From 171539d42d560bf37abbfdfba86bb0f22986f84e Mon Sep 17 00:00:00 2001
From: Germain Souquet <germain@souquet.com>
Date: Thu, 20 May 2021 15:26:02 +0100
Subject: [PATCH] Simplify EventTile structure

Only render MessageTimestamp to the DOM when a tile is hovered
---
 src/components/structures/MessagePanel.js | 65 +++++++++++------------
 src/components/views/rooms/EventTile.tsx  | 46 ++++++++++------
 2 files changed, 61 insertions(+), 50 deletions(-)

diff --git a/src/components/structures/MessagePanel.js b/src/components/structures/MessagePanel.js
index d1071a9e19..2fb9a2df29 100644
--- a/src/components/structures/MessagePanel.js
+++ b/src/components/structures/MessagePanel.js
@@ -645,39 +645,36 @@ export default class MessagePanel extends React.Component {
 
         // use txnId as key if available so that we don't remount during sending
         ret.push(
-            <li
-                key={mxEv.getTxnId() || eventId}
-                ref={this._collectEventNode.bind(this, eventId)}
-                data-scroll-tokens={scrollToken}
-            >
-                <TileErrorBoundary mxEvent={mxEv}>
-                    <EventTile
-                        mxEvent={mxEv}
-                        continuation={continuation}
-                        isRedacted={mxEv.isRedacted()}
-                        replacingEventId={mxEv.replacingEventId()}
-                        editState={isEditing && this.props.editState}
-                        onHeightChanged={this._onHeightChanged}
-                        readReceipts={readReceipts}
-                        readReceiptMap={this._readReceiptMap}
-                        showUrlPreview={this.props.showUrlPreview}
-                        checkUnmounting={this._isUnmounting}
-                        eventSendStatus={mxEv.getAssociatedStatus()}
-                        tileShape={this.props.tileShape}
-                        isTwelveHour={this.props.isTwelveHour}
-                        permalinkCreator={this.props.permalinkCreator}
-                        last={last}
-                        lastInSection={willWantDateSeparator}
-                        lastSuccessful={isLastSuccessful}
-                        isSelectedEvent={highlight}
-                        getRelationsForEvent={this.props.getRelationsForEvent}
-                        showReactions={this.props.showReactions}
-                        layout={this.props.layout}
-                        enableFlair={this.props.enableFlair}
-                        showReadReceipts={this.props.showReadReceipts}
-                    />
-                </TileErrorBoundary>
-            </li>,
+            <TileErrorBoundary key={mxEv.getTxnId() || eventId} mxEvent={mxEv}>
+                <EventTile
+                    as="li"
+                    data-scroll-tokens={scrollToken}
+                    ref={this._collectEventNode.bind(this, eventId)}
+                    mxEvent={mxEv}
+                    continuation={continuation}
+                    isRedacted={mxEv.isRedacted()}
+                    replacingEventId={mxEv.replacingEventId()}
+                    editState={isEditing && this.props.editState}
+                    onHeightChanged={this._onHeightChanged}
+                    readReceipts={readReceipts}
+                    readReceiptMap={this._readReceiptMap}
+                    showUrlPreview={this.props.showUrlPreview}
+                    checkUnmounting={this._isUnmounting}
+                    eventSendStatus={mxEv.getAssociatedStatus()}
+                    tileShape={this.props.tileShape}
+                    isTwelveHour={this.props.isTwelveHour}
+                    permalinkCreator={this.props.permalinkCreator}
+                    last={last}
+                    lastInSection={willWantDateSeparator}
+                    lastSuccessful={isLastSuccessful}
+                    isSelectedEvent={highlight}
+                    getRelationsForEvent={this.props.getRelationsForEvent}
+                    showReactions={this.props.showReactions}
+                    layout={this.props.layout}
+                    enableFlair={this.props.enableFlair}
+                    showReadReceipts={this.props.showReadReceipts}
+                />
+            </TileErrorBoundary>,
         );
 
         return ret;
@@ -779,7 +776,7 @@ export default class MessagePanel extends React.Component {
     }
 
     _collectEventNode = (eventId, node) => {
-        this.eventNodes[eventId] = node;
+        this.eventNodes[eventId] = node?.ref?.current;
     }
 
     // once dynamic content in the events load, make the scrollPanel check the
diff --git a/src/components/views/rooms/EventTile.tsx b/src/components/views/rooms/EventTile.tsx
index 19c5a7acaa..884669e398 100644
--- a/src/components/views/rooms/EventTile.tsx
+++ b/src/components/views/rooms/EventTile.tsx
@@ -277,6 +277,9 @@ interface IProps {
 
     // Helper to build permalinks for the room
     permalinkCreator?: RoomPermalinkCreator;
+
+    // Symbol of the root node
+    as?: string
 }
 
 interface IState {
@@ -291,6 +294,8 @@ interface IState {
     previouslyRequestedKeys: boolean;
     // The Relations model from the JS SDK for reactions to `mxEvent`
     reactions: Relations;
+
+    hover: boolean;
 }
 
 @replaceableComponent("views.rooms.EventTile")
@@ -322,6 +327,8 @@ export default class EventTile extends React.Component<IProps, IState> {
             previouslyRequestedKeys: false,
             // The Relations model from the JS SDK for reactions to `mxEvent`
             reactions: this.getReactions(),
+
+            hover: false,
         };
 
         // don't do RR animations until we are mounted
@@ -333,6 +340,8 @@ export default class EventTile extends React.Component<IProps, IState> {
         // to determine if we've already subscribed and use a combination of other flags to find
         // out if we should even be subscribed at all.
         this.isListeningForReceipts = false;
+
+        this.ref = React.createRef();
     }
 
     /**
@@ -960,7 +969,7 @@ export default class EventTile extends React.Component<IProps, IState> {
             onFocusChange={this.onActionBarFocusChange}
         /> : undefined;
 
-        const timestamp = this.props.mxEvent.getTs() ?
+        const timestamp = this.props.mxEvent.getTs() && this.state.hover ?
             <MessageTimestamp showTwelveHour={this.props.isTwelveHour} ts={this.props.mxEvent.getTs()} /> : null;
 
         const keyRequestHelpText =
@@ -1131,11 +1140,20 @@ export default class EventTile extends React.Component<IProps, IState> {
 
                 // tab-index=-1 to allow it to be focusable but do not add tab stop for it, primarily for screen readers
                 return (
-                    <div className={classes} tabIndex={-1} aria-live={ariaLive} aria-atomic="true">
-                        { ircTimestamp }
-                        { sender }
-                        { ircPadlock }
-                        <div className="mx_EventTile_line">
+                    React.createElement(this.props.as || "div", {
+                        "ref": this.ref,
+                        "className": classes,
+                        "tabIndex": -1,
+                        "aria-live": ariaLive,
+                        "aria-atomic": "true",
+                        "data-scroll-tokens": this.props["data-scroll-tokens"],
+                        "onMouseEnter": () => this.setState({ hover: true }),
+                        "onMouseLeave": () => this.setState({ hover: false }),
+                    }, [
+                        ircTimestamp,
+                        sender,
+                        ircPadlock,
+                        <div className="mx_EventTile_line" key="mx_EventTile_line">
                             { groupTimestamp }
                             { groupPadlock }
                             { thread }
@@ -1152,16 +1170,12 @@ export default class EventTile extends React.Component<IProps, IState> {
                             { keyRequestInfo }
                             { reactionsRow }
                             { actionBar }
-                        </div>
-                        {msgOption}
-                        {
-                            // The avatar goes after the event tile as it's absolutely positioned to be over the
-                            // event tile line, so needs to be later in the DOM so it appears on top (this avoids
-                            // the need for further z-indexing chaos)
-                        }
-                        { avatar }
-                    </div>
-                );
+                        </div>,
+                        msgOption,
+                        avatar,
+
+                    ])
+                )
             }
         }
     }