Backend Implementation

/**
 * Abstract base class for HTTP connections
 * Defines the interface for HTTP connection implementations
 */
abstract class Connection {
  /** Current state of the connection */
  readyState: ReadyState;
  
  /** The HTTP request associated with this connection */
  request: Request;
  
  /** Observable stream of the HTTP response */
  response: Observable<Response>;
}

/**
 * Abstract factory for creating HTTP connections
 * Provides pluggable backend architecture
 */
abstract class ConnectionBackend {
  /**
   * Creates a new connection for the given request
   * @param request - HTTP request to create connection for
   * @returns Connection instance for handling the request
   */
  abstract createConnection(request: any): Connection;
}

/**
 * Factory for creating XMLHttpRequest instances
 * Injectable service for browser XMLHttpRequest creation
 */
class BrowserXhr {
  /**
   * Creates a new XMLHttpRequest instance
   * @returns New XMLHttpRequest object
   */
  build(): XMLHttpRequest;
}

/**
 * XMLHttpRequest-based HTTP connection implementation
 * Handles XMLHttpRequest lifecycle and response processing
 */
class XHRConnection implements Connection {
  /**
   * Creates a new XHR connection
   * @param req - HTTP request to execute
   * @param browserXHR - XMLHttpRequest factory
   * @param baseResponseOptions - Default response options
   */
  constructor(req: Request, browserXHR: BrowserXhr, baseResponseOptions?: ResponseOptions);
  
  /** HTTP request for this connection */
  request: Request;
  
  /** Observable response stream */
  response: Observable<Response>;
  
  /** Current connection state */
  readyState: ReadyState;
  
  /**
   * Sets detected content type on request
   * @param req - Request to modify
   * @param _xhr - XMLHttpRequest instance
   */
  setDetectedContentType(req: any, _xhr: any): void;
}

/**
 * Backend that creates XMLHttpRequest connections
 * Injectable service for XMLHttpRequest-based HTTP operations
 */
class XHRBackend implements ConnectionBackend {
  /**
   * Creates a new XHR backend
   * @param _browserXHR - XMLHttpRequest factory
   * @param _baseResponseOptions - Default response options
   * @param _xsrfStrategy - XSRF protection strategy
   */
  constructor(
    private _browserXHR: BrowserXhr,
    private _baseResponseOptions: ResponseOptions,
    private _xsrfStrategy: XSRFStrategy
  );
  
  /**
   * Creates a new XMLHttpRequest connection
   * @param request - HTTP request to execute
   * @returns XHRConnection instance
   */
  createConnection(request: Request): XHRConnection;
}

import { XHRBackend, BrowserXhr, BaseResponseOptions, CookieXSRFStrategy } from '@angular/http';

class XHRBackendService {
  
  // Create XHR backend with dependencies
  createXHRBackend(): XHRBackend {
    const browserXhr = new BrowserXhr();
    const responseOptions = new BaseResponseOptions();
    const xsrfStrategy = new CookieXSRFStrategy();
    
    return new XHRBackend(browserXhr, responseOptions, xsrfStrategy);
  }
  
  // Make request using XHR backend
  makeXHRRequest(): Observable<Response> {
    const backend = this.createXHRBackend();
    const request = new Request({
      method: RequestMethod.Get,
      url: '/api/data',
      headers: new Headers({ 'Accept': 'application/json' })
    });
    
    const connection = backend.createConnection(request);
    return connection.response;
  }
}

/** Global namespace for JSONP callbacks */
const JSONP_HOME: string; // '__ng_jsonp__'

/**
 * DOM manipulation service for JSONP requests
 * Handles script injection and cleanup for JSONP operations
 */
class BrowserJsonp {
  constructor();
  
  /**
   * Creates a script element for JSONP request
   * @param url - URL for the JSONP request
   * @returns Script element configured for JSONP
   */
  build(url: string): HTMLScriptElement;
  
  /**
   * Generates next unique request ID
   * @returns Unique string identifier for request
   */
  nextRequestID(): string;
  
  /**
   * Gets callback function name for request ID
   * @param id - Request identifier
   * @returns Callback function name
   */
  requestCallback(id: string): string;
  
  /**
   * Exposes connection in global scope for callback
   * @param id - Request identifier
   * @param connection - Connection to expose
   */
  exposeConnection(id: string, connection: any): void;
  
  /**
   * Removes connection from global scope
   * @param id - Request identifier
   */
  removeConnection(id: string): void;
  
  /**
   * Appends script element to DOM to initiate request
   * @param node - Script element to append
   */
  send(node: HTMLScriptElement): void;
  
  /**
   * Removes script element from DOM
   * @param node - Script element to remove
   */
  cleanup(node: HTMLScriptElement): void;
}

/**
 * JSONP connection implementation using script injection
 * Handles JSONP request lifecycle and response processing
 */
class JSONPConnection implements Connection {
  /**
   * Creates a new JSONP connection
   * @param req - HTTP request to execute
   * @param _dom - DOM manipulation service
   * @param baseResponseOptions - Default response options
   */
  constructor(req: Request, private _dom: BrowserJsonp, private baseResponseOptions?: ResponseOptions);
  
  /** Current connection state */
  readyState: ReadyState;
  
  /** HTTP request for this connection */
  request: Request;
  
  /** Observable response stream */
  response: Observable<Response>;
  
  /**
   * Handles completion of JSONP request
   * @param data - Response data from JSONP callback
   */
  finished(data?: any): void;
}

/**
 * Backend that creates JSONP connections
 * Injectable service for JSONP-based HTTP operations
 */
class JSONPBackend extends ConnectionBackend {
  /**
   * Creates a new JSONP backend
   * @param _browserJSONP - DOM manipulation service
   * @param _baseResponseOptions - Default response options
   */
  constructor(private _browserJSONP: BrowserJsonp, private _baseResponseOptions: ResponseOptions);
  
  /**
   * Creates a new JSONP connection
   * @param request - HTTP request to execute
   * @returns JSONPConnection instance
   */
  createConnection(request: Request): JSONPConnection;
}

import { JSONPBackend, BrowserJsonp, BaseResponseOptions } from '@angular/http';

class JSONPBackendService {
  
  // Create JSONP backend
  createJSONPBackend(): JSONPBackend {
    const browserJsonp = new BrowserJsonp();
    const responseOptions = new BaseResponseOptions();
    
    return new JSONPBackend(browserJsonp, responseOptions);
  }
  
  // Make JSONP request
  makeJSONPRequest(): Observable<Response> {
    const backend = this.createJSONPBackend();
    const request = new Request({
      method: RequestMethod.Get,
      url: 'https://api.external.com/data?callback=JSONP_CALLBACK'
    });
    
    const connection = backend.createConnection(request);
    return connection.response;
  }
  
  // Handle JSONP with error handling
  safeJSONPRequest(url: string): Observable<any> {
    const backend = this.createJSONPBackend();
    const request = new Request({
      method: RequestMethod.Get,
      url: url
    });
    
    const connection = backend.createConnection(request);
    
    return connection.response.pipe(
      map(response => response.json()),
      timeout(10000), // 10 second timeout
      catchError(error => {
        console.error('JSONP request failed:', error);
        return throwError('JSONP request timeout or failed');
      })
    );
  }
}

/**
 * Abstract base class for XSRF protection strategies
 * Defines interface for configuring XSRF protection on requests
 */
abstract class XSRFStrategy {
  /**
   * Configures XSRF protection on HTTP request
   * @param req - Request to configure with XSRF protection
   */
  abstract configureRequest(req: Request): void;
}

/**
 * Cookie-based XSRF protection strategy
 * Reads XSRF token from cookie and adds it to request headers
 */
class CookieXSRFStrategy implements XSRFStrategy {
  /**
   * Creates cookie-based XSRF strategy
   * @param _cookieName - Name of cookie containing XSRF token (default: 'XSRF-TOKEN')
   * @param _headerName - Name of header to add token to (default: 'X-XSRF-TOKEN')
   */
  constructor(private _cookieName: string = 'XSRF-TOKEN', private _headerName: string = 'X-XSRF-TOKEN');
  
  /**
   * Configures request with XSRF token from cookie
   * @param req - Request to configure
   */
  configureRequest(req: Request): void;
}

import { CookieXSRFStrategy, XSRFStrategy } from '@angular/http';

class XSRFService {
  
  // Create default XSRF strategy
  createDefaultXSRFStrategy(): CookieXSRFStrategy {
    return new CookieXSRFStrategy();
  }
  
  // Create custom XSRF strategy
  createCustomXSRFStrategy(): CookieXSRFStrategy {
    return new CookieXSRFStrategy('MY_XSRF_TOKEN', 'X-MY-XSRF-TOKEN');
  }
  
  // Apply XSRF protection to request
  protectRequest(request: Request): void {
    const xsrfStrategy = this.createDefaultXSRFStrategy();
    xsrfStrategy.configureRequest(request);
  }
}

// Custom XSRF strategy implementation
class CustomXSRFStrategy implements XSRFStrategy {
  
  configureRequest(req: Request): void {
    // Custom XSRF token logic
    const token = this.getXSRFToken();
    if (token) {
      req.headers.set('X-CSRF-Token', token);
    }
  }
  
  private getXSRFToken(): string | null {
    // Custom token retrieval logic
    return localStorage.getItem('csrfToken');
  }
}

import { ConnectionBackend, Connection, Request, Response } from '@angular/http';
import { Observable } from 'rxjs';

// Custom backend for special requirements
class CustomBackend extends ConnectionBackend {
  
  constructor(private config: any) {
    super();
  }
  
  createConnection(request: Request): Connection {
    return new CustomConnection(request, this.config);
  }
}

class CustomConnection implements Connection {
  readyState: ReadyState;
  request: Request;
  response: Observable<Response>;
  
  constructor(request: Request, private config: any) {
    this.request = request;
    this.readyState = ReadyState.Unsent;
    this.response = this.createResponse();
  }
  
  private createResponse(): Observable<Response> {
    // Custom response creation logic
    return new Observable(observer => {
      // Custom HTTP handling logic
      this.performCustomRequest()
        .then(result => {
          const response = new Response({
            body: result,
            status: 200,
            statusText: 'OK',
            url: this.request.url
          });
          observer.next(response);
          observer.complete();
        })
        .catch(error => {
          observer.error(error);
        });
    });
  }
  
  private async performCustomRequest(): Promise<any> {
    // Custom request implementation
    return fetch(this.request.url)
      .then(response => response.json());
  }
}

import { Injectable, NgModule } from '@angular/core';
import { Http, ConnectionBackend, RequestOptions } from '@angular/http';

// Custom HTTP factory with backend selection
export function httpFactory(
  xhrBackend: XHRBackend,
  jsonpBackend: JSONPBackend,
  requestOptions: RequestOptions
): Http {
  // Choose backend based on environment or configuration
  const backend = shouldUseJSONP() ? jsonpBackend : xhrBackend;
  return new Http(backend, requestOptions);
}

function shouldUseJSONP(): boolean {
  // Logic to determine if JSONP should be used
  return window.location.protocol === 'file:';
}

@NgModule({
  providers: [
    {
      provide: Http,
      useFactory: httpFactory,
      deps: [XHRBackend, JSONPBackend, RequestOptions]
    }
  ]
})
export class CustomHttpModule {}

class ConnectionStateService {
  private connections: Map<string, Connection> = new Map();
  
  trackConnection(id: string, connection: Connection): void {
    this.connections.set(id, connection);
    
    // Monitor connection state
    this.monitorConnection(id, connection);
  }
  
  private monitorConnection(id: string, connection: Connection): void {
    // Log state changes
    console.log(`Connection ${id} state:`, ReadyState[connection.readyState]);
    
    connection.response.subscribe({
      next: response => {
        console.log(`Connection ${id} received response:`, response.status);
      },
      error: error => {
        console.error(`Connection ${id} error:`, error);
        this.connections.delete(id);
      },
      complete: () => {
        console.log(`Connection ${id} completed`);
        this.connections.delete(id);
      }
    });
  }
  
  getActiveConnections(): Connection[] {
    return Array.from(this.connections.values())
      .filter(conn => conn.readyState !== ReadyState.Done);
  }
  
  cancelAllConnections(): void {
    this.connections.forEach((connection, id) => {
      if (connection.readyState !== ReadyState.Done) {
        // Implementation would need cancellation logic
        console.log(`Cancelling connection ${id}`);
      }
    });
    this.connections.clear();
  }
}

class ErrorHandlingBackend extends ConnectionBackend {
  
  constructor(private wrappedBackend: ConnectionBackend) {
    super();
  }
  
  createConnection(request: Request): Connection {
    const originalConnection = this.wrappedBackend.createConnection(request);
    
    return new ErrorHandlingConnection(originalConnection);
  }
}

class ErrorHandlingConnection implements Connection {
  readyState: ReadyState;
  request: Request;
  response: Observable<Response>;
  
  constructor(private originalConnection: Connection) {
    this.readyState = originalConnection.readyState;
    this.request = originalConnection.request;
    
    this.response = originalConnection.response.pipe(
      retry(3), // Retry failed requests
      catchError(this.handleError),
      timeout(30000) // 30 second timeout
    );
  }
  
  private handleError = (error: any): Observable<Response> => {
    console.error('HTTP request failed:', error);
    
    // Create error response
    const errorResponse = new Response({
      body: JSON.stringify({ error: 'Request failed' }),
      status: error.status || 500,
      statusText: error.statusText || 'Internal Server Error',
      url: this.request.url
    });
    
    return Observable.of(errorResponse);
  }
}