WIP checkpoint: Presence & status model + endpoints (Redis heartbeat)

backend/app/services/presence.py

@@ -0,0 +1,186 @@
+"""Redis-backed presence store.
+
+Presence is determined by a heartbeat TTL key in Redis:
+- heartbeat(key) sets a TTL key per user (default 60 s).
+- is_online(user_id) checks whether the key exists.
+- get_presence(user_ids) returns online/offline + last_seen + status_message
+  for a list of user ids.
+
+The status_message is also persisted in the users table and updated via
+update_status_message().
+"""
+
+from __future__ import annotations
+
+import logging
+from datetime import datetime, timezone
+from typing import Any
+
+import redis.asyncio as aioredis
+
+from app.config import settings
+
+logger = logging.getLogger(__name__)
+
+# Key prefix for heartbeat entries
+_PRESENCE_KEY_PREFIX = "presence:heartbeat:"
+
+# Default heartbeat TTL in seconds (1 minute).
+# Clients should heartbeat at least once per interval.
+_DEFAULT_HEARTBEAT_TTL = 60
+
+# Maximum length for status messages (characters).
+_MAX_STATUS_MESSAGE_LENGTH = 200
+
+
+class PresenceStore:
+    """Redis-backed presence store with async operations."""
+
+    def __init__(self, redis_url: str = settings.REDIS_URL, heartbeat_ttl: int = _DEFAULT_HEARTBEAT_TTL):
+        self._redis_url = redis_url
+        self._heartbeat_ttl = heartbeat_ttl
+        self._client: aioredis.Redis | None = None
+
+    # ------------------------------------------------------------------
+    # Lifecycle
+    # ------------------------------------------------------------------
+
+    async def connect(self) -> None:
+        """Connect to Redis."""
+        self._client = aioredis.from_url(
+            self._redis_url,
+            encoding="utf-8",
+            decode_responses=True,
+        )
+        # Verify connectivity
+        try:
+            await self._client.ping()
+        except Exception as exc:
+            logger.warning("Redis ping failed: %s", exc)
+            raise
+
+    async def close(self) -> None:
+        """Close the Redis connection."""
+        if self._client is not None:
+            await self._client.close()
+            self._client = None
+
+    @property
+    def client(self) -> aioredis.Redis:
+        """Return the Redis client, raising if not connected."""
+        if self._client is None:
+            raise RuntimeError("PresenceStore is not connected. Call connect() first.")
+        return self._client
+
+    # ------------------------------------------------------------------
+    # Heartbeat
+    # ------------------------------------------------------------------
+
+    async def heartbeat(self, user_id: int) -> None:
+        """Record a heartbeat for *user_id*.
+
+        Sets a TTL key so that the user is considered online as long as
+        heartbeats arrive at least once per heartbeat_ttl seconds.
+        """
+        key = self._heartbeat_key(user_id)
+        await self.client.set(key, "1", ex=self._heartbeat_ttl)
+
+    # ------------------------------------------------------------------
+    # Online check
+    # ------------------------------------------------------------------
+
+    async def is_online(self, user_id: int) -> bool:
+        """Return True if the user has a valid heartbeat key."""
+        key = self._heartbeat_key(user_id)
+        exists = await self.client.exists(key)
+        return bool(exists)
+
+    # ------------------------------------------------------------------
+    # Presence lookup
+    # ------------------------------------------------------------------
+
+    async def get_presence(
+        self,
+        user_ids: list[int],
+        db: Any,  # AsyncSession — imported here to avoid circular imports
+    ) -> dict[int, dict[str, Any]]:
+        """Return presence info for a list of user ids.
+
+        Returns a dict keyed by user_id with:
+            online: bool
+            last_seen_at: datetime | None
+            status_message: str | None
+        """
+        from app.models.user import User
+        from sqlalchemy import select
+
+        result = await db.execute(select(User).where(User.id.in_(user_ids)))
+        users = result.scalars().all()
+        user_map = {u.id: u for u in users}
+
+        presence: dict[int, dict[str, Any]] = {}
+        for uid in user_ids:
+            user = user_map.get(uid)
+            online = await self.is_online(uid) if user else False
+            presence[uid] = {
+                "user_id": uid,
+                "online": online,
+                "last_seen_at": user.last_seen_at if user else None,
+                "status_message": user.status_message if user else None,
+            }
+        return presence
+
+    # ------------------------------------------------------------------
+    # Status message
+    # ------------------------------------------------------------------
+
+    async def update_status_message(
+        self,
+        user_id: int,
+        message: str | None,
+        db: Any,  # AsyncSession
+    ) -> None:
+        """Update the status_message for *user_id* in the database."""
+        from app.models.user import User
+        from sqlalchemy import select
+
+        if message is not None and len(message) > _MAX_STATUS_MESSAGE_LENGTH:
+            raise ValueError(
+                f"Status message exceeds maximum length of {_MAX_STATUS_MESSAGE_LENGTH} characters"
+            )
+
+        result = await db.execute(select(User).where(User.id == user_id))
+        user = result.scalar_one_or_none()
+        if user is None:
+            raise ValueError(f"User {user_id} not found")
+
+        user.status_message = message
+        user.last_seen_at = datetime.now(timezone.utc)
+        await db.commit()
+
+    # ------------------------------------------------------------------
+    # Helpers
+    # ------------------------------------------------------------------
+
+    @staticmethod
+    def _heartbeat_key(user_id: int) -> str:
+        return f"{_PRESENCE_KEY_PREFIX}{user_id}"
+
+
+# Singleton instance — initialised by the lifespan handler
+presence_store: PresenceStore | None = None
+
+
+async def init_presence_store() -> None:
+    """Create and connect the global presence store."""
+    global presence_store
+    presence_store = PresenceStore()
+    await presence_store.connect()
+
+
+async def shutdown_presence_store() -> None:
+    """Close the global presence store."""
+    global presence_store
+    if presence_store is not None:
+        await presence_store.close()
+        presence_store = None