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TREK/wiki/Offline-Mode-and-PWA.md
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Offline Mode and PWA

TREK can be installed as a Progressive Web App (PWA) and used without an internet connection for previously synced trips.

Install as an app (PWA)

TREK must be served over HTTPS — the install prompt does not appear on plain HTTP.

iOS (Safari):

  1. Open TREK in Safari.
  2. Tap the Share button.
  3. Select Add to Home Screen.

Android (Chrome / Edge):

  1. Open TREK in the browser.
  2. Tap the browser menu.
  3. Select Install app or Add to Home Screen.

Once installed, TREK launches in standalone mode (fullscreen, no browser UI) using the TREK icon.

What works offline

TREK uses Workbox service-worker caching plus an IndexedDB database (Dexie) for structured trip data. The following content is available offline after the first sync:

Service-worker cache (Workbox)

Content Cache name Strategy Duration Max entries
CartoDB / OpenStreetMap map tiles map-tiles CacheFirst 30 days 1 000
Leaflet / CDN assets (unpkg) cdn-libs CacheFirst 365 days 30
API responses (trips, places, bookings, etc.) api-data NetworkFirst (5 s timeout) 24 hours 200
Cover images and avatars (/uploads/covers, /uploads/avatars) user-uploads CacheFirst 7 days 300
App shell (HTML / JS / CSS) precache Precached Until next deploy

Note: The API cache excludes sensitive endpoints — /api/auth, /api/admin, /api/backup, and /api/settings are always fetched from the network.

IndexedDB (Dexie) — structured trip data

On login, after each trip-list refresh, and on WebSocket reconnect, TREK runs a background sync that writes full trip bundles into IndexedDB:

  • Trips, days, places, packing items, to-dos, budget items, reservations, accommodations, trip members, tags, and categories.
  • Non-photo file attachments (PDFs, documents, etc.) are downloaded and stored as blobs in IndexedDB.
  • Map tiles are pre-fetched into the service-worker map-tiles cache for zoom levels 1016 across each trip's bounding box (capped at ~50 MB of tiles per sync).

Sync scope and eviction

  • Only ongoing and future trips are cached (trips whose end_date is today or later, or has no end date).
  • Trips that ended more than 7 days ago are automatically evicted from IndexedDB on the next sync.

Offline Cache (Settings → Offline)

The Offline Cache section under Settings → Offline shows the current state of the local cache.

Stats panel:

  • Cached trips — number of trips stored in IndexedDB (Dexie).
  • Pending changes — number of actions taken offline that are queued to sync.

Actions:

  • Re-sync now — forces a full sync with the server. Disabled when you are offline.
  • Clear cache — removes all offline trip data from IndexedDB. You can re-sync any time while online.

Each cached trip entry shows the trip name, date range, place count, and file count, plus the time of the last successful sync.

Limitations

  • New trips created while offline are queued and synced when connectivity is restored.
  • Photo uploads require connectivity; non-photo file attachments are pre-cached automatically during sync.
  • Real-time collaboration features require an active WebSocket connection.
  • Mapbox GL tiles are not cached by the service worker (Mapbox manages its own tile cache internally).

See also