# Backend Conversion to Drogon - Implementation Summary

## Overview

The WizardMerge C++ backend has been successfully converted from a command-line interface (CLI) application to a modern HTTP API server using the Drogon web framework.

## Changes Made

### 1. Core Architecture Changes

#### HTTP Server Implementation
- **New**: `src/main.cpp` - Now runs as an HTTP server using Drogon
- **Previous**: CLI tool that processed files directly
- **Current**: HTTP API server that accepts JSON requests

#### API Controller
- **Added**: `src/controllers/MergeController.h` - HTTP controller interface
- **Added**: `src/controllers/MergeController.cc` - Controller implementation
- **Endpoint**: POST /api/merge - Performs three-way merge operations

### 2. Build System Updates

#### Dependencies
- **Added**: Drogon framework (via Conan)
- **Updated**: `conanfile.py` - Added Drogon 1.9.3 dependency
- **Updated**: `CMakeLists.txt` - Integrated Drogon, made it optional

#### Build Flexibility
The build system now supports multiple installation methods:
1. **Conan** - Automatic dependency management
2. **Docker** - Containerized deployment
3. **Manual** - Direct system installation of Drogon
4. **Library-only** - Build without Drogon (library remains functional)

### 3. Configuration

#### Server Configuration
- **Added**: `config.json` - Drogon server configuration
  - Port: 8080 (default)
  - Threads: 4
  - Logging: INFO level to ./logs
  - Max body size: 10MB

### 4. Deployment Support

#### Docker
- **Added**: `Dockerfile` - Multi-stage build for production deployment
- **Added**: `docker-compose.yml` - Easy orchestration

#### Installation Script
- **Added**: `install_drogon.sh` - Automated Drogon installation from source

#### Build Script Enhancement
- **Updated**: `build.sh` - Now supports multiple build paths with fallbacks

### 5. Documentation

#### API Documentation
- **Updated**: `backend/README.md` - Comprehensive API documentation
- **Added**: `examples/README.md` - API usage examples
- **Updated**: `BUILD.md` - Updated build instructions
- **Updated**: Main `README.md` - Architecture overview

#### Examples
- **Added**: `examples/api_client.py` - Python client example
- **Added**: `examples/test_api.sh` - curl-based test scripts

## API Specification

### Endpoint: POST /api/merge

**Request Format:**
```json
{
  "base": ["line1", "line2", "..."],
  "ours": ["line1", "line2", "..."],
  "theirs": ["line1", "line2", "..."]
}
```

**Response Format:**
```json
{
  "merged": ["merged_line1", "merged_line2", "..."],
  "conflicts": [
    {
      "start_line": 0,
      "end_line": 5,
      "base_lines": ["..."],
      "our_lines": ["..."],
      "their_lines": ["..."]
    }
  ],
  "has_conflicts": false
}
```

**Error Responses:**
- 400 Bad Request - Invalid JSON or missing fields
- 500 Internal Server Error - Processing error

## Deployment Options

### 1. Docker (Recommended for Production)
```bash
docker-compose up -d
```

### 2. Direct Installation
```bash
./install_drogon.sh
./build.sh
cd build && ./wizardmerge-cli
```

### 3. Development
```bash
./build.sh
cd build && ./wizardmerge-cli config.json
```

## Backward Compatibility

### Library Compatibility
- The core merge library (`libwizardmerge.a`) remains unchanged
- All existing merge algorithms work identically
- Unit tests continue to pass without modification

### Breaking Changes
- CLI interface removed (replaced with HTTP API)
- Direct file I/O removed (now uses JSON over HTTP)

### Migration Path
For users needing CLI functionality:
1. Use the HTTP API with curl/scripts
2. Write a thin CLI wrapper around the HTTP API
3. Link against `libwizardmerge.a` directly in custom applications

## Testing

### Unit Tests
- All existing unit tests pass
- Tests use the library directly, unaffected by HTTP layer

### Integration Testing
- Python client example demonstrates API usage
- Shell script examples for curl-based testing
- Docker-based deployment testing

## Security

### Security Analysis
- CodeQL scan: No vulnerabilities found
- Code review: All issues addressed

### Security Features
- JSON validation on all inputs
- Request body size limits (10MB default)
- Type-safe JSON conversions
- Exception handling for all endpoints

## Performance Considerations

### Drogon Benefits
- High-concurrency, non-blocking I/O
- 150k+ requests/sec capability
- Multi-threaded request processing (4 threads default)
- HTTP/1.1 support with keep-alive

### Resource Usage
- Minimal memory footprint
- Efficient JSON parsing with JsonCpp
- Static library linking for core algorithms

## Future Enhancements

### Potential Improvements
1. WebSocket support for real-time conflict resolution
2. Additional endpoints for batch processing
3. File upload support for direct file merging
4. Authentication/authorization layer
5. Rate limiting for production use
6. Metrics and monitoring endpoints

### Scalability
- Horizontal scaling via load balancer
- Stateless design allows multiple instances
- Docker Swarm or Kubernetes ready

## Files Changed/Added

### Modified Files
- `backend/CMakeLists.txt` - Build configuration
- `backend/conanfile.py` - Dependencies
- `backend/src/main.cpp` - Server implementation
- `backend/build.sh` - Build script
- `backend/README.md` - Documentation
- `BUILD.md` - Build guide
- `README.md` - Main documentation

### Added Files
- `backend/config.json` - Server configuration
- `backend/Dockerfile` - Container definition
- `backend/docker-compose.yml` - Orchestration
- `backend/install_drogon.sh` - Installation script
- `backend/src/controllers/MergeController.h` - Controller header
- `backend/src/controllers/MergeController.cc` - Controller implementation
- `backend/examples/README.md` - Examples documentation
- `backend/examples/api_client.py` - Python client
- `backend/examples/test_api.sh` - Shell test scripts

## Conclusion

The conversion to Drogon provides a modern, scalable HTTP API while maintaining the core merge algorithm functionality. The implementation includes comprehensive documentation, multiple deployment options, and maintains backward compatibility at the library level. The flexible build system ensures developers can work in various environments, from containerized deployments to manual installations.
