<!DOCTYPE html>
<meta charset="utf-8">
<title>Length unit 'ch' used in pseudo elements should be recalculated after loading a web font</title>
<link rel="help" href="https://www.w3.org/TR/css-values-4/#font-relative-lengths">
<link rel="help" href="https://drafts.csswg.org/css-pseudo-4/#first-letter-styling">
<link rel="author" href="xiaochengh@chromium.org">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
.container {
  font: 25px/1 "custom font", monospace;
}

.before::before,
.after::after,
.first-letter::first-letter,
.first-line::first-line {
  font-family: monospace;
  font-size: 1ch; /* Refers to originating element's font metrics, which are different from self font metrics. */
}

.before::before,
.after::after {
  content: 'text';
}

/* Defined separately so that browsers that haven't shipped it can still pass other tests. */
.marker::marker {
  font-family: monospace;
  font-size: 1ch;
  content: 'text';
}

</style>

<div class="container before"></div>
<div class="container after"></div>
<div class="container first-letter">text</div>
<div class="container first-line">text</div>
<li class="container marker"></li>

<script>
function parseFontSizeInPx(element, pseudoElement) {
  const value = getComputedStyle(element, pseudoElement).fontSize;
  if (!value.endsWith('px'))
    return NaN;
  return parseFloat(value);
}

const testCases = ['before', 'after', 'first-letter', 'first-line', 'marker'];
const elements = testCases.map(testCase => document.querySelector('.' + testCase));
const asyncTests = testCases.map(
    testCase => async_test(`ch in pseudo-element ::${testCase} should be recalculated after loading a web font`));

// Before loading custom font, tests should be rendered with monospace
// fallback and have a '1ch' measurement much shorter than 25px.
for (let i = 0; i < testCases.length; ++i) {
  asyncTests[i].step(() => {
    const fontSizePx = parseFontSizeInPx(elements[i], '::' + testCases[i]);
    assert_less_than(fontSizePx, 24);
  });
}

// Insert custom font into style sheet and load it
const customFont = new FontFace('custom font', 'url(/fonts/Ahem.ttf)');
document.fonts.add(customFont);

// After loading custom font, tests should be rendered with the custom font,
// which is Ahem, and have a '1ch' measurement that equals 25px.
customFont.load().then(
    () => {
      for (let i = 0; i < testCases.length; ++i) {
        asyncTests[i].step(() => {
          const fontSizePx = parseFontSizeInPx(elements[i], '::' + testCases[i]);
          assert_approx_equals(fontSizePx, 25, 0.1);
          asyncTests[i].done();
        });
      }
    },
    () => {
      for (let i = 0; i < testCases.length; ++i) {
        asyncTests[i].step(() => {
          assert_unreached('Failed to load font');
        });
      }
    }
);
</script>