Feature: scan and generate missing thumbnails in background on startup

backend/workers/thumbnails.go

@@ -48,9 +48,64 @@ func InitThumbnailManager(cfg *config.Config, db *database.DB) {
 			DB:     db,
 		}
 		Instance.Start(2) // Run 2 concurrent workers
+		go Instance.ScanMissingThumbnails()
 	})
 }
 
+func (m *ThumbnailManager) ScanMissingThumbnails() {
+	time.Sleep(5 * time.Second) // wait for server to settle
+	log.Println("Scanning for missing thumbnails...")
+	rows, err := m.DB.Query("SELECT path, checksum FROM files WHERE checksum IS NOT NULL AND checksum != ''")
+	if err != nil {
+		log.Printf("Failed to query files for missing thumbnails: %v\n", err)
+		return
+	}
+	defer rows.Close()
+
+	count := 0
+	for rows.Next() {
+		var path, checksum string
+		if err := rows.Scan(&path, &checksum); err != nil {
+			continue
+		}
+
+		destPath := filepath.Join(m.Config.ThumbnailDir, checksum+".jpg")
+		if _, err := os.Stat(destPath); err == nil {
+			continue // Thumbnail already exists
+		}
+
+		ext := strings.ToLower(filepath.Ext(path))
+		var mimeType string
+		if ext == ".jpg" || ext == ".png" || ext == ".gif" || ext == ".webp" || ext == ".svg" || ext == ".jpeg" {
+			mimeType = "image/"
+		} else if ext == ".mp4" || ext == ".webm" || ext == ".ogg" || ext == ".mov" || ext == ".mkv" || ext == ".avi" {
+			mimeType = "video/"
+		} else if ext == ".mp3" || ext == ".flac" || ext == ".wav" || ext == ".m4a" || ext == ".aac" {
+			mimeType = "audio/"
+		} else if ext == ".docx" || ext == ".pptx" || ext == ".xlsx" {
+			mimeType = "application/"
+		} else {
+			continue
+		}
+
+		job := ThumbnailJob{
+			FilePath: path,
+			Checksum: checksum,
+			MimeType: mimeType,
+		}
+
+		// Use blocking send so we don't drop jobs, but it throttles the scanner
+		m.Queue <- job
+		count++
+	}
+
+	if count > 0 {
+		log.Printf("Enqueued %d missing thumbnails for generation\n", count)
+	} else {
+		log.Println("No missing thumbnails found.")
+	}
+}
+
 func (m *ThumbnailManager) Start(workers int) {
 	for i := 0; i < workers; i++ {
 		m.wg.Add(1)