# Geutebruck Cross-Switching API - Architecture

**Version**: 1.0.0 (MVP)
**Last Updated**: 2025-12-08
**Status**: In Development

---

## Overview

The Geutebruck Cross-Switching API provides a modern REST API for controlling video routing between cameras (video inputs) and monitors/viewers (video outputs) in Geutebruck surveillance systems. The system acts as a bridge between the native GeViScope/GeViSoft SDK and modern web/mobile applications.

**Core Functionality**:
- 🔐 User authentication with JWT tokens
- 📹 Camera discovery and management
- 🖥️ Monitor/viewer discovery and status
- 🔀 Cross-switching operations (route camera to monitor)
- 📊 Routing state tracking and audit logging

---

## System Architecture

### High-Level Architecture

```
┌─────────────────┐
│   Client Apps   │  (Postman, curl, custom apps)
└────────┬────────┘
         │ HTTP/REST
         ▼
┌─────────────────┐
│  FastAPI Server │  (Python 3.11)
│  Port: 8000     │
└────────┬────────┘
         │
    ┌────┴────┬───────────┬──────────┐
    │         │           │          │
    ▼         ▼           ▼          ▼
┌────────┐ ┌────────┐ ┌────────┐ ┌─────────┐
│ PostgreSQL│ │ Redis  │ │SDK Bridge│ │Auth/JWT │
│ Port:5432│ │Port:6379│ │Port:50051│ │ Service │
└─────────┘ └────────┘ └────┬───┘ └─────────┘
                             │ gRPC
                             ▼
                      ┌──────────────┐
                      │  GeViScope   │
                      │  SDK (.NET)  │
                      └──────┬───────┘
                             │ TCP/IP
                             ▼
                      ┌──────────────┐
                      │  GeViServer  │
                      │  Port: 7700+ │
                      └──────┬───────┘
                             │
                    ┌────────┴────────┐
                    ▼                 ▼
              ┌──────────┐      ┌──────────┐
              │ Cameras  │      │ GSCView  │
              │ (Inputs) │      │ Viewers  │
              └──────────┘      └──────────┘
```

---

## Component Details

### 1. FastAPI Server (Python)

**Purpose**: REST API layer handling HTTP requests, authentication, and business logic

**Technology Stack**:
- Python 3.11+
- FastAPI (web framework)
- SQLAlchemy (ORM)
- Pydantic (validation)
- PyJWT (authentication)

**Key Responsibilities**:
- Accept HTTP REST requests from clients
- Authenticate users and generate JWT tokens
- Validate request data
- Communicate with SDK Bridge via gRPC
- Store routing state in PostgreSQL
- Cache camera/monitor lists in Redis
- Audit log all operations
- Return HTTP responses to clients

**Port**: 8000

---

### 2. SDK Bridge (C# .NET 8.0)

**Purpose**: gRPC service that wraps the GeViScope SDK, translating between modern gRPC and legacy SDK

**Technology Stack**:
- C# .NET 8.0
- Grpc.AspNetCore
- GeViScope SDK (.NET Framework 4.8 DLL)
- Serilog (logging)

**Key Responsibilities**:
- Connect to GeViServer using GeViScope SDK
- Enumerate cameras (GetFirstVideoInput / GetNextVideoInput)
- Enumerate monitors (GetFirstVideoOutput / GetNextVideoOutput)
- Execute cross-switching (CrossSwitch action)
- Clear monitors (ClearVideoOutput action)
- Translate SDK errors to gRPC status codes
- Maintain connection health with retry logic

**Why Separate Service?**:
- ✅ Isolates SDK crashes from Python API
- ✅ Enables independent scaling
- ✅ Clear separation of concerns (SDK complexity vs API logic)
- ✅ Type-safe gRPC communication
- ✅ Can run on different machines if needed

**Port**: 50051 (gRPC)

---

### 3. PostgreSQL Database

**Purpose**: Persistent storage for users, routing state, and audit logs

**Schema**:
```sql
users:
  - id (UUID, primary key)
  - username (unique)
  - password_hash (bcrypt)
  - role (viewer, operator, administrator)
  - created_at, updated_at

crossswitch_routes:
  - id (UUID, primary key)
  - camera_id (int)
  - monitor_id (int)
  - switched_at (timestamp)
  - switched_by_user_id (UUID, FK to users)

audit_logs:
  - id (UUID, primary key)
  - user_id (UUID, FK to users)
  - action (string)
  - target (string)
  - timestamp (timestamp)
  - details (JSON)
```

**Port**: 5432

---

### 4. Redis

**Purpose**: Session storage, caching, and future pub/sub for events

**Usage**:
- **Session Storage**: JWT tokens and user sessions
- **Caching**: Camera list (60s TTL), monitor list (60s TTL)
- **Future**: Pub/sub for real-time routing updates

**Port**: 6379

---

### 5. GeViScope SDK & GeViServer

**GeViServer**:
- Backend service managing surveillance system
- Handles actual video routing
- Controls GSCView viewers
- Manages camera inputs and outputs

**GeViScope SDK**:
- .NET Framework 4.8 DLL (GeViProcAPINET_4_0.dll)
- Provides C# wrapper for GeViServer communication
- Uses action-based message passing
- State query pattern for enumeration

**Ports**: 7700, 7701, 7703

---

## Data Flow

### 1. Authentication Flow

```
Client → POST /api/v1/auth/login
         { username: "admin", password: "secret" }
           ↓
         FastAPI validates credentials
           ↓
         Hash password with bcrypt
           ↓
         Query PostgreSQL for user
           ↓
         Generate JWT token (1hr expiry)
           ↓
         Store session in Redis
           ↓
Client ← { access_token: "eyJ...", token_type: "bearer" }
```

### 2. Camera Discovery Flow

```
Client → GET /api/v1/cameras
         Header: Authorization: Bearer eyJ...
           ↓
         FastAPI validates JWT
           ↓
         Check Redis cache for camera list
           ↓ (cache miss)
         gRPC call to SDK Bridge: ListCameras()
           ↓
         SDK Bridge → GeViScope SDK
                    → CSQGetFirstVideoInput()
                    → CSQGetNextVideoInput() (loop)
           ↓
         SDK Bridge ← Camera list
           ↓
         FastAPI ← gRPC response
           ↓
         Store in Redis (60s TTL)
           ↓
Client ← { cameras: [
           { id: 1, name: "Camera 1", has_ptz: false },
           { id: 2, name: "Front Gate", has_ptz: true }
         ]}
```

### 3. Cross-Switching Flow

```
Client → POST /api/v1/crossswitch
         { camera_id: 7, monitor_id: 3, mode: 0 }
           ↓
         FastAPI validates JWT (requires operator role)
           ↓
         Validate camera_id and monitor_id exist
           ↓
         gRPC call to SDK Bridge: ExecuteCrossSwitch(7, 3, 0)
           ↓
         SDK Bridge → GeViScope SDK
                    → SendMessage("CrossSwitch(7, 3, 0)")
           ↓
         GeViServer executes cross-switch
           ↓
         SDK Bridge ← Success confirmation
           ↓
         FastAPI stores route in PostgreSQL
           ↓
         FastAPI logs to audit_logs table
           ↓
Client ← { success: true, message: "Camera 7 routed to monitor 3" }
```

---

## Security Architecture

### Authentication & Authorization

**Authentication**: JWT (JSON Web Tokens)
- Access tokens: 1 hour lifetime
- Refresh tokens: 7 days lifetime (future)
- Tokens stored in Redis for quick invalidation
- Bcrypt password hashing (cost factor: 12)

**Authorization**: Role-Based Access Control (RBAC)

| Role | Permissions |
|------|------------|
| **Viewer** | Read cameras, Read monitors, Read routing state |
| **Operator** | Viewer + Execute cross-switch, Clear monitors |
| **Administrator** | Operator + User management, Configuration |

### API Security

- ✅ HTTPS enforced in production (TLS 1.2+)
- ✅ CORS configured for allowed origins
- ✅ Rate limiting (60 requests/minute per IP)
- ✅ JWT secret key from environment (not hardcoded)
- ✅ Database credentials in environment variables
- ✅ No stack traces exposed to clients
- ✅ Audit logging for all operations

---

## Scalability Considerations

### Current Architecture (MVP)
- Single FastAPI instance
- Single SDK Bridge instance
- Single GeViServer connection

### Future Horizontal Scaling

**FastAPI Layer**:
- ✅ Stateless design enables multiple instances
- ✅ Load balancer in front (nginx/HAProxy)
- ✅ Shared PostgreSQL and Redis

**SDK Bridge Layer**:
- ⚠️ Limited by GeViServer connection capacity
- Consider: Connection pooling pattern
- Consider: Multiple SDK Bridge instances if needed

**Database Layer**:
- PostgreSQL read replicas for camera/monitor queries
- Redis Cluster for high availability

---

## Error Handling

### SDK Bridge Error Translation

| SDK Error | gRPC Status | HTTP Status |
|-----------|-------------|-------------|
| Connection Failed | UNAVAILABLE | 503 Service Unavailable |
| Invalid Channel | INVALID_ARGUMENT | 400 Bad Request |
| Permission Denied | PERMISSION_DENIED | 403 Forbidden |
| Timeout | DEADLINE_EXCEEDED | 504 Gateway Timeout |
| Unknown | INTERNAL | 500 Internal Server Error |

### Retry Logic
- SDK Bridge connection: 3 attempts with exponential backoff
- gRPC calls from FastAPI: 2 attempts with 1s delay
- Transient errors logged but not exposed to client

---

## Monitoring & Observability

### Logging

**FastAPI**:
- Structured JSON logs (Structlog)
- Log levels: DEBUG, INFO, WARNING, ERROR
- Correlation IDs for request tracing

**SDK Bridge**:
- Serilog with file and console sinks
- Separate logs for SDK communication

### Metrics (Future)

**Prometheus Endpoint**: `/metrics`
- Request count by endpoint
- Request latency (p50, p95, p99)
- Active cross-switch operations
- gRPC call success/failure rates
- Cache hit/miss rates

### Health Checks

**Endpoint**: `GET /api/v1/health`

Returns:
```json
{
  "status": "healthy",
  "components": {
    "database": "up",
    "redis": "up",
    "sdk_bridge": "up"
  },
  "timestamp": "2025-12-08T15:30:00Z"
}
```

---

## Deployment Architecture

### Development Environment
```
Localhost:
  - PostgreSQL (Docker or native)
  - Redis (Docker or native)
  - SDK Bridge (.NET)
  - FastAPI (uvicorn --reload)
  - GeViServer (C:\GEVISOFT\GeViServer.exe)
```

### Production Environment (Windows Server)
```
Windows Server 2016+:
  - GeViServer (native Windows service)
  - SDK Bridge (Windows service via NSSM)
  - PostgreSQL (Docker or native)
  - Redis (Docker or native)
  - FastAPI (Docker or uvicorn behind nginx)
  - Nginx (reverse proxy with SSL termination)
```

### Network Requirements
- Port 8000: FastAPI (HTTPS in production)
- Port 50051: SDK Bridge gRPC (internal only)
- Port 5432: PostgreSQL (internal only)
- Port 6379: Redis (internal only)
- Port 7700-7703: GeViServer (internal only)

---

## Technology Choices Rationale

### Why Python FastAPI?
- ✅ Modern async Python framework
- ✅ Automatic OpenAPI documentation
- ✅ Fast development cycle
- ✅ Rich ecosystem (SQLAlchemy, Pydantic)
- ✅ Easy to expand with new features

### Why C# SDK Bridge?
- ✅ GeViScope SDK is .NET Framework 4.8
- ✅ gRPC provides type-safe communication
- ✅ Isolates SDK complexity
- ✅ Can run on separate machine if needed

### Why PostgreSQL?
- ✅ Mature, reliable, ACID compliant
- ✅ JSON support for flexible audit logs
- ✅ Good performance for relational data

### Why Redis?
- ✅ Fast in-memory caching
- ✅ Session storage
- ✅ Future: pub/sub for events

### Why gRPC (not REST for SDK Bridge)?
- ✅ Type-safe protocol buffers
- ✅ Efficient binary protocol
- ✅ Streaming support (future)
- ✅ Language-agnostic

---

## Future Enhancements (Phase 2)

1. **GeViSet Configuration Management**
   - Retrieve action mappings from GeViServer
   - Modify configurations via API
   - Export/import to CSV
   - Push configurations back to server

2. **Real-Time Event Stream**
   - WebSocket endpoint for routing changes
   - Redis pub/sub for event distribution
   - Monitor status change notifications

3. **PTZ Camera Control**
   - Pan/tilt/zoom commands
   - Preset positions
   - Tour sequences

4. **Multi-Tenancy**
   - Organization/tenant isolation
   - Per-tenant GeViServer connections

5. **Advanced Analytics**
   - Routing history reports
   - Usage patterns
   - Performance metrics

---

## Development Workflow

1. **Setup**: `.\scripts\setup_dev_environment.ps1`
2. **Start Services**: `.\scripts\start_services.ps1`
3. **Database Migrations**: `alembic upgrade head`
4. **Run Tests**: `pytest tests/ -v`
5. **Code Quality**: `ruff check src/api` + `black src/api`
6. **API Docs**: http://localhost:8000/docs

---

## References

- **FastAPI Documentation**: https://fastapi.tiangolo.com
- **gRPC .NET**: https://grpc.io/docs/languages/csharp/
- **GeViScope SDK**: See `docs/SDK_INTEGRATION_LESSONS.md`
- **SQLAlchemy**: https://docs.sqlalchemy.org
- **Pydantic**: https://docs.pydantic.dev

---

**Document Version**: 1.0
**Architecture Status**: ✅ Defined, 🔄 In Development
**Last Review**: 2025-12-08