Automatically focus the WYSIWYG composer when you enter a room

src/components/views/rooms/wysiwyg_composer/WysiwygComposer.tsx

@@ -15,13 +15,14 @@ limitations under the License.
 */
 
 import React, { useCallback, useState } from 'react';
-import { useWysiwyg } from "@matrix-org/matrix-wysiwyg";
 import { IEventRelation, MatrixEvent } from 'matrix-js-sdk/src/models/event';
+import { useWysiwyg } from "@matrix-org/matrix-wysiwyg";
 
-import { useRoomContext } from '../../../../contexts/RoomContext';
-import { sendMessage } from './message';
 import { RoomPermalinkCreator } from '../../../../utils/permalinks/Permalinks';
+import { sendMessage } from './message';
 import { useMatrixClientContext } from '../../../../contexts/MatrixClientContext';
+import { useRoomContext } from '../../../../contexts/RoomContext';
+import { useWysiwygActionHandler } from './useWysiwygActionHandler';
 
 interface WysiwygProps {
     disabled?: boolean;
@@ -51,6 +52,8 @@ export function WysiwygComposer(
         ref.current?.focus();
     }, [content, mxClient, roomContext, wysiwyg, props, ref]);
 
+    useWysiwygActionHandler(disabled, ref);
+
     return (
         <div className="mx_WysiwygComposer">
             <div className="mx_WysiwygComposer_container">

src/components/views/rooms/wysiwyg_composer/useWysiwygActionHandler.ts

@@ -0,0 +1,74 @@
+/*
+Copyright 2022 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { useRef } from "react";
+
+import defaultDispatcher from "../../../../dispatcher/dispatcher";
+import { Action } from "../../../../dispatcher/actions";
+import { ActionPayload } from "../../../../dispatcher/payloads";
+import { IRoomState } from "../../../structures/RoomView";
+import { TimelineRenderingType } from "../../../../contexts/RoomContext";
+import { useDispatcher } from "../../../../hooks/useDispatcher";
+import { useRoomContext } from "../../../../contexts/RoomContext";
+
+export function useWysiwygActionHandler(
+    disabled: boolean,
+    composerElement: React.MutableRefObject<HTMLElement>,
+) {
+    const roomContext = useRoomContext();
+    const timeoutId = useRef<number>();
+
+    useDispatcher(defaultDispatcher, (payload: ActionPayload) => {
+        // don't let the user into the composer if it is disabled - all of these branches lead
+        // to the cursor being in the composer
+        if (disabled) return;
+
+        const context = payload.context ?? TimelineRenderingType.Room;
+
+        switch (payload.action) {
+            case "reply_to_event":
+            case Action.FocusSendMessageComposer:
+                focusComposer(composerElement, context, roomContext, timeoutId);
+                break;
+            // TODO: case Action.ComposerInsert: - see SendMessageComposer
+        }
+    });
+}
+
+function focusComposer(
+    composerElement: React.MutableRefObject<HTMLElement>,
+    renderingType: TimelineRenderingType,
+    roomContext: IRoomState,
+    timeoutId: React.MutableRefObject<number>,
+) {
+    if (renderingType === roomContext.timelineRenderingType) {
+        // Immediately set the focus, so if you start typing it
+        // will appear in the composer
+        composerElement.current?.focus();
+        // If we call focus immediate, the focus _is_ in the right
+        // place, but the cursor is invisible, presumably because
+        // some other event is still processing.
+        // The following line ensures that the cursor is actually
+        // visible in composer.
+        if (timeoutId.current) {
+            clearTimeout(timeoutId.current);
+        }
+        timeoutId.current = setTimeout(
+            () => composerElement.current?.focus(),
+            200,
+        );
+    }
+}