<!DOCTYPE html>
<title>Tests position fallback with scrollers with mixed writing modes</title>
<link rel="author" href="mailto:xiaochengh@chromium.org">
<link rel="help" href="https://drafts.csswg.org/css-anchor-1/#scroll">
<link rel="help" href="https://drafts.csswg.org/css-anchor-1/#fallback-apply">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="support/test-common.js"></script>

<style>
body {
  margin: 0;
}

#vrl-scroller {
  writing-mode: vertical-rl;
  overflow-x: scroll;
  width: calc(100vw - 90px);
  height: 400px;
  outline: 1px solid black;
}

#anchor {
  anchor-name: --a;
  width: 100px;
  height: 100px;
  margin-left: 1000px;
  background: orange;
}

#anchored {
  position: fixed;
  width: 100px;
  height: 100px;
  background: green;
  anchor-scroll: --a;
  position-fallback: --pf;
}

@position-fallback --pf {
  /* Top of the anchor */
  @try { bottom: anchor(--a top); left: anchor(--a left); }
  /* Bottom of the anchor */
  @try { top: anchor(--a bottom); left: anchor(--a left); }
  /* Left of the anchor */
  @try { top: anchor(--a top); right: anchor(--a left); }
}
</style>

<div style="height: 200px"></div>
<div id="vrl-scroller">
  <div id="anchor"></div>
</div>
<div style="height: 1000px"></div>
<div id="anchored"></div>

<script>
promise_test(async () => {
  await waitUntilNextAnimationFrame();
  assert_fallback_position(anchored, anchor, 'top');
}, 'Should use the first fallback position at the initial scroll offsets');

promise_test(async () => {
  document.documentElement.scrollTop = 101;
  await waitUntilNextAnimationFrame();
  assert_fallback_position(anchored, anchor, 'bottom');
}, 'Should use the second fallback position after scrolling viewport down');

promise_test(async () => {
  let vrlScroller = document.getElementById('vrl-scroller');
  vrlScroller.scrollLeft = -100;
  await waitUntilNextAnimationFrame();
  assert_fallback_position(anchored, anchor, 'left');
}, 'Should use the third fallback position after scrolling the vrl scroller left');
</script>
