Collapse redactions into an event list summary

src/components/structures/MessagePanel.js

@@ -1001,6 +1001,97 @@ class CreationGrouper {
     }
 }
 
+class RedactionGrouper {
+    static canStartGroup = function(panel, ev) {
+        return panel._shouldShowEvent(ev) && ev.isRedacted();
+    }
+
+    constructor(panel, ev, prevEvent, lastShownEvent) {
+        this.panel = panel;
+        this.readMarker = panel._readMarkerForEvent(
+            ev.getId(),
+            ev === lastShownEvent,
+        );
+        this.events = [ev];
+        this.prevEvent = prevEvent;
+        this.lastShownEvent = lastShownEvent;
+    }
+
+    shouldGroup(ev) {
+        if (this.panel._wantsDateSeparator(this.events[0], ev.getDate())) {
+            return false;
+        }
+        return ev.isRedacted();
+    }
+
+    add(ev) {
+        this.readMarker = this.readMarker || this.panel._readMarkerForEvent(
+            ev.getId(),
+            ev === this.lastShownEvent,
+        );
+        this.events.push(ev);
+    }
+
+    getTiles() {
+        if (!this.events || !this.events.length) return [];
+
+        const DateSeparator = sdk.getComponent('messages.DateSeparator');
+        const EventListSummary = sdk.getComponent('views.elements.EventListSummary');
+
+        const panel = this.panel;
+        const ret = [];
+        const lastShownEvent = this.lastShownEvent;
+
+        if (panel._wantsDateSeparator(this.prevEvent, this.events[0].getDate())) {
+            const ts = this.events[0].getTs();
+            ret.push(
+                <li key={ts+'~'}><DateSeparator key={ts+'~'} ts={ts} /></li>,
+            );
+        }
+
+        const key = "redactioneventlistsummary-" + (
+            this.prevEvent ? this.events[0].getId() : "initial"
+        );
+
+        const senders = new Set();
+        let eventTiles = this.events.map((e) => {
+            senders.add(e.sender);
+            // In order to prevent DateSeparators from appearing in the expanded form,
+            // render each member event as if the previous one was itself.
+            // This way, the timestamp of the previous event === the
+            // timestamp of the current event, and no DateSeparator is inserted.
+            return panel._getTilesForEvent(e, e, e === lastShownEvent);
+        }).reduce((a, b) => a.concat(b), []);
+
+        if (eventTiles.length === 0) {
+            eventTiles = null;
+        }
+
+        ret.push(
+            <EventListSummary
+                key={key}
+                threshold={2}
+                events={this.events}
+                onToggle={panel._onHeightChanged} // Update scroll state
+                summaryMembers={Array.from(senders)}
+                summaryText={_t("%(count)s messages deleted.", { count: eventTiles.length })}
+            >
+                { eventTiles }
+            </EventListSummary>,
+        );
+
+        if (this.readMarker) {
+            ret.push(this.readMarker);
+        }
+
+        return ret;
+    }
+
+    getNewPrevEvent() {
+        return this.events[0];
+    }
+}
+
 // Wrap consecutive member events in a ListSummary, ignore if redacted
 class MemberGrouper {
     static canStartGroup = function(panel, ev) {
@@ -1111,4 +1202,4 @@ class MemberGrouper {
 }
 
 // all the grouper classes that we use
-const groupers = [CreationGrouper, MemberGrouper];
+const groupers = [CreationGrouper, MemberGrouper, RedactionGrouper];