<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src=/resources/testdriver.js></script>
<script src=/resources/testdriver-actions.js></script>
<script src=/resources/testdriver-vendor.js></script>
<style></style>
<!--
  Web-font styled text that gets resized after an interaction stops LCP
  observation should not make a new LCP emission.
-->
<textarea id='input'></textarea>
<div class="test">LCP: Web Font Styled Text Resize</div>
<script>
  function addCSSRules() {
    styleSheet = document.styleSheets[0];
    fontRuleSet = "@font-face {\
      font-family: 'ADTestFaceInteraction';\
      src: url('/fonts/AD.woff');\
      font-display: swap;\
    }";
    fontAtRule = ".test {\
      font-family: 'ADTestFaceInteraction';\
    } ";
    styleSheet.insertRule(fontRuleSet);
    styleSheet.insertRule(fontAtRule);
  }

  function LCPEntryList(t) {
    return new Promise(resolve => {
      let = lcpEntries = [];
      new PerformanceObserver((entryList, observer) => {
        lcpEntries = lcpEntries.concat(entryList.getEntries());
        if (lcpEntries) {
          // Adding timeout to wait a bit more so that if there are more than
          // expected LCP entries emitted, they can be observed.
          t.step_timeout(() => {
            resolve(lcpEntries);
            observer.disconnect();
          }, 200);
        }
      }).observe({ type: 'largest-contentful-paint', buffered: true });
    });
  }

  promise_test(async t => {
    await document.fonts.ready;
    let system_font_size = document.getElementsByClassName('test')[0].offsetHeight;

    // Verify an LCP entry is emitted.
    let entryList = await LCPEntryList(t);
    assert_equals(entryList.length, 1, 'Text with system font should make a LCP emission.');

    let lcpEntryBeforeInteraction = entryList[0];

    // Add event listener so that CSS rule would be added after there's an
    // input.
    let inputElement = document.getElementById('input');
    inputElement.addEventListener('keydown', addCSSRules);

    // Send key as input.
    await test_driver.send_keys(inputElement, 'k');

    // Wait for web font to load.
    await document.fonts.ready;

    // Verify web font is downloaded.
    assert_own_property(window, 'PerformanceResourceTiming', "ResourceTiming not supported");
    let url = '/fonts/AD.woff';
    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 ADTestFaceInteraction'), 'Font should be the web font added');

    // Verify web font is applied.
    let web_font_size = document.getElementsByClassName('test')[0].offsetHeight;
    assert_not_equals(web_font_size, system_font_size, 'Web font swap should happen');

    // Assert there is only 1 LCP entry, which verifies the added web font does
    // not make a new LCP entry after an input.
    entryList = await LCPEntryList(t);
    assert_equals(entryList.length, 1, 'Text with system font should not make a LCP emission.');

    // Verify the LCP entry is the same one emitted before interaction by
    // asserting the size is the same.
    assert_equals(lcpEntryBeforeInteraction.size, entryList[0].size, 'There should be only 1 LCP entry emitted.');

  }, "LCP should be not updated if the web font styled text resize occurs after an interaction happens");
</script>
