Fix timeline jumps (#10001)

* Avoid two-step rendering of statuses as much as possible

Cache width shared by Video player, MediaGallery and Cards at the
ScrollableList level, pass it down through StatusList and Notifications.

* Adjust scroll when new preview cards appear

* Adjust scroll when statuses above the current scroll position are deleted

6 files changed, 134 insertions, 12 deletions

diff --git a/app/javascript/mastodon/components/media_gallery.js b/app/javascript/mastodon/components/media_gallery.js
index c507920d0..a2bc95255 100644
--- a/app/javascript/mastodon/components/media_gallery.js
+++ b/app/javascript/mastodon/components/media_gallery.js
@@ -194,6 +194,8 @@ class MediaGallery extends React.PureComponent {
     height: PropTypes.number.isRequired,
     onOpenMedia: PropTypes.func.isRequired,
     intl: PropTypes.object.isRequired,
+    defaultWidth: PropTypes.number,
+    cacheWidth: PropTypes.func,
   };
 
   static defaultProps = {
@@ -202,6 +204,7 @@ class MediaGallery extends React.PureComponent {
 
   state = {
     visible: displayMedia !== 'hide_all' && !this.props.sensitive || displayMedia === 'show_all',
+    width: this.props.defaultWidth,
   };
 
   componentWillReceiveProps (nextProps) {
@@ -221,6 +224,7 @@ class MediaGallery extends React.PureComponent {
   handleRef = (node) => {
     if (node /*&& this.isStandaloneEligible()*/) {
       // offsetWidth triggers a layout, so only calculate when we need to
+      if (this.props.cacheWidth) this.props.cacheWidth(node.offsetWidth);
       this.setState({
         width: node.offsetWidth,
       });
@@ -233,8 +237,10 @@ class MediaGallery extends React.PureComponent {
   }
 
   render () {
-    const { media, intl, sensitive, height } = this.props;
-    const { width, visible } = this.state;
+    const { media, intl, sensitive, height, defaultWidth } = this.props;
+    const { visible } = this.state;
+
+    const width = this.state.width || defaultWidth;
 
     let children;
 
diff --git a/app/javascript/mastodon/components/scrollable_list.js b/app/javascript/mastodon/components/scrollable_list.js
index fec06e263..0376cf85a 100644
--- a/app/javascript/mastodon/components/scrollable_list.js
+++ b/app/javascript/mastodon/components/scrollable_list.js
@@ -40,6 +40,7 @@ export default class ScrollableList extends PureComponent {
 
   state = {
     fullscreen: null,
+    cachedMediaWidth: 250, // Default media/card width using default Mastodon theme
   };
 
   intersectionObserverWrapper = new IntersectionObserverWrapper();
@@ -130,6 +131,20 @@ export default class ScrollableList extends PureComponent {
     this.handleScroll();
   }
 
+  getScrollPosition = () => {
+    if (this.node && (this.node.scrollTop > 0 || this.mouseMovedRecently)) {
+      return { height: this.node.scrollHeight, top: this.node.scrollTop };
+    } else {
+      return null;
+    }
+  }
+
+  updateScrollBottom = (snapshot) => {
+    const newScrollTop = this.node.scrollHeight - snapshot;
+
+    this.setScrollTop(newScrollTop);
+  }
+
   getSnapshotBeforeUpdate (prevProps) {
     const someItemInserted = React.Children.count(prevProps.children) > 0 &&
       React.Children.count(prevProps.children) < React.Children.count(this.props.children) &&
@@ -150,6 +165,12 @@ export default class ScrollableList extends PureComponent {
     }
   }
 
+  cacheMediaWidth = (width) => {
+    if (width && this.state.cachedMediaWidth !== width) {
+      this.setState({ cachedMediaWidth: width });
+    }
+  }
+
   componentWillUnmount () {
     this.clearMouseIdleTimer();
     this.detachScrollListener();
@@ -239,7 +260,12 @@ export default class ScrollableList extends PureComponent {
                 intersectionObserverWrapper={this.intersectionObserverWrapper}
                 saveHeightKey={trackScroll ? `${this.context.router.route.location.key}:${scrollKey}` : null}
               >
-                {child}
+                {React.cloneElement(child, {
+                  getScrollPosition: this.getScrollPosition,
+                  updateScrollBottom: this.updateScrollBottom,
+                  cachedMediaWidth: this.state.cachedMediaWidth,
+                  cacheMediaWidth: this.cacheMediaWidth,
+                })}
               </IntersectionObserverArticleContainer>
             ))}
 
diff --git a/app/javascript/mastodon/components/status.js b/app/javascript/mastodon/components/status.js
index 2be6c4b36..386404b57 100644
--- a/app/javascript/mastodon/components/status.js
+++ b/app/javascript/mastodon/components/status.js
@@ -69,6 +69,10 @@ class Status extends ImmutablePureComponent {
     onMoveUp: PropTypes.func,
     onMoveDown: PropTypes.func,
     showThread: PropTypes.bool,
+    getScrollPosition: PropTypes.func,
+    updateScrollBottom: PropTypes.func,
+    cacheMediaWidth: PropTypes.func,
+    cachedMediaWidth: PropTypes.number,
   };
 
   // Avoid checking props that are functions (and whose equality will always
@@ -80,6 +84,43 @@ class Status extends ImmutablePureComponent {
     'hidden',
   ];
 
+  // Track height changes we know about to compensate scrolling
+  componentDidMount () {
+    this.didShowCard = !this.props.muted && !this.props.hidden && this.props.status.get('card');
+  }
+
+  getSnapshotBeforeUpdate () {
+    if (this.props.getScrollPosition) {
+      return this.props.getScrollPosition();
+    } else {
+      return null;
+    }
+  }
+
+  // Compensate height changes
+  componentDidUpdate (prevProps, prevState, snapshot) {
+    const doShowCard  = !this.props.muted && !this.props.hidden && this.props.status.get('card');
+    if (doShowCard && !this.didShowCard) {
+      this.didShowCard = true;
+      if (snapshot !== null && this.props.updateScrollBottom) {
+        if (this.node && this.node.offsetTop < snapshot.top) {
+          this.props.updateScrollBottom(snapshot.height - snapshot.top);
+        }
+      }
+    }
+  }
+
+  componentWillUnmount() {
+    if (this.node && this.props.getScrollPosition) {
+      const position = this.props.getScrollPosition();
+      if (position !== null && this.node.offsetTop < position.top) {
+        requestAnimationFrame(() => {
+          this.props.updateScrollBottom(position.height - position.top);
+        });
+      }
+    }
+  }
+
   handleClick = () => {
     if (this.props.onClick) {
       this.props.onClick();
@@ -166,6 +207,10 @@ class Status extends ImmutablePureComponent {
     }
   }
 
+  handleRef = c => {
+    this.node = c;
+  }
+
   render () {
     let media = null;
     let statusAvatar, prepend, rebloggedByText;
@@ -180,7 +225,7 @@ class Status extends ImmutablePureComponent {
 
     if (hidden) {
       return (
-        <div>
+        <div ref={this.handleRef}>
           {status.getIn(['account', 'display_name']) || status.getIn(['account', 'username'])}
           {status.get('content')}
         </div>
@@ -195,7 +240,7 @@ class Status extends ImmutablePureComponent {
 
       return (
         <HotKeys handlers={minHandlers}>
-          <div className='status__wrapper status__wrapper--filtered focusable' tabIndex='0'>
+          <div className='status__wrapper status__wrapper--filtered focusable' tabIndex='0' ref={this.handleRef}>
             <FormattedMessage id='status.filtered' defaultMessage='Filtered' />
           </div>
         </HotKeys>
@@ -243,11 +288,12 @@ class Status extends ImmutablePureComponent {
                 preview={video.get('preview_url')}
                 src={video.get('url')}
                 alt={video.get('description')}
-                width={239}
+                width={this.props.cachedMediaWidth}
                 height={110}
                 inline
                 sensitive={status.get('sensitive')}
                 onOpenVideo={this.handleOpenVideo}
+                cacheWidth={this.props.cacheMediaWidth}
               />
             )}
           </Bundle>
@@ -255,7 +301,16 @@ class Status extends ImmutablePureComponent {
       } else {
         media = (
           <Bundle fetchComponent={MediaGallery} loading={this.renderLoadingMediaGallery}>
-            {Component => <Component media={status.get('media_attachments')} sensitive={status.get('sensitive')} height={110} onOpenMedia={this.props.onOpenMedia} />}
+            {Component => (
+              <Component
+                media={status.get('media_attachments')}
+                sensitive={status.get('sensitive')}
+                height={110}
+                onOpenMedia={this.props.onOpenMedia}
+                cacheWidth={this.props.cacheMediaWidth}
+                defaultWidth={this.props.cachedMediaWidth}
+              />
+            )}
           </Bundle>
         );
       }
@@ -265,6 +320,8 @@ class Status extends ImmutablePureComponent {
           onOpenMedia={this.props.onOpenMedia}
           card={status.get('card')}
           compact
+          cacheWidth={this.props.cacheMediaWidth}
+          defaultWidth={this.props.cachedMediaWidth}
         />
       );
     }
@@ -291,7 +348,7 @@ class Status extends ImmutablePureComponent {
 
     return (
       <HotKeys handlers={handlers}>
-        <div className={classNames('status__wrapper', `status__wrapper-${status.get('visibility')}`, { 'status__wrapper-reply': !!status.get('in_reply_to_id'), read: unread === false, focusable: !this.props.muted })} tabIndex={this.props.muted ? null : 0} data-featured={featured ? 'true' : null} aria-label={textForScreenReader(intl, status, rebloggedByText, !status.get('hidden'))}>
+        <div className={classNames('status__wrapper', `status__wrapper-${status.get('visibility')}`, { 'status__wrapper-reply': !!status.get('in_reply_to_id'), read: unread === false, focusable: !this.props.muted })} tabIndex={this.props.muted ? null : 0} data-featured={featured ? 'true' : null} aria-label={textForScreenReader(intl, status, rebloggedByText, !status.get('hidden'))} ref={this.handleRef}>
           {prepend}
 
           <div className={classNames('status', `status-${status.get('visibility')}`, { 'status-reply': !!status.get('in_reply_to_id'), muted: this.props.muted, read: unread === false })} data-id={status.get('id')}>
diff --git a/app/javascript/mastodon/features/notifications/components/notification.js b/app/javascript/mastodon/features/notifications/components/notification.js
index 0bd8d47c3..9669b6e7d 100644
--- a/app/javascript/mastodon/features/notifications/components/notification.js
+++ b/app/javascript/mastodon/features/notifications/components/notification.js
@@ -35,6 +35,10 @@ class Notification extends ImmutablePureComponent {
     onToggleHidden: PropTypes.func.isRequired,
     status: PropTypes.option,
     intl: PropTypes.object.isRequired,
+    getScrollPosition: PropTypes.func,
+    updateScrollBottom: PropTypes.func,
+    cacheMediaWidth: PropTypes.func,
+    cachedMediaWidth: PropTypes.number,
   };
 
   handleMoveUp = () => {
@@ -129,6 +133,10 @@ class Notification extends ImmutablePureComponent {
         onMoveDown={this.handleMoveDown}
         onMoveUp={this.handleMoveUp}
         contextType='notifications'
+        getScrollPosition={this.props.getScrollPosition}
+        updateScrollBottom={this.props.updateScrollBottom}
+        cachedMediaWidth={this.props.cachedMediaWidth}
+        cacheMediaWidth={this.props.cacheMediaWidth}
       />
     );
   }
@@ -149,7 +157,17 @@ class Notification extends ImmutablePureComponent {
             </span>
           </div>
 
-          <StatusContainer id={notification.get('status')} account={notification.get('account')} muted withDismiss hidden={!!this.props.hidden} />
+          <StatusContainer
+            id={notification.get('status')}
+            account={notification.get('account')}
+            muted
+            withDismiss
+            hidden={!!this.props.hidden}
+            getScrollPosition={this.props.getScrollPosition}
+            updateScrollBottom={this.props.updateScrollBottom}
+            cachedMediaWidth={this.props.cachedMediaWidth}
+            cacheMediaWidth={this.props.cacheMediaWidth}
+          />
         </div>
       </HotKeys>
     );
@@ -171,7 +189,17 @@ class Notification extends ImmutablePureComponent {
             </span>
           </div>
 
-          <StatusContainer id={notification.get('status')} account={notification.get('account')} muted withDismiss hidden={this.props.hidden} />
+          <StatusContainer
+            id={notification.get('status')}
+            account={notification.get('account')}
+            muted
+            withDismiss
+            hidden={this.props.hidden}
+            getScrollPosition={this.props.getScrollPosition}
+            updateScrollBottom={this.props.updateScrollBottom}
+            cachedMediaWidth={this.props.cachedMediaWidth}
+            cacheMediaWidth={this.props.cacheMediaWidth}
+          />
         </div>
       </HotKeys>
     );
diff --git a/app/javascript/mastodon/features/status/components/card.js b/app/javascript/mastodon/features/status/components/card.js
index 8237de84d..0eff54411 100644
--- a/app/javascript/mastodon/features/status/components/card.js
+++ b/app/javascript/mastodon/features/status/components/card.js
@@ -61,6 +61,8 @@ export default class Card extends React.PureComponent {
     maxDescription: PropTypes.number,
     onOpenMedia: PropTypes.func.isRequired,
     compact: PropTypes.bool,
+    defaultWidth: PropTypes.number,
+    cacheWidth: PropTypes.func,
   };
 
   static defaultProps = {
@@ -69,7 +71,7 @@ export default class Card extends React.PureComponent {
   };
 
   state = {
-    width: 280,
+    width: this.props.defaultWidth || 280,
     embedded: false,
   };
 
@@ -112,6 +114,7 @@ export default class Card extends React.PureComponent {
 
   setRef = c => {
     if (c) {
+      if (this.props.cacheWidth) this.props.cacheWidth(c.offsetWidth);
       this.setState({ width: c.offsetWidth });
     }
   }
diff --git a/app/javascript/mastodon/features/video/index.js b/app/javascript/mastodon/features/video/index.js
index 15a5de4b8..894fe78d9 100644
--- a/app/javascript/mastodon/features/video/index.js
+++ b/app/javascript/mastodon/features/video/index.js
@@ -100,6 +100,7 @@ class Video extends React.PureComponent {
     onCloseVideo: PropTypes.func,
     detailed: PropTypes.bool,
     inline: PropTypes.bool,
+    cacheWidth: PropTypes.func,
     intl: PropTypes.object.isRequired,
   };
 
@@ -109,7 +110,7 @@ class Video extends React.PureComponent {
     volume: 0.5,
     paused: true,
     dragging: false,
-    containerWidth: false,
+    containerWidth: this.props.width,
     fullscreen: false,
     hovered: false,
     muted: false,
@@ -129,6 +130,7 @@ class Video extends React.PureComponent {
     this.player = c;
 
     if (c) {
+      if (this.props.cacheWidth) this.props.cacheWidth(this.player.offsetWidth);
       this.setState({
         containerWidth: c.offsetWidth,
       });