# NDJSON Refactor Summary

## ✅ What Was Done

### 1. Refactored `StructuredSummarizer` Service
**File:** `app/services/structured_summarizer.py`

#### Added/Modified:
- **Updated `_build_system_prompt()`**: Now instructs the model to output NDJSON patches instead of a single JSON object
- **Added `_empty_state()`**: Creates the initial empty state structure
- **Added `_apply_patch()`**: Applies NDJSON patches to the state (handles `set`, `append`, and `done` operations)
- **Added `summarize_structured_stream_ndjson()`**: New async generator method that:
  - Uses deterministic decoding (`do_sample=False`, `temperature=0.0`)
  - Parses NDJSON line-by-line with buffering
  - Applies patches to build up state incrementally
  - Yields structured events with `delta`, `state`, `done`, `tokens_used`, and `latency_ms`
  - Handles errors gracefully

#### Preserved:
- ✅ Class name: `StructuredSummarizer`
- ✅ Logging style
- ✅ Model loading/warmup logic
- ✅ Settings usage
- ✅ Existing `summarize_structured_stream()` method (unchanged)

### 2. Created New API Endpoint
**File:** `app/api/v4/structured_summary.py`

#### Added:
- **`/api/v4/scrape-and-summarize/stream-ndjson`** endpoint
- **`_stream_generator_ndjson()`** helper function
- Supports both URL and text modes
- Wraps NDJSON events in SSE format
- Includes metadata events when requested

### 3. Created Test Suite

#### Test Files Created:

1. **`test_v4_ndjson.py`** - Direct service test (requires model loaded)
2. **`test_v4_ndjson_mock.py`** - Mock test without model (validates protocol logic) ✅ PASSED
3. **`test_v4_ndjson_http.py`** - HTTP endpoint test (requires server running)

---

## 🎯 NDJSON Protocol Specification

### Target Logical Object
```json
{
  "title": "string",
  "main_summary": "string",
  "key_points": ["string"],
  "category": "string",
  "sentiment": "positive" | "negative" | "neutral",
  "read_time_min": number
}
```

### Patch Operations

#### 1. Set scalar field
```json
{"op": "set", "field": "title", "value": "Example Title"}
{"op": "set", "field": "category", "value": "Tech"}
{"op": "set", "field": "sentiment", "value": "positive"}
{"op": "set", "field": "read_time_min", "value": 3}
{"op": "set", "field": "main_summary", "value": "Summary text..."}
```

#### 2. Append to array
```json
{"op": "append", "field": "key_points", "value": "First key point"}
{"op": "append", "field": "key_points", "value": "Second key point"}
```

#### 3. Signal completion
```json
{"op": "done"}
```

### Event Structure

Each streamed event has this structure:
```json
{
  "delta": {<patch>} | null,
  "state": {<current_combined_state>} | null,
  "done": boolean,
  "tokens_used": number,
  "latency_ms": number (optional, final event only),
  "error": "string" (optional, only on error)
}
```

---

## 🧪 How to Test

### Option 1: Mock Test (No Model Required) ✅ WORKING
```bash
python test_v4_ndjson_mock.py
```
**Status:** ✅ Passed all validations
- Tests protocol logic
- Validates state management
- Shows expected event flow

### Option 2: Direct Service Test (Requires Model)
```bash
python test_v4_ndjson.py
```
**Requirements:**
- Model must be loaded in the environment
- Transformers library installed

### Option 3: HTTP Endpoint Test (Requires Running Server)
```bash
# Terminal 1: Start server
./start-server.sh

# Terminal 2: Run test
python test_v4_ndjson_http.py
```

---

## 📊 Test Results

### Mock Test Results ✅
```
Total events: 12
Total tokens: 55

Final State:
{
  "title": "Qwen2.5-0.5B: Efficient AI for Edge Computing",
  "main_summary": "Qwen2.5-0.5B is a compact language model...",
  "key_points": [
    "Compact 0.5B parameter model designed for edge devices...",
    "Strong performance on instruction following...",
    "Supports multiple languages...",
    "Significantly lower memory and computational requirements...",
    "Ideal for applications requiring efficiency and low latency"
  ],
  "category": "Tech",
  "sentiment": "positive",
  "read_time_min": 3
}

Validations:
✅ title: present
✅ main_summary: present
✅ key_points: 5 items
✅ category: present
✅ sentiment: valid value (positive)
✅ read_time_min: present

✅ ALL VALIDATIONS PASSED - Protocol is working correctly!
```

---

## 🔄 Migration Path

### Current State
- ✅ Old method still works: `summarize_structured_stream()`
- ✅ New method available: `summarize_structured_stream_ndjson()`
- ✅ Old endpoint still works: `/api/v4/scrape-and-summarize/stream`
- ✅ New endpoint available: `/api/v4/scrape-and-summarize/stream-ndjson`

### When Ready to Switch
1. Update your frontend/client to use the new endpoint
2. Consume events using the new structure:
   ```javascript
   // Parse SSE event
   const event = JSON.parse(eventData);
   
   // Use current full state
   const currentState = event.state;
   
   // Or use delta for fine-grained updates
   const patch = event.delta;
   
   // Check completion
   if (event.done) {
     console.log('Final latency:', event.latency_ms);
   }
   ```
3. Once migrated, you can optionally remove the old method (or keep both)

---

## 🎉 Benefits of NDJSON Protocol

1. **Incremental State Updates**: Client sees partial results as they're generated
2. **Fine-Grained Control**: Can update UI field-by-field
3. **Deterministic**: Uses greedy decoding for consistent results
4. **Structured Events**: Clear separation of deltas and state
5. **Error Handling**: Graceful error reporting with proper event structure
6. **Backwards Compatible**: Old endpoint continues to work

---

## 📝 Next Steps

1. ✅ **Protocol logic verified** - Mock test passed
2. ⏳ **Test with actual model** - Run when model is loaded
3. ⏳ **Test HTTP endpoint** - Run when server is up
4. ⏳ **Update frontend** - Integrate new endpoint in client
5. ⏳ **Monitor production** - Compare performance with old method

---

## 🐛 Troubleshooting

### Model not loaded
```
❌ ERROR: Model not available. Please check model initialization.
```
**Solution:** Make sure `transformers` and `torch` are installed and model files are available.

### Server not running
```
❌ Could not connect to server at http://localhost:7860
```
**Solution:** Start the server with `./start-server.sh`

### Invalid JSON in stream
If the model outputs invalid JSON, it will be logged as a warning and skipped:
```
Failed to parse NDJSON line: {...}... Error: ...
```
**Solution:** This is handled gracefully - other valid patches will still be processed.

---

## 📚 Files Modified/Created

### Modified:
- `app/services/structured_summarizer.py` - Added NDJSON streaming method
- `app/api/v4/structured_summary.py` - Added new endpoint

### Created:
- `test_v4_ndjson.py` - Direct service test
- `test_v4_ndjson_mock.py` - Mock test ✅
- `test_v4_ndjson_http.py` - HTTP endpoint test
- `NDJSON_REFACTOR_SUMMARY.md` - This file

---

**Status:** ✅ Refactor complete and protocol validated
**Ready for:** Model testing and integration