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# Development Best Practices

This guide outlines the best practices for developing tools and features for the Home Assistant MCP.

## Code Style

### TypeScript

1. Use TypeScript for all new code
2. Enable strict mode
3. Use explicit types
4. Avoid `any` type
5. Use interfaces over types
6. Document with JSDoc comments

    /**
     * Represents a device in the system.
     * @interface
     */
    interface Device {
        /** Unique device identifier */
        id: string;

        /** Human-readable device name */
        name: string;

        /** Device state */
        state: DeviceState;
    }

### Naming Conventions

1. Use PascalCase for:
2. Classes
3. Interfaces
4. Types

5. Enums

6. Use camelCase for:

7. Variables
8. Functions
9. Methods

10. Properties

11. Use UPPER_SNAKE_CASE for:

12. Constants
13. Enum values

    class DeviceManager {
        private readonly DEFAULT_TIMEOUT = 5000;

        async getDeviceState(deviceId: string): Promise<DeviceState> {
            // Implementation
        }
    }

## Architecture

### SOLID Principles

1. Single Responsibility
2. Each class/module has one job

3. Split complex functionality

4. Open/Closed

5. Open for extension

6. Closed for modification

7. Liskov Substitution

8. Subtypes must be substitutable

9. Use interfaces properly

10. Interface Segregation

11. Keep interfaces focused

12. Split large interfaces

13. Dependency Inversion

14. Depend on abstractions
15. Use dependency injection

### Example

    // Bad
    class DeviceManager {
        async getState() { /* ... */ }
        async setState() { /* ... */ }
        async sendNotification() { /* ... */ }  // Wrong responsibility
    }

    // Good
    class DeviceManager {
        constructor(
            private notifier: NotificationService
        ) {}

        async getState() { /* ... */ }
        async setState() { /* ... */ }
    }

    class NotificationService {
        async send() { /* ... */ }
    }

## Error Handling

### Best Practices

1. Use custom error classes
2. Include error codes
3. Provide meaningful messages
4. Include error context
5. Handle async errors
6. Log appropriately

    class DeviceError extends Error {
        constructor(
            message: string,
            public code: string,
            public context: Record<string, any>
        ) {
            super(message);
            this.name = 'DeviceError';
        }
    }

    try {
        await device.connect();
    } catch (error) {
        throw new DeviceError(
            'Failed to connect to device',
            'DEVICE_CONNECTION_ERROR',
            { deviceId: device.id, attempt: 1 }
        );
    }

## Testing

### Guidelines

1. Write unit tests first
2. Use meaningful descriptions
3. Test edge cases
4. Mock external dependencies
5. Keep tests focused
6. Use test fixtures

    describe('DeviceManager', () => {
        let manager: DeviceManager;
        let mockDevice: jest.Mocked<Device>;

        beforeEach(() => {
            mockDevice = {
                id: 'test_device',
                getState: jest.fn()
            };
            manager = new DeviceManager(mockDevice);
        });

        it('should get device state', async () => {
            mockDevice.getState.mockResolvedValue('on');
            const state = await manager.getDeviceState();
            expect(state).toBe('on');
        });
    });

## Performance

### Optimization

1. Use caching
2. Implement pagination
3. Optimize database queries
4. Use connection pooling
5. Implement rate limiting
6. Batch operations

    class DeviceCache {
        private cache = new Map<string, CacheEntry>();
        private readonly TTL = 60000;  // 1 minute

        async getDevice(id: string): Promise<Device> {
            const cached = this.cache.get(id);
            if (cached && Date.now() - cached.timestamp < this.TTL) {
                return cached.device;
            }

            const device = await this.fetchDevice(id);
            this.cache.set(id, {
                device,
                timestamp: Date.now()
            });

            return device;
        }
    }

## Security

### Guidelines

1. Validate all input
2. Use parameterized queries
3. Implement rate limiting
4. Use proper authentication
5. Follow OWASP guidelines
6. Sanitize output

    class InputValidator {
        static validateDeviceId(id: string): boolean {
            return /^[a-zA-Z0-9_-]{1,64}$/.test(id);
        }

        static sanitizeOutput(data: any): any {
            // Implement output sanitization
            return data;
        }
    }

## Documentation

### Standards

1. Use JSDoc comments
2. Document interfaces
3. Include examples
4. Document errors
5. Keep docs updated
6. Use markdown

    /**
     * Manages device operations.
     * @class
     */
    class DeviceManager {
        /**
         * Gets the current state of a device.
         * @param {string} deviceId - The device identifier.
         * @returns {Promise<DeviceState>} The current device state.
         * @throws {DeviceError} If device is not found or unavailable.
         * @example
         * const state = await deviceManager.getDeviceState('living_room_light');
         */
        async getDeviceState(deviceId: string): Promise<DeviceState> {
            // Implementation
        }
    }

## Logging

### Best Practices

1. Use appropriate levels
2. Include context
3. Structure log data
4. Handle sensitive data
5. Implement rotation
6. Use correlation IDs

    class Logger {
        info(message: string, context: Record<string, any>) {
            console.log(JSON.stringify({
                level: 'info',
                message,
                context,
                timestamp: new Date().toISOString(),
                correlationId: context.correlationId
            }));
        }
    }

## Version Control

### Guidelines

1. Use meaningful commits
2. Follow branching strategy
3. Write good PR descriptions
4. Review code thoroughly
5. Keep changes focused
6. Use conventional commits

    # Good commit messages
    git commit -m "feat(device): add support for zigbee devices"
    git commit -m "fix(api): handle timeout errors properly"

## See Also

- Tool Development Guide
- Interface Documentation
- Testing Guide

February 5, 2025
February 5, 2025
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