<!DOCTYPE html>
<meta name="viewport" content="width=device-width,initial-scale=1">
<link rel="help" href="https://w3c.github.io/IntersectionObserver/#calculate-intersection-rect-algo">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="./resources/intersection-observer-test-utils.js"></script>

<style>
@keyframes clippath {
  0% {
    clip-path: inset(30%);
  }
  100% {
    clip-path: inset(40%);
  }
}
body { margin: 0 }
pre, #log {
  position: absolute;
  top: 0;
  left: 200px;
}
#target {
  position: absolute;
  top: 0px;
  background-color: green;
  width: 100px;
  height: 100px;
}
#container {
  margin: 20px;
  position: relative;
  padding: 8px;
  width: 0px;
  height: 0px;
}
.animation {
  animation: clippath 100s steps(2, jump-end);
}
</style>

<div id="container">
  <div id="target"></div>
</div>

<script>
var vw = document.documentElement.clientWidth;
var vh = document.documentElement.clientHeight;

var target = undefined;
var container = undefined;
var observer = undefined;
var entries = [];

// See crbug.com/40690885. In principle, this test should not need this,
// however browser support of updating intersection obsevers in response
// to animations (and in particular, clip-paths) is spotty. Forcing a
// fresh listener allows the test to guard against regression of
// crbug.com/394244260, and test that resolution of clip rects with
// animations isn't particularly broken in some way.
async function forceReset() {
  if(observer) { observer.disconnect(); }
  observer = new IntersectionObserver(function(changes) {
    entries = entries.concat(changes)
  }, {
    root: container
  });
  observer.observe(target);
  await waitForNotification();
}

promise_test(async function(t) {
  target = document.getElementById("target");
  container = document.getElementById("container");
  await forceReset();

  // See intersection-observer-test-utils.js for the meaning of these values.
  checkLastEntry(
    entries,
    0,
    [28, 128, 20, 120, 28, 36, 20, 36, 20, 36, 20, 36, true],
  );
  target.className = "animation";
  await forceReset();

  checkLastEntry(
    entries,
    1,
    [28, 128, 20, 120, 0, 0, 0, 0, 20, 36, 20, 36, false],
  );
  target.className = "";
  await forceReset();

  checkLastEntry(
    entries,
    2,
    [28, 128, 20, 120, 28, 36, 20, 36, 20, 36, 20, 36, true],
  );
});
</script>