Use book or chapter URL in VS integration depending on "book_as_single_document" flag

Add the plumbing needed to make the VitalSource integration return either the
book or chapter URL depending on the value of the "book_as_single_document"
flag. Additionally handle changes in this flag after the integration is created
by notifying the guest about the URI change.

When the flag is enabled, the "book URL" is currently a placeholder that will
in future be replaced by a real value fetched from the `<mosaic-book>`
element in the container frame.

src/annotator/features.js

@@ -11,7 +11,7 @@ import { warnOnce } from '../shared/warn-once';
  *
  * @type {string[]}
  */
-const annotatorFlags = ['html_side_by_side'];
+const annotatorFlags = ['book_as_single_document', 'html_side_by_side'];
 
 /**
  * An observable container of feature flags.

src/annotator/integrations/index.js

@@ -25,7 +25,9 @@ export function createIntegration(annotator) {
 
   const vsFrameRole = vitalSourceFrameRole();
   if (vsFrameRole === 'content') {
-    return new VitalSourceContentIntegration();
+    return new VitalSourceContentIntegration(document.body, {
+      features: annotator.features,
+    });
   }
 
   return new HTMLIntegration({ features: annotator.features });

src/annotator/integrations/test/vitalsource-test.js

 import { delay, waitFor } from '../../../test-util/wait';
+import { FeatureFlags } from '../../features';
 import {
   VitalSourceInjector,
   VitalSourceContentIntegration,
@@ -54,12 +55,14 @@ class FakeVitalSourceViewer {
 }
 
 describe('annotator/integrations/vitalsource', () => {
+  let featureFlags;
   let fakeViewer;
   let FakeHTMLIntegration;
   let fakeHTMLIntegration;
   let fakeInjectClient;
 
   beforeEach(() => {
+    featureFlags = new FeatureFlags();
     fakeViewer = new FakeVitalSourceViewer();
 
     fakeHTMLIntegration = {
@@ -192,7 +195,9 @@ describe('annotator/integrations/vitalsource', () => {
     let integrations;
 
     function createIntegration() {
-      const integration = new VitalSourceContentIntegration();
+      const integration = new VitalSourceContentIntegration(document.body, {
+        features: featureFlags,
+      });
       integrations.push(integration);
       return integration;
     }
@@ -279,7 +284,8 @@ describe('annotator/integrations/vitalsource', () => {
         history.back();
       });
 
-      it('returns book URL excluding query string', async () => {
+      context('when "book_as_single_document" flag is off', () => {
+        it('returns book chapter URL excluding query string', async () => {
           const integration = createIntegration();
           const uri = await integration.uri();
           const parsedURL = new URL(uri);
@@ -292,6 +298,32 @@ describe('annotator/integrations/vitalsource', () => {
         });
       });
 
+      context('when "book_as_single_document" flag is on', () => {
+        it('returns book reader URL', async () => {
+          featureFlags.update({ book_as_single_document: true });
+          const integration = createIntegration();
+          const uri = await integration.uri();
+          assert.equal(
+            uri,
+            'https://bookshelf.vitalsource.com/reader/books/1234'
+          );
+        });
+      });
+
+      it('updates when "book_as_single_document" flag changes', async () => {
+        const uriChanged = sinon.stub();
+        const integration = createIntegration();
+        integration.on('uriChanged', uriChanged);
+        const uri1 = await integration.uri();
+
+        featureFlags.update({ book_as_single_document: true });
+
+        assert.calledOnce(uriChanged);
+        const uri2 = await integration.uri();
+        assert.notEqual(uri1, uri2);
+      });
+    });
+
     context('in PDF documents', () => {
       let FakeImageTextLayer;
       let fakeImageTextLayer;

src/annotator/integrations/vitalsource.ts

@@ -8,7 +8,12 @@ import { preserveScrollPosition } from './html-side-by-side';
 import { ImageTextLayer } from './image-text-layer';
 import { injectClient } from '../hypothesis-injector';
 
-import type { Anchor, Integration, SidebarLayout } from '../../types/annotator';
+import type {
+  Anchor,
+  FeatureFlags as IFeatureFlags,
+  Integration,
+  SidebarLayout,
+} from '../../types/annotator';
 import type { Selector } from '../../types/api';
 import type { InjectConfig } from '../hypothesis-injector';
 
@@ -201,21 +206,36 @@ export class VitalSourceContentIntegration
   extends TinyEmitter
   implements Integration
 {
+  private _features: IFeatureFlags;
   private _htmlIntegration: HTMLIntegration;
   private _listeners: ListenerCollection;
   private _textLayer?: ImageTextLayer;
 
-  constructor(container: HTMLElement = document.body) {
+  constructor(
+    container: HTMLElement = document.body,
+    options: { features: IFeatureFlags }
+  ) {
     super();
 
-    const features = new FeatureFlags();
+    this._features = options.features;
+
+    // If the book_as_single_document flag changed, this will change the
+    // document URI returned by this integration.
+    this._features.on('flagsChanged', () => {
+      this.emit('uriChanged');
+    });
+
+    const htmlFeatures = new FeatureFlags();
 
     // Forcibly enable the side-by-side feature for VS books. This feature is
     // only behind a flag for regular web pages, which are typically more
     // complex and varied than EPUB books.
-    features.update({ html_side_by_side: true });
+    htmlFeatures.update({ html_side_by_side: true });
 
-    this._htmlIntegration = new HTMLIntegration({ container, features });
+    this._htmlIntegration = new HTMLIntegration({
+      container,
+      features: htmlFeatures,
+    });
 
     this._listeners = new ListenerCollection();
 
@@ -339,6 +359,12 @@ export class VitalSourceContentIntegration
   }
 
   async uri() {
+    if (this._bookIsSingleDocument()) {
+      // Dummy book ID that will in future be replaced with a real value
+      // retrieved via the `<mosaic-book>` element's API.
+      const bookId = '1234';
+      return `https://bookshelf.vitalsource.com/reader/books/${bookId}`;
+    } else {
       // An example of a typical URL for the chapter content in the Bookshelf reader is:
       //
       // https://jigsaw.vitalsource.com/books/9781848317703/epub/OPS/xhtml/chapter_001.html#cfi=/6/10%5B;vnd.vst.idref=chap001%5D!/4
@@ -355,8 +381,17 @@ export class VitalSourceContentIntegration
       uri.search = '';
       return uri.toString();
     }
+  }
 
   async scrollToAnchor(anchor: Anchor) {
     return this._htmlIntegration.scrollToAnchor(anchor);
   }
+
+  /**
+   * Return true if the feature flag to treat books as one document is enabled,
+   * as opposed to treating each chapter/segment/page as a separate document.
+   */
+  _bookIsSingleDocument(): boolean {
+    return this._features.flagEnabled('book_as_single_document');
+  }
 }