# 09. Image Caching & Lazy Loading

meta:
  id: ios-production-09
  feature: ios-production
  priority: P2
  depends_on: []
  tags: [performance, caching, production]

objective:
- Implement efficient image caching and lazy loading to improve app performance and reduce network usage

deliverables:
- URLSession-based image caching
- Lazy loading for lists and grids
- Image optimization pipeline
- Memory and disk cache limits

steps:
1. Implement image caching:
   - Use URLCache with memory (50MB) and disk (100MB) limits
   - Or integrate Kingfisher or Nuke for advanced caching
   - Configure cache expiration (7 days default)
   - Add cache cleanup on low memory warnings
2. Add lazy loading:
   - Use LazyVStack and LazyHGrid for lists
   - Implement pagination for long lists (alerts, exposures)
   - Add prefetching for adjacent items
   - Show placeholder while loading
3. Optimize images:
   - Request appropriate sizes from backend (thumbnail, full)
   - Use WebP or HEIC format where supported
   - Compress images before upload (VoicePrint, document scan)
   - Implement progressive JPEG loading
4. Add loading states:
   - Skeleton placeholders while images load
   - Error state with retry button
   - Fade-in animation when image loads
5. Implement memory management:
   - Clear image cache on memory warning
   - Limit concurrent image downloads (max 5)
   - Cancel downloads for off-screen images
6. Add offline support:
   - Cache images for offline viewing
   - Show cached images when offline
   - Queue uploads for when online

tests:
- Unit: Test cache hit/miss behavior
- Performance: Test scrolling with 1000 images
- Memory: Verify no memory leaks with image loading

acceptance_criteria:
- Images cached with 50MB memory / 100MB disk limits
- Lazy loading on all lists and grids
- Pagination for lists >50 items
- Image placeholders while loading
- Cache cleared on memory warning
- Offline image viewing working
- Progressive loading for large images
- No memory leaks in image loading pipeline
- Smooth 60fps scrolling on image-heavy screens

validation:
- Scroll through alert list → smooth, no stuttering
- Turn on airplane mode → cached images still visible
- Monitor memory → stable during image browsing
- Check cache directory → images stored with correct expiration

notes:
- Kingfisher is the most popular Swift image caching library
- Nuke is lighter and faster for advanced use cases
- Consider using SwiftUI AsyncImage for simple cases
- Always test on physical device, not just simulator