Add planner previews and streaming

server/streamer.py

@@ -0,0 +1,38 @@
+from __future__ import annotations
+
+from collections import defaultdict
+from typing import Any, DefaultDict, Dict, List
+
+from fastapi import WebSocket
+from websockets.exceptions import ConnectionClosedError
+
+
+class ScreenshotStreamer:
+    """Keeps websocket listeners and pushes screenshot updates."""
+
+    def __init__(self) -> None:
+        self._listeners: DefaultDict[str, List[WebSocket]] = defaultdict(list)
+
+    async def connect(self, websocket: WebSocket, grid_id: str | None = None) -> str:
+        await websocket.accept()
+        key = grid_id or "*"
+        self._listeners[key].append(websocket)
+        return key
+
+    def disconnect(self, websocket: WebSocket, grid_key: str | None = None) -> None:
+        key = grid_key or "*"
+        sockets = self._listeners.get(key)
+        if not sockets:
+            return
+        if websocket in sockets:
+            sockets.remove(websocket)
+        if not sockets:
+            self._listeners.pop(key, None)
+
+    async def broadcast(self, grid_id: str, payload: Dict[str, Any]) -> None:
+        listeners = list(self._listeners.get(grid_id, [])) + list(self._listeners.get("*", []))
+        for websocket in listeners:
+            try:
+                await websocket.send_json(payload)
+            except (ConnectionClosedError, RuntimeError):
+                self.disconnect(websocket, grid_id)