<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
  @font-face {
    font-family: 'ADTestFaceSwap';
    src: url('/fonts/AD.woff?pipe=trickle(d0.5)');
    font-display: swap;
  }

  .test {
    font-family: 'ADTestFaceSwap';
  }

</style>
<!--
  Web-font styled text that gets resized during swap period should make a
  LCP emission if the new size is larger than the existing LCP element size.
-->
<div class="test">LCP: Web Font Styled Text Resize</div>
<script>
  function LCPEntryList() {
    return new Promise(resolve => {
      let = lcpEntries = [];
      new PerformanceObserver((entryList, observer) => {
        lcpEntries = lcpEntries.concat(entryList.getEntries());
        if (lcpEntries.length == 2) {
          resolve(lcpEntries);
          observer.disconnect();
        }
      }).observe({ type: 'largest-contentful-paint', buffered: true });
    });
  }

  promise_test(async t => {
    await document.fonts.ready;

    // Verify web font is downloaded.
    assert_own_property(window, 'PerformanceResourceTiming', "ResourceTiming not supported");
    let url = '/fonts/AD.woff?pipe=trickle(d0.5)';
    var absoluteURL = new URL(url, location.href).href;
    assert_equals(performance.getEntriesByName(absoluteURL).length, 1, 'Web font\
    should be downloaded');

    // Verify web font is available.
    assert_true(document.fonts.check('16px ADTestFaceSwap'), 'Font should be the web font added');

    let entryList = await LCPEntryList();

    // Verify there are 2 LCP entries emitted.
    assert_equals(entryList.length, 2, 'There should be 2 LCP entries. The 1st one corresponds to the system font and the 2nd the web font.')

    // Verify the size of 2nd LCP entry is larger than that of the 1st one.
    assert_greater_than(entryList[1].size, entryList[0].size, 'The size of 2ndLCP entry should be larger than that of the 1st one.');

  }, "LCP should be updated if the web font styled text resizes to be larger   during the swap period");
</script>
