feat(backend): who of the given people is online now in one request

backend/src/utils/read/presence.py

@@ -48,6 +48,29 @@ async def current_presence(
     return PresenceSample(**dict(row)) if row is not None else None
 
 
+_ONLINE = """
+SELECT peer_id, ts, status, last_online_date, next_offline_date
+FROM (
+    SELECT DISTINCT ON (peer_id)
+           peer_id, ts, status, last_online_date, next_offline_date
+    FROM presence
+    WHERE account_id = $1 AND peer_id = ANY($2::bigint[])
+      AND ts > now() - interval '1 hour'
+    ORDER BY peer_id, ts DESC
+) latest
+WHERE status = 'online' AND next_offline_date > now()
+"""
+
+
+async def online_now(
+    pool: asyncpg.Pool, account_id: int, peer_ids: list[int]
+) -> list[PresenceSample]:
+    if not peer_ids:
+        return []
+    rows = await pool.fetch(_ONLINE, account_id, peer_ids)
+    return [PresenceSample(**dict(row)) for row in rows]
+
+
 async def presence_hourly(
     pool: asyncpg.Pool,
     account_id: int,