First Push

backend/events.py

@@ -0,0 +1,49 @@
+"""Server-Sent Event bus for pushing updates to displays.
+
+Events are scoped by user_id so that each user's display only receives
+updates about their own data (alarms, calendar, pomodoro, ...).
+"""
+import json
+import queue
+import threading
+
+
+class EventBus:
+    """Simple pub/sub event system with SSE support.
+
+    publish(event_type, data, user_id=None): when user_id is given, only
+    subscribers registered for that user receive the event.
+    """
+
+    def __init__(self):
+        self._subscribers: list[tuple[int | None, queue.Queue]] = []
+        self._lock = threading.Lock()
+
+    def subscribe(self, user_id: int | None = None) -> queue.Queue:
+        """Subscribe to events. user_id=None receives ALL events (broadcast)."""
+        q: queue.Queue = queue.Queue()
+        with self._lock:
+            self._subscribers.append((user_id, q))
+        return q
+
+    def unsubscribe(self, q: queue.Queue):
+        with self._lock:
+            self._subscribers = [(uid, sq) for uid, sq in self._subscribers if sq is not q]
+
+    def publish(self, event_type: str, data: dict, user_id: int | None = None):
+        msg = json.dumps({"type": event_type, "data": data})
+        with self._lock:
+            dead = []
+            for sub_uid, q in self._subscribers:
+                if sub_uid is not None and user_id is not None and sub_uid != user_id:
+                    continue
+                try:
+                    q.put_nowait(msg)
+                except queue.Full:
+                    dead.append((sub_uid, q))
+            for item in dead:
+                self._subscribers.remove(item)
+
+    def broadcast(self):
+        """Send heartbeat to all subscribers."""
+        self.publish("heartbeat", {"ts": __import__("time").time()})