feat: auto-refresh calendar subscriptions

backend/calendar_refresh.py

@@ -0,0 +1,108 @@
+from __future__ import annotations
+
+import asyncio
+import logging
+from collections.abc import Callable
+from datetime import UTC, datetime, timedelta
+
+from fastapi import HTTPException
+from sqlalchemy import or_, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from . import calendar as calendar_service
+from .models import CalendarSubscription, utcnow
+
+logger = logging.getLogger(__name__)
+DEFAULT_REFRESH_INTERVAL = timedelta(minutes=15)
+DEFAULT_POLL_SECONDS = 60
+
+
+async def refresh_subscription_cache(
+    db: AsyncSession,
+    row: CalendarSubscription,
+    *,
+    fail_without_cache: bool = True,
+) -> bool:
+    requested_url = row.url
+    requested_version = getattr(row, "updated_at", None)
+    try:
+        result = await asyncio.to_thread(
+            calendar_service.fetch_calendar,
+            requested_url,
+            etag=row.etag,
+            last_modified=row.last_modified,
+        )
+        await db.refresh(row)
+        if row.url != requested_url or getattr(row, "updated_at", None) != requested_version:
+            return False
+        if result.not_modified:
+            if not row.ics_cache:
+                raise HTTPException(502, "calendar returned not modified without cache")
+        elif result.content is not None:
+            # Parse before replacing a known-good cache.
+            calendar_service.parse_ics_events(
+                result.content,
+                row.name,
+                row.color,
+                datetime.now(UTC) - timedelta(days=1),
+                datetime.now(UTC) + timedelta(days=1),
+                "UTC",
+            )
+            row.ics_cache = result.content.decode("utf-8-sig")
+            row.etag = result.etag
+            row.last_modified = result.last_modified
+        row.refreshed_at = utcnow()
+        row.last_error = None
+        await db.commit()
+        return True
+    except Exception as exc:
+        error = exc.detail if isinstance(exc, HTTPException) else str(exc)
+        if not row.ics_cache and fail_without_cache:
+            await db.rollback()
+            raise HTTPException(502, error) from exc
+        row.last_error = error
+        await db.commit()
+        return False
+
+
+async def refresh_due_subscriptions(
+    db: AsyncSession,
+    *,
+    now: datetime | None = None,
+    refresh_interval: timedelta = DEFAULT_REFRESH_INTERVAL,
+) -> int:
+    current = now or datetime.now(UTC)
+    cutoff = current - refresh_interval
+    rows = (await db.scalars(select(CalendarSubscription).where(
+        CalendarSubscription.enabled.is_(True),
+        or_(
+            CalendarSubscription.refreshed_at.is_(None),
+            CalendarSubscription.refreshed_at <= cutoff,
+        ),
+    ).order_by(CalendarSubscription.refreshed_at, CalendarSubscription.created_at))).all()
+    for row in rows:
+        try:
+            await refresh_subscription_cache(db, row, fail_without_cache=False)
+        except Exception:
+            await db.rollback()
+            logger.exception("Unexpected calendar refresh failure", extra={"subscription_id": str(row.id)})
+    return len(rows)
+
+
+async def calendar_refresh_loop(
+    session_factory: Callable[[], AsyncSession],
+    stop_event: asyncio.Event,
+    *,
+    refresh_interval: timedelta = DEFAULT_REFRESH_INTERVAL,
+    poll_seconds: int = DEFAULT_POLL_SECONDS,
+) -> None:
+    while not stop_event.is_set():
+        try:
+            async with session_factory() as db:
+                await refresh_due_subscriptions(db, refresh_interval=refresh_interval)
+        except Exception:
+            logger.exception("Calendar background refresh cycle failed")
+        try:
+            await asyncio.wait_for(stop_event.wait(), timeout=poll_seconds)
+        except TimeoutError:
+            pass