import asyncio
from typing import Dict, Set, Any

class Hub:
    def __init__(self):
        self._lock = asyncio.Lock()
        self._subs: Dict[int, Set[Any]] = {}  # panel_id -> set[WebSocket]

    async def subscribe(self, panel_id: int, ws):
        async with self._lock:
            self._subs.setdefault(panel_id, set()).add(ws)

    async def unsubscribe(self, panel_id: int, ws):
        async with self._lock:
            s = self._subs.get(panel_id)
            if s and ws in s:
                s.remove(ws)
            if s and len(s) == 0:
                self._subs.pop(panel_id, None)

    async def connections(self, panel_id: int):
        async with self._lock:
            return list(self._subs.get(panel_id, set()))

hub = Hub()