<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="./resources/intersection-observer-test-utils.js"></script>

<style>
pre, #log {
  position: absolute;
  top: 0;
  left: 200px;
}
.spacer {
  height: calc(100vh + 100px);
}

</style>
<div id="leading-space" class="spacer"></div>
<div id="trailing-space" class="spacer"></div>

<script>
// Pick this number to be comfortably greater than the length of two frames at 60Hz.
var timeSkew = 40;

var topWindowEntries = [];
var iframeWindowEntries = [];
var targetIframe;
var topWindowTimeBeforeNotification;
var iframeWindowTimeBeforeNotification;

async_test(function(t) {
  t.step_timeout(function() {
    targetIframe = document.createElement("iframe");
    assert_true(!!targetIframe, "iframe exists");
    targetIframe.src = "resources/timestamp-subframe.html";
    var trailingSpace = document.getElementById("trailing-space");
    assert_true(!!trailingSpace, "trailing-space exists");
    trailingSpace.parentNode.insertBefore(targetIframe, trailingSpace);
    targetIframe.onload = function() {
      var target = targetIframe.contentDocument.getElementById("target");
      var iframeScroller = targetIframe.contentDocument.scrollingElement;

      // Observer created here, callback created in iframe context.  Timestamps should be
      // from this window.
      var observer = new IntersectionObserver(
          targetIframe.contentDocument.createObserverCallback(topWindowEntries), {});
      assert_true(!!observer, "Observer exists");
      observer.observe(target);

      // Callback created here, observer created in iframe.  Timestamps should be
      // from iframe window.
      observer = targetIframe.contentDocument.createObserver(function(newEntries) {
        iframeWindowEntries = iframeWindowEntries.concat(newEntries);
      });
      observer.observe(target);
      runTestCycle(step1, "First rAF after iframe is loaded.");
      t.done();
    };
  }, timeSkew);
}, "Check that timestamps correspond to the to execution context that created the observer.");

function step1() {
  document.scrollingElement.scrollTop = 200;
  targetIframe.contentDocument.scrollingElement.scrollTop = 250;
  topWindowTimeBeforeNotification = performance.now();
  iframeWindowTimeBeforeNotification = targetIframe.contentWindow.performance.now();
  runTestCycle(step2, "Generate notifications.");
  assert_equals(topWindowEntries.length, 1, "One notification to top window observer.");
  assert_equals(iframeWindowEntries.length, 1, "One notification to iframe observer.");
}

function step2() {
  document.scrollingElement.scrollTop = 0;
  var topWindowTimeAfterNotification = performance.now();
  var iframeWindowTimeAfterNotification = targetIframe.contentWindow.performance.now();

  assert_approx_equals(
      topWindowEntries[1].time - topWindowTimeBeforeNotification,
      iframeWindowEntries[1].time - iframeWindowTimeBeforeNotification,
      // Since all intersections are computed in a tight loop between 2 frames,
      // an epsilon of 16ms (the length of one frame at 60Hz) turned out to be
      // reliable, even at slow frame rates.
      16,
      "Notification times are relative to the expected time origins");

  assert_equals(topWindowEntries.length, 2, "Top window observer has two notifications.");
  assert_between_inclusive(
      topWindowEntries[1].time,
      topWindowTimeBeforeNotification,
      topWindowTimeAfterNotification,
      "Notification to top window observer is within the expected range.");

  assert_equals(iframeWindowEntries.length, 2, "Iframe observer has two notifications.");
  assert_between_inclusive(
      iframeWindowEntries[1].time,
      iframeWindowTimeBeforeNotification,
      iframeWindowTimeAfterNotification,
      "Notification to iframe observer is within the expected range.");
}
</script>