# 11. Background Fetch & Sync Optimization

meta:
  id: ios-production-11
  feature: ios-production
  priority: P2
  depends_on: []
  tags: [performance, background, production]

objective:
- Optimize background fetch and data sync to keep app data fresh without draining battery

deliverables:
- Background fetch configuration
- Efficient sync strategy
- Battery usage optimization
- Background task handling

steps:
1. Configure background fetch:
   - Enable Background Fetch in Signing & Capabilities
   - Set minimum fetch interval (15 minutes)
   - Implement application(_:performFetchWithCompletionHandler)
   - Or use BGAppRefreshTask for iOS 13+
2. Optimize sync strategy:
   - Sync only changed data (delta sync)
   - Use If-Modified-Since or ETag headers
   - Prioritize critical data (alerts, exposures)
   - Defer non-critical sync (reports, historical data)
3. Implement background tasks:
   - Use BGProcessingTask for heavy operations
   - Schedule periodic dark web scans
   - Schedule spam database updates
   - Handle task expiration gracefully
4. Optimize battery usage:
   - Batch network requests
   - Use cellular data efficiently
   - Defer sync until WiFi available (optional)
   - Respect low power mode
5. Handle push notification sync:
   - Silent push notifications for urgent updates
   - Content-available: 1 for background processing
   - Wake app for critical alerts
6. Add sync status indicators:
   - Last sync timestamp in settings
   - Sync progress for large operations
   - Offline mode indicator

tests:
- Unit: Test background task scheduling
- Integration: Test fetch completion within 30 seconds
- Battery: Verify minimal battery impact over 24 hours

acceptance_criteria:
- Background fetch enabled and configured
- Data syncs every 15 minutes minimum
- Delta sync reducing data transfer by >50%
- Background tasks complete within 30 seconds
- Battery impact <5% per day from background activity
- Silent push notifications trigger data refresh
- Low power mode respected (reduced sync frequency)
- Sync status visible to user in settings
- No background task terminations due to timeouts

validation:
- Simulate background fetch → data refreshed
- Check battery settings → Kordant background activity minimal
- Receive silent push → app updates in background
- Enable low power mode → sync frequency reduced
- Monitor network usage → delta sync working

notes:
- iOS limits background fetch frequency based on app usage patterns
- BGAppRefreshTask is modern replacement for performFetch
- Always call completion handler or setTaskCompleted
- Background processing tasks require specific entitlements