Add thread notification with server assistance (MSC3773) (#9400)

Co-authored-by: Janne Mareike Koschinski <janne@kuschku.de>

src/components/views/rooms/NotificationBadge/StatelessNotificationBadge.tsx

@@ -0,0 +1,81 @@
+/*
+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 React, { MouseEvent } from "react";
+import classNames from "classnames";
+
+import { formatCount } from "../../../../utils/FormattingUtils";
+import AccessibleButton from "../../elements/AccessibleButton";
+import { NotificationColor } from "../../../../stores/notifications/NotificationColor";
+
+interface Props {
+    symbol: string | null;
+    count: number;
+    color: NotificationColor;
+    onClick?: (ev: MouseEvent) => void;
+    onMouseOver?: (ev: MouseEvent) => void;
+    onMouseLeave?: (ev: MouseEvent) => void;
+    children?: React.ReactChildren | JSX.Element;
+    label?: string;
+}
+
+export function StatelessNotificationBadge({
+    symbol,
+    count,
+    color,
+    ...props }: Props) {
+    // Don't show a badge if we don't need to
+    if (color === NotificationColor.None) return null;
+
+    const hasUnreadCount = color >= NotificationColor.Grey && (!!count || !!symbol);
+
+    const isEmptyBadge = symbol === null && count === 0;
+
+    if (symbol === null && count > 0) {
+        symbol = formatCount(count);
+    }
+
+    const classes = classNames({
+        'mx_NotificationBadge': true,
+        'mx_NotificationBadge_visible': isEmptyBadge ? true : hasUnreadCount,
+        'mx_NotificationBadge_highlighted': color === NotificationColor.Red,
+        'mx_NotificationBadge_dot': isEmptyBadge,
+        'mx_NotificationBadge_2char': symbol?.length > 0 && symbol?.length < 3,
+        'mx_NotificationBadge_3char': symbol?.length > 2,
+    });
+
+    if (props.onClick) {
+        return (
+            <AccessibleButton
+                aria-label={props.label}
+                {...props}
+                className={classes}
+                onClick={props.onClick}
+                onMouseOver={props.onMouseOver}
+                onMouseLeave={props.onMouseLeave}
+            >
+                <span className="mx_NotificationBadge_count">{ symbol }</span>
+                { props.children }
+            </AccessibleButton>
+        );
+    }
+
+    return (
+        <div className={classes}>
+            <span className="mx_NotificationBadge_count">{ symbol }</span>
+        </div>
+    );
+}