# BYOEH Developer Guide

## Quick Start

### Prerequisites

- Python 3.10+
- Node.js 18+
- Docker & Docker Compose
- OpenAI API Key (for embeddings)

### Setup

1. **Start services:**
```bash
docker-compose up -d qdrant
```

2. **Configure environment:**
```env
QDRANT_URL=http://localhost:6333
OPENAI_API_KEY=sk-your-key
BYOEH_ENCRYPTION_ENABLED=true
```

3. **Run klausur-service:**
```bash
cd klausur-service/backend
pip install -r requirements.txt
uvicorn main:app --reload --port 8086
```

4. **Run frontend:**
```bash
cd klausur-service/frontend
npm install
npm run dev
```

## Client-Side Encryption

The encryption service (`encryption.ts`) handles all cryptographic operations in the browser:

### Encrypting a File

```typescript
import { encryptFile, generateSalt } from '../services/encryption'

const file = document.getElementById('fileInput').files[0]
const passphrase = 'user-secret-password'

const encrypted = await encryptFile(file, passphrase)
// Result:
// {
//   encryptedData: ArrayBuffer,
//   keyHash: string,      // SHA-256 hash for verification
//   salt: string,         // Hex-encoded salt
//   iv: string            // Hex-encoded initialization vector
// }
```

### Decrypting Content

```typescript
import { decryptText, verifyPassphrase } from '../services/encryption'

// First verify the passphrase
const isValid = await verifyPassphrase(passphrase, salt, expectedKeyHash)

if (isValid) {
  const decrypted = await decryptText(encryptedBase64, passphrase, salt)
}
```

## Backend API Usage

### Upload an Erwartungshorizont

```python
# The upload endpoint accepts FormData with:
# - file: encrypted binary blob
# - metadata_json: JSON string with metadata

POST /api/v1/eh/upload
Content-Type: multipart/form-data

{
  "file": <encrypted_blob>,
  "metadata_json": {
    "metadata": {
      "title": "Deutsch LK 2025",
      "subject": "deutsch",
      "niveau": "eA",
      "year": 2025,
      "aufgaben_nummer": "Aufgabe 1"
    },
    "encryption_key_hash": "abc123...",
    "salt": "def456...",
    "rights_confirmed": true,
    "original_filename": "erwartungshorizont.pdf"
  }
}
```

### Index for RAG

```python
POST /api/v1/eh/{eh_id}/index
Content-Type: application/json

{
  "passphrase": "user-secret-password"
}
```

The backend will:
1. Verify the passphrase against stored key hash
2. Decrypt the file
3. Extract text from PDF
4. Chunk the text (1000 chars, 200 overlap)
5. Generate OpenAI embeddings
6. Re-encrypt each chunk
7. Index in Qdrant with tenant filter

### RAG Query

```python
POST /api/v1/eh/rag-query
Content-Type: application/json

{
  "query_text": "Wie sollte die Einleitung strukturiert sein?",
  "passphrase": "user-secret-password",
  "subject": "deutsch",      # Optional filter
  "limit": 5                 # Max results
}
```

Response:
```json
{
  "context": "Die Einleitung sollte...",
  "sources": [
    {
      "text": "Die Einleitung sollte...",
      "eh_id": "uuid",
      "eh_title": "Deutsch LK 2025",
      "chunk_index": 2,
      "score": 0.89
    }
  ],
  "query": "Wie sollte die Einleitung strukturiert sein?"
}
```

## Key Sharing Implementation

### Invitation Flow (Recommended)

The invitation flow provides a two-phase sharing process: Invite -> Accept

```typescript
import { ehApi } from '../services/api'

// 1. First examiner sends invitation to second examiner
const invitation = await ehApi.inviteToEH(ehId, {
  invitee_email: 'zweitkorrektor@school.de',
  role: 'second_examiner',
  klausur_id: 'klausur-uuid',  // Optional: link to specific Klausur
  message: 'Bitte fuer Zweitkorrektur nutzen',
  expires_in_days: 14  // Default: 14 days
})
// Returns: { invitation_id, eh_id, invitee_email, role, expires_at, eh_title }

// 2. Second examiner sees pending invitation
const pending = await ehApi.getPendingInvitations()
// [{ invitation: {...}, eh: { id, title, subject, niveau, year } }]

// 3. Second examiner accepts invitation
const accepted = await ehApi.acceptInvitation(
  invitationId,
  encryptedPassphrase  // Passphrase encrypted for recipient
)
// Returns: { status: 'accepted', share_id, eh_id, role, klausur_id }
```

### Invitation Management

```typescript
// Get invitations sent by current user
const sent = await ehApi.getSentInvitations()

// Decline an invitation (as invitee)
await ehApi.declineInvitation(invitationId)

// Revoke a pending invitation (as inviter)
await ehApi.revokeInvitation(invitationId)

// Get complete access chain for an EH
const chain = await ehApi.getAccessChain(ehId)
// Returns: { eh_id, eh_title, owner, active_shares, pending_invitations, revoked_shares }
```

### Direct Sharing (Legacy)

For immediate sharing without invitation:

```typescript
// First examiner shares directly with second examiner
await ehApi.shareEH(ehId, {
  user_id: 'second-examiner-uuid',
  role: 'second_examiner',
  encrypted_passphrase: encryptedPassphrase, // Encrypted for recipient
  passphrase_hint: 'Das uebliche Passwort',
  klausur_id: 'klausur-uuid'  // Optional
})
```

### Accessing Shared EH

```typescript
// Second examiner gets shared EH
const shared = await ehApi.getSharedWithMe()
// [{ eh: {...}, share: {...} }]

// Query using provided passphrase
const result = await ehApi.ragQuery({
  query_text: 'search query',
  passphrase: decryptedPassphrase,
  subject: 'deutsch'
})
```

### Revoking Access

```typescript
// List all shares for an EH
const shares = await ehApi.listShares(ehId)

// Revoke a share
await ehApi.revokeShare(ehId, shareId)
```

## Klausur Integration

### Automatic EH Prompt

The `KorrekturPage` shows an EH upload prompt after the first student work is uploaded:

```typescript
// In KorrekturPage.tsx
useEffect(() => {
  if (
    currentKlausur?.students.length === 1 &&
    linkedEHs.length === 0 &&
    !ehPromptDismissed
  ) {
    setShowEHPrompt(true)
  }
}, [currentKlausur?.students.length])
```

### Linking EH to Klausur

```typescript
// After EH upload, auto-link to Klausur
await ehApi.linkToKlausur(ehId, klausurId)

// Get linked EH for a Klausur
const linked = await klausurEHApi.getLinkedEH(klausurId)
```

## Frontend Components

### EHUploadWizard Props

```typescript
interface EHUploadWizardProps {
  onClose: () => void
  onComplete?: (ehId: string) => void
  defaultSubject?: string     // Pre-fill subject
  defaultYear?: number        // Pre-fill year
  klausurId?: string          // Auto-link after upload
}

// Usage
<EHUploadWizard
  onClose={() => setShowWizard(false)}
  onComplete={(ehId) => console.log('Uploaded:', ehId)}
  defaultSubject={klausur.subject}
  defaultYear={klausur.year}
  klausurId={klausur.id}
/>
```

### Wizard Steps

1. **file** - PDF file selection with drag & drop
2. **metadata** - Form for title, subject, niveau, year
3. **rights** - Rights confirmation checkbox
4. **encryption** - Passphrase input with strength meter
5. **summary** - Review and confirm upload

## Qdrant Operations

### Collection Schema

```python
# Collection: bp_eh
{
  "vectors": {
    "size": 1536,           # OpenAI text-embedding-3-small
    "distance": "Cosine"
  }
}

# Point payload
{
  "tenant_id": "school-uuid",
  "eh_id": "eh-uuid",
  "chunk_index": 0,
  "encrypted_content": "base64...",
  "training_allowed": false  # ALWAYS false
}
```

### Tenant-Isolated Search

```python
from qdrant_service import search_eh

results = await search_eh(
    query_embedding=embedding,
    tenant_id="school-uuid",
    subject="deutsch",
    limit=5
)
```

## Testing

### Unit Tests

```bash
cd klausur-service/backend
pytest tests/test_byoeh.py -v
```

### Test Structure

```python
# tests/test_byoeh.py
class TestBYOEH:
    def test_upload_eh(self, client, auth_headers):
        """Test EH upload with encryption"""
        pass

    def test_index_eh(self, client, auth_headers, uploaded_eh):
        """Test EH indexing for RAG"""
        pass

    def test_rag_query(self, client, auth_headers, indexed_eh):
        """Test RAG query returns relevant chunks"""
        pass

    def test_share_eh(self, client, auth_headers, uploaded_eh):
        """Test sharing EH with another user"""
        pass
```

### Frontend Tests

```typescript
// EHUploadWizard.test.tsx
describe('EHUploadWizard', () => {
  it('completes all steps successfully', async () => {
    // ...
  })

  it('validates passphrase strength', async () => {
    // ...
  })

  it('auto-links to klausur when klausurId provided', async () => {
    // ...
  })
})
```

## Error Handling

### Common Errors

| Error | Cause | Solution |
|-------|-------|----------|
| `Passphrase verification failed` | Wrong passphrase | Ask user to re-enter |
| `EH not found` | Invalid ID or deleted | Check ID, reload list |
| `Access denied` | User not owner/shared | Check permissions |
| `Qdrant connection failed` | Service unavailable | Check Qdrant container |

### Error Response Format

```json
{
  "detail": "Passphrase verification failed"
}
```

## Security Considerations

### Do's

- Store key hash, never the key itself
- Always filter by tenant_id
- Log all access in audit trail
- Use HTTPS in production

### Don'ts

- Never log passphrase or decrypted content
- Never store passphrase in localStorage
- Never send passphrase as URL parameter
- Never return decrypted content without auth

## Performance Tips

### Chunking Configuration

```python
CHUNK_SIZE = 1000    # Characters per chunk
CHUNK_OVERLAP = 200  # Overlap for context continuity
```

### Embedding Batching

```python
# Generate embeddings in batches of 20
EMBEDDING_BATCH_SIZE = 20
```

### Qdrant Optimization

```python
# Use HNSW index for fast approximate search
# Collection is automatically optimized on creation
```

## Debugging

### Enable Debug Logging

```python
import logging
logging.getLogger('byoeh').setLevel(logging.DEBUG)
```

### Check Qdrant Status

```bash
curl http://localhost:6333/collections/bp_eh
```

### Verify Encryption

```typescript
import { isEncryptionSupported } from '../services/encryption'

if (!isEncryptionSupported()) {
  console.error('Web Crypto API not available')
}
```

## Migration Notes

### From v1.0 to v1.1

1. Added key sharing system
2. Added Klausur linking
3. EH prompt after student upload

No database migrations required - all data structures are additive.