<!DOCTYPE html>
<title>
  Updating the snap alignment of a snap container's content should make the snap
  container resnap accordingly.
</title>
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
div {
  position: absolute;
  margin: 0;
}

#scroller {
  height: 200px;
  width: 200px;
  overflow: hidden;
  scroll-snap-type: both mandatory;
}

#initial-target {
  width: 300px;
  height: 300px;
  top: 100px;
  left: 100px;
  background-color: green;
  scroll-snap-align: start;
}

#other-target {
  width: 300px;
  height: 300px;
  top: 300px;
  left: 300px;
  background-color: red;
  scroll-snap-align: start;
}

.area {
  width: 2000px;
  height: 2000px;
}

.snap-area {
  scroll-snap-align: start !important;
}
</style>

<div id="scroller">
  <div class="area"></div>
  <div id="initial-target"></div>
  <div id="other-target"></div>
</div>

<script>
const initial_target = document.getElementById("initial-target");
const other_target = document.getElementById("other-target");
const scroller = document.getElementById("scroller");

function cleanup() {
  initial_target.style.setProperty("scroll-snap-align", "start");
  other_target.style.setProperty("scroll-snap-align", "start");
  initial_target.removeAttribute("class");
}

test(t => {
  t.add_cleanup(cleanup);
  scroller.scrollTo(0,0);
  assert_equals(scroller.scrollTop, 100);
  assert_equals(scroller.scrollLeft, 100);

  initial_target.style.setProperty("scroll-snap-align", "end");
  // target.top + target.height - scroller.height
  assert_equals(scroller.scrollTop, 200);
  assert_equals(scroller.scrollLeft, 200);
}, "Changing the current target's snap alignment should make the scroller"
+ " resnap to it even if another snap position is closer to the current offset");

test(t => {
  t.add_cleanup(cleanup);
  scroller.scrollTo(0,0);
  assert_equals(scroller.scrollTop, 100);
  assert_equals(scroller.scrollLeft, 100);

  initial_target.style.setProperty("scroll-snap-align", "none");
  assert_equals(scroller.scrollTop, 300);
  assert_equals(scroller.scrollLeft, 300);
}, "Removing the current target's snap alignment should make the scroller"
+ " resnap to a new snap area.");

test(t => {
  t.add_cleanup(cleanup);
  initial_target.style.setProperty("scroll-snap-align", "none");
  other_target.style.setProperty("scroll-snap-align", "none");

  scroller.scrollTo(0,0);
  assert_equals(scroller.scrollTop, 0);
  assert_equals(scroller.scrollLeft, 0);

  initial_target.style.setProperty("scroll-snap-align", "start");
  assert_equals(scroller.scrollTop, 100);
  assert_equals(scroller.scrollLeft, 100);
}, "Changing an element snap alignment from none to start should make the"
+ "scroller resnap.");

test(t => {
  t.add_cleanup(cleanup);
  initial_target.style.setProperty("scroll-snap-align", "none");
  other_target.style.setProperty("scroll-snap-align", "none");

  scroller.scrollTo(0,0);
  assert_equals(scroller.scrollTop, 0);
  assert_equals(scroller.scrollLeft, 0);

  initial_target.classList.add("snap-area");
  assert_equals(scroller.scrollTop, 100);
  assert_equals(scroller.scrollLeft, 100);
}, "Changing an element snap alignment from none to start by adding a class"
+ " should make the scroller resnap.");
</script>
