<!doctype html>
<meta charset=utf-8>
<title>Seamlessly updating the playback rate of an animation</title>
<link rel="help"
  href="https://drafts.csswg.org/web-animations-1/#seamlessly-updating-the-playback-rate-of-an-animation">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="../../testcommon.js"></script>
<body>
<div id="log"></div>
<script>
'use strict';

promise_test(async t => {
  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
  await animation.ready;

  animation.currentTime = 50 * MS_PER_SEC;

  animation.updatePlaybackRate(0.5);
  await animation.ready;
  // Since the animation is in motion (and we want to test it while it is in
  // motion!) we can't assert that the current time == 50s but we can check
  // that the current time is NOT re-calculated by simply substituting in the
  // new playback rate (i.e. without adjusting the start time). If that were
  // the case the currentTime would jump to 25s. So we just test the currentTime
  // hasn't gone backwards.
  assert_greater_than_equal(animation.currentTime, 50 * MS_PER_SEC,
    'Reducing the playback rate should not change the current time ' +
    'of a playing animation');

  animation.updatePlaybackRate(2);
  await animation.ready;
  // Likewise, we test here that the current time does not jump to 100s as it
  // would if we naively applied a playbackRate of 2 without adjusting the
  // startTime.
  assert_less_than(animation.currentTime, 100 * MS_PER_SEC,
    'Increasing the playback rate should not change the current time ' +
    'of a playing animation');
}, 'Updating the playback rate maintains the current time');

promise_test(async t => {
  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
  await animation.ready;

  assert_false(animation.pending);
  animation.updatePlaybackRate(2);
  assert_true(animation.pending);
}, 'Updating the playback rate while running makes the animation pending');

promise_test(async t => {
  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
  animation.currentTime = 50 * MS_PER_SEC;
  assert_true(animation.pending);

  animation.updatePlaybackRate(0.5);

  // Check that the hold time is updated as expected
  assert_time_equals_literal(animation.currentTime, 50 * MS_PER_SEC);

  await animation.ready;

  // As above, check that the currentTime is not calculated by simply
  // substituting in the updated playbackRate without updating the startTime.
  assert_greater_than_equal(animation.currentTime, 50 * MS_PER_SEC,
    'Reducing the playback rate should not change the current time ' +
    'of a play-pending animation');
}, 'Updating the playback rate on a play-pending animation maintains'
   + ' the current time');

promise_test(async t => {
  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
  animation.currentTime = 50 * MS_PER_SEC;
  await animation.ready;

  animation.pause();
  animation.updatePlaybackRate(0.5);

  assert_greater_than_equal(animation.currentTime, 50 * MS_PER_SEC);
}, 'Updating the playback rate on a pause-pending animation maintains'
   + ' the current time');

promise_test(async t => {
  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);

  animation.updatePlaybackRate(2);
  animation.updatePlaybackRate(3);
  animation.updatePlaybackRate(4);

  assert_equals(animation.playbackRate, 1);
  await animation.ready;

  assert_equals(animation.playbackRate, 4);
}, 'If a pending playback rate is set multiple times, the latest wins');

test(t => {
  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
  animation.cancel();

  animation.updatePlaybackRate(2);
  assert_equals(animation.playbackRate, 2);
  assert_false(animation.pending);
}, 'In the idle state, the playback rate is applied immediately');

promise_test(async t => {
  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
  animation.pause();
  await animation.ready;

  animation.updatePlaybackRate(2);
  assert_equals(animation.playbackRate, 2);
  assert_false(animation.pending);
}, 'In the paused state, the playback rate is applied immediately');

promise_test(async t => {
  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
  animation.finish();
  assert_time_equals_literal(animation.currentTime, 100 * MS_PER_SEC);
  assert_false(animation.pending);

  animation.updatePlaybackRate(2);
  assert_equals(animation.playbackRate, 2);
  assert_time_equals_literal(animation.currentTime, 100 * MS_PER_SEC);
  assert_false(animation.pending);
}, 'Updating the playback rate on a finished animation maintains'
   + ' the current time');

promise_test(async t => {
  const animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
  animation.finish();
  assert_time_equals_literal(animation.currentTime, 100 * MS_PER_SEC);
  assert_false(animation.pending);

  animation.updatePlaybackRate(0);
  assert_equals(animation.playbackRate, 0);
  assert_time_equals_literal(animation.currentTime, 100 * MS_PER_SEC);
  assert_false(animation.pending);
}, 'Updating the playback rate to zero on a finished animation maintains'
   + ' the current time');

</script>
</body>