/**
 * @license
 * Copyright 2020 Google LLC
 *
 * 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.
 */

export function utcTimestampToDateString(
  utcTimestamp?: string | number
): string | undefined {
  if (!utcTimestamp) {
    return undefined;
  }
  try {
    // Convert to date object.
    const date = new Date(Number(utcTimestamp));
    // Test date is valid.
    if (!isNaN(date.getTime())) {
      // Convert to UTC date string.
      return date.toUTCString();
    }
  } catch (e) {
    // Do nothing. undefined will be returned.
  }
  return undefined;
}