View our Demo Video!

This project now includes a "Semantic Flashcards" feature powered by MongoDB Atlas. It runs a local Express server alongside the Expo app to handle data synchronization and vector search.

The backend is located in the server/ directory.

1. Install Dependencies

   cd server
   npm install

2. Environment Variables Ensure your root .env includes:

   # MongoDB Atlas Connection String
   MONGODB_URI=mongodb+srv://<user>:<password>@cluster.mongodb.net/?retryWrites=true&w=majority
   
   # Enable Sync Feature
   EXPO_PUBLIC_ENABLE_MONGODB_SYNC=true
   
   # Base URL for local dev (Android Emulator: 10.0.2.2, iOS Simulator: localhost)
   EXPO_PUBLIC_API_BASE_URL=http://localhost:3000/api
   
   # Gemini API Key (for embeddings)
   EXPO_PUBLIC_GEMINI_API_KEY=AIza...

3. Run Server

   cd server
   npm run dev
   # Server runs on http://localhost:3000

To enable "Struggled With" mode, you must create a Vector Search Index in MongoDB Atlas.

1. Go to your Cluster -> Atlas Search -> Create Search Index.
2. Select JSON Editor.
3. Select Database: (your db name), Collection: flashcards.
4. Index Name: vector_index.
5. Configuration JSON:

   {
     "fields": [
       {
         "numDimensions": 768,
         "path": "embedding",
         "similarity": "cosine",
         "type": "vector"
       }
     ]
   }

   (Note: Gemini text-embedding-004 uses 768 dimensions. If using a different model, adjust numDimensions.)

1. Start Session: Talk to the AI agent. Make some intentional mistakes (e.g., say "Je suis fini" instead of "J'ai fini").
2. End Session: Tap "End Session". This triggers the background sync (POST /sync-session).
3. Embeddings: The server automatically queues generating embeddings for your mistakes and flashcards (POST /embed-pending triggered after sync).
4. Go to Flashcards:
   • Toggle "By Scenario" (Standard view).
   • Toggle "Struggled With" (Semantic view).
5. Observe: You should see flashcards conceptually related to your recent mistakes (e.g., if you messed up "finir", you might see cards about finishing tasks or past tense verbs).

• Mongo Disabled: Set ENABLE_MONGODB_SYNC=false. App should behave exactly as before (local storage only).
• Sync: Finish a session. Check MongoDB Atlas collection sessions. Data should appear.
• Embeddings: Check flashcards collection. Field embedding should be populated (array of numbers).
• Vector Search: Toggle "Struggled With". Use server logs (npm run dev) to see if /api/flashcards/struggles is called and returns results.

• Network Error: Ensure EXPO_PUBLIC_API_BASE_URL is correct. iOS Simulator uses localhost, Android Emulator uses 10.0.2.2.
• No Embeddings: Check server console for Gemini API errors.