feat: Add debug endpoint for playlist troubleshooting

- Add /api/songs/debug/playlist/:name endpoint
- Debug endpoint shows playlist structure and track data
- Lists all available playlists when target not found
- Shows track IDs and whether songs exist for those IDs
- Helps diagnose playlist loading issues
- Useful for troubleshooting missing songs in playlists

This will help identify why songs are not showing in playlists like 'Disco'.

packages/backend/src/routes/songs.ts

@@ -4,6 +4,101 @@ import { Playlist } from '../models/Playlist.js';
 
 const router = express.Router();
 
+// Debug endpoint to check playlist data
+router.get('/debug/playlist/:name', async (req: Request, res: Response) => {
+  try {
+    const playlistName = req.params.name;
+    console.log(`Debug: Checking playlist "${playlistName}"`);
+
+    // Get all playlists
+    const allPlaylists = await Playlist.find({});
+    console.log(`Debug: Found ${allPlaylists.length} playlist documents`);
+
+    // Find the specific playlist
+    const findPlaylistRecursively = (nodes: any[], targetName: string): any => {
+      for (const node of nodes) {
+        if (node.name === targetName) {
+          return node;
+        }
+        if (node.children && node.children.length > 0) {
+          const found = findPlaylistRecursively(node.children, targetName);
+          if (found) return found;
+        }
+      }
+      return null;
+    };
+
+    let playlist = null;
+    for (const playlistDoc of allPlaylists) {
+      playlist = findPlaylistRecursively([playlistDoc], playlistName);
+      if (playlist) break;
+    }
+
+    if (!playlist) {
+      // List all available playlists
+      const getAllPlaylistNames = (nodes: any[]): string[] => {
+        const names: string[] = [];
+        for (const node of nodes) {
+          names.push(node.name);
+          if (node.children && node.children.length > 0) {
+            names.push(...getAllPlaylistNames(node.children));
+          }
+        }
+        return names;
+      };
+
+      const allNames: string[] = [];
+      for (const playlistDoc of allPlaylists) {
+        allNames.push(...getAllPlaylistNames([playlistDoc]));
+      }
+
+      return res.json({
+        error: `Playlist "${playlistName}" not found`,
+        availablePlaylists: allNames,
+        playlistDocuments: allPlaylists.map(p => ({ name: p.name, type: p.type }))
+      });
+    }
+
+    // Get track IDs from playlist
+    const getAllTrackIds = (node: any): string[] => {
+      if (node.type === 'playlist' && node.tracks) {
+        return node.tracks;
+      }
+      if (node.type === 'folder' && node.children) {
+        return node.children.flatMap((child: any) => getAllTrackIds(child));
+      }
+      return [];
+    };
+
+    const trackIds = getAllTrackIds(playlist);
+
+    // Check if songs exist for these track IDs
+    const songs = await Song.find({ id: { $in: trackIds } }).lean();
+    const songIds = songs.map(s => s.id);
+
+    res.json({
+      playlist: {
+        name: playlist.name,
+        type: playlist.type,
+        trackIds: trackIds,
+        trackCount: trackIds.length
+      },
+      songs: {
+        found: songIds,
+        foundCount: songs.length,
+        missing: trackIds.filter(id => !songIds.includes(id))
+      },
+      debug: {
+        playlistStructure: playlist,
+        allPlaylistDocuments: allPlaylists.length
+      }
+    });
+  } catch (error) {
+    console.error('Debug error:', error);
+    res.status(500).json({ error: 'Debug endpoint error', details: error });
+  }
+});
+
 // Get songs with pagination and search
 router.get('/', async (req: Request, res: Response) => {
   try {