fix(aio): ensure that only one request per document is made

aio/src/app/documents/document.service.spec.ts

@@ -1,31 +1,132 @@
 import { ReflectiveInjector } from '@angular/core';
-import { Location, LocationStrategy } from '@angular/common';
-import { MockLocationStrategy } from '@angular/common/testing';
-import { Http, ConnectionBackend, RequestOptions, BaseRequestOptions } from '@angular/http';
+import { Http, ConnectionBackend, RequestOptions, BaseRequestOptions, Response, ResponseOptions } from '@angular/http';
+
+import { Observable } from 'rxjs/Observable';
+import { Subscription } from 'rxjs/Subscription';
+import { BehaviorSubject } from 'rxjs/BehaviorSubject';
+
 import { MockBackend } from '@angular/http/testing';
 import { LocationService } from 'app/shared/location.service';
+import { MockLocationService } from 'testing/location.service';
 import { Logger } from 'app/shared/logger.service';
-import { DocumentService } from './document.service';
+import { MockLogger } from 'testing/logger.service';
+import { DocumentService, DocumentContents } from './document.service';
+
+
+const CONTENT_URL_PREFIX = 'content/docs/';
+
+function createResponse(body: any) {
+  return new Response(new ResponseOptions({ body: JSON.stringify(body) }));
+}
+
+function createInjector(initialUrl: string) {
+  return ReflectiveInjector.resolveAndCreate([
+      DocumentService,
+      { provide: LocationService, useFactory: () => new MockLocationService(initialUrl) },
+      { provide: ConnectionBackend, useClass: MockBackend },
+      { provide: RequestOptions, useClass: BaseRequestOptions },
+      { provide: Logger, useClass: MockLogger },
+      Http,
+  ]);
+}
+
+function getServices(initialUrl: string = '') {
+  const injector = createInjector(initialUrl);
+  return {
+    backend: injector.get(ConnectionBackend) as MockBackend,
+    location: injector.get(LocationService) as MockLocationService,
+    service: injector.get(DocumentService) as DocumentService,
+    logger: injector.get(Logger) as MockLogger
+  };
+}
 
 describe('DocumentService', () => {
 
-  let injector: ReflectiveInjector;
-
-  beforeEach(() => {
-    injector = ReflectiveInjector.resolveAndCreate([
-        DocumentService,
-        LocationService,
-        Location,
-        { provide: LocationStrategy, useClass: MockLocationStrategy },
-        { provide: ConnectionBackend, useClass: MockBackend },
-        { provide: RequestOptions, useClass: BaseRequestOptions },
-        Http,
-        Logger
-    ]);
-  });
-
   it('should be creatable', () => {
-    const service: DocumentService = injector.get(DocumentService);
+    const { service } = getServices();
     expect(service).toBeTruthy();
   });
+
+  describe('currentDocument', () => {
+
+    it('should fetch a document for the initial location url', () => {
+      const { service, backend } = getServices('initial/url');
+      const connections = backend.connectionsArray;
+      service.currentDocument.subscribe();
+
+      expect(connections.length).toEqual(1);
+      expect(connections[0].request.url).toEqual(CONTENT_URL_PREFIX + 'initial/url.json');
+      expect(backend.connectionsArray[0].request.url).toEqual(CONTENT_URL_PREFIX + 'initial/url.json');
+    });
+
+    it('should emit a document each time the location changes', () => {
+      let latestDocument: DocumentContents;
+      const doc0 = { title: 'doc 0' };
+      const doc1 = { title: 'doc 1' };
+      const { service, backend, location } = getServices('initial/url');
+      const connections = backend.connectionsArray;
+
+      service.currentDocument.subscribe(doc => latestDocument = doc);
+      expect(latestDocument).toBeUndefined();
+
+      connections[0].mockRespond(createResponse(doc0));
+      expect(latestDocument).toEqual(doc0);
+
+      location.urlSubject.next('new/url');
+      connections[1].mockRespond(createResponse(doc1));
+      expect(latestDocument).toEqual(doc1);
+    });
+
+    it('should emit the not-found document if the document is not found on the server', () => {
+
+    });
+
+    it('should not make a request to the server if the doc is in the cache already', () => {
+      let latestDocument: DocumentContents;
+      let subscription: Subscription;
+
+      const doc0 = { title: 'doc 0' };
+      const doc1 = { title: 'doc 1' };
+      const { service, backend, location } = getServices('url/0');
+      const connections = backend.connectionsArray;
+
+      subscription = service.currentDocument.subscribe(doc => latestDocument = doc);
+      expect(connections.length).toEqual(1);
+      connections[0].mockRespond(createResponse(doc0));
+      expect(latestDocument).toEqual(doc0);
+      subscription.unsubscribe();
+
+      // modify the response so we can check that future subscriptions do not trigger another request
+      connections[0].response.next(createResponse({ title: 'error 0' }));
+
+      subscription = service.currentDocument.subscribe(doc => latestDocument = doc);
+      location.urlSubject.next('url/1');
+      expect(connections.length).toEqual(2);
+      connections[1].mockRespond(createResponse(doc1));
+      expect(latestDocument).toEqual(doc1);
+      subscription.unsubscribe();
+
+      // modify the response so we can check that future subscriptions do not trigger another request
+      connections[1].response.next(createResponse({ title: 'error 1' }));
+
+      subscription = service.currentDocument.subscribe(doc => latestDocument = doc);
+      location.urlSubject.next('url/0');
+      expect(connections.length).toEqual(2);
+      expect(latestDocument).toEqual(doc0);
+      subscription.unsubscribe();
+
+      subscription = service.currentDocument.subscribe(doc => latestDocument = doc);
+      location.urlSubject.next('url/1');
+      expect(connections.length).toEqual(2);
+      expect(latestDocument).toEqual(doc1);
+      subscription.unsubscribe();
+    });
+
+
+    it('should map the "empty" location to the correct document request', () => {
+      let latestDocument: DocumentContents;
+      const { service, backend } = getServices();
+      service.currentDocument.subscribe(doc => latestDocument = doc);
+    });
+  });
 });

aio/src/app/documents/document.service.ts

@@ -2,6 +2,7 @@ import { Injectable } from '@angular/core';
 import { Http, Response } from '@angular/http';
 
 import { Observable } from 'rxjs/Observable';
+import { AsyncSubject } from 'rxjs/AsyncSubject';
 import 'rxjs/add/operator/switchMap';
 
 import { LocationService } from 'app/shared/location.service';
@@ -37,7 +38,8 @@ export class DocumentService {
   private fetchDocument(url: string) {
     const path = this.computePath(url);
     this.logger.log('fetching document from', path);
-    return this.http
+    const subject = new AsyncSubject();
+    this.http
       .get(path)
       .map(res => res.json())
       .catch((error: Response) => {
@@ -48,7 +50,9 @@ export class DocumentService {
         } else {
           throw error;
         }
-      });
+      })
+      .subscribe(subject);
+    return subject.asObservable();
   }
 
   private computePath(url) {