nsIStyleRule*
nsAnimationManager::CheckAnimationRule(nsStyleContext* aStyleContext,
                                       mozilla::dom::Element* aElement)
{
  if (!mPresContext->IsProcessingAnimationStyleChange()) {
    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();
    ElementAnimations *ea =
      GetElementAnimations(aElement, aStyleContext->GetPseudoType(), false);
    if (!ea &&
        disp->mAnimationNameCount == 1 &&
        disp->mAnimations[0].GetName().IsEmpty()) {
      return nullptr;
    }

    // build the animations list
    InfallibleTArray<ElementAnimation> newAnimations;
    BuildAnimations(aStyleContext, newAnimations);

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

    TimeStamp refreshTime = mPresContext->RefreshDriver()->MostRecentRefresh();

    if (ea) {
      ea->mStyleRule = nullptr;
      ea->mStyleRuleRefreshTime = TimeStamp();
      ea->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 (!ea->mAnimations.IsEmpty()) {
        for (uint32_t newIdx = 0, newEnd = newAnimations.Length();
             newIdx != newEnd; ++newIdx) {
          ElementAnimation *newAnim = &newAnimations[newIdx];

          // Find the matching animation with this name in the old list
          // of animations.  Because of this code, they must all have
          // the same start time, though they might differ in pause
          // state.  So if a page uses multiple copies of the same
          // animation in one element's animation list, and gives them
          // different pause states, they, well, get what they deserve.
          // We'll use the last one since it's more likely to be the one
          // doing something.
          const ElementAnimation *oldAnim = nullptr;
          for (uint32_t oldIdx = ea->mAnimations.Length(); oldIdx-- != 0; ) {
            const ElementAnimation *a = &ea->mAnimations[oldIdx];
            if (a->mName == newAnim->mName) {
              oldAnim = a;
              break;
            }
          }
          if (!oldAnim) {
            continue;
          }

          newAnim->mStartTime = oldAnim->mStartTime;
          newAnim->mLastNotification = oldAnim->mLastNotification;

          if (oldAnim->IsPaused()) {
            if (newAnim->IsPaused()) {
              // Copy pause start just like start time.
              newAnim->mPauseStart = oldAnim->mPauseStart;
            } else {
              // Handle change in pause state by adjusting start
              // time to unpause.
              newAnim->mStartTime += refreshTime - oldAnim->mPauseStart;
            }
          }
        }
      }
    } else {
      ea = GetElementAnimations(aElement, aStyleContext->GetPseudoType(),
                                true);
    }
    ea->mAnimations.SwapElements(newAnimations);
    ea->mNeedsRefreshes = true;

    ea->EnsureStyleRuleFor(refreshTime, mPendingEvents, false);
    // 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)
{
  if (!mPresContext->IsProcessingAnimationStyleChange()) {
    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();
    ElementAnimationCollection* collection =
      GetElementAnimations(aElement, aStyleContext->GetPseudoType(), false);
    if (!collection &&
        disp->mAnimationNameCount == 1 &&
        disp->mAnimations[0].GetName().IsEmpty()) {
      return nullptr;
    }

    // build the animations list
    dom::AnimationTimeline* timeline = aElement->OwnerDoc()->Timeline();
    ElementAnimationPtrArray newAnimations;
    BuildAnimations(aStyleContext, timeline, newAnimations);

    if (newAnimations.IsEmpty()) {
      if (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;) {
          ElementAnimation* 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<ElementAnimation> oldAnim;
          size_t oldIdx = collection->mAnimations.Length();
          while (oldIdx-- != 0) {
            ElementAnimation* a = collection->mAnimations[oldIdx];
            if (a->mName == newAnim->mName) {
              oldAnim = a;
              break;
            }
          }
          if (!oldAnim) {
            continue;
          }

          // Update the old from the new so we can keep the original object
          // identity (and any expando properties attached to it).
          oldAnim->mTiming = newAnim->mTiming;
          oldAnim->mProperties = newAnim->mProperties;

          // Reset compositor state so animation will be re-synchronized.
          oldAnim->mIsRunningOnCompositor = false;

          // Handle changes in play state.
          if (!oldAnim->IsPaused() && newAnim->IsPaused()) {
            // Start pause at current time.
            oldAnim->mPauseStart = timeline->GetCurrentTimeStamp();
          } else if (oldAnim->IsPaused() && !newAnim->IsPaused()) {
            const TimeStamp& now = timeline->GetCurrentTimeStamp();
            if (!now.IsNull()) {
              // FIXME: Once we store the start time and pause start as
              // offsets (not timestamps) we should be able to update the
              // start time to something more appropriate when now IsNull.
              // Handle change in pause state by adjusting start time to
              // unpause.
              oldAnim->mStartTime += now - oldAnim->mPauseStart;
            }
            oldAnim->mPauseStart = TimeStamp();
          }
          oldAnim->mPlayState = newAnim->mPlayState;

          // 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 = nullptr;
          newAnimations.ReplaceElementAt(newIdx, oldAnim);
          collection->mAnimations.RemoveElementAt(oldIdx);
        }
      }
    } else {
      collection =
        GetElementAnimations(aElement, aStyleContext->GetPseudoType(), true);
    }
    collection->mAnimations.SwapElements(newAnimations);
    collection->mNeedsRefreshes = true;

    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());
}