# Project Card Thumbnail Enhancement

## Task 22.3: Update project card to display thumbnails

**Status:** ✅ Complete  
**Requirements:** 2.1.7, 2.1.8

## Overview

Enhanced the project card thumbnail display in `ProjectsView.vue` with loading states, lazy loading, smooth transitions, and robust error handling for optimal performance and user experience.

## Implementation Details

### 1. Loading Skeleton

Added a loading skeleton that displays while thumbnails are being fetched:

```vue
<div
  v-if="isThumbnailLoading(project.id)"
  class="w-full h-full animate-pulse bg-gradient-to-br from-muted to-muted/50"
>
  <div class="w-full h-full flex items-center justify-center">
    <div class="animate-spin rounded-full h-8 w-8 border-b-2 border-primary/30"></div>
  </div>
</div>
```

**Features:**
- Pulsing gradient background animation
- Spinning loader icon
- Smooth visual feedback during load

### 2. Lazy Loading with Intersection Observer

Implemented viewport-based lazy loading using the Intersection Observer API:

```typescript
const observer = new IntersectionObserver(
  (entries) => {
    entries.forEach((entry) => {
      if (entry.isIntersecting) {
        const projectId = parseInt(entry.target.getAttribute('data-project-id') || '0')
        const project = projects.find(p => p.id === projectId)
        
        if (project?.thumbnail_url && !thumbnailBlobUrls.value.has(projectId)) {
          loadThumbnail(projectId, project.thumbnail_url)
          observer.unobserve(entry.target)
        }
      }
    })
  },
  {
    rootMargin: '50px', // Start loading 50px before visible
    threshold: 0.01
  }
)
```

**Benefits:**
- Thumbnails only load when cards are near the viewport
- Reduces initial page load time
- Improves performance with many projects
- 50px rootMargin for smooth preloading
- Includes fallback for browsers without Intersection Observer support

### 3. Native Lazy Loading

Added native browser lazy loading as an additional optimization layer:

```vue
<img
  :src="getThumbnailUrl(project.id)"
  :alt="project.name"
  loading="lazy"
  class="w-full h-full object-cover transition-opacity duration-300"
/>
```

### 4. Smooth Fade-in Transition

Implemented smooth opacity transition when thumbnails load:

```vue
<img
  :class="{ 
    'opacity-0': !isThumbnailLoaded(project.id), 
    'opacity-100': isThumbnailLoaded(project.id) 
  }"
  @load="onThumbnailLoad(project.id)"
  @error="onThumbnailError(project.id)"
/>
```

**Features:**
- Images start invisible (opacity-0)
- Fade to full opacity on load
- 300ms transition duration
- Prevents flash of unstyled content

### 5. Enhanced Fallback Display

Improved the fallback display for projects without thumbnails:

```vue
<div class="w-full h-full flex items-center justify-center bg-gradient-to-br from-primary/10 to-primary/5">
  <div class="text-center">
    <div class="text-4xl font-bold text-primary/40 mb-1">
      {{ getProjectInitials(project.name) }}
    </div>
    <FolderOpen class="h-8 w-8 mx-auto text-primary/30" />
  </div>
</div>
```

**Features:**
- Displays project initials (first 2 letters or first letter of first 2 words)
- Shows folder icon for visual context
- Gradient background for aesthetic appeal
- Consistent with overall design system

### 6. State Management

Added comprehensive state tracking for thumbnail loading:

```typescript
const thumbnailBlobUrls = ref<Map<number, string>>(new Map())
const thumbnailLoadingStates = ref<Map<number, boolean>>(new Map())
const thumbnailLoadedStates = ref<Map<number, boolean>>(new Map())
const thumbnailErrorStates = ref<Map<number, boolean>>(new Map())
```

**Helper Methods:**
- `getThumbnailUrl(projectId)` - Returns blob URL for project
- `isThumbnailLoading(projectId)` - Checks if thumbnail is loading
- `isThumbnailLoaded(projectId)` - Checks if thumbnail has loaded
- `onThumbnailLoad(projectId)` - Handles successful load event
- `onThumbnailError(projectId)` - Handles load error event
- `loadThumbnail(projectId, url)` - Fetches thumbnail and creates blob URL
- `loadAllThumbnails()` - Sets up Intersection Observer
- `getProjectInitials(name)` - Generates initials for fallback display

### 7. Error Handling

Robust error handling for failed thumbnail loads:

```typescript
const onThumbnailError = (projectId: number) => {
  thumbnailErrorStates.value.set(projectId, true)
  thumbnailLoadingStates.value.set(projectId, false)
  // Revoke the blob URL on error
  const blobUrl = thumbnailBlobUrls.value.get(projectId)
  if (blobUrl) {
    URL.revokeObjectURL(blobUrl)
    thumbnailBlobUrls.value.delete(projectId)
  }
}
```

**Features:**
- Catches image load errors
- Revokes blob URLs on error
- Falls back to placeholder display
- Tracks error state per project

### 8. Memory Management

Proper cleanup to prevent memory leaks:

```typescript
onUnmounted(() => {
  // Clean up all blob URLs to prevent memory leaks
  thumbnailBlobUrls.value.forEach(url => URL.revokeObjectURL(url))
  thumbnailBlobUrls.value.clear()
  thumbnailLoadingStates.value.clear()
  thumbnailLoadedStates.value.clear()
  thumbnailErrorStates.value.clear()
})
```

**Features:**
- Revokes all blob URLs on unmount
- Clears all state maps
- Prevents duplicate loading with state checks
- Revokes old URLs before creating new ones

## Performance Optimizations

1. **Intersection Observer** - Viewport-based loading with 50px margin
2. **Native Lazy Loading** - Browser-level optimization
3. **Blob URL Caching** - Prevents re-fetching already loaded thumbnails
4. **State Checks** - Prevents duplicate loading attempts
5. **Memory Cleanup** - Proper blob URL revocation
6. **Smooth Transitions** - CSS-based opacity transitions (no JavaScript animation)

## Requirements Coverage

### Requirement 2.1.7
> "THE VFX_System SHALL display the project thumbnail on project cards in the projects list page"

✅ **Satisfied** - Thumbnails display in the project card header section with proper aspect ratio, object-fit, and authenticated access via blob URLs.

### Requirement 2.1.8
> "WHEN no thumbnail is uploaded, THE VFX_System SHALL display a default placeholder image or project initials"

✅ **Satisfied** - Projects without thumbnails show a visually appealing fallback with project initials and a folder icon on a gradient background.

## Testing

### Manual Testing Steps

1. Start backend: `cd backend && uvicorn main:app --reload`
2. Start frontend: `cd frontend && npm run dev`
3. Navigate to Projects page
4. Upload thumbnails for some projects via Project Settings
5. Verify:
   - Loading skeleton appears during thumbnail load
   - Thumbnails fade in smoothly when loaded
   - Projects without thumbnails show initials + folder icon
   - Scroll performance is smooth with many projects
   - Thumbnails only load when cards are near viewport
   - Error handling works if thumbnail URL is invalid

### Test File

Created `frontend/test-project-card-thumbnails.html` with comprehensive test documentation and verification checklist.

## Files Modified

- `frontend/src/views/ProjectsView.vue` - Enhanced thumbnail display with loading states, lazy loading, and error handling

## Files Created

- `frontend/test-project-card-thumbnails.html` - Test documentation
- `frontend/docs/project-card-thumbnail-enhancement.md` - This document

## Browser Compatibility

- ✅ Modern browsers with Intersection Observer support
- ✅ Fallback for browsers without Intersection Observer
- ✅ Native lazy loading where supported
- ✅ Graceful degradation for older browsers

## Future Enhancements

Potential improvements for future iterations:

1. **Progressive Image Loading** - Load low-quality placeholder first, then high-quality
2. **WebP Support** - Serve WebP format for better compression
3. **Thumbnail Caching** - Use Service Worker for offline caching
4. **Skeleton Shimmer** - More sophisticated loading animation
5. **Retry Logic** - Automatic retry on failed loads

## Conclusion

Task 22.3 has been successfully completed with all requirements satisfied. The implementation provides a smooth, performant, and visually appealing thumbnail display system for project cards with robust error handling and memory management.
