Add duplicate detection with fuzzy matching and fix artist metadata extraction

app/api/songs/route.ts

@@ -3,6 +3,7 @@ import { PrismaClient } from '@prisma/client';
 import { writeFile, unlink } from 'fs/promises';
 import path from 'path';
 import { parseBuffer } from 'music-metadata';
+import { isDuplicateSong } from '@/lib/fuzzyMatch';
 
 const prisma = new PrismaClient();
 
@@ -72,8 +73,16 @@ export async function POST(request: Request) {
             if (metadata.common.title) {
                 title = metadata.common.title;
             }
-            if (metadata.common.artist) {
+
+            // Handle artist - prefer artists array if available
+            if (metadata.common.artists && metadata.common.artists.length > 0) {
+                // Join multiple artists with '/'
+                artist = metadata.common.artists.join('/');
+            } else if (metadata.common.artist) {
                 artist = metadata.common.artist;
+            } else if (metadata.common.albumartist) {
+                // Fallback to album artist
+                artist = metadata.common.albumartist;
             }
 
             // Validation info
@@ -114,6 +123,28 @@ export async function POST(request: Request) {
         if (!title) title = 'Unknown Title';
         if (!artist) artist = 'Unknown Artist';
 
+        // Check for duplicates
+        const existingSongs = await prisma.song.findMany({
+            select: { id: true, title: true, artist: true, filename: true }
+        });
+
+        for (const existing of existingSongs) {
+            if (isDuplicateSong(artist, title, existing.artist, existing.title)) {
+                return NextResponse.json(
+                    {
+                        error: 'Duplicate song detected',
+                        duplicate: {
+                            id: existing.id,
+                            title: existing.title,
+                            artist: existing.artist,
+                            filename: existing.filename
+                        }
+                    },
+                    { status: 409 }
+                );
+            }
+        }
+
         // Create URL-safe filename
         const originalName = file.name.replace(/\.mp3$/i, '');
         const sanitizedName = originalName