Merge branch 'toger5/connectionLostBanner' into connectionlostbanner_lk

NB. I had to more or less rewrite this as it had been refactored in the livekit branch.

src/DisconnectedBanner.tsx

@@ -0,0 +1,53 @@
+/*
+Copyright 2023 New Vector Ltd
+
+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 classNames from "classnames";
+import { HTMLAttributes, ReactNode } from "react";
+import { useTranslation } from "react-i18next";
+
+import styles from "./DisconnectedBanner.module.css";
+import { ValidClientState, useClientState } from "./ClientContext";
+
+interface DisconnectedBannerProps extends HTMLAttributes<HTMLElement> {
+  children?: ReactNode;
+  className?: string;
+}
+
+export function DisconnectedBanner({
+  children,
+  className,
+  ...rest
+}: DisconnectedBannerProps) {
+  const { t } = useTranslation();
+  const clientState = useClientState();
+  let shouldShowBanner = false;
+
+  if (clientState?.state === "valid") {
+    const validClientState = clientState as ValidClientState;
+    shouldShowBanner = validClientState.disconnected;
+  }
+
+  return (
+    <>
+      {shouldShowBanner && (
+        <div className={classNames(styles.banner, className)} {...rest}>
+          {children}
+          {t("Connectivity to the server has been lost.")}
+        </div>
+      )}
+    </>
+  );
+}