import {ConnectionBackend, Connection} from '../interfaces';
import {ReadyState, RequestMethod, ResponseType} from '../enums';
import {Request} from '../static_request';
import {Response} from '../static_response';
import {Headers} from '../headers';
import {ResponseOptions} from '../base_response_options';
import {Injectable} from '@angular/core';
import {BrowserXhr} from './browser_xhr';
import {isPresent, isString} from '../../src/facade/lang';
import {Observable} from 'rxjs/Observable';
import {Observer} from 'rxjs/Observer';
import {isSuccess, getResponseURL} from '../http_utils';

const XSSI_PREFIX = ')]}\',\n';

/**
 * Creates connections using `XMLHttpRequest`. Given a fully-qualified
 * request, an `XHRConnection` will immediately create an `XMLHttpRequest` object and send the
 * request.
 *
 * This class would typically not be created or interacted with directly inside applications, though
 * the {@link MockConnection} may be interacted with in tests.
 */
export class XHRConnection implements Connection {
  request: Request;
  /**
   * Response {@link EventEmitter} which emits a single {@link Response} value on load event of
   * `XMLHttpRequest`.
   */
  response: Observable<Response>;
  readyState: ReadyState;
  constructor(req: Request, browserXHR: BrowserXhr, baseResponseOptions?: ResponseOptions) {
    this.request = req;
    this.response = new Observable<Response>((responseObserver: Observer<Response>) => {
      let _xhr: XMLHttpRequest = browserXHR.build();
      _xhr.open(RequestMethod[req.method].toUpperCase(), req.url);

      // load event handler
      let onLoad = () => {
        // responseText is the old-school way of retrieving response (supported by IE8 & 9)
        // response/responseType properties were introduced in XHR Level2 spec (supported by
        // IE10)
        let body = isPresent(_xhr.response) ? _xhr.response : _xhr.responseText;
        // Implicitly strip a potential XSSI prefix.
        if (isString(body) && body.startsWith(XSSI_PREFIX)) {
          body = body.substring(XSSI_PREFIX.length);
        }
        let headers = Headers.fromResponseHeaderString(_xhr.getAllResponseHeaders());

        let url = getResponseURL(_xhr);

        // normalize IE9 bug (http://bugs.jquery.com/ticket/1450)
        let status: number = _xhr.status === 1223 ? 204 : _xhr.status;

        // fix status code when it is 0 (0 status is undocumented).
        // Occurs when accessing file resources or on Android 4.1 stock browser
        // while retrieving files from application cache.
        if (status === 0) {
          status = body ? 200 : 0;
        }
        var responseOptions = new ResponseOptions({body, status, headers, url});
        if (isPresent(baseResponseOptions)) {
          responseOptions = baseResponseOptions.merge(responseOptions);
        }
        let response = new Response(responseOptions);
        if (isSuccess(status)) {
          responseObserver.next(response);
          // TODO(gdi2290): defer complete if array buffer until done
          responseObserver.complete();
          return;
        }
        responseObserver.error(response);
      };
      // error event handler
      let onError = (err: any) => {
        var responseOptions = new ResponseOptions({body: err, type: ResponseType.Error});
        if (isPresent(baseResponseOptions)) {
          responseOptions = baseResponseOptions.merge(responseOptions);
        }
        responseObserver.error(new Response(responseOptions));
      };

      if (isPresent(req.headers)) {
        req.headers.forEach((values, name) => _xhr.setRequestHeader(name, values.join(',')));
      }

      _xhr.addEventListener('load', onLoad);
      _xhr.addEventListener('error', onError);

      _xhr.send(this.request.text());

      return () => {
        _xhr.removeEventListener('load', onLoad);
        _xhr.removeEventListener('error', onError);
        _xhr.abort();
      };
    });
  }
}

/**
 * Creates {@link XHRConnection} instances.
 *
 * This class would typically not be used by end users, but could be
 * overridden if a different backend implementation should be used,
 * such as in a node backend.
 *
 * ### Example
 *
 * ```
 * import {Http, MyNodeBackend, HTTP_PROVIDERS, BaseRequestOptions} from '@angular/http';
 * @Component({
 *   viewProviders: [
 *     HTTP_PROVIDERS,
 *     provide(Http, {useFactory: (backend, options) => {
 *       return new Http(backend, options);
 *     }, deps: [MyNodeBackend, BaseRequestOptions]})]
 * })
 * class MyComponent {
 *   constructor(http:Http) {
 *     http.request('people.json').subscribe(res => this.people = res.json());
 *   }
 * }
 * ```
 *
 **/
@Injectable()
export class XHRBackend implements ConnectionBackend {
  constructor(private _browserXHR: BrowserXhr, private _baseResponseOptions: ResponseOptions) {}
  createConnection(request: Request): XHRConnection {
    return new XHRConnection(request, this._browserXHR, this._baseResponseOptions);
  }
}