<!DOCTYPE html>
<title>Length unit 'ch' should be recalculated after loading a web font</title>
<link rel="help" href="https://www.w3.org/TR/css-font-loading-3/#font-face-load">
<link rel="help" href="https://www.w3.org/TR/css-values-3/#font-relative-lengths">
<link rel="author" href="mailto:xiaochengh@chromium.org">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
.container {
  font: 25px/1 "custom font", monospace;
}

.test {
  width: 1ch;
}
</style>

<div class="container">
  <div class="test"></div>
</div>

<div class="container" style="display: contents">
  <div class="test"></div>
</div>

<div class="container" style="display: none">
  <div class="test"></div>
</div>

<script>
function parseWidthInPx(element) {
  const value = getComputedStyle(element).width;
  if (!value.endsWith('px'))
    return NaN;
  return parseFloat(value);
}

const testCases = document.querySelectorAll('.test');

const asyncTests = [
  async_test('ch in a normal div should be recalculated after loading a web font'),
  async_test('ch in display:contents should be recalculated after loading a web font'),
  async_test('ch in display:none 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 widthPx = parseWidthInPx(testCases[i]);
    assert_less_than(widthPx, 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 widthPx = parseWidthInPx(testCases[i]);
          assert_approx_equals(widthPx, 25, 0.1);
          asyncTests[i].done();
        });
      }
    },
    () => {
      for (let i = 0; i < testCases.length; ++i) {
        asyncTests[i].step(() => {
          assert_unreached('Failed to load font');
        });
      }
    }
);
</script>
