/*
 * 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
 *
 *     https://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 { onHidden } from './onHidden.js';
let firstHiddenTime;
export const getFirstHidden = () => {
    if (firstHiddenTime === undefined) {
        // If the document is hidden when this code runs, assume it was hidden
        // since navigation start. This isn't a perfect heuristic, but it's the
        // best we can do until an API is available to support querying past
        // visibilityState.
        firstHiddenTime = document.visibilityState === 'hidden' ? 0 : Infinity;
        // Update the time if/when the document becomes hidden.
        onHidden(({ timeStamp }) => firstHiddenTime = timeStamp, true);
    }
    return {
        get timeStamp() {
            return firstHiddenTime;
        }
    };
};