gecko-dev/dom/animation/Animation.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "Animation.h"
#include "AnimationUtils.h"
#include "mozilla/dom/AnimationBinding.h"
#include "mozilla/dom/AnimationPlaybackEvent.h"
#include "mozilla/dom/DocumentTimeline.h"
#include "mozilla/AnimationEventDispatcher.h"
#include "mozilla/AnimationTarget.h"
#include "mozilla/AutoRestore.h"
#include "mozilla/Maybe.h" // For Maybe
#include "mozilla/TypeTraits.h" // For std::forward<>
#include "nsAnimationManager.h" // For CSSAnimation
#include "nsDOMMutationObserver.h" // For nsAutoAnimationMutationBatch
#include "nsIDocument.h" // For nsIDocument
#include "nsIPresShell.h" // For nsIPresShell
#include "nsThreadUtils.h" // For nsRunnableMethod and nsRevocableEventPtr
#include "nsTransitionManager.h" // For CSSTransition
#include "PendingAnimationTracker.h" // For PendingAnimationTracker

namespace mozilla {
namespace dom {

// Static members
uint64_t Animation::sNextAnimationIndex = 0;

NS_IMPL_CYCLE_COLLECTION_INHERITED(Animation, DOMEventTargetHelper,
                                   mTimeline,
                                   mEffect,
                                   mReady,
                                   mFinished)

NS_IMPL_ADDREF_INHERITED(Animation, DOMEventTargetHelper)
NS_IMPL_RELEASE_INHERITED(Animation, DOMEventTargetHelper)

NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Animation)
NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)

JSObject*
Animation::WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
{
  return dom::Animation_Binding::Wrap(aCx, this, aGivenProto);
}

// ---------------------------------------------------------------------------
//
// Utility methods
//
// ---------------------------------------------------------------------------

namespace {
  // A wrapper around nsAutoAnimationMutationBatch that looks up the
  // appropriate document from the supplied animation.
  class MOZ_RAII AutoMutationBatchForAnimation {
  public:
    explicit AutoMutationBatchForAnimation(const Animation& aAnimation
                                           MOZ_GUARD_OBJECT_NOTIFIER_PARAM) {
      MOZ_GUARD_OBJECT_NOTIFIER_INIT;
      Maybe<NonOwningAnimationTarget> target =
        nsNodeUtils::GetTargetForAnimation(&aAnimation);
      if (!target) {
        return;
      }

      // For mutation observers, we use the OwnerDoc.
      nsIDocument* doc = target->mElement->OwnerDoc();
      if (!doc) {
        return;
      }

      mAutoBatch.emplace(doc);
    }

  private:
    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
    Maybe<nsAutoAnimationMutationBatch> mAutoBatch;
  };
}

// ---------------------------------------------------------------------------
//
// Animation interface:
//
// ---------------------------------------------------------------------------
/* static */ already_AddRefed<Animation>
Animation::Constructor(const GlobalObject& aGlobal,
                       AnimationEffect* aEffect,
                       const Optional<AnimationTimeline*>& aTimeline,
                       ErrorResult& aRv)
{
  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aGlobal.GetAsSupports());
  RefPtr<Animation> animation = new Animation(global);

  AnimationTimeline* timeline;
  if (aTimeline.WasPassed()) {
    timeline = aTimeline.Value();
  } else {
    nsIDocument* document =
      AnimationUtils::GetCurrentRealmDocument(aGlobal.Context());
    if (!document) {
      aRv.Throw(NS_ERROR_FAILURE);
      return nullptr;
    }
    timeline = document->Timeline();
  }

  animation->SetTimelineNoUpdate(timeline);
  animation->SetEffectNoUpdate(aEffect);

  return animation.forget();
}

void
Animation::SetId(const nsAString& aId)
{
  if (mId == aId) {
    return;
  }
  mId = aId;
  nsNodeUtils::AnimationChanged(this);
}

void
Animation::SetEffect(AnimationEffect* aEffect)
{
  SetEffectNoUpdate(aEffect);
  PostUpdate();
}

// https://drafts.csswg.org/web-animations/#setting-the-target-effect
void
Animation::SetEffectNoUpdate(AnimationEffect* aEffect)
{
  RefPtr<Animation> kungFuDeathGrip(this);

  if (mEffect == aEffect) {
    return;
  }

  AutoMutationBatchForAnimation mb(*this);
  bool wasRelevant = mIsRelevant;

  if (mEffect) {
    // We need to notify observers now because once we set mEffect to null
    // we won't be able to find the target element to notify.
    if (mIsRelevant) {
      nsNodeUtils::AnimationRemoved(this);
    }

    // Break links with the old effect and then drop it.
    RefPtr<AnimationEffect> oldEffect = mEffect;
    mEffect = nullptr;
    oldEffect->SetAnimation(nullptr);

    // The following will not do any notification because mEffect is null.
    UpdateRelevance();
  }

  if (aEffect) {
    // Break links from the new effect to its previous animation, if any.
    RefPtr<AnimationEffect> newEffect = aEffect;
    Animation* prevAnim = aEffect->GetAnimation();
    if (prevAnim) {
      prevAnim->SetEffect(nullptr);
    }

    // Create links with the new effect. SetAnimation(this) will also update
    // mIsRelevant of this animation, and then notify mutation observer if
    // needed by calling Animation::UpdateRelevance(), so we don't need to
    // call it again.
    mEffect = newEffect;
    mEffect->SetAnimation(this);

    // Notify possible add or change.
    // If the target is different, the change notification will be ignored by
    // AutoMutationBatchForAnimation.
    if (wasRelevant && mIsRelevant) {
      nsNodeUtils::AnimationChanged(this);
    }

    ReschedulePendingTasks();
  }

  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
}

void
Animation::SetTimeline(AnimationTimeline* aTimeline)
{
  SetTimelineNoUpdate(aTimeline);
  PostUpdate();
}

// https://drafts.csswg.org/web-animations/#setting-the-timeline
void
Animation::SetTimelineNoUpdate(AnimationTimeline* aTimeline)
{
  if (mTimeline == aTimeline) {
    return;
  }

  StickyTimeDuration activeTime = mEffect
                                  ? mEffect->GetComputedTiming().mActiveTime
                                  : StickyTimeDuration();

  RefPtr<AnimationTimeline> oldTimeline = mTimeline;
  if (oldTimeline) {
    oldTimeline->RemoveAnimation(this);
  }

  mTimeline = aTimeline;
  if (!mStartTime.IsNull()) {
    mHoldTime.SetNull();
  }

  if (!aTimeline) {
    MaybeQueueCancelEvent(activeTime);
  }
  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
}

// https://drafts.csswg.org/web-animations/#set-the-animation-start-time
void
Animation::SetStartTime(const Nullable<TimeDuration>& aNewStartTime)
{
  // Return early if the start time will not change. However, if we
  // are pending, then setting the start time to any value
  // including the current value has the effect of aborting
  // pending tasks so we should not return early in that case.
  if (!Pending() && aNewStartTime == mStartTime) {
    return;
  }

  AutoMutationBatchForAnimation mb(*this);

  Nullable<TimeDuration> timelineTime;
  if (mTimeline) {
    // The spec says to check if the timeline is active (has a resolved time)
    // before using it here, but we don't need to since it's harmless to set
    // the already null time to null.
    timelineTime = mTimeline->GetCurrentTime();
  }
  if (timelineTime.IsNull() && !aNewStartTime.IsNull()) {
    mHoldTime.SetNull();
  }

  Nullable<TimeDuration> previousCurrentTime = GetCurrentTime();

  ApplyPendingPlaybackRate();
  mStartTime = aNewStartTime;

  if (!aNewStartTime.IsNull()) {
    if (mPlaybackRate != 0.0) {
      mHoldTime.SetNull();
    }
  } else {
    mHoldTime = previousCurrentTime;
  }

  CancelPendingTasks();
  if (mReady) {
    // We may have already resolved mReady, but in that case calling
    // MaybeResolve is a no-op, so that's okay.
    mReady->MaybeResolve(this);
  }

  UpdateTiming(SeekFlag::DidSeek, SyncNotifyFlag::Async);
  if (IsRelevant()) {
    nsNodeUtils::AnimationChanged(this);
  }
  PostUpdate();
}

// https://drafts.csswg.org/web-animations/#current-time
Nullable<TimeDuration>
Animation::GetCurrentTimeForHoldTime(
  const Nullable<TimeDuration>& aHoldTime) const
{
  Nullable<TimeDuration> result;
  if (!aHoldTime.IsNull()) {
    result = aHoldTime;
    return result;
  }

  if (mTimeline && !mStartTime.IsNull()) {
    Nullable<TimeDuration> timelineTime = mTimeline->GetCurrentTime();
    if (!timelineTime.IsNull()) {
      result = CurrentTimeFromTimelineTime(
        timelineTime.Value(), mStartTime.Value(), mPlaybackRate);
    }
  }
  return result;
}

// https://drafts.csswg.org/web-animations/#set-the-current-time
void
Animation::SetCurrentTime(const TimeDuration& aSeekTime)
{
  // Return early if the current time has not changed. However, if we
  // are pause-pending, then setting the current time to any value
  // including the current value has the effect of aborting the
  // pause so we should not return early in that case.
  if (mPendingState != PendingState::PausePending &&
      Nullable<TimeDuration>(aSeekTime) == GetCurrentTime()) {
    return;
  }

  AutoMutationBatchForAnimation mb(*this);

  SilentlySetCurrentTime(aSeekTime);

  if (mPendingState == PendingState::PausePending) {
    // Finish the pause operation
    mHoldTime.SetValue(aSeekTime);

    ApplyPendingPlaybackRate();
    mStartTime.SetNull();

    if (mReady) {
      mReady->MaybeResolve(this);
    }
    CancelPendingTasks();
  }

  UpdateTiming(SeekFlag::DidSeek, SyncNotifyFlag::Async);
  if (IsRelevant()) {
    nsNodeUtils::AnimationChanged(this);
  }
  PostUpdate();
}

// https://drafts.csswg.org/web-animations/#set-the-playback-rate
void
Animation::SetPlaybackRate(double aPlaybackRate)
{
  mPendingPlaybackRate.reset();

  if (aPlaybackRate == mPlaybackRate) {
    return;
  }

  AutoMutationBatchForAnimation mb(*this);

  Nullable<TimeDuration> previousTime = GetCurrentTime();
  mPlaybackRate = aPlaybackRate;
  if (!previousTime.IsNull()) {
    SetCurrentTime(previousTime.Value());
  }

  // In the case where GetCurrentTime() returns the same result before and
  // after updating mPlaybackRate, SetCurrentTime will return early since,
  // as far as it can tell, nothing has changed.
  // As a result, we need to perform the following updates here:
  // - update timing (since, if the sign of the playback rate has changed, our
  //   finished state may have changed),
  // - dispatch a change notification for the changed playback rate, and
  // - update the playback rate on animations on layers.
  UpdateTiming(SeekFlag::DidSeek, SyncNotifyFlag::Async);
  if (IsRelevant()) {
    nsNodeUtils::AnimationChanged(this);
  }
  PostUpdate();
}

// https://drafts.csswg.org/web-animations/#seamlessly-update-the-playback-rate
void
Animation::UpdatePlaybackRate(double aPlaybackRate)
{
  if (mPendingPlaybackRate && mPendingPlaybackRate.value() == aPlaybackRate) {
    return;
  }

  mPendingPlaybackRate = Some(aPlaybackRate);

  // If we already have a pending task, there is nothing more to do since the
  // playback rate will be applied then.
  if (Pending()) {
    return;
  }

  AutoMutationBatchForAnimation mb(*this);

  AnimationPlayState playState = PlayState();
  if (playState == AnimationPlayState::Idle ||
      playState == AnimationPlayState::Paused) {
    // We are either idle or paused. In either case we can apply the pending
    // playback rate immediately.
    ApplyPendingPlaybackRate();

    // We don't need to update timing or post an update here because:
    //
    // * the current time hasn't changed -- it's either unresolved or fixed
    //   with a hold time -- so the output won't have changed
    // * the finished state won't have changed even if the sign of the
    //   playback rate changed since we're not finished (we're paused or idle)
    // * the playback rate on layers doesn't need to be updated since we're not
    //   moving. Once we get a start time etc. we'll update the playback rate
    //   then.
    //
    // All we need to do is update observers so that, e.g. DevTools, report the
    // right information.
    if (IsRelevant()) {
      nsNodeUtils::AnimationChanged(this);
    }
  } else if (playState == AnimationPlayState::Finished) {
    MOZ_ASSERT(mTimeline && !mTimeline->GetCurrentTime().IsNull(),
               "If we have no active timeline, we should be idle or paused");
    if (aPlaybackRate != 0) {
      // The unconstrained current time can only be unresolved if either we
      // don't have an active timeline (and we already asserted that is not
      // true) or we have an unresolved start time (in which case we should be
      // paused).
      MOZ_ASSERT(!GetUnconstrainedCurrentTime().IsNull(),
                 "Unconstrained current time should be resolved");
      TimeDuration unconstrainedCurrentTime =
        GetUnconstrainedCurrentTime().Value();
      TimeDuration timelineTime = mTimeline->GetCurrentTime().Value();
      mStartTime = StartTimeFromTimelineTime(
        timelineTime, unconstrainedCurrentTime, aPlaybackRate);
    } else {
      mStartTime = mTimeline->GetCurrentTime();
    }

    ApplyPendingPlaybackRate();

    // Even though we preserve the current time, we might now leave the finished
    // state (e.g. if the playback rate changes sign) so we need to update
    // timing.
    UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
    if (IsRelevant()) {
      nsNodeUtils::AnimationChanged(this);
    }
    PostUpdate();
  } else {
    ErrorResult rv;
    Play(rv, LimitBehavior::Continue);
    MOZ_ASSERT(!rv.Failed(),
               "We should only fail to play when using auto-rewind behavior");
  }
}

// https://drafts.csswg.org/web-animations/#play-state
AnimationPlayState
Animation::PlayState() const
{
  Nullable<TimeDuration> currentTime = GetCurrentTime();
  if (currentTime.IsNull() && !Pending()) {
    return AnimationPlayState::Idle;
  }

  if (mPendingState == PendingState::PausePending ||
      (mStartTime.IsNull() && !Pending())) {
    return AnimationPlayState::Paused;
  }

  if (!currentTime.IsNull() &&
      ((mPlaybackRate > 0.0 && currentTime.Value() >= EffectEnd()) ||
       (mPlaybackRate < 0.0 && currentTime.Value() <= TimeDuration())))  {
    return AnimationPlayState::Finished;
  }

  return AnimationPlayState::Running;
}

Promise*
Animation::GetReady(ErrorResult& aRv)
{
  nsCOMPtr<nsIGlobalObject> global = GetOwnerGlobal();
  if (!mReady && global) {
    mReady = Promise::Create(global, aRv); // Lazily create on demand
  }
  if (!mReady) {
    aRv.Throw(NS_ERROR_FAILURE);
    return nullptr;
  }
  if (!Pending()) {
    mReady->MaybeResolve(this);
  }
  return mReady;
}

Promise*
Animation::GetFinished(ErrorResult& aRv)
{
  nsCOMPtr<nsIGlobalObject> global = GetOwnerGlobal();
  if (!mFinished && global) {
    mFinished = Promise::Create(global, aRv); // Lazily create on demand
  }
  if (!mFinished) {
    aRv.Throw(NS_ERROR_FAILURE);
    return nullptr;
  }
  if (mFinishedIsResolved) {
    MaybeResolveFinishedPromise();
  }
  return mFinished;
}

void
Animation::Cancel()
{
  CancelNoUpdate();
  PostUpdate();
}

// https://drafts.csswg.org/web-animations/#finish-an-animation
void
Animation::Finish(ErrorResult& aRv)
{
  double effectivePlaybackRate = CurrentOrPendingPlaybackRate();

  if (effectivePlaybackRate == 0 ||
      (effectivePlaybackRate > 0 && EffectEnd() == TimeDuration::Forever())) {
    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
    return;
  }

  AutoMutationBatchForAnimation mb(*this);

  ApplyPendingPlaybackRate();

  // Seek to the end
  TimeDuration limit =
    mPlaybackRate > 0 ? TimeDuration(EffectEnd()) : TimeDuration(0);
  bool didChange = GetCurrentTime() != Nullable<TimeDuration>(limit);
  SilentlySetCurrentTime(limit);

  // If we are paused or play-pending we need to fill in the start time in
  // order to transition to the finished state.
  //
  // We only do this, however, if we have an active timeline. If we have an
  // inactive timeline we can't transition into the finished state just like
  // we can't transition to the running state (this finished state is really
  // a substate of the running state).
  if (mStartTime.IsNull() &&
      mTimeline &&
      !mTimeline->GetCurrentTime().IsNull()) {
    mStartTime = StartTimeFromTimelineTime(
      mTimeline->GetCurrentTime().Value(), limit, mPlaybackRate);
    didChange = true;
  }

  // If we just resolved the start time for a pause or play-pending
  // animation, we need to clear the task. We don't do this as a branch of
  // the above however since we can have a play-pending animation with a
  // resolved start time if we aborted a pause operation.
  if (!mStartTime.IsNull() &&
      (mPendingState == PendingState::PlayPending ||
       mPendingState == PendingState::PausePending)) {
    if (mPendingState == PendingState::PausePending) {
      mHoldTime.SetNull();
    }
    CancelPendingTasks();
    didChange = true;
    if (mReady) {
      mReady->MaybeResolve(this);
    }
  }
  UpdateTiming(SeekFlag::DidSeek, SyncNotifyFlag::Sync);
  if (didChange && IsRelevant()) {
    nsNodeUtils::AnimationChanged(this);
  }
  PostUpdate();
}

void
Animation::Play(ErrorResult& aRv, LimitBehavior aLimitBehavior)
{
  PlayNoUpdate(aRv, aLimitBehavior);
  PostUpdate();
}

// https://drafts.csswg.org/web-animations/#reverse-an-animation
void
Animation::Reverse(ErrorResult& aRv)
{
  if (!mTimeline || mTimeline->GetCurrentTime().IsNull()) {
    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
    return;
  }

  double effectivePlaybackRate = CurrentOrPendingPlaybackRate();

  if (effectivePlaybackRate == 0.0) {
    return;
  }

  Maybe<double> originalPendingPlaybackRate = mPendingPlaybackRate;

  mPendingPlaybackRate = Some(-effectivePlaybackRate);

  Play(aRv, LimitBehavior::AutoRewind);

  // If Play() threw, restore state and don't report anything to mutation
  // observers.
  if (aRv.Failed()) {
    mPendingPlaybackRate = originalPendingPlaybackRate;
  }

  // Play(), above, unconditionally calls PostUpdate so we don't need to do
  // it here.
}

// ---------------------------------------------------------------------------
//
// JS wrappers for Animation interface:
//
// ---------------------------------------------------------------------------

Nullable<double>
Animation::GetStartTimeAsDouble() const
{
  return AnimationUtils::TimeDurationToDouble(mStartTime);
}

void
Animation::SetStartTimeAsDouble(const Nullable<double>& aStartTime)
{
  return SetStartTime(AnimationUtils::DoubleToTimeDuration(aStartTime));
}

Nullable<double>
Animation::GetCurrentTimeAsDouble() const
{
  return AnimationUtils::TimeDurationToDouble(GetCurrentTime());
}

void
Animation::SetCurrentTimeAsDouble(const Nullable<double>& aCurrentTime,
                                        ErrorResult& aRv)
{
  if (aCurrentTime.IsNull()) {
    if (!GetCurrentTime().IsNull()) {
      aRv.Throw(NS_ERROR_DOM_TYPE_ERR);
    }
    return;
  }

  return SetCurrentTime(TimeDuration::FromMilliseconds(aCurrentTime.Value()));
}

// ---------------------------------------------------------------------------

void
Animation::Tick()
{
  // Finish pending if we have a pending ready time, but only if we also
  // have an active timeline.
  if (mPendingState != PendingState::NotPending &&
      !mPendingReadyTime.IsNull() &&
      mTimeline &&
      !mTimeline->GetCurrentTime().IsNull()) {
    // Even though mPendingReadyTime is initialized using TimeStamp::Now()
    // during the *previous* tick of the refresh driver, it can still be
    // ahead of the *current* timeline time when we are using the
    // vsync timer so we need to clamp it to the timeline time.
    TimeDuration currentTime = mTimeline->GetCurrentTime().Value();
    if (currentTime < mPendingReadyTime.Value()) {
      mPendingReadyTime.SetValue(currentTime);
    }
    FinishPendingAt(mPendingReadyTime.Value());
    mPendingReadyTime.SetNull();
  }

  if (IsPossiblyOrphanedPendingAnimation()) {
    MOZ_ASSERT(mTimeline && !mTimeline->GetCurrentTime().IsNull(),
               "Orphaned pending animations should have an active timeline");
    FinishPendingAt(mTimeline->GetCurrentTime().Value());
  }

  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);

  if (!mEffect) {
    return;
  }

  // Update layers if we are newly finished.
  KeyframeEffect* keyframeEffect = mEffect->AsKeyframeEffect();
  if (keyframeEffect &&
      !keyframeEffect->Properties().IsEmpty() &&
      !mFinishedAtLastComposeStyle &&
      PlayState() == AnimationPlayState::Finished) {
    PostUpdate();
  }
}

void
Animation::TriggerOnNextTick(const Nullable<TimeDuration>& aReadyTime)
{
  // Normally we expect the play state to be pending but it's possible that,
  // due to the handling of possibly orphaned animations in Tick(), this
  // animation got started whilst still being in another document's pending
  // animation map.
  if (!Pending()) {
    return;
  }

  // If aReadyTime.IsNull() we'll detect this in Tick() where we check for
  // orphaned animations and trigger this animation anyway
  mPendingReadyTime = aReadyTime;
}

void
Animation::TriggerNow()
{
  // Normally we expect the play state to be pending but when an animation
  // is cancelled and its rendered document can't be reached, we can end up
  // with the animation still in a pending player tracker even after it is
  // no longer pending.
  if (!Pending()) {
    return;
  }

  // If we don't have an active timeline we can't trigger the animation.
  // However, this is a test-only method that we don't expect to be used in
  // conjunction with animations without an active timeline so generate
  // a warning if we do find ourselves in that situation.
  if (!mTimeline || mTimeline->GetCurrentTime().IsNull()) {
    NS_WARNING("Failed to trigger an animation with an active timeline");
    return;
  }

  FinishPendingAt(mTimeline->GetCurrentTime().Value());
}

Nullable<TimeDuration>
Animation::GetCurrentOrPendingStartTime() const
{
  Nullable<TimeDuration> result;

  // If we have a pending playback rate, work out what start time we will use
  // when we come to updating that playback rate.
  //
  // This logic roughly shadows that in ResumeAt but is just different enough
  // that it is difficult to extract out the common functionality (and
  // extracting that functionality out would make it harder to match ResumeAt up
  // against the spec).
  if (mPendingPlaybackRate && !mPendingReadyTime.IsNull() &&
      !mStartTime.IsNull()) {
    // If we have a hold time, use it as the current time to match.
    TimeDuration currentTimeToMatch =
      !mHoldTime.IsNull()
        ? mHoldTime.Value()
        : CurrentTimeFromTimelineTime(
            mPendingReadyTime.Value(), mStartTime.Value(), mPlaybackRate);

    result = StartTimeFromTimelineTime(
      mPendingReadyTime.Value(), currentTimeToMatch, *mPendingPlaybackRate);
    return result;
  }

  if (!mStartTime.IsNull()) {
    result = mStartTime;
    return result;
  }

  if (mPendingReadyTime.IsNull() || mHoldTime.IsNull()) {
    return result;
  }

  // Calculate the equivalent start time from the pending ready time.
  result = StartTimeFromTimelineTime(
    mPendingReadyTime.Value(), mHoldTime.Value(), mPlaybackRate);

  return result;
}

TimeStamp
Animation::AnimationTimeToTimeStamp(const StickyTimeDuration& aTime) const
{
  // Initializes to null. Return the same object every time to benefit from
  // return-value-optimization.
  TimeStamp result;

  // We *don't* check for mTimeline->TracksWallclockTime() here because that
  // method only tells us if the timeline times can be converted to
  // TimeStamps that can be compared to TimeStamp::Now() or not, *not*
  // whether the timelines can be converted to TimeStamp values at all.
  //
  // Furthermore, we want to be able to use this method when the refresh driver
  // is under test control (in which case TracksWallclockTime() will return
  // false).
  //
  // Once we introduce timelines that are not time-based we will need to
  // differentiate between them here and determine how to sort their events.
  if (!mTimeline) {
    return result;
  }

  // Check the time is convertible to a timestamp
  if (aTime == TimeDuration::Forever() ||
      mPlaybackRate == 0.0 ||
      mStartTime.IsNull()) {
    return result;
  }

  // Invert the standard relation:
  //   current time = (timeline time - start time) * playback rate
  TimeDuration timelineTime =
    TimeDuration(aTime).MultDouble(1.0 / mPlaybackRate) + mStartTime.Value();

  result = mTimeline->ToTimeStamp(timelineTime);
  return result;
}

TimeStamp
Animation::ElapsedTimeToTimeStamp(
  const StickyTimeDuration& aElapsedTime) const
{
  TimeDuration delay = mEffect
                       ? mEffect->SpecifiedTiming().Delay()
                       : TimeDuration();
  return AnimationTimeToTimeStamp(aElapsedTime + delay);
}

// https://drafts.csswg.org/web-animations/#silently-set-the-current-time
void
Animation::SilentlySetCurrentTime(const TimeDuration& aSeekTime)
{
  if (!mHoldTime.IsNull() ||
      mStartTime.IsNull() ||
      !mTimeline ||
      mTimeline->GetCurrentTime().IsNull() ||
      mPlaybackRate == 0.0) {
    mHoldTime.SetValue(aSeekTime);
    if (!mTimeline || mTimeline->GetCurrentTime().IsNull()) {
      mStartTime.SetNull();
    }
  } else {
    mStartTime = StartTimeFromTimelineTime(
      mTimeline->GetCurrentTime().Value(), aSeekTime, mPlaybackRate);
  }

  mPreviousCurrentTime.SetNull();
}

// https://drafts.csswg.org/web-animations/#cancel-an-animation
void
Animation::CancelNoUpdate()
{
  if (PlayState() != AnimationPlayState::Idle) {
    ResetPendingTasks();

    if (mFinished) {
      mFinished->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
    }
    ResetFinishedPromise();

    QueuePlaybackEvent(NS_LITERAL_STRING("cancel"),
                       GetTimelineCurrentTimeAsTimeStamp());
  }

  StickyTimeDuration activeTime = mEffect
                                  ? mEffect->GetComputedTiming().mActiveTime
                                  : StickyTimeDuration();

  mHoldTime.SetNull();
  mStartTime.SetNull();

  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);

  if (mTimeline) {
    mTimeline->RemoveAnimation(this);
  }
  MaybeQueueCancelEvent(activeTime);
}

bool
Animation::ShouldBeSynchronizedWithMainThread(
  nsCSSPropertyID aProperty,
  const nsIFrame* aFrame,
  AnimationPerformanceWarning::Type& aPerformanceWarning) const
{
  // Only synchronize playing animations
  if (!IsPlaying()) {
    return false;
  }

  // Currently only transform animations need to be synchronized
  if (aProperty != eCSSProperty_transform) {
    return false;
  }

  KeyframeEffect* keyframeEffect = mEffect
                                   ? mEffect->AsKeyframeEffect()
                                   : nullptr;
  if (!keyframeEffect) {
    return false;
  }

  // Are we starting at the same time as other geometric animations?
  // We check this before calling ShouldBlockAsyncTransformAnimations, partly
  // because it's cheaper, but also because it's often the most useful thing
  // to know when you're debugging performance.
  if (mSyncWithGeometricAnimations &&
      keyframeEffect->HasAnimationOfProperty(eCSSProperty_transform)) {
    aPerformanceWarning = AnimationPerformanceWarning::Type::
                          TransformWithSyncGeometricAnimations;
    return true;
  }

  return keyframeEffect->
           ShouldBlockAsyncTransformAnimations(aFrame, aPerformanceWarning);
}

void
Animation::UpdateRelevance()
{
  bool wasRelevant = mIsRelevant;
  mIsRelevant = HasCurrentEffect() || IsInEffect();

  // Notify animation observers.
  if (wasRelevant && !mIsRelevant) {
    nsNodeUtils::AnimationRemoved(this);
  } else if (!wasRelevant && mIsRelevant) {
    nsNodeUtils::AnimationAdded(this);
  }
}

bool
Animation::HasLowerCompositeOrderThan(const Animation& aOther) const
{
  // 0. Object-equality case
  if (&aOther == this) {
    return false;
  }

  // 1. CSS Transitions sort lowest
  {
    auto asCSSTransitionForSorting =
      [] (const Animation& anim) -> const CSSTransition*
      {
        const CSSTransition* transition = anim.AsCSSTransition();
        return transition && transition->IsTiedToMarkup() ?
               transition :
               nullptr;
      };
    auto thisTransition  = asCSSTransitionForSorting(*this);
    auto otherTransition = asCSSTransitionForSorting(aOther);
    if (thisTransition && otherTransition) {
      return thisTransition->HasLowerCompositeOrderThan(*otherTransition);
    }
    if (thisTransition || otherTransition) {
      // Cancelled transitions no longer have an owning element. To be strictly
      // correct we should store a strong reference to the owning element
      // so that if we arrive here while sorting cancel events, we can sort
      // them in the correct order.
      //
      // However, given that cancel events are almost always queued
      // synchronously in some deterministic manner, we can be fairly sure
      // that cancel events will be dispatched in a deterministic order
      // (which is our only hard requirement until specs say otherwise).
      // Furthermore, we only reach here when we have events with equal
      // timestamps so this is an edge case we can probably ignore for now.
      return thisTransition;
    }
  }

  // 2. CSS Animations sort next
  {
    auto asCSSAnimationForSorting =
      [] (const Animation& anim) -> const CSSAnimation*
      {
        const CSSAnimation* animation = anim.AsCSSAnimation();
        return animation && animation->IsTiedToMarkup() ? animation : nullptr;
      };
    auto thisAnimation  = asCSSAnimationForSorting(*this);
    auto otherAnimation = asCSSAnimationForSorting(aOther);
    if (thisAnimation && otherAnimation) {
      return thisAnimation->HasLowerCompositeOrderThan(*otherAnimation);
    }
    if (thisAnimation || otherAnimation) {
      return thisAnimation;
    }
  }

  // Subclasses of Animation repurpose mAnimationIndex to implement their
  // own brand of composite ordering. However, by this point we should have
  // handled any such custom composite ordering so we should now have unique
  // animation indices.
  MOZ_ASSERT(mAnimationIndex != aOther.mAnimationIndex,
             "Animation indices should be unique");

  // 3. Finally, generic animations sort by their position in the global
  // animation array.
  return mAnimationIndex < aOther.mAnimationIndex;
}

void
Animation::WillComposeStyle()
{
  mFinishedAtLastComposeStyle = (PlayState() == AnimationPlayState::Finished);

  MOZ_ASSERT(mEffect);

  KeyframeEffect* keyframeEffect = mEffect->AsKeyframeEffect();
  if (keyframeEffect) {
    keyframeEffect->WillComposeStyle();
  }
}

void
Animation::ComposeStyle(RawServoAnimationValueMap& aComposeResult,
                        const nsCSSPropertyIDSet& aPropertiesToSkip)
{
  if (!mEffect) {
    return;
  }

  // In order to prevent flicker, there are a few cases where we want to use
  // a different time for rendering that would otherwise be returned by
  // GetCurrentTime. These are:
  //
  // (a) For animations that are pausing but which are still running on the
  //     compositor. In this case we send a layer transaction that removes the
  //     animation but which also contains the animation values calculated on
  //     the main thread. To prevent flicker when this occurs we want to ensure
  //     the timeline time used to calculate the main thread animation values
  //     does not lag far behind the time used on the compositor. Ideally we
  //     would like to use the "animation ready time" calculated at the end of
  //     the layer transaction as the timeline time but it will be too late to
  //     update the style rule at that point so instead we just use the current
  //     wallclock time.
  //
  // (b) For animations that are pausing that we have already taken off the
  //     compositor. In this case we record a pending ready time but we don't
  //     apply it until the next tick. However, while waiting for the next tick,
  //     we should still use the pending ready time as the timeline time. If we
  //     use the regular timeline time the animation may appear jump backwards
  //     if the main thread's timeline time lags behind the compositor.
  //
  // (c) For animations that are play-pending due to an aborted pause operation
  //     (i.e. a pause operation that was interrupted before we entered the
  //     paused state). When we cancel a pending pause we might momentarily take
  //     the animation off the compositor, only to re-add it moments later. In
  //     that case the compositor might have been ahead of the main thread so we
  //     should use the current wallclock time to ensure the animation doesn't
  //     temporarily jump backwards.
  //
  // To address each of these cases we temporarily tweak the hold time
  // immediately before updating the style rule and then restore it immediately
  // afterwards. This is purely to prevent visual flicker. Other behavior
  // such as dispatching events continues to rely on the regular timeline time.
  bool pending = Pending();
  {
    AutoRestore<Nullable<TimeDuration>> restoreHoldTime(mHoldTime);

    if (pending && mHoldTime.IsNull() && !mStartTime.IsNull()) {
      Nullable<TimeDuration> timeToUse = mPendingReadyTime;
      if (timeToUse.IsNull() &&
          mTimeline &&
          mTimeline->TracksWallclockTime()) {
        timeToUse = mTimeline->ToTimelineTime(TimeStamp::Now());
      }
      if (!timeToUse.IsNull()) {
        mHoldTime = CurrentTimeFromTimelineTime(
          timeToUse.Value(), mStartTime.Value(), mPlaybackRate);
      }
    }

    KeyframeEffect* keyframeEffect = mEffect->AsKeyframeEffect();
    if (keyframeEffect) {
      keyframeEffect->ComposeStyle(aComposeResult, aPropertiesToSkip);
    }
  }

  MOZ_ASSERT(pending == Pending(),
             "Pending state should not change during the course of compositing");
}

void
Animation::NotifyEffectTimingUpdated()
{
  MOZ_ASSERT(mEffect,
             "We should only update timing effect when we have a target "
             "effect");
  UpdateTiming(Animation::SeekFlag::NoSeek,
               Animation::SyncNotifyFlag::Async);
}

void
Animation::NotifyGeometricAnimationsStartingThisFrame()
{
  if (!IsNewlyStarted() || !mEffect) {
    return;
  }

  mSyncWithGeometricAnimations = true;
}

// https://drafts.csswg.org/web-animations/#play-an-animation
void
Animation::PlayNoUpdate(ErrorResult& aRv, LimitBehavior aLimitBehavior)
{
  AutoMutationBatchForAnimation mb(*this);

  bool abortedPause = mPendingState == PendingState::PausePending;

  double effectivePlaybackRate = CurrentOrPendingPlaybackRate();

  Nullable<TimeDuration> currentTime = GetCurrentTime();
  if (effectivePlaybackRate > 0.0 &&
      (currentTime.IsNull() ||
       (aLimitBehavior == LimitBehavior::AutoRewind &&
        (currentTime.Value() < TimeDuration() ||
         currentTime.Value() >= EffectEnd())))) {
    mHoldTime.SetValue(TimeDuration(0));
  } else if (effectivePlaybackRate < 0.0 &&
             (currentTime.IsNull() ||
              (aLimitBehavior == LimitBehavior::AutoRewind &&
               (currentTime.Value() <= TimeDuration() ||
                currentTime.Value() > EffectEnd())))) {
    if (EffectEnd() == TimeDuration::Forever()) {
      aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
      return;
    }
    mHoldTime.SetValue(TimeDuration(EffectEnd()));
  } else if (effectivePlaybackRate == 0.0 && currentTime.IsNull()) {
    mHoldTime.SetValue(TimeDuration(0));
  }

  bool reuseReadyPromise = false;
  if (mPendingState != PendingState::NotPending) {
    CancelPendingTasks();
    reuseReadyPromise = true;
  }

  // If the hold time is null then we're already playing normally and,
  // typically, we can bail out here.
  //
  // However, there are two cases where we can't do that:
  //
  // (a) If we just aborted a pause. In this case, for consistency, we need to
  //     go through the motions of doing an asynchronous start.
  //
  // (b) If we have timing changes (specifically a change to the playbackRate)
  //     that should be applied asynchronously.
  //
  if (mHoldTime.IsNull() && !abortedPause && !mPendingPlaybackRate) {
    return;
  }

  // Clear the start time until we resolve a new one. We do this except
  // for the case where we are aborting a pause and don't have a hold time.
  //
  // If we're aborting a pause and *do* have a hold time (e.g. because
  // the animation is finished or we just applied the auto-rewind behavior
  // above) we should respect it by clearing the start time. If we *don't*
  // have a hold time we should keep the current start time so that the
  // the animation continues moving uninterrupted by the aborted pause.
  //
  // (If we're not aborting a pause, mHoldTime must be resolved by now
  //  or else we would have returned above.)
  if (!mHoldTime.IsNull()) {
    mStartTime.SetNull();
  }

  if (!reuseReadyPromise) {
    // Clear ready promise. We'll create a new one lazily.
    mReady = nullptr;
  }

  mPendingState = PendingState::PlayPending;

  // Clear flag that causes us to sync transform animations with the main
  // thread for now. We'll set this when we go to set up compositor
  // animations if it applies.
  mSyncWithGeometricAnimations = false;

  nsIDocument* doc = GetRenderedDocument();
  if (doc) {
    PendingAnimationTracker* tracker =
      doc->GetOrCreatePendingAnimationTracker();
    tracker->AddPlayPending(*this);
  } else {
    TriggerOnNextTick(Nullable<TimeDuration>());
  }

  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
  if (IsRelevant()) {
    nsNodeUtils::AnimationChanged(this);
  }
}

// https://drafts.csswg.org/web-animations/#pause-an-animation
void
Animation::Pause(ErrorResult& aRv)
{
  if (IsPausedOrPausing()) {
    return;
  }

  AutoMutationBatchForAnimation mb(*this);

  // If we are transitioning from idle, fill in the current time
  if (GetCurrentTime().IsNull()) {
    if (mPlaybackRate >= 0.0) {
      mHoldTime.SetValue(TimeDuration(0));
    } else {
      if (EffectEnd() == TimeDuration::Forever()) {
        aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
        return;
      }
      mHoldTime.SetValue(TimeDuration(EffectEnd()));
    }
  }

  bool reuseReadyPromise = false;
  if (mPendingState == PendingState::PlayPending) {
    CancelPendingTasks();
    reuseReadyPromise = true;
  }

  if (!reuseReadyPromise) {
    // Clear ready promise. We'll create a new one lazily.
    mReady = nullptr;
  }

  mPendingState = PendingState::PausePending;

  nsIDocument* doc = GetRenderedDocument();
  if (doc) {
    PendingAnimationTracker* tracker =
      doc->GetOrCreatePendingAnimationTracker();
    tracker->AddPausePending(*this);
  } else {
    TriggerOnNextTick(Nullable<TimeDuration>());
  }

  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
  if (IsRelevant()) {
    nsNodeUtils::AnimationChanged(this);
  }

  PostUpdate();
}

// https://drafts.csswg.org/web-animations/#play-an-animation
void
Animation::ResumeAt(const TimeDuration& aReadyTime)
{
  // This method is only expected to be called for an animation that is
  // waiting to play. We can easily adapt it to handle other states
  // but it's currently not necessary.
  MOZ_ASSERT(mPendingState == PendingState::PlayPending,
             "Expected to resume a play-pending animation");
  MOZ_ASSERT(!mHoldTime.IsNull() || !mStartTime.IsNull(),
             "An animation in the play-pending state should have either a"
             " resolved hold time or resolved start time");

  AutoMutationBatchForAnimation mb(*this);
  bool hadPendingPlaybackRate = mPendingPlaybackRate.isSome();

  if (!mHoldTime.IsNull()) {
    // The hold time is set, so we don't need any special handling to preserve
    // the current time.
    ApplyPendingPlaybackRate();
    mStartTime =
      StartTimeFromTimelineTime(aReadyTime, mHoldTime.Value(), mPlaybackRate);
    if (mPlaybackRate != 0) {
      mHoldTime.SetNull();
    }
  } else if (!mStartTime.IsNull() && mPendingPlaybackRate) {
    // Apply any pending playback rate, preserving the current time.
    TimeDuration currentTimeToMatch = CurrentTimeFromTimelineTime(
      aReadyTime, mStartTime.Value(), mPlaybackRate);
    ApplyPendingPlaybackRate();
    mStartTime =
      StartTimeFromTimelineTime(aReadyTime, currentTimeToMatch, mPlaybackRate);
    if (mPlaybackRate == 0) {
      mHoldTime.SetValue(currentTimeToMatch);
    }
  }

  mPendingState = PendingState::NotPending;

  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);

  // If we had a pending playback rate, we will have now applied it so we need
  // to notify observers.
  if (hadPendingPlaybackRate && IsRelevant()) {
    nsNodeUtils::AnimationChanged(this);
  }

  if (mReady) {
    mReady->MaybeResolve(this);
  }
}

void
Animation::PauseAt(const TimeDuration& aReadyTime)
{
  MOZ_ASSERT(mPendingState == PendingState::PausePending,
             "Expected to pause a pause-pending animation");

  if (!mStartTime.IsNull() && mHoldTime.IsNull()) {
    mHoldTime = CurrentTimeFromTimelineTime(
      aReadyTime, mStartTime.Value(), mPlaybackRate);
  }
  ApplyPendingPlaybackRate();
  mStartTime.SetNull();
  mPendingState = PendingState::NotPending;

  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);

  if (mReady) {
    mReady->MaybeResolve(this);
  }
}

void
Animation::UpdateTiming(SeekFlag aSeekFlag, SyncNotifyFlag aSyncNotifyFlag)
{
  // We call UpdateFinishedState before UpdateEffect because the former
  // can change the current time, which is used by the latter.
  UpdateFinishedState(aSeekFlag, aSyncNotifyFlag);
  UpdateEffect();

  if (mTimeline) {
    mTimeline->NotifyAnimationUpdated(*this);
  }
}

// https://drafts.csswg.org/web-animations/#update-an-animations-finished-state
void
Animation::UpdateFinishedState(SeekFlag aSeekFlag,
                               SyncNotifyFlag aSyncNotifyFlag)
{
  Nullable<TimeDuration> currentTime = GetCurrentTime();
  TimeDuration effectEnd = TimeDuration(EffectEnd());

  if (!mStartTime.IsNull() &&
      mPendingState == PendingState::NotPending) {
    if (mPlaybackRate > 0.0 &&
        !currentTime.IsNull() &&
        currentTime.Value() >= effectEnd) {
      if (aSeekFlag == SeekFlag::DidSeek) {
        mHoldTime = currentTime;
      } else if (!mPreviousCurrentTime.IsNull()) {
        mHoldTime.SetValue(std::max(mPreviousCurrentTime.Value(), effectEnd));
      } else {
        mHoldTime.SetValue(effectEnd);
      }
    } else if (mPlaybackRate < 0.0 &&
               !currentTime.IsNull() &&
               currentTime.Value() <= TimeDuration()) {
      if (aSeekFlag == SeekFlag::DidSeek) {
        mHoldTime = currentTime;
      } else if (!mPreviousCurrentTime.IsNull()) {
        mHoldTime.SetValue(std::min(mPreviousCurrentTime.Value(),
                                    TimeDuration(0)));
      } else {
        mHoldTime.SetValue(0);
      }
    } else if (mPlaybackRate != 0.0 &&
               !currentTime.IsNull() &&
               mTimeline &&
               !mTimeline->GetCurrentTime().IsNull()) {
      if (aSeekFlag == SeekFlag::DidSeek && !mHoldTime.IsNull()) {
        mStartTime =
          StartTimeFromTimelineTime(mTimeline->GetCurrentTime().Value(),
                                    mHoldTime.Value(),
                                    mPlaybackRate);
      }
      mHoldTime.SetNull();
    }
  }

  bool currentFinishedState = PlayState() == AnimationPlayState::Finished;
  if (currentFinishedState && !mFinishedIsResolved) {
    DoFinishNotification(aSyncNotifyFlag);
  } else if (!currentFinishedState && mFinishedIsResolved) {
    ResetFinishedPromise();
  }
  // We must recalculate the current time to take account of any mHoldTime
  // changes the code above made.
  mPreviousCurrentTime = GetCurrentTime();
}

void
Animation::UpdateEffect()
{
  if (mEffect) {
    UpdateRelevance();

    KeyframeEffect* keyframeEffect = mEffect->AsKeyframeEffect();
    if (keyframeEffect) {
      keyframeEffect->NotifyAnimationTimingUpdated();
    }
  }
}

void
Animation::FlushUnanimatedStyle() const
{
  nsIDocument* doc = GetRenderedDocument();
  if (doc) {
    doc->FlushPendingNotifications(
      ChangesToFlush(FlushType::Style, false /* flush animations */));
  }
}

void
Animation::PostUpdate()
{
  if (!mEffect) {
    return;
  }

  KeyframeEffect* keyframeEffect = mEffect->AsKeyframeEffect();
  if (!keyframeEffect) {
    return;
  }
  keyframeEffect->RequestRestyle(EffectCompositor::RestyleType::Layer);
}

void
Animation::CancelPendingTasks()
{
  if (mPendingState == PendingState::NotPending) {
    return;
  }

  nsIDocument* doc = GetRenderedDocument();
  if (doc) {
    PendingAnimationTracker* tracker = doc->GetPendingAnimationTracker();
    if (tracker) {
      if (mPendingState == PendingState::PlayPending) {
        tracker->RemovePlayPending(*this);
      } else {
        tracker->RemovePausePending(*this);
      }
    }
  }

  mPendingState = PendingState::NotPending;
  mPendingReadyTime.SetNull();
}

// https://drafts.csswg.org/web-animations/#reset-an-animations-pending-tasks
void
Animation::ResetPendingTasks()
{
  if (mPendingState == PendingState::NotPending) {
    return;
  }

  CancelPendingTasks();
  ApplyPendingPlaybackRate();

  if (mReady) {
    mReady->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
    mReady = nullptr;
  }
}

void
Animation::ReschedulePendingTasks()
{
  if (mPendingState == PendingState::NotPending) {
    return;
  }

  mPendingReadyTime.SetNull();

  nsIDocument* doc = GetRenderedDocument();
  if (doc) {
    PendingAnimationTracker* tracker =
      doc->GetOrCreatePendingAnimationTracker();
    if (mPendingState == PendingState::PlayPending &&
        !tracker->IsWaitingToPlay(*this)) {
      tracker->AddPlayPending(*this);
    } else if (mPendingState == PendingState::PausePending &&
               !tracker->IsWaitingToPause(*this)) {
      tracker->AddPausePending(*this);
    }
  }
}

bool
Animation::IsPossiblyOrphanedPendingAnimation() const
{
  // Check if we are pending but might never start because we are not being
  // tracked.
  //
  // This covers the following cases:
  //
  // * We started playing but our effect's target element was orphaned
  //   or bound to a different document.
  //   (note that for the case of our effect changing we should handle
  //   that in SetEffect)
  // * We started playing but our timeline became inactive.
  //   In this case the pending animation tracker will drop us from its hashmap
  //   when we have been painted.
  // * When we started playing we couldn't find a PendingAnimationTracker to
  //   register with (perhaps the effect had no document) so we simply
  //   set mPendingState in PlayNoUpdate and relied on this method to catch us
  //   on the next tick.

  // If we're not pending we're ok.
  if (mPendingState == PendingState::NotPending) {
    return false;
  }

  // If we have a pending ready time then we will be started on the next
  // tick.
  if (!mPendingReadyTime.IsNull()) {
    return false;
  }

  // If we don't have an active timeline then we shouldn't start until
  // we do.
  if (!mTimeline || mTimeline->GetCurrentTime().IsNull()) {
    return false;
  }

  // If we have no rendered document, or we're not in our rendered document's
  // PendingAnimationTracker then there's a good chance no one is tracking us.
  //
  // If we're wrong and another document is tracking us then, at worst, we'll
  // simply start/pause the animation one tick too soon. That's better than
  // never starting/pausing the animation and is unlikely.
  nsIDocument* doc = GetRenderedDocument();
  if (!doc) {
    return true;
  }

  PendingAnimationTracker* tracker = doc->GetPendingAnimationTracker();
  return !tracker ||
         (!tracker->IsWaitingToPlay(*this) &&
          !tracker->IsWaitingToPause(*this));
}

StickyTimeDuration
Animation::EffectEnd() const
{
  if (!mEffect) {
    return StickyTimeDuration(0);
  }

  return mEffect->SpecifiedTiming().EndTime();
}

nsIDocument*
Animation::GetRenderedDocument() const
{
  if (!mEffect || !mEffect->AsKeyframeEffect()) {
    return nullptr;
  }

  return mEffect->AsKeyframeEffect()->GetRenderedDocument();
}

nsIDocument*
Animation::GetTimelineDocument() const
{
  return mTimeline ? mTimeline->GetDocument() : nullptr;
}

class AsyncFinishNotification : public MicroTaskRunnable
{
public:
  explicit AsyncFinishNotification(Animation* aAnimation)
  : MicroTaskRunnable()
  , mAnimation(aAnimation)
  {}

  virtual void Run(AutoSlowOperation& aAso) override
  {
    mAnimation->DoFinishNotificationImmediately(this);
    mAnimation = nullptr;
  }

  virtual bool Suppressed() override
  {
    nsIGlobalObject* global = mAnimation->GetOwnerGlobal();
    return global && global->IsInSyncOperation();
  }

private:
  RefPtr<Animation> mAnimation;
};

void
Animation::DoFinishNotification(SyncNotifyFlag aSyncNotifyFlag)
{
  CycleCollectedJSContext* context = CycleCollectedJSContext::Get();

  if (aSyncNotifyFlag == SyncNotifyFlag::Sync) {
    DoFinishNotificationImmediately();
  } else if (!mFinishNotificationTask) {
    RefPtr<MicroTaskRunnable> runnable = new AsyncFinishNotification(this);
    context->DispatchToMicroTask(do_AddRef(runnable));
    mFinishNotificationTask = runnable.forget();
  }
}

void
Animation::ResetFinishedPromise()
{
  mFinishedIsResolved = false;
  mFinished = nullptr;
}

void
Animation::MaybeResolveFinishedPromise()
{
  if (mFinished) {
    mFinished->MaybeResolve(this);
  }
  mFinishedIsResolved = true;
}

void
Animation::DoFinishNotificationImmediately(MicroTaskRunnable* aAsync)
{
  if (aAsync && aAsync != mFinishNotificationTask) {
    return;
  }

  mFinishNotificationTask = nullptr;

  if (PlayState() != AnimationPlayState::Finished) {
    return;
  }

  MaybeResolveFinishedPromise();

  QueuePlaybackEvent(NS_LITERAL_STRING("finish"),
                     AnimationTimeToTimeStamp(EffectEnd()));
}

void
Animation::QueuePlaybackEvent(const nsAString& aName,
                              TimeStamp&& aScheduledEventTime)
{
  // Use document for timing.
  // https://drafts.csswg.org/web-animations-1/#document-for-timing
  nsIDocument* doc = GetTimelineDocument();
  if (!doc) {
    return;
  }

  nsPresContext* presContext = doc->GetPresContext();
  if (!presContext) {
    return;
  }

  AnimationPlaybackEventInit init;

  if (aName.EqualsLiteral("finish")) {
    init.mCurrentTime = GetCurrentTimeAsDouble();
  }
  if (mTimeline) {
    init.mTimelineTime = mTimeline->GetCurrentTimeAsDouble();
  }

  RefPtr<AnimationPlaybackEvent> event =
    AnimationPlaybackEvent::Constructor(this, aName, init);
  event->SetTrusted(true);

  presContext->AnimationEventDispatcher()->
    QueueEvent(AnimationEventInfo(aName,
                                  std::move(event),
                                  std::move(aScheduledEventTime),
                                  this));
}

bool
Animation::IsRunningOnCompositor() const
{
  return mEffect &&
         mEffect->AsKeyframeEffect() &&
         mEffect->AsKeyframeEffect()->IsRunningOnCompositor();
}


} // namespace dom
} // namespace mozilla