<!DOCTYPE html>
<meta name="timeout" content="long">
<html>
<title>View transitions: CSS Animations are paused while render-blocked</title>
<link rel="help" href="https://github.com/WICG/view-transitions">
<link rel="author" href="mailto:khushalsagar@chromium.org">

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<style>
@keyframes fade {
  from {
    opacity: 0;
  }
}

div {
  width: 100px;
  height: 100px;
  background: blue;
  contain: paint;
  view-transition-name: target;
}

.animated {
  animation: fade 0.5s;
}
</style>

<div id=target></div>

<script>
let renderBlocked = true;

promise_test(() => {
  assert_implements(document.startViewTransition, "Missing document.startViewTransition");
  return new Promise(async (resolve, reject) => {
    requestAnimationFrame(() => {
      document.startViewTransition(() => {
        return new Promise(async (inner_resolve) => {
          step_timeout(() => {
            renderBlocked = false;
            inner_resolve();
          }, 1000);
        });
      });

      target.classList.toggle("animated");
      target.onanimationend = () => {
        if (renderBlocked)
          reject();
        else
          resolve();
      };
    });
  });
}, "CSS animation is blocked until prepare callback");
</script>
