Display relative time in thread panel event tile (#7068)

* Null-guard for missing root event in thread panel

* Add formatRelativeTime date utility

* Display relative time format in thread panel event tiles

src/DateUtils.ts

@@ -149,12 +149,20 @@ export function formatSeconds(inSeconds: number): string {
 }
 
 const MILLIS_IN_DAY = 86400000;
+function withinPast24Hours(prevDate: Date, nextDate: Date): boolean {
+    return Math.abs(prevDate.getTime() - nextDate.getTime()) <= MILLIS_IN_DAY;
+}
+
+function withinCurrentYear(prevDate: Date, nextDate: Date): boolean {
+    return prevDate.getFullYear() === nextDate.getFullYear();
+}
+
 export function wantsDateSeparator(prevEventDate: Date, nextEventDate: Date): boolean {
     if (!nextEventDate || !prevEventDate) {
         return false;
     }
     // Return early for events that are > 24h apart
-    if (Math.abs(prevEventDate.getTime() - nextEventDate.getTime()) > MILLIS_IN_DAY) {
+    if (!withinPast24Hours(prevEventDate, nextEventDate)) {
         return true;
     }
 
@@ -178,3 +186,18 @@ export function formatFullDateNoDayNoTime(date: Date) {
         pad(date.getDate())
     );
 }
+
+export function formatRelativeTime(date: Date, showTwelveHour = false): string {
+    const now = new Date(Date.now());
+    if (withinPast24Hours(date, now)) {
+        return formatTime(date, showTwelveHour);
+    } else {
+        const months = getMonthsArray();
+        let relativeDate = `${months[date.getMonth()]} ${date.getDate()}`;
+
+        if (!withinCurrentYear(date, now)) {
+            relativeDate += `, ${date.getFullYear()}`;
+        }
+        return relativeDate;
+    }
+}

src/components/views/messages/MessageTimestamp.tsx

@@ -16,7 +16,7 @@ limitations under the License.
 */
 
 import React from 'react';
-import { formatFullDate, formatTime, formatFullTime } from '../../../DateUtils';
+import { formatFullDate, formatTime, formatFullTime, formatRelativeTime } from '../../../DateUtils';
 import { replaceableComponent } from "../../../utils/replaceableComponent";
 
 interface IProps {
@@ -24,6 +24,7 @@ interface IProps {
     showTwelveHour?: boolean;
     showFullDate?: boolean;
     showSeconds?: boolean;
+    showRelative?: boolean;
 }
 
 @replaceableComponent("views.messages.MessageTimestamp")
@@ -31,7 +32,9 @@ export default class MessageTimestamp extends React.Component<IProps> {
     public render() {
         const date = new Date(this.props.ts);
         let timestamp;
-        if (this.props.showFullDate) {
+        if (this.props.showRelative) {
+            timestamp = formatRelativeTime(date, this.props.showTwelveHour);
+        } else if (this.props.showFullDate) {
             timestamp = formatFullDate(date, this.props.showTwelveHour, this.props.showSeconds);
         } else if (this.props.showSeconds) {
             timestamp = formatFullTime(date, this.props.showTwelveHour);

src/components/views/rooms/EventTile.tsx

@@ -1132,7 +1132,11 @@ export default class EventTile extends React.Component<IProps, IState> {
             || this.state.actionBarFocused);
 
         const timestamp = showTimestamp ?
-            <MessageTimestamp showTwelveHour={this.props.isTwelveHour} ts={this.props.mxEvent.getTs()} /> : null;
+            <MessageTimestamp
+                showRelative={this.props.tileShape === TileShape.ThreadPanel}
+                showTwelveHour={this.props.isTwelveHour}
+                ts={this.props.mxEvent.getTs()}
+            /> : null;
 
         const keyRequestHelpText =
             <div className="mx_EventTile_keyRequestInfo_tooltip_contents">