import { bindReporter } from './lib/bindReporter.js';
import { getActivationStart } from './lib/getActivationStart.js';
import { getVisibilityWatcher } from './lib/getVisibilityWatcher.js';
import { initMetric } from './lib/initMetric.js';
import { observe } from './lib/observe.js';
import { whenActivated } from './lib/whenActivated.js';

const FCPThresholds = [1800, 3e3];
const onFCP = (onReport, opts = {}) => {
  whenActivated(() => {
    const visibilityWatcher = getVisibilityWatcher();
    const metric = initMetric("FCP");
    let report;
    const handleEntries = (entries) => {
      for (const entry of entries) {
        if (entry.name === "first-contentful-paint") {
          po.disconnect();
          if (entry.startTime < visibilityWatcher.firstHiddenTime) {
            metric.value = Math.max(entry.startTime - getActivationStart(), 0);
            metric.entries.push(entry);
            report(true);
          }
        }
      }
    };
    const po = observe("paint", handleEntries);
    if (po) {
      report = bindReporter(onReport, metric, FCPThresholds, opts.reportAllChanges);
    }
  });
};

export { FCPThresholds, onFCP };
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