MVVM RoomSummaryCard Topic (#29710)

* feat: create roomSummaryCardTopic view model

* chore: add comments and small update on test mock

src/components/viewmodels/right_panel/RoomSummaryCardTopicViewModel.tsx

@@ -0,0 +1,84 @@
+/*
+Copyright 2025 New Vector Ltd.
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only
+Please see LICENSE files in the repository root for full details.
+*/
+
+import { type SyntheticEvent, useState } from "react";
+import { EventType, type Room, type ContentHelpers } from "matrix-js-sdk/src/matrix";
+import { type Optional } from "matrix-events-sdk";
+
+import { useRoomState } from "../../../hooks/useRoomState";
+import defaultDispatcher from "../../../dispatcher/dispatcher";
+import { onRoomTopicLinkClick } from "../../views/elements/RoomTopic";
+import { useTopic } from "../../../hooks/room/useTopic";
+
+export interface RoomTopicState {
+    /**
+     * The topic of the room, the value is taken from the room state
+     */
+    topic: Optional<ContentHelpers.TopicState>;
+    /**
+     * Whether the topic is expanded or not
+     */
+    expanded: boolean;
+    /**
+     * Whether the user have the permission to edit the topic
+     */
+    canEditTopic: boolean;
+    /**
+     * The callback when the edit button is clicked
+     */
+    onEditClick: (e: SyntheticEvent) => void;
+    /**
+     * When the expand button is clicked, it changes expanded state
+     */
+    onExpandedClick: (ev: SyntheticEvent) => void;
+    /**
+     * The callback when the topic link is clicked
+     */
+    onTopicLinkClick: React.MouseEventHandler<HTMLElement>;
+}
+
+/**
+ * The view model for the room topic used in the RoomSummaryCard
+ * @param room - the room to get the topic from
+ * @returns the room topic state
+ */
+export function useRoomTopicViewModel(room: Room): RoomTopicState {
+    const [expanded, setExpanded] = useState(true);
+
+    const topic = useTopic(room);
+
+    const canEditTopic = useRoomState(room, (state) =>
+        state.maySendStateEvent(EventType.RoomTopic, room.client.getSafeUserId()),
+    );
+
+    const onEditClick = (e: SyntheticEvent): void => {
+        e.preventDefault();
+        e.stopPropagation();
+        defaultDispatcher.dispatch({ action: "open_room_settings" });
+    };
+
+    const onExpandedClick = (e: SyntheticEvent): void => {
+        e.preventDefault();
+        e.stopPropagation();
+        setExpanded((_expanded) => !_expanded);
+    };
+
+    const onTopicLinkClick = (e: React.MouseEvent): void => {
+        if (e.target instanceof HTMLAnchorElement) {
+            onRoomTopicLinkClick(e);
+            return;
+        }
+    };
+
+    return {
+        topic,
+        expanded,
+        canEditTopic,
+        onEditClick,
+        onExpandedClick,
+        onTopicLinkClick,
+    };
+}