Implement legal terms, Android client compatibility and more

backend/services/main/presence_service.py

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+"""In-memory user presence derived from WebSocket connections only."""
+from __future__ import annotations
+
+from datetime import datetime
+
+from fastapi import WebSocket
+
+
+class PresenceService:
+    def __init__(self) -> None:
+        self._connections: dict[int, set[WebSocket]] = {}
+        self._last_seen: dict[int, datetime] = {}
+
+    def register_connection(self, user_id: int, websocket: WebSocket) -> bool:
+        """Track a live connection. Returns True if the user became online."""
+        connections = self._connections.setdefault(user_id, set())
+        was_online = bool(connections)
+        connections.add(websocket)
+        return not was_online
+
+    def unregister_connection(self, user_id: int, websocket: WebSocket) -> tuple[bool, datetime | None]:
+        """Remove a connection. Returns (became_offline, last_seen) when the last conn drops."""
+        connections = self._connections.get(user_id)
+        if not connections:
+            return False, self._last_seen.get(user_id)
+
+        connections.discard(websocket)
+        if connections:
+            return False, None
+
+        del self._connections[user_id]
+        last_seen = datetime.now()
+        self._last_seen[user_id] = last_seen
+        return True, last_seen
+
+    def touch(self, user_id: int) -> None:
+        """Refresh activity timestamp while online."""
+        if self.is_online(user_id):
+            self._last_seen[user_id] = datetime.now()
+
+    def is_online(self, user_id: int) -> bool:
+        connections = self._connections.get(user_id)
+        return bool(connections)
+
+    def get_last_seen(self, user_id: int) -> datetime | None:
+        if self.is_online(user_id):
+            return self._last_seen.get(user_id) or datetime.now()
+        return self._last_seen.get(user_id)
+
+    def get_presence(self, user_id: int) -> tuple[bool, datetime | None]:
+        online = self.is_online(user_id)
+        if online:
+            return True, self.get_last_seen(user_id)
+        last_seen = self._last_seen.get(user_id)
+        return False, last_seen
+
+    def remove_user(self, user_id: int) -> None:
+        """Drop all presence state for a deleted user."""
+        self._connections.pop(user_id, None)
+        self._last_seen.pop(user_id, None)
+
+
+presence_service = PresenceService()