/*
 * Copyright 2022 Palantir Technologies, Inc. All rights reserved.
 *
 * 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 { UTC_TIME } from "./timezoneItems";

/**
 * Keep the returned timezone constant for a page load.
 */
let memoizedTimezone: string | null = null;

/**
 * Gets the users current time zone, for example "Europe/Oslo".
 * This is currently backed by the browser or computer's locale setting.
 */
export function getCurrentTimezone(): string {
    if (memoizedTimezone === null) {
        // Unsupported in IE, which newer Blueprint components do not support.
        // In the unlikely case that the browser API returns undefined, we default to UTC.
        // @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat/resolvedOptions
        memoizedTimezone = Intl.DateTimeFormat().resolvedOptions().timeZone ?? UTC_TIME.ianaCode;
    }
    return memoizedTimezone;
}