fix: save scroll position on exit from video xblock fullscreen mode (#1077)

* fix: save scroll position on exit from video xblock fullscreen mode

* fix: update tests

src/courseware/course/bookmark/BookmarkButton.test.jsx

@@ -1,12 +1,12 @@
 import React from 'react';
 import MockAdapter from 'axios-mock-adapter';
 import { getAuthenticatedHttpClient } from '@edx/frontend-platform/auth';
-import { getConfig } from '@edx/frontend-platform';
 import { Factory } from 'rosie';
 import {
   render, screen, fireEvent, initializeTestStore, waitFor, authenticatedUser, logUnhandledRequests,
 } from '../../../setupTest';
 import { BookmarkButton } from './index';
+import { getBookmarksBaseUrl } from './data/api';
 
 describe('Bookmark Button', () => {
   let axiosMock;
@@ -32,7 +32,8 @@ describe('Bookmark Button', () => {
     mockData.unitId = nonBookmarkedUnitBlock.id;
 
     axiosMock = new MockAdapter(getAuthenticatedHttpClient());
-    const bookmarkUrl = `${getConfig().LMS_BASE_URL}/api/bookmarks/v1/bookmarks/`;
+    const bookmarkUrl = getBookmarksBaseUrl();
+
     axiosMock.onPost(bookmarkUrl).reply(200, { });
 
     const bookmarkDeleteUrlRegExp = new RegExp(`${bookmarkUrl}*,*`);

src/courseware/course/bookmark/data/api.js

@@ -1,13 +1,13 @@
 import { getConfig } from '@edx/frontend-platform';
 import { getAuthenticatedHttpClient, getAuthenticatedUser } from '@edx/frontend-platform/auth';
 
-const bookmarksBaseUrl = `${getConfig().LMS_BASE_URL}/api/bookmarks/v1/bookmarks/`;
+export const getBookmarksBaseUrl = () => `${getConfig().LMS_BASE_URL}/api/bookmarks/v1/bookmarks/`;
 
 export async function createBookmark(usageId) {
-  return getAuthenticatedHttpClient().post(bookmarksBaseUrl, { usage_id: usageId });
+  return getAuthenticatedHttpClient().post(getBookmarksBaseUrl(), { usage_id: usageId });
 }
 
 export async function deleteBookmark(usageId) {
   const { username } = getAuthenticatedUser();
-  return getAuthenticatedHttpClient().delete(`${bookmarksBaseUrl}${username},${usageId}/`);
+  return getAuthenticatedHttpClient().delete(`${getBookmarksBaseUrl()}${username},${usageId}/`);
 }

src/courseware/course/sequence/Unit.jsx

@@ -96,6 +96,7 @@ function Unit({
   const [showError, setShowError] = useState(false);
   const [modalOptions, setModalOptions] = useState({ open: false });
   const [shouldDisplayHonorCode, setShouldDisplayHonorCode] = useState(false);
+  const [windowTopOffset, setWindowTopOffset] = useState(null);
 
   const unit = useModel('units', id);
   const course = useModel('coursewareMeta', courseId);
@@ -123,6 +124,13 @@ function Unit({
     } = data;
     if (type === 'plugin.resize') {
       setIframeHeight(payload.height);
+
+      // We observe exit from the video xblock full screen mode
+      // and do page scroll to the previously saved scroll position
+      if (windowTopOffset !== null) {
+        window.scrollTo(0, Number(windowTopOffset));
+      }
+
       if (!hasLoaded && iframeHeight === 0 && payload.height > 0) {
         setHasLoaded(true);
         if (onLoaded) {
@@ -132,12 +140,16 @@ function Unit({
     } else if (type === 'plugin.modal') {
       payload.open = true;
       setModalOptions(payload);
+    } else if (type === 'plugin.videoFullScreen') {
+      // We listen for this message from LMS to know when we need to
+      // save or reset scroll position on toggle video xblock full screen mode.
+      setWindowTopOffset(payload.open ? window.scrollY : null);
     } else if (data.offset) {
       // We listen for this message from LMS to know when the page needs to
       // be scrolled to another location on the page.
       window.scrollTo(0, data.offset + document.getElementById('unit-iframe').offsetTop);
     }
-  }, [id, setIframeHeight, hasLoaded, iframeHeight, setHasLoaded, onLoaded]);
+  }, [id, setIframeHeight, hasLoaded, iframeHeight, setHasLoaded, onLoaded, setWindowTopOffset, windowTopOffset]);
   useEventListener('message', receiveMessage);
   useEffect(() => {
     sendUrlHashToFrame(document.getElementById('unit-iframe'));

src/courseware/course/sequence/Unit.test.jsx

@@ -131,6 +131,21 @@ describe('Unit', () => {
     expect(window.scrollY === testMessageWithOffset.offset);
   });
 
+  it('scrolls page on MessageEvent when receiving videoFullScreen state', async () => {
+    // Set message to contain video full screen data.
+    const defaultTopOffset = 800;
+    const testMessageWithOtherHeight = { ...messageEvent, payload: { height: 500 } };
+    const testMessageWithFullscreenState = (isOpen) => ({ type: 'plugin.videoFullScreen', payload: { open: isOpen } });
+    render(<Unit {...mockData} />);
+    Object.defineProperty(window, 'scrollY', { value: defaultTopOffset, writable: true });
+    window.postMessage(testMessageWithFullscreenState(true), '*');
+    window.postMessage(testMessageWithFullscreenState(false), '*');
+    window.postMessage(testMessageWithOtherHeight, '*');
+
+    await expect(waitFor(() => expect(window.scrollTo()).toHaveBeenCalledTimes(1)));
+    expect(window.scrollY === defaultTopOffset);
+  });
+
   it('ignores MessageEvent with unhandled type', async () => {
     // Clone message and set different type.
     const testMessageWithUnhandledType = { ...messageEvent, type: 'wrong type' };