Add optional mobile guide toast

This adds an optional toast which Element deployments can enable to nudge users
towards the mobile apps once they are inside the app.

Part of https://github.com/vector-im/element-web/issues/16283

src/toasts/MobileGuideToast.ts

@@ -0,0 +1,61 @@
+/*
+Copyright 2021 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 { _t } from "../languageHandler";
+import GenericToast from "../components/views/toasts/GenericToast";
+import ToastStore from "../stores/ToastStore";
+
+const onAccept = () => {
+    window.location.href = "mobile_guide/";
+};
+
+const onReject = () => {
+    document.cookie = "element_mobile_redirect_to_guide=false;path=/;max-age=14400";
+    hideToast();
+};
+
+const TOAST_KEY = "mobileguide";
+
+export const showToast = () => {
+    const isIos = /iPad|iPhone|iPod/.test(navigator.userAgent) && !window.MSStream;
+    const isAndroid = /Android/.test(navigator.userAgent);
+    if (!isIos && !isAndroid) {
+        return;
+    }
+    if (document.cookie.includes("element_mobile_redirect_to_guide=false")) {
+        return;
+    }
+    ToastStore.sharedInstance().addOrReplaceToast({
+        key: TOAST_KEY,
+        title: _t("Mobile experience"),
+        props: {
+            description: _t(
+                "Element Web is currently experimental on mobile. " +
+                "The native apps are recommended for most people.",
+            ),
+            acceptLabel: _t("Learn more"),
+            onAccept,
+            rejectLabel: _t("Dismiss"),
+            onReject,
+        },
+        component: GenericToast,
+        priority: 99,
+    });
+};
+
+export const hideToast = () => {
+    ToastStore.sharedInstance().dismissToast(TOAST_KEY);
+};