Event bus basics

app/events/__init__.py

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+from concurrent.futures import ThreadPoolExecutor
+from dataclasses import dataclass
+from functools import wraps
+from typing import Dict, List, Callable
+
+from injectable import injectable, inject
+
+
+@dataclass
+class Event:
+  pass
+
+
+@injectable(singleton=True)
+class SimpleEventBus:
+  def __init__(self):
+    self._handlers: Dict[type, List[Callable]] = {}
+    self._executor = ThreadPoolExecutor()
+
+  def publish(self, event: Event) -> None:
+      for handler in self._handlers.get(type(event), []):
+        # Fire-and-forget execution
+        self._executor.submit(handler, event)
+
+  def subscribe(self, event_type: type, handler: Callable) -> None:
+    if event_type not in self._handlers:
+      self._handlers[event_type] = []
+    self._handlers[event_type].append(handler)
+
+  @staticmethod
+  def on(event: type) -> Callable:
+    def outer(func):
+      inject(SimpleEventBus).subscribe(event, func)
+
+      @wraps(func)
+      def wrapper(*args, **kwargs):
+        return func(*args, **kwargs)
+
+      return wrapper
+
+    return outer