Add new thread message preview (#18958) (#6953)

Closes https://github.com/vector-im/element-web/issues/18958

src/stores/room-list/MessagePreviewStore.ts

@@ -27,6 +27,7 @@ import { CallHangupEvent } from "./previews/CallHangupEvent";
 import { StickerEventPreview } from "./previews/StickerEventPreview";
 import { ReactionEventPreview } from "./previews/ReactionEventPreview";
 import { UPDATE_EVENT } from "../AsyncStore";
+import { Thread } from "matrix-js-sdk/src/models/thread";
 
 // Emitted event for when a room's preview has changed. First argument will the room for which
 // the change happened.
@@ -108,6 +109,15 @@ export class MessagePreviewStore extends AsyncStoreWithClient<IState> {
         return previews.get(inTagId);
     }
 
+    public generateThreadPreview(thread: Thread): string {
+        const lastEvent = thread.replyToEvent;
+        const previewDef = PREVIEWS[lastEvent.getType()];
+        // TODO: Handle case where we don't have
+        if (!previewDef) return '';
+        const previewText = previewDef.previewer.getTextFor(lastEvent, null, true);
+        return previewText ?? '';
+    }
+
     private async generatePreview(room: Room, tagId?: TagID) {
         const events = room.timeline;
         if (!events) return; // should only happen in tests

src/stores/room-list/previews/MessageEventPreview.ts

@@ -23,7 +23,7 @@ import ReplyThread from "../../../components/views/elements/ReplyThread";
 import { getHtmlText } from "../../../HtmlUtils";
 
 export class MessageEventPreview implements IPreview {
-    public getTextFor(event: MatrixEvent, tagId?: TagID): string {
+    public getTextFor(event: MatrixEvent, tagId?: TagID, isThread?: boolean): string {
         let eventContent = event.getContent();
 
         if (event.isRelation("m.replace")) {
@@ -64,7 +64,7 @@ export class MessageEventPreview implements IPreview {
             return _t("* %(senderName)s %(emote)s", { senderName: getSenderName(event), emote: body });
         }
 
-        if (isSelf(event) || !shouldPrefixMessagesIn(event.getRoomId(), tagId)) {
+        if (isThread || isSelf(event) || !shouldPrefixMessagesIn(event.getRoomId(), tagId)) {
             return body;
         } else {
             return _t("%(senderName)s: %(message)s", { senderName: getSenderName(event), message: body });

src/stores/room-list/previews/ReactionEventPreview.ts

@@ -23,7 +23,7 @@ import SettingsStore from "../../../settings/SettingsStore";
 import DMRoomMap from "../../../utils/DMRoomMap";
 
 export class ReactionEventPreview implements IPreview {
-    public getTextFor(event: MatrixEvent, tagId?: TagID): string {
+    public getTextFor(event: MatrixEvent, tagId?: TagID, isThread?: boolean): string {
         const showDms = SettingsStore.getValue("feature_roomlist_preview_reactions_dms");
         const showAll = SettingsStore.getValue("feature_roomlist_preview_reactions_all");
 
@@ -41,7 +41,7 @@ export class ReactionEventPreview implements IPreview {
         const reaction = relation.key;
         if (!reaction) return null; // invalid reaction (unknown format)
 
-        if (isSelf(event) || !shouldPrefixMessagesIn(event.getRoomId(), tagId)) {
+        if (isThread || isSelf(event) || !shouldPrefixMessagesIn(event.getRoomId(), tagId)) {
             return reaction;
         } else {
             return _t("%(senderName)s: %(reaction)s", { senderName: getSenderName(event), reaction });

src/stores/room-list/previews/StickerEventPreview.ts

@@ -21,11 +21,11 @@ import { getSenderName, isSelf, shouldPrefixMessagesIn } from "./utils";
 import { _t } from "../../../languageHandler";
 
 export class StickerEventPreview implements IPreview {
-    public getTextFor(event: MatrixEvent, tagId?: TagID): string {
+    public getTextFor(event: MatrixEvent, tagId?: TagID, isThread?: boolean): string {
         const stickerName = event.getContent()['body'];
         if (!stickerName) return null;
 
-        if (isSelf(event) || !shouldPrefixMessagesIn(event.getRoomId(), tagId)) {
+        if (isThread || isSelf(event) || !shouldPrefixMessagesIn(event.getRoomId(), tagId)) {
             return stickerName;
         } else {
             return _t("%(senderName)s: %(stickerName)s", { senderName: getSenderName(event), stickerName });