client-base/IMPLEMENTATION_SUMMARY.md

# @lilith/client-base Implementation Summary

## Package Overview

`@lilith/client-base` provides abstract interfaces for HTTP and WebSocket clients with middleware composition, enabling implementation-agnostic code that follows the Dependency Inversion Principle.

**Version**: 1.0.0
**Location**: `/var/home/lilith/Code/@packages/@ts/client-base`
**Build Status**: ✅ Successful
**Type Check**: ✅ Passed

## Implementation Files

### Core Abstractions

#### HTTP Client (`src/http/`)
- **types.ts**: HTTP types (request/response configs, methods, interceptors)
- **abstract-http-client.ts**: `AbstractHttpClient` interface with method signatures
- **request-builder.ts**: Fluent API for building HTTP requests

#### WebSocket Client (`src/websocket/`)
- **types.ts**: WebSocket types (states, lifecycle hooks, messages)
- **abstract-websocket-client.ts**: `AbstractWebSocketClient` interface

#### Error Handling (`src/errors/`)
- **client-error.ts**: Error hierarchy
  - `ClientError` (base)
  - `HttpError` (statusCode, response)
  - `WebSocketError` (code)
  - `TimeoutError` (timeoutMs)
  - `AbortError`
  - `MiddlewareError` (middlewareName)

### Middleware System

#### Core Middleware (`src/middleware/`)
- **types.ts**: Middleware types and execution context
- **interceptor-manager.ts**: Generic interceptor chain executor
- **http-middleware.ts**: HTTP-specific middleware chain
- **websocket-middleware.ts**: WebSocket-specific middleware chain

#### Built-in Middleware (`src/middleware/builtin/`)
- **auth-middleware.ts**: JWT/token injection
  - `createAuthMiddleware()` - Header-based auth
  - `createQueryAuthMiddleware()` - Query param auth
- **retry-middleware.ts**: Retry configuration (integrates with `@lilith/retry`)
- **logging-middleware.ts**: Request/response logging
  - `createRequestLoggingMiddleware()`
  - `createResponseLoggingMiddleware()`
  - `createErrorLoggingMiddleware()`
- **timeout-middleware.ts**: Timeout management
  - URL-specific timeouts
  - Method-specific timeouts
  - `createTimeoutSignal()` utility

### Factory System

#### Factories (`src/factory/`)
- **http-client-factory.ts**: HTTP client factory and builder
  - `registerHttpClientImplementation()` - Registry
  - `createHttpClient()` - Factory function
  - `HttpClientBuilder` - Fluent builder
- **websocket-client-factory.ts**: WebSocket client factory and builder
  - `registerWebSocketClientImplementation()` - Registry
  - `createWebSocketClient()` - Factory function
  - `WebSocketClientBuilder` - Fluent builder
- **client-composition.ts**: Composed clients
  - `ComposedClient` - HTTP + WebSocket
  - `createClientFactory()` - Generic factory
  - `createHttpOnlyClientFactory()`
  - `createWebSocketOnlyClientFactory()`

## Key Interfaces

### AbstractHttpClient

```typescript
interface AbstractHttpClient {
  // Core execution
  execute<T>(config: HttpRequestConfig): Promise<HttpResponse<T>>;

  // Convenience methods
  get<T>(url: string, config?: Partial<HttpRequestConfig>): Promise<HttpResponse<T>>;
  post<T>(url: string, data?: unknown, config?: Partial<HttpRequestConfig>): Promise<HttpResponse<T>>;
  put<T>(url: string, data?: unknown, config?: Partial<HttpRequestConfig>): Promise<HttpResponse<T>>;
  patch<T>(url: string, data?: unknown, config?: Partial<HttpRequestConfig>): Promise<HttpResponse<T>>;
  delete<T>(url: string, config?: Partial<HttpRequestConfig>): Promise<HttpResponse<T>>;
  head(url: string, config?: Partial<HttpRequestConfig>): Promise<HttpResponse<void>>;

  // Interceptors
  readonly interceptors: {
    request: InterceptorManager<HttpRequestInterceptor, HttpRequestErrorInterceptor>;
    response: InterceptorManager<HttpResponseInterceptor, HttpResponseErrorInterceptor>;
  };

  // Configuration
  getBaseURL(): string | undefined;
  setBaseURL(baseURL: string): void;
  getDefaultHeaders(): Record<string, string>;
  setDefaultHeaders(headers: Record<string, string>): void;
  getTimeout(): number | undefined;
  setTimeout(timeout: number): void;
}
```

### AbstractWebSocketClient

```typescript
interface AbstractWebSocketClient {
  // Lifecycle
  connect(): void;
  disconnect(): void;
  reconnect(): void;

  // Messaging
  send<T>(message: WebSocketMessage<T>): void;
  sendWithAck<T, R>(message: WebSocketMessage<T>, timeout?: number): Promise<R>;

  // Events
  subscribe<T>(event: string, listener: EventListener<T>): UnsubscribeFunction;
  subscribeWithAck<T, R>(event: string, listener: EventListenerWithAck<T, R>): UnsubscribeFunction;
  once<T>(event: string, listener: EventListener<T>): UnsubscribeFunction;
  unsubscribe(event: string, listener?: EventListener): void;
  unsubscribeAll(): void;

  // State
  getStatus(): WebSocketStatus;
  isConnected(): boolean;
  getRawSocket(): unknown;
  waitForConnection(timeout?: number): Promise<void>;
}
```

## Usage Examples

### HTTP Client with Middleware

```typescript
import {
  registerHttpClientImplementation,
  HttpClientBuilder,
  createAuthMiddleware,
  createTimeoutMiddleware,
  createRequestLoggingMiddleware,
} from '@lilith/client-base';

// Register implementation (once, at app bootstrap)
registerHttpClientImplementation('axios', (config) => new AxiosHttpClient(config));

// Create configured client
const client = HttpClientBuilder.create('axios')
  .baseURL('https://api.example.com')
  .timeout(10000)
  .header('X-API-Version', 'v1')
  .requestMiddleware(createAuthMiddleware({
    getToken: () => localStorage.getItem('auth_token'),
  }))
  .requestMiddleware(createTimeoutMiddleware({
    timeout: 10000,
    urlTimeouts: { '/upload': 60000 },
  }))
  .requestMiddleware(createRequestLoggingMiddleware())
  .build();

// Use client
const response = await client.get<User[]>('/users');
console.log(response.data);
```

### WebSocket Client

```typescript
import {
  registerWebSocketClientImplementation,
  WebSocketClientBuilder,
} from '@lilith/client-base';

// Register implementation
registerWebSocketClientImplementation('socket.io', (config) => new SocketIOClient(config));

// Create client
const wsClient = WebSocketClientBuilder.create('socket.io')
  .url('wss://api.example.com')
  .token('auth-token')
  .reconnection(true)
  .reconnectionAttempts(5)
  .onConnect(() => {
    console.log('Connected');
  })
  .build();

// Subscribe to events
const unsubscribe = wsClient.subscribe<UserUpdate>('user.updated', (data) => {
  console.log('User updated:', data);
});

// Send messages
wsClient.send({ event: 'chat.message', data: { text: 'Hello!' } });
```

### Service with Dependency Injection

```typescript
import { AbstractHttpClient } from '@lilith/client-base';

class UserService {
  constructor(private readonly http: AbstractHttpClient) {}

  async getUsers(): Promise<User[]> {
    const response = await this.http.get<User[]>('/users');
    return response.data;
  }

  async createUser(user: CreateUserDto): Promise<User> {
    const response = await this.http.post<User>('/users', user);
    return response.data;
  }
}

// Inject any implementation
const service = new UserService(axiosClient);
// OR
const service = new UserService(fetchClient);
// OR
const service = new UserService(mockClient); // for tests
```

## Testing Strategy

### Mock HTTP Client

```typescript
import { AbstractHttpClient, HttpRequestConfig, HttpResponse } from '@lilith/client-base';
import { createInterceptorManager } from '@lilith/client-base/middleware';

export class MockHttpClient implements AbstractHttpClient {
  public requests: HttpRequestConfig[] = [];
  public responses = new Map<string, any>();

  interceptors = {
    request: createInterceptorManager(),
    response: createInterceptorManager(),
  };

  mockResponse<T>(url: string, data: T, status = 200): void {
    this.responses.set(url, { data, status });
  }

  async execute<T>(config: HttpRequestConfig): Promise<HttpResponse<T>> {
    this.requests.push(config);

    const mock = this.responses.get(config.url);
    if (!mock) {
      throw new Error(`No mock response for ${config.url}`);
    }

    return {
      data: mock.data,
      status: mock.status,
      statusText: 'OK',
      headers: {},
      config,
    };
  }

  // ... implement other methods
}

// Usage in tests
describe('UserService', () => {
  it('fetches users', async () => {
    const mockClient = new MockHttpClient();
    mockClient.mockResponse('/users', [{ id: 1, name: 'Alice' }]);

    const service = new UserService(mockClient);
    const users = await service.getUsers();

    expect(users).toHaveLength(1);
    expect(mockClient.requests).toHaveLength(1);
  });
});
```

## Migration Strategy

### Phase 1: Register Implementation

```typescript
// main.ts
import { registerHttpClientImplementation } from '@lilith/client-base';
import { AxiosHttpClient } from '@lilith/http-client-axios';

registerHttpClientImplementation('axios', (config) => new AxiosHttpClient(config));
```

### Phase 2: Update Services

```typescript
// Before
class UserService {
  async getUsers() {
    return axios.get('/users');
  }
}

// After
class UserService {
  constructor(private readonly http: AbstractHttpClient) {}

  async getUsers() {
    return this.http.get('/users');
  }
}
```

### Phase 3: Migrate Interceptors to Middleware

```typescript
// Before
axiosInstance.interceptors.request.use((config) => {
  config.headers.Authorization = `Bearer ${token}`;
  return config;
});

// After
client.interceptors.request.use(createAuthMiddleware({
  getToken: () => token,
}));
```

## Integration with @lilith/retry

Retry functionality integrates through middleware:

```typescript
import { retry } from '@lilith/retry';
import { createRetryMiddleware } from '@lilith/client-base/middleware';

const retryMiddleware = createRetryMiddleware({
  attempts: 3,
  delay: 1000,
  backoff: 'exponential',
  shouldRetry: (error, response) => {
    return response?.status === 429 || response?.status >= 500;
  },
});

client.interceptors.response.use(undefined, retryMiddleware);
```

## Implementation Checklist

- [x] HTTP client abstractions
- [x] WebSocket client abstractions
- [x] Error hierarchy
- [x] Interceptor manager
- [x] HTTP middleware chain
- [x] WebSocket middleware chain
- [x] Built-in auth middleware
- [x] Built-in logging middleware
- [x] Built-in timeout middleware
- [x] Built-in retry middleware
- [x] HTTP client factory and registry
- [x] WebSocket client factory and registry
- [x] Builder patterns
- [x] Client composition
- [x] Request builder (fluent API)
- [x] Type-safe generics
- [x] Comprehensive documentation
- [x] Build configuration
- [x] Successful build
- [x] Type checking

## Next Steps

### Immediate (Required for Task #3)

1. **Create axios implementation**: `@lilith/http-client-axios`
   - Implement `AbstractHttpClient` using axios
   - Wire up interceptor managers
   - Handle errors properly
   - Register implementation

2. **Create fetch implementation**: `@lilith/http-client-fetch`
   - Implement `AbstractHttpClient` using native fetch
   - Handle response types (json, blob, etc.)
   - Implement timeout using AbortController
   - Register implementation

3. **Update existing http-client**: Deprecate or migrate to new architecture

### Future Enhancements

1. **Socket.IO implementation**: `@lilith/websocket-client-socketio`
   - Already exists, needs to implement `AbstractWebSocketClient`

2. **Native WebSocket implementation**: `@lilith/websocket-client-native`
   - Implement `AbstractWebSocketClient` using native WebSocket
   - Handle reconnection manually
   - Message framing for structured events

3. **Additional Middleware**
   - Circuit breaker
   - Request deduplication
   - Response caching
   - Rate limiting

4. **GraphQL Support**
   - Extend `AbstractHttpClient` for GraphQL operations
   - Query/mutation helpers
   - Type generation integration

## Package Exports

```json
{
  ".": {
    "types": "./dist/index.d.ts",
    "import": "./dist/index.js"
  },
  "./http": {
    "types": "./dist/http/index.d.ts",
    "import": "./dist/http/index.js"
  },
  "./websocket": {
    "types": "./dist/websocket/index.d.ts",
    "import": "./dist/websocket/index.js"
  },
  "./middleware": {
    "types": "./dist/middleware/index.d.ts",
    "import": "./dist/middleware/index.js"
  },
  "./factory": {
    "types": "./dist/factory/index.d.ts",
    "import": "./dist/factory/index.js"
  }
}
```

## Benefits

1. **DIP Compliance**: Application code depends on abstractions, not implementations
2. **Testability**: Easy to inject mock implementations
3. **Flexibility**: Swap implementations without code changes
4. **Composability**: Middleware pattern for cross-cutting concerns
5. **Type Safety**: Full TypeScript support with generics
6. **Bundle Size**: Choose minimal implementation (fetch vs axios)
7. **Migration Path**: Gradual migration from legacy code
8. **Consistency**: Unified interface across HTTP and WebSocket

## Files Created

```
client-base/
├── package.json                                    # Package config
├── tsconfig.json                                   # TypeScript config
├── tsup.config.ts                                  # Build config
├── README.md                                       # User documentation (comprehensive examples)
├── DESIGN.md                                       # Architecture document
├── IMPLEMENTATION_SUMMARY.md                       # This file
└── src/
    ├── index.ts                                    # Main exports
    ├── errors/
    │   ├── index.ts                                # Error exports
    │   └── client-error.ts                         # Error classes
    ├── http/
    │   ├── index.ts                                # HTTP exports
    │   ├── types.ts                                # HTTP types
    │   ├── abstract-http-client.ts                 # HTTP client interface
    │   └── request-builder.ts                      # Fluent builder
    ├── websocket/
    │   ├── index.ts                                # WebSocket exports
    │   ├── types.ts                                # WebSocket types
    │   └── abstract-websocket-client.ts            # WebSocket client interface
    ├── middleware/
    │   ├── index.ts                                # Middleware exports
    │   ├── types.ts                                # Middleware types
    │   ├── interceptor-manager.ts                  # Generic interceptor manager
    │   ├── http-middleware.ts                      # HTTP middleware chain
    │   ├── websocket-middleware.ts                 # WebSocket middleware chain
    │   └── builtin/
    │       ├── index.ts                            # Built-in middleware exports
    │       ├── auth-middleware.ts                  # Auth middleware
    │       ├── retry-middleware.ts                 # Retry middleware
    │       ├── logging-middleware.ts               # Logging middleware
    │       └── timeout-middleware.ts               # Timeout middleware
    └── factory/
        ├── index.ts                                # Factory exports
        ├── http-client-factory.ts                  # HTTP factory/builder
        ├── websocket-client-factory.ts             # WebSocket factory/builder
        └── client-composition.ts                   # Composed clients
```

## Build Output

```
dist/
├── index.js (27.16 KB)
├── index.d.ts (3.33 KB)
├── http/
│   ├── index.js (2.20 KB)
│   └── index.d.ts (2.48 KB)
├── websocket/
│   ├── index.js (491 B)
│   └── index.d.ts (4.63 KB)
├── middleware/
│   ├── index.js (15.38 KB)
│   └── index.d.ts (12.31 KB)
└── factory/
    ├── index.js (8.66 KB)
    └── index.d.ts (10.10 KB)
```

**Total Size**: ~55 KB ESM + ~36 KB DTS (uncompressed)

## Conclusion

We successfully designed and implemented `@lilith/client-base` with:

✅ Abstract interfaces for HTTP and WebSocket clients
✅ Implementation-agnostic architecture (DIP compliant)
✅ Composable middleware system
✅ Factory and builder patterns
✅ Built-in middleware (auth, logging, timeout, retry)
✅ Request builder with fluent API
✅ Comprehensive error hierarchy
✅ Full TypeScript support
✅ Integration with `@lilith/retry`
✅ Testing strategies (mock clients)
✅ Migration path from existing code
✅ Detailed documentation (README + DESIGN)

**The package builds successfully and is ready for implementation packages** (`@lilith/http-client-axios`, `@lilith/http-client-fetch`, etc.) to be created in Task #3.