Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });

const bindReporter = require('./lib/bindReporter.js');
const getActivationStart = require('./lib/getActivationStart.js');
const getVisibilityWatcher = require('./lib/getVisibilityWatcher.js');
const initMetric = require('./lib/initMetric.js');
const observe = require('./lib/observe.js');
const whenActivated = require('./lib/whenActivated.js');

/*
 * 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.
 */


/** Thresholds for FCP. See https://web.dev/articles/fcp#what_is_a_good_fcp_score */
const FCPThresholds = [1800, 3000];

/**
 * Calculates the [FCP](https://web.dev/articles/fcp) value for the current page and
 * calls the `callback` function once the value is ready, along with the
 * relevant `paint` performance entry used to determine the value. The reported
 * value is a `DOMHighResTimeStamp`.
 */
const onFCP = (onReport, opts = {}) => {
  whenActivated.whenActivated(() => {
    const visibilityWatcher = getVisibilityWatcher.getVisibilityWatcher();
    const metric = initMetric.initMetric('FCP');
    let report;

    const handleEntries = (entries) => {
      for (const entry of entries) {
        if (entry.name === 'first-contentful-paint') {
          po.disconnect();

          // Only report if the page wasn't hidden prior to the first paint.
          if (entry.startTime < visibilityWatcher.firstHiddenTime) {
            // The activationStart reference is used because FCP should be
            // relative to page activation rather than navigation start if the
            // page was prerendered. But in cases where `activationStart` occurs
            // after the FCP, this time should be clamped at 0.
            metric.value = Math.max(entry.startTime - getActivationStart.getActivationStart(), 0);
            metric.entries.push(entry);
            report(true);
          }
        }
      }
    };

    const po = observe.observe('paint', handleEntries);

    if (po) {
      report = bindReporter.bindReporter(onReport, metric, FCPThresholds, opts.reportAllChanges);
    }
  });
};

exports.FCPThresholds = FCPThresholds;
exports.onFCP = onFCP;
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