# Control Service Development Guide

## Overview

The Hotel Pi Control Service is a Node.js WebSocket server that:
- Listens for HDMI-CEC remote input
- Translates input to navigation events
- Executes system commands (launch apps, etc.)
- Communicates with the frontend via WebSocket

## Architecture

```
src/
├── server.js          # Main server & WebSocket handler
├── cec-handler.js     # HDMI-CEC input processing
├── commands.js        # System command execution
└── ...

package.json           # Dependencies
.eslintrc.json         # Linting config
Dockerfile             # Container image
```

## Setup & Development

### Local Setup

```bash
cd control-service
npm install
npm run dev
```

Server runs on http://localhost:3001

### Commands

```bash
npm run dev    # Start with hot reload
npm run start  # Run production
npm run lint   # Check code style
```

## Core Modules

### server.js

Main HTTP/WebSocket server.

**Features:**
- HTTP server on port 3001
- WebSocket server for client connections
- Health check endpoint (`GET /health`)
- Message routing to handlers

**HTTP Routes:**
```
GET  /              - Server info
GET  /health        - Health status
WS   /              - WebSocket connection
```

**WebSocket Messages:**

Client → Server:
- `launch-plex` - Launch Plex media center
- `return-to-kiosk` - Kill current app, return to kiosk
- `restart-kiosk` - Restart kiosk application
- `execute` - Execute shell command
- `ping` - Ping for heartbeat

Server → Client:
- `connected` - Connection confirmed
- `input` - Remote input event
- `error` - Error message
- Response to commands

### cec-handler.js

HDMI-CEC input listener.

**Class: CECHandler**

```javascript
const cec = new CECHandler(devicePath);

await cec.init();              // Initialize CEC
cec.on('input', callback);     // Listen for input
cec.startMonitoring(callback); // Start listening
```

**Input Event Mapping:**
```
CEC Button → Event Type
OK/Select → select
Up arrow  → up
Down arrow → down
Left arrow → left
Right arrow → right
Exit/Back → back
```

**Notes:**
- Requires `cec-client` system package
- Device path: `/dev/ttyAMA0` (Raspberry Pi UART)
- Gracefully falls back if cec-client unavailable

### commands.js

System command executor.

**Class: CommandExecutor**

```javascript
const executor = new CommandExecutor(config);

await executor.launchPlex();        // Launch Plex
await executor.restartKiosk();      // Restart kiosk
await executor.returnToKiosk();     // Kill Plex, return to kiosk
await executor.executeCommand(cmd); // Execute arbitrary command
executor.getHealth();               // Get service health
```

**Configuration:**
```javascript
{
  plexLaunchCommand: '/usr/bin/plex-htpc',
  kioskLaunchCommand: '/home/pi/scripts/launch-kiosk.sh'
}
```

**Executing Commands:**

```javascript
// Launch Plex
const result = await executor.launchPlex();
// Returns: { success: true, message: '...' }

// Execute custom command
const result = await executor.executeCommand('ls -la /tmp');
// Returns: { success: true, stdout: '...', stderr: '' }
```

## WebSocket Protocol

### Connection Lifecycle

1. Client connects to `ws://localhost:3001`
2. Server sends `{ type: 'connected', payload: {...} }`
3. Client can send commands
4. Server processes and responds
5. Client can emit input events

### Example Client Usage

```javascript
const ws = new WebSocket('ws://localhost:3001');

ws.onopen = () => {
  console.log('Connected');
  ws.send(JSON.stringify({
    type: 'launch-plex',
    payload: {}
  }));
};

ws.onmessage = (event) => {
  const data = JSON.parse(event.data);
  console.log('Response:', data);
};

ws.onerror = (error) => {
  console.error('Error:', error);
};

ws.onclose = () => {
  console.log('Disconnected');
};
```

### Message Format

All messages are JSON:

```json
{
  "type": "command-name",
  "payload": {
    "key": "value"
  }
}
```

## Configuration

### Environment Variables

```bash
PORT=3001                              # Server port
CEC_DEVICE=/dev/ttyAMA0                # CEC serial device
PLEX_LAUNCH_COMMAND=/usr/bin/plex-htpc # Plex executable
KIOSK_LAUNCH_COMMAND=/home/pi/...      # Kiosk script path
```

### Runtime Options

Edit `config` object in `server.js`:

```javascript
const executor = new CommandExecutor({
  plexLaunchCommand: process.env.PLEX_LAUNCH_COMMAND,
  kioskLaunchCommand: process.env.KIOSK_LAUNCH_COMMAND,
});
```

## Building & Deployment

### Docker Build

```bash
docker build -t hotel-pi-control .
docker run -p 3001:3001 hotel-pi-control
```

### Production Deployment

```bash
# Build for production
npm run build

# Start service
npm run start
```

### Systemd Service

Create `/etc/systemd/system/hotel-pi-control.service`:

```ini
[Unit]
Description=Hotel Pi Control Service
After=network.target

[Service]
Type=simple
User=pi
WorkingDirectory=/home/pi/hotel-pi
ExecStart=/usr/bin/node src/server.js
Restart=always
RestartSec=10
Environment="PATH=/usr/local/bin:/usr/bin"

[Install]
WantedBy=multi-user.target
```

Enable:
```bash
sudo systemctl daemon-reload
sudo systemctl enable hotel-pi-control
sudo systemctl start hotel-pi-control
```

## Error Handling

### Connection Errors

```javascript
// Client disconnected
ws.on('close', () => {
  console.log('Client disconnected');
  clients.delete(ws);
});

// WebSocket error
ws.on('error', (error) => {
  console.error('WebSocket error:', error.message);
});
```

### Command Execution Errors

Commands wrap in try-catch and return success flag:

```javascript
try {
  await executor.launchPlex();
  // Send success response
} catch (error) {
  ws.send(JSON.stringify({
    type: 'error',
    payload: { message: error.message }
  }));
}
```

## Logging

Service logs to console with emoji indicators:

```
✓ Success
✗ Error
❌ Critical error
📡 Connection event
🎮 Input event
🎬 Plex launch
🔙 Return to kiosk
⚙ Command execution
🛑 Shutdown
```

For persistent logs, redirect output:

```bash
npm run start > /var/log/hotel-pi-control.log 2>&1 &
```

## Testing

### Health Check

```bash
curl http://localhost:3001/health

{
  "status": "healthy",
  "timestamp": "2024-03-20T12:34:56Z",
  "processes": ["plex"]
}
```

### WebSocket Test

Using `wscat`:
```bash
npm install -g wscat
wscat -c ws://localhost:3001

# Type messages:
> {"type":"ping","payload":{}}

< {"type":"pong","timestamp":"..."}
```

### Command Testing

```bash
# Execute command
curl -X POST http://localhost:3001 \
  -H "Content-Type: application/json" \
  -d '{"type":"execute","payload":{"command":"echo hello"}}'

# Test launch (won't actually launch without Plex installed)
curl -X POST http://localhost:3001 \
  -H "Content-Type: application/json" \
  -d '{"type":"launch-plex","payload":{}}'
```

## Troubleshooting

### Port Already in Use

```bash
# Find process using port 3001
lsof -i :3001

# Kill process
kill -9 <PID>
```

### CEC Not Working

```bash
# Check if cec-client is installed
which cec-client

# Install if missing (Ubuntu/Debian)
sudo apt-get install libcec-dev

# Test CEC connection
echo "as" | cec-client -s
```

### WebSocket Connection Fails

- Verify server is running: `curl http://localhost:3001`
- Check firewall: `sudo ufw allow 3001`
- Check browser console for CORS/connection errors
- Verify WebSocket URL in frontend `.env`

### Memory Leaks

Check active connections:
```bash
# In health response
curl http://localhost:3001/health | jq '.processes'

# Monitor over time
watch curl http://localhost:3001/health
```

## Performance Optimization

1. **Connection Pooling:**
   - Reuse WebSocket connections
   - Don't create new connection per message

2. **Message Batching:**
   - Send multiple events in one message if possible
   - Avoid rapid successive messages

3. **Resource Cleanup:**
   - Properly close WebSocket connections
   - Kill child processes when done

4. **Monitoring:**
   - Log important events
   - Track connection count
   - Monitor memory usage

## Security Considerations

1. **Input Validation:**
   - Validate command strings
   - Prevent shell injection
   - Whitelist allowed commands

2. **Authentication:**
   - In production, add auth before executing commands
   - Use JWT or similar for WebSocket auth

3. **CORS:**
   - Configure CORS_ORIGIN for specific domains
   - Don't allow all origins in production

4. **Network:**
   - Firewall port 3001 to local network only
   - Use HTTPS/WSS in production
   - Disable debug endpoints in production

## Code Quality

### Linting

```bash
npm run lint
```

### Best Practices

- Use async/await (not callbacks)
- Handle errors in try-catch
- Log all important events
- Close connections properly
- Validate input data

## Resources

- [Node.js Docs](https://nodejs.org/docs/)
- [ws Library](https://github.com/websockets/ws)
- [libcec Documentation](https://github.com/libcec/libcec)