nsIStyleRule*
nsAnimationManager::CheckAnimationRule(nsStyleContext* aStyleContext,
                                       mozilla::dom::Element* aElement)
{
  if (!mPresContext->IsDynamic()) {
    // For print or print preview, ignore animations.
    return nullptr;
  }

  // Everything that causes our animation data to change triggers a
  // style change, which in turn triggers a non-animation restyle.
  // Likewise, when we initially construct frames, we're not in a
  // style change, but also not in an animation restyle.

  const nsStyleDisplay* disp = aStyleContext->StyleDisplay();
  AnimationCollection* collection =
    GetAnimations(aElement, aStyleContext->GetPseudoType(), false);
  if (!collection &&
      disp->mAnimationNameCount == 1 &&
      disp->mAnimations[0].GetName().IsEmpty()) {
    return nullptr;
  }

  nsAutoAnimationMutationBatch mb(aElement);

  // build the animations list
  dom::DocumentTimeline* timeline = aElement->OwnerDoc()->Timeline();
  AnimationPtrArray newAnimations;
  if (!aStyleContext->IsInDisplayNoneSubtree()) {
    BuildAnimations(aStyleContext, aElement, timeline, newAnimations);
  }

  if (newAnimations.IsEmpty()) {
    if (collection) {
      // There might be transitions that run now that animations don't
      // override them.
      mPresContext->TransitionManager()->
        UpdateCascadeResultsWithAnimationsToBeDestroyed(collection);

      collection->Destroy();
    }
    return nullptr;
  }

  if (collection) {
    collection->mStyleRule = nullptr;
    collection->mStyleRuleRefreshTime = TimeStamp();
    collection->UpdateAnimationGeneration(mPresContext);

    // Copy over the start times and (if still paused) pause starts
    // for each animation (matching on name only) that was also in the
    // old list of animations.
    // This means that we honor dynamic changes, which isn't what the
    // spec says to do, but WebKit seems to honor at least some of
    // them.  See
    // http://lists.w3.org/Archives/Public/www-style/2011Apr/0079.html
    // In order to honor what the spec said, we'd copy more data over
    // (or potentially optimize BuildAnimations to avoid rebuilding it
    // in the first place).
    if (!collection->mAnimations.IsEmpty()) {

      for (size_t newIdx = newAnimations.Length(); newIdx-- != 0;) {
        Animation* newAnim = newAnimations[newIdx];

        // Find the matching animation with this name in the old list
        // of animations.  We iterate through both lists in a backwards
        // direction which means that if there are more animations in
        // the new list of animations with a given name than in the old
        // list, it will be the animations towards the of the beginning of
        // the list that do not match and are treated as new animations.
        nsRefPtr<CSSAnimation> oldAnim;
        size_t oldIdx = collection->mAnimations.Length();
        while (oldIdx-- != 0) {
          CSSAnimation* a = collection->mAnimations[oldIdx]->AsCSSAnimation();
          MOZ_ASSERT(a, "All animations in the CSS Animation collection should"
                        " be CSSAnimation objects");
          if (a->Name() == newAnim->Name()) {
            oldAnim = a;
            break;
          }
        }
        if (!oldAnim) {
          continue;
        }

        bool animationChanged = false;

        // Update the old from the new so we can keep the original object
        // identity (and any expando properties attached to it).
        if (oldAnim->GetEffect() && newAnim->GetEffect()) {
          KeyframeEffectReadOnly* oldEffect = oldAnim->GetEffect();
          KeyframeEffectReadOnly* newEffect = newAnim->GetEffect();
          animationChanged =
            oldEffect->Timing() != newEffect->Timing() ||
            oldEffect->Properties() != newEffect->Properties();
          oldEffect->Timing() = newEffect->Timing();
          oldEffect->Properties() = newEffect->Properties();
        }

        // Reset compositor state so animation will be re-synchronized.
        oldAnim->ClearIsRunningOnCompositor();

        // Handle changes in play state. If the animation is idle, however,
        // changes to animation-play-state should *not* restart it.
        if (oldAnim->PlayState() != AnimationPlayState::Idle) {
          // CSSAnimation takes care of override behavior so that,
          // for example, if the author has called pause(), that will
          // override the animation-play-state.
          // (We should check newAnim->IsStylePaused() but that requires
          //  downcasting to CSSAnimation and we happen to know that
          //  newAnim will only ever be paused by calling PauseFromStyle
          //  making IsPausedOrPausing synonymous in this case.)
          if (!oldAnim->IsStylePaused() && newAnim->IsPausedOrPausing()) {
            oldAnim->PauseFromStyle();
            animationChanged = true;
          } else if (oldAnim->IsStylePaused() &&
                    !newAnim->IsPausedOrPausing()) {
            oldAnim->PlayFromStyle();
            animationChanged = true;
          }
        }

        if (animationChanged) {
          nsNodeUtils::AnimationChanged(oldAnim);
        }

        // Replace new animation with the (updated) old one and remove the
        // old one from the array so we don't try to match it any more.
        //
        // Although we're doing this while iterating this is safe because
        // we're not changing the length of newAnimations and we've finished
        // iterating over the list of old iterations.
        newAnim->CancelFromStyle();
        newAnim = nullptr;
        newAnimations.ReplaceElementAt(newIdx, oldAnim);
        collection->mAnimations.RemoveElementAt(oldIdx);

        // We've touched the old animation's timing properties, so this
        // could update the old animation's relevance.
        oldAnim->UpdateRelevance();
      }
    }
  } else {
    collection =
      GetAnimations(aElement, aStyleContext->GetPseudoType(), true);
  }
  collection->mAnimations.SwapElements(newAnimations);
  collection->mNeedsRefreshes = true;
  collection->Tick();

  // Cancel removed animations
  for (size_t newAnimIdx = newAnimations.Length(); newAnimIdx-- != 0; ) {
    newAnimations[newAnimIdx]->CancelFromStyle();
  }

  UpdateCascadeResults(aStyleContext, collection);

  TimeStamp refreshTime = mPresContext->RefreshDriver()->MostRecentRefresh();
  UpdateStyleAndEvents(collection, refreshTime,
                       EnsureStyleRule_IsNotThrottled);
  // We don't actually dispatch the mPendingEvents now.  We'll either
  // dispatch them the next time we get a refresh driver notification
  // or the next time somebody calls
  // nsPresShell::FlushPendingNotifications.
  if (!mPendingEvents.IsEmpty()) {
    mPresContext->Document()->SetNeedStyleFlush();
  }

  return GetAnimationRule(aElement, aStyleContext->GetPseudoType());
}
nsIStyleRule*
nsAnimationManager::CheckAnimationRule(nsStyleContext* aStyleContext,
                                       mozilla::dom::Element* aElement)
{
  // Ignore animations for print or print preview, and for elements
  // that are not attached to the document tree.
  if (!mPresContext->IsDynamic() || !aElement->IsInComposedDoc()) {
    return nullptr;
  }

  // Everything that causes our animation data to change triggers a
  // style change, which in turn triggers a non-animation restyle.
  // Likewise, when we initially construct frames, we're not in a
  // style change, but also not in an animation restyle.

  const nsStyleDisplay* disp = aStyleContext->StyleDisplay();
  AnimationCollection* collection =
    GetAnimationCollection(aElement,
                           aStyleContext->GetPseudoType(),
                           false /* aCreateIfNeeded */);
  if (!collection &&
      disp->mAnimationNameCount == 1 &&
      disp->mAnimations[0].GetName().IsEmpty()) {
    return nullptr;
  }

  nsAutoAnimationMutationBatch mb(aElement->OwnerDoc());

  // build the animations list
  dom::DocumentTimeline* timeline = aElement->OwnerDoc()->Timeline();
  AnimationPtrArray newAnimations;
  if (!aStyleContext->IsInDisplayNoneSubtree()) {
    BuildAnimations(aStyleContext, aElement, timeline, newAnimations);
  }

  if (newAnimations.IsEmpty()) {
    if (collection) {
      collection->Destroy();
    }
    return nullptr;
  }

  if (collection) {
    collection->mStyleRuleRefreshTime = TimeStamp();
    EffectSet* effectSet =
      EffectSet::GetEffectSet(aElement, aStyleContext->GetPseudoType());
    if (effectSet) {
      effectSet->UpdateAnimationGeneration(mPresContext);
    }

    // Copy over the start times and (if still paused) pause starts
    // for each animation (matching on name only) that was also in the
    // old list of animations.
    // This means that we honor dynamic changes, which isn't what the
    // spec says to do, but WebKit seems to honor at least some of
    // them.  See
    // http://lists.w3.org/Archives/Public/www-style/2011Apr/0079.html
    // In order to honor what the spec said, we'd copy more data over
    // (or potentially optimize BuildAnimations to avoid rebuilding it
    // in the first place).
    if (!collection->mAnimations.IsEmpty()) {

      for (size_t newIdx = newAnimations.Length(); newIdx-- != 0;) {
        Animation* newAnim = newAnimations[newIdx];

        // Find the matching animation with this name in the old list
        // of animations.  We iterate through both lists in a backwards
        // direction which means that if there are more animations in
        // the new list of animations with a given name than in the old
        // list, it will be the animations towards the of the beginning of
        // the list that do not match and are treated as new animations.
        RefPtr<CSSAnimation> oldAnim;
        size_t oldIdx = collection->mAnimations.Length();
        while (oldIdx-- != 0) {
          CSSAnimation* a = collection->mAnimations[oldIdx]->AsCSSAnimation();
          MOZ_ASSERT(a, "All animations in the CSS Animation collection should"
                        " be CSSAnimation objects");
          if (a->AnimationName() ==
              newAnim->AsCSSAnimation()->AnimationName()) {
            oldAnim = a;
            break;
          }
        }
        if (!oldAnim) {
          // FIXME: Bug 1134163 - We shouldn't queue animationstart events
          // until the animation is actually ready to run. However, we
          // currently have some tests that assume that these events are
          // dispatched within the same tick as the animation is added
          // so we need to queue up any animationstart events from newly-created
          // animations.
          newAnim->AsCSSAnimation()->QueueEvents();
          continue;
        }

        bool animationChanged = false;

        // Update the old from the new so we can keep the original object
        // identity (and any expando properties attached to it).
        if (oldAnim->GetEffect() && newAnim->GetEffect()) {
          KeyframeEffectReadOnly* oldEffect = oldAnim->GetEffect();
          KeyframeEffectReadOnly* newEffect = newAnim->GetEffect();
          animationChanged =
            oldEffect->Timing() != newEffect->Timing() ||
            oldEffect->Properties() != newEffect->Properties();
          oldEffect->SetTiming(newEffect->Timing());

          // To preserve the mIsRunningOnCompositor value on each property,
          // we copy it from the old effect to the new effect since, in the
          // following step, we will completely clobber the properties on the
          // old effect with the values on the new effect.
          CopyIsRunningOnCompositor(*oldEffect, *newEffect);
          oldEffect->Properties() = newEffect->Properties();
        }

        // Handle changes in play state. If the animation is idle, however,
        // changes to animation-play-state should *not* restart it.
        if (oldAnim->PlayState() != AnimationPlayState::Idle) {
          // CSSAnimation takes care of override behavior so that,
          // for example, if the author has called pause(), that will
          // override the animation-play-state.
          // (We should check newAnim->IsStylePaused() but that requires
          //  downcasting to CSSAnimation and we happen to know that
          //  newAnim will only ever be paused by calling PauseFromStyle
          //  making IsPausedOrPausing synonymous in this case.)
          if (!oldAnim->IsStylePaused() && newAnim->IsPausedOrPausing()) {
            oldAnim->PauseFromStyle();
            animationChanged = true;
          } else if (oldAnim->IsStylePaused() &&
                    !newAnim->IsPausedOrPausing()) {
            oldAnim->PlayFromStyle();
            animationChanged = true;
          }
        }

        oldAnim->CopyAnimationIndex(*newAnim->AsCSSAnimation());

        // Updating the effect timing above might already have caused the
        // animation to become irrelevant so only add a changed record if
        // the animation is still relevant.
        if (animationChanged && oldAnim->IsRelevant()) {
          nsNodeUtils::AnimationChanged(oldAnim);
        }

        // Replace new animation with the (updated) old one and remove the
        // old one from the array so we don't try to match it any more.
        //
        // Although we're doing this while iterating this is safe because
        // we're not changing the length of newAnimations and we've finished
        // iterating over the list of old iterations.
        newAnim->CancelFromStyle();
        newAnim = nullptr;
        newAnimations.ReplaceElementAt(newIdx, oldAnim);
        collection->mAnimations.RemoveElementAt(oldIdx);
      }
    }
  } else {
    collection = GetAnimationCollection(aElement,
                                        aStyleContext->GetPseudoType(),
                                        true /* aCreateIfNeeded */);
    for (Animation* animation : newAnimations) {
      // FIXME: Bug 1134163 - As above, we have shouldn't actually need to
      // queue events here. (But we do for now since some tests expect
      // animationstart events to be dispatched immediately.)
      animation->AsCSSAnimation()->QueueEvents();
    }
  }
  collection->mAnimations.SwapElements(newAnimations);
  collection->mStyleChanging = true;

  // Cancel removed animations
  for (size_t newAnimIdx = newAnimations.Length(); newAnimIdx-- != 0; ) {
    newAnimations[newAnimIdx]->CancelFromStyle();
  }

  EffectCompositor::UpdateCascadeResults(aElement,
                                         aStyleContext->GetPseudoType(),
                                         aStyleContext);

  TimeStamp refreshTime = mPresContext->RefreshDriver()->MostRecentRefresh();
  collection->EnsureStyleRuleFor(refreshTime);
  // We don't actually dispatch the pending events now.  We'll either
  // dispatch them the next time we get a refresh driver notification
  // or the next time somebody calls
  // nsPresShell::FlushPendingNotifications.
  if (mEventDispatcher.HasQueuedEvents()) {
    mPresContext->Document()->SetNeedStyleFlush();
  }

  return GetAnimationRule(aElement, aStyleContext->GetPseudoType());
}