Design a file upload feature for an AI chat application.

To design a file upload feature for an AI chat application, we can consider the following:

1. User Interface (UI): A button or drag-and-drop area in the chat window allows users to select files. Upon selection, a preview or thumbnail of the file should be displayed.
2. Backend Storage: Uploaded files should be stored securely, likely in a cloud storage service (like AWS S3, Google Cloud Storage) or a dedicated file server. The database will store metadata about the file.
3. Database Schema: The database will contain a files table with columns such as file_id, file_name, file_url (pointing to the stored file), thumbnail_url, upload_timestamp, and user_id (who uploaded it).
4. Chat Integration: Each file upload needs to be associated with a specific chat session. This can be achieved by creating a linking table (e.g., chat_files) that maps chat_id to file_id.
5. File Handling: Upon upload, the system should generate a unique identifier for the file, potentially create a thumbnail for quick previews, and store the actual file content in the designated storage. The database is then updated with the file's metadata and its association with the chat.
6. Security: Implement measures to prevent unauthorized access, validate file types, and scan for malware.