feat(aio): add document service

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

@@ -0,0 +1,14 @@
+import { TestBed, inject } from '@angular/core/testing';
+import { DocumentService } from './document.service';
+
+describe('DocumentService', () => {
+  beforeEach(() => {
+    TestBed.configureTestingModule({
+      providers: [DocumentService]
+    });
+  });
+
+  it('should ...', inject([DocumentService], (service: DocumentService) => {
+    expect(service).toBeTruthy();
+  }));
+});

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

@@ -0,0 +1,54 @@
+import { Injectable } from '@angular/core';
+import { Http, Response } from '@angular/http';
+
+import { Observable } from 'rxjs/Observable';
+import 'rxjs/add/operator/switchMap';
+
+import { DocumentContents } from './document';
+import { LocationService } from '../shared/location.service';
+import { Logger } from '../shared/logger.service';
+
+const FILE_NOT_FOUND_DOC = 'file-not-found';
+
+@Injectable()
+export class DocumentService {
+
+  private cache = new Map<string, Observable<DocumentContents>>();
+
+  currentDocument: Observable<DocumentContents>;
+
+  constructor(private logger: Logger, private http: Http, location: LocationService) {
+    // Whenever the URL changes we try to get the appropriate doc
+    this.currentDocument = location.currentUrl.switchMap(url => this.getDocument(url));
+  }
+
+  private getDocument(url: string) {
+    this.logger.log('getting document', url);
+    if ( !this.cache.has(url)) {
+      this.cache.set(url, this.fetchDocument(url));
+    }
+    return this.cache.get(url);
+  }
+
+  private fetchDocument(url: string) {
+    const path = this.computePath(url);
+    this.logger.log('fetching document from', path);
+    return this.http
+      .get(path)
+      .map(res => res.json())
+      .catch((error: Response) => {
+        if (error.status === 404 && url !== FILE_NOT_FOUND_DOC) {
+          this.logger.error(`Document file not found at '${url}'`);
+          // using `getDocument` means that we can fetch the 404 doc contents from the server and cache it
+          return this.getDocument(FILE_NOT_FOUND_DOC);
+        } else {
+          throw error;
+        }
+      });
+  }
+
+  private computePath(url) {
+    url = url.startsWith('/') ? url : '/' + url;
+    return 'content/docs' + url + '.json';
+  }
+}