Implement AI Playlist Generator for Playlist Recomendations (api/ai-playlist)

[tran2106]

- Create a POST endpoint at /auth/spotify/ai-playlist to receive user prompts from the frontend.

2. Prompt Validation

• Validate the incoming prompt:
  • If prompt is too short or not music-related (eexample "hi"), return a friendly message suggesting the user send a mood, genre, or vibe.

3. Gemini AI Integration

• Send valid prompts to Gemini AI.
• Parse Gemini’s response to extract a JSON list of { song, artist } pairs.

4. Output Validation

• Validate Gemini’s output:
  • If output is invalid or empty, return a fallback message to the frontend.

5. Spotify Track Search

• For each { song, artist } from Gemini, search Spotify’s API for matching track IDs.
• Collect valid Spotify track URIs.

6. Playlist Creation

• Use the authenticated user’s Spotify token to create a new playlist named AI Playlist: [prompt].
• Add the collected tracks to the playlist via Spotify API.

7. Response Handling

• If playlist creation is successful, return { playlistUrl: "https://open.spotify.com/playlist/..." }.
• If prompt is invalid or playlist creation fails, return { message: "Send a mood, genre, or vibe and I can make a playlist for you." }.

8. Error Handling & Logging

• Log errors at each step for debugging.
• Return appropriate error messages to the frontend.