.worker.start()
-    if _Singleton.messaging_template is not None:
-        event_topic = _Singleton.messaging_template.destinations.topic(
-            "public.worker.event"
-        )
+
+@lru_cache
+def context() -> BlueskyContext:
+    ctx = BlueskyContext()
+    ctx.with_config(config().env)
+    return ctx
+
+
+@lru_cache
+def worker() -> Worker:
+    worker = TaskWorker(
+        context(),
+        broadcast_statuses=config().env.events.broadcast_status_events,
+    )
+    worker.start()
+    return worker
+
+
+@lru_cache
+def messaging_template() -> MessagingTemplate | None:
+    stomp_config = config().stomp
+    if stomp_config is not None:
+        template = StompMessagingTemplate.autoconfigured(stomp_config)
+
+        task_worker = worker()
+        event_topic = template.destinations.topic("public.worker.event")
 
         _publish_event_streams(
             {
-                _Singleton.worker.worker_events: event_topic,
-                _Singleton.worker.progress_events: event_topic,
-                _Singleton.worker.data_events: event_topic,
+                task_worker.worker_events: event_topic,
+                task_worker.progress_events: event_topic,
+                task_worker.data_events: event_topic,
             }
         )
-        _Singleton.messaging_template.connect()
-    _Singleton.initialized = True
+        template.connect()
+        return template
+    else:
+        return None
+
+
+def setup(config: ApplicationConfig) -> None:
+    """Creates and starts a worker with supplied config"""
+
+    set_config(config)
+
+    # Eagerly initialize worker and messaging connection
+
+    logging.basicConfig(level=config.logging.level)
+    worker()
+    messaging_template()
+
+
+def teardown() -> None:
+    worker().stop()
+    if (template := messaging_template()) is not None:
+        template.disconnect()
+    context.cache_clear()
+    worker.cache_clear()
+    messaging_template.cache_clear()
 
 
 def _publish_event_streams(streams_to_destinations: Mapping[EventStream, str]) -> None:
@@ -84,130 +98,87 @@ def _publish_event_streams(streams_to_destinations: Mapping[EventStream, str]) -
 
 def _publish_event_stream(stream: EventStream, destination: str) -> None:
     def forward_message(event: Any, correlation_id: str | None) -> None:
-        if _Singleton.messaging_template is not None:
-            _Singleton.messaging_template.send(destination, event, None, correlation_id)
+        if (template := messaging_template()) is not None:
+            template.send(destination, event, None, correlation_id)
 
     stream.subscribe(forward_message)
 
 
-def stop_worker() -> None:
-    if not _Singleton.initialized:
-        raise InitialisationException(
-            "Cannot stop worker as it hasn't been started yet"
-        )
-    _Singleton.initialized = False
-    _Singleton.worker.stop()
-    if (
-        _Singleton.messaging_template is not None
-        and _Singleton.messaging_template.is_connected()
-    ):
-        _Singleton.messaging_template.disconnect()
-
-
 def get_plans() -> list[PlanModel]:
     """Get all available plans in the BlueskyContext"""
-    _ensure_worker_started()
-    return [PlanModel.from_plan(plan) for plan in _Singleton.context.plans.values()]
+    return [PlanModel.from_plan(plan) for plan in context().plans.values()]
 
 
 def get_plan(name: str) -> PlanModel:
     """Get plan by name from the BlueskyContext"""
-    _ensure_worker_started()
-    return PlanModel.from_plan(_Singleton.context.plans[name])
+    return PlanModel.from_plan(context().plans[name])
 
 
 def get_devices() -> list[DeviceModel]:
     """Get all available devices in the BlueskyContext"""
-    _ensure_worker_started()
-    return [
-        DeviceModel.from_device(device)
-        for device in _Singleton.context.devices.values()
-    ]
+    return [DeviceModel.from_device(device) for device in context().devices.values()]
 
 
 def get_device(name: str) -> DeviceModel:
     """Retrieve device by name from the BlueskyContext"""
-    _ensure_worker_started()
-    return DeviceModel.from_device(_Singleton.context.devices[name])
+    return DeviceModel.from_device(context().devices[name])
 
 
 def submit_task(task: Task) -> str:
     """Submit a task to be run on begin_task"""
-    _ensure_worker_started()
-    return _Singleton.worker.submit_task(task)
+    return worker().submit_task(task)
 
 
 def clear_task(task_id: str) -> str:
     """Remove a task from the worker"""
-    _ensure_worker_started()
-    return _Singleton.worker.clear_task(task_id)
+    return worker().clear_task(task_id)
 
 
 def begin_task(task: WorkerTask) -> WorkerTask:
     """Trigger a task. Will fail if the worker is busy"""
-    _ensure_worker_started()
     if task.task_id is not None:
-        _Singleton.worker.begin_task(task.task_id)
+        worker().begin_task(task.task_id)
     return task
 
 
 def get_tasks_by_status(status: TaskStatusEnum) -> list[TrackableTask]:
     """Retrieve a list of tasks based on their status."""
-    _ensure_worker_started()
-    return _Singleton.worker.get_tasks_by_status(status)
+    return worker().get_tasks_by_status(status)
 
 
 def get_active_task() -> TrackableTask | None:
     """Task the worker is currently running"""
-    _ensure_worker_started()
-    return _Singleton.worker.get_active_task()
+    return worker().get_active_task()
 
 
 def get_worker_state() -> WorkerState:
     """State of the worker"""
-    _ensure_worker_started()
-    return _Singleton.worker.state
+    return worker().state
 
 
 def pause_worker(defer: bool | None) -> None:
     """Command the worker to pause"""
-    _ensure_worker_started()
-    _Singleton.worker.pause(defer)
+    worker().pause(defer)
 
 
 def resume_worker() -> None:
     """Command the worker to resume"""
-    _ensure_worker_started()
-    _Singleton.worker.resume()
+    worker().resume()
 
 
 def cancel_active_task(failure: bool, reason: str | None) -> str:
     """Remove the currently active task from the worker if there is one
     Returns the task_id of the active task"""
-    _ensure_worker_started()
-    return _Singleton.worker.cancel_active_task(failure, reason)
+    return worker().cancel_active_task(failure, reason)
 
 
 def get_tasks() -> list[TrackableTask]:
     """Return a list of all tasks on the worker,
     any one of which can be triggered with begin_task"""
-    _ensure_worker_started()
-    return _Singleton.worker.get_tasks()
+    return worker().get_tasks()
 
 
 def get_task_by_id(task_id: str) -> TrackableTask | None:
     """Returns a task matching the task ID supplied,
     if the worker knows of it"""
-    _ensure_worker_started()
-    return _Singleton.worker.get_task_by_id(task_id)
-
-
-def get_state() -> bool:
-    """Initialization state"""
-    return _Singleton.initialized
-
-
-def _ensure_worker_started() -> None:
-    if _Singleton.initialized:
-        return
-    raise InitialisationException("Worker must be stared before it is used")
+    return worker().get_task_by_id(task_id)