feat(upload): improve folder browser UX and performance - add loading state, fix chevron visibility, implement backend caching with 5min TTL, add cache invalidation on file operations

packages/backend/src/routes/music.ts

@@ -95,6 +95,9 @@ router.post('/upload', upload.single('file'), async (req, res) => {
 
     await musicFile.save();
 
+    // Invalidate folder cache since we added a new file
+    invalidateFolderCache();
+
     // Optionally add to a special playlist for scanning
     if (markForScan) {
       try {
@@ -191,6 +194,9 @@ router.post('/batch-upload', upload.array('files', 10), async (req, res) => {
 
         await musicFile.save();
         results.push({ success: true, musicFile });
+        
+        // Invalidate folder cache since we added a new file
+        invalidateFolderCache();
       } catch (error) {
         console.error(`Error uploading ${file.originalname}:`, error);
         results.push({ success: false, fileName: file.originalname, error: (error as Error).message });
@@ -223,17 +229,51 @@ router.get('/files', async (req, res) => {
 /**
  * List folders in the S3 bucket for folder selection
  */
+// Cache for folder listing to improve performance
+let folderCache: { folders: string[]; timestamp: number } | null = null;
+const CACHE_DURATION = 5 * 60 * 1000; // 5 minutes
+
+// Function to invalidate folder cache
+const invalidateFolderCache = () => {
+  folderCache = null;
+};
+
 router.get('/folders', async (req, res) => {
   try {
+    // Check if we have a valid cached result
+    if (folderCache && (Date.now() - folderCache.timestamp) < CACHE_DURATION) {
+      return res.json({ folders: folderCache.folders });
+    }
+
     const folders = await s3Service.listAllFolders('');
-    // Include root option as empty string
-    res.json({ folders: ['', ...folders] });
+    const result = ['', ...folders];
+    
+    // Cache the result
+    folderCache = {
+      folders: result,
+      timestamp: Date.now()
+    };
+    
+    res.json({ folders: result });
   } catch (error) {
     console.error('Error fetching S3 folders:', error);
     res.status(500).json({ error: 'Failed to fetch S3 folders' });
   }
 });
 
+/**
+ * Force refresh folder cache
+ */
+router.post('/folders/refresh', async (req, res) => {
+  try {
+    invalidateFolderCache();
+    res.json({ message: 'Folder cache refreshed successfully' });
+  } catch (error) {
+    console.error('Error refreshing folder cache:', error);
+    res.status(500).json({ error: 'Failed to refresh folder cache' });
+  }
+});
+
 /**
  * Sync S3 files with database - now uses background job system
  */
@@ -256,6 +296,9 @@ router.post('/sync-s3', async (req, res) => {
       status: 'started'
     });
     
+    // Invalidate folder cache since sync might change folder structure
+    invalidateFolderCache();
+    
   } catch (error) {
     console.error('❌ Error starting S3 sync job:', error);
     res.status(500).json({ error: 'Failed to start S3 sync job' });
@@ -396,6 +439,9 @@ router.delete('/:id', async (req, res) => {
     // Delete from database
     await MusicFile.findByIdAndDelete(req.params.id);
 
+    // Invalidate folder cache since we removed a file
+    invalidateFolderCache();
+
     res.json({ message: 'Music file deleted successfully' });
   } catch (error) {
     console.error('Delete error:', error);

packages/frontend/src/components/FolderBrowser.tsx

@@ -135,6 +135,9 @@ const FolderBrowser: React.FC<FolderBrowserProps> = ({
                 toggleFolder(node.path);
               }}
               aria-label={expanded ? 'Collapse folder' : 'Expand folder'}
+              color="gray.300"
+              _hover={{ bg: 'gray.700', color: 'white' }}
+              _active={{ bg: 'gray.600' }}
             />
           ) : (
             <Box w="32px" />

packages/frontend/src/components/MusicUpload.tsx

@@ -14,6 +14,7 @@ import {
   Icon,
   Input,
   Checkbox,
+  Spinner,
   useToast,
 } from '@chakra-ui/react';
 import { FiUpload, FiMusic, FiCheck, FiX } from 'react-icons/fi';
@@ -35,6 +36,7 @@ export const MusicUpload: React.FC<MusicUploadProps> = ({ onUploadComplete }) =>
   const [isUploading, setIsUploading] = useState(false);
   const [targetFolder, setTargetFolder] = useState<string>('uploads');
   const [folders, setFolders] = useState<string[]>([]);
+  const [isLoadingFolders, setIsLoadingFolders] = useState(true);
   const [markForScan, setMarkForScan] = useState<boolean>(true);
   const toast = useToast();
 
@@ -126,6 +128,7 @@ export const MusicUpload: React.FC<MusicUploadProps> = ({ onUploadComplete }) =>
   React.useEffect(() => {
     (async () => {
       try {
+        setIsLoadingFolders(true);
         const res = await fetch('/api/music/folders');
         if (!res.ok) throw new Error('Failed to load folders');
         const data = await res.json();
@@ -138,6 +141,8 @@ export const MusicUpload: React.FC<MusicUploadProps> = ({ onUploadComplete }) =>
         }
       } catch (e) {
         // ignore, keep text input fallback
+      } finally {
+        setIsLoadingFolders(false);
       }
     })();
   }, []);
@@ -150,7 +155,19 @@ export const MusicUpload: React.FC<MusicUploadProps> = ({ onUploadComplete }) =>
     <VStack spacing={4} align="stretch" w="full">
       <Box>
         <Text color="gray.300" fontSize="sm" mb={3}>Target S3 folder</Text>
-        {folders.length > 0 ? (
+        {isLoadingFolders ? (
+          <Box
+            p={6}
+            textAlign="center"
+            bg="gray.800"
+            border="1px solid"
+            borderColor="gray.700"
+            borderRadius="md"
+          >
+            <Spinner size="md" color="blue.400" mb={3} />
+            <Text color="gray.400" fontSize="sm">Loading folder structure...</Text>
+          </Box>
+        ) : folders.length > 0 ? (
           <FolderBrowser
             folders={folders}
             selectedFolder={targetFolder}