/*
 * Copyright (C) 2021 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "config.h"
#include "Styleable.h"

#include "Animation.h"
#include "AnimationEffect.h"
#include "AnimationList.h"
#include "AnimationTimeline.h"
#include "CSSAnimation.h"
#include "CSSPropertyAnimation.h"
#include "CSSTransition.h"
#include "DeclarativeAnimation.h"
#include "Document.h"
#include "DocumentTimeline.h"
#include "Element.h"
#include "KeyframeEffect.h"
#include "KeyframeEffectStack.h"
#include "RenderElement.h"
#include "RenderListItem.h"
#include "RenderListMarker.h"
#include "RenderStyle.h"
#include "StylePropertyShorthand.h"
#include "StyleResolver.h"
#include "StyleScope.h"
#include "WebAnimation.h"
#include "WebAnimationUtilities.h"

namespace WebCore {

const std::optional<const Styleable> Styleable::fromRenderer(const RenderElement& renderer)
{
    switch (renderer.style().styleType()) {
    case PseudoId::Backdrop:
        for (auto& topLayerElement : renderer.document().topLayerElements()) {
            if (topLayerElement->renderer() && topLayerElement->renderer()->backdropRenderer() == &renderer)
                return Styleable(topLayerElement.get(), PseudoId::Backdrop);
        }
        break;
    case PseudoId::Marker:
        if (auto* ancestor = renderer.parent()) {
            while (ancestor && !ancestor->element())
                ancestor = ancestor->parent();
            ASSERT(is<RenderListItem>(ancestor));
            ASSERT(downcast<RenderListItem>(ancestor)->markerRenderer() == &renderer);
            return Styleable(*ancestor->element(), PseudoId::Marker);
        }
        break;
    case PseudoId::After:
    case PseudoId::Before:
    case PseudoId::None:
        if (auto* element = renderer.element())
            return fromElement(*element);
        break;
    default:
        return std::nullopt;
    }

    return std::nullopt;
}

RenderElement* Styleable::renderer() const
{
    switch (pseudoId) {
    case PseudoId::After:
        if (auto* afterPseudoElement = element.afterPseudoElement())
            return afterPseudoElement->renderer();
        break;
    case PseudoId::Backdrop:
        if (auto* hostRenderer = element.renderer())
            return hostRenderer->backdropRenderer().get();
        break;
    case PseudoId::Before:
        if (auto* beforePseudoElement = element.beforePseudoElement())
            return beforePseudoElement->renderer();
        break;
    case PseudoId::Marker:
        if (is<RenderListItem>(element.renderer())) {
            auto* markerRenderer = downcast<RenderListItem>(*element.renderer()).markerRenderer();
            if (markerRenderer && !markerRenderer->style().hasEffectiveContentNone())
                return markerRenderer;
        }
        break;
    case PseudoId::None:
        return element.renderer();
    default:
        return nullptr;
    }

    return nullptr;
}

void Styleable::animationWasAdded(WebAnimation& animation) const
{
    ensureAnimations().add(&animation);
}

static inline bool removeCSSTransitionFromMap(CSSTransition& transition, PropertyToTransitionMap& cssTransitionsByProperty)
{
    auto transitionIterator = cssTransitionsByProperty.find(transition.property());
    if (transitionIterator == cssTransitionsByProperty.end() || transitionIterator->value != &transition)
        return false;

    cssTransitionsByProperty.remove(transitionIterator);
    return true;
}

void Styleable::removeDeclarativeAnimationFromListsForOwningElement(WebAnimation& animation) const
{
    ASSERT(is<DeclarativeAnimation>(animation));

    if (is<CSSTransition>(animation)) {
        auto& transition = downcast<CSSTransition>(animation);
        if (!removeCSSTransitionFromMap(transition, ensureRunningTransitionsByProperty()))
            removeCSSTransitionFromMap(transition, ensureCompletedTransitionsByProperty());
    }
}

void Styleable::animationWasRemoved(WebAnimation& animation) const
{
    ensureAnimations().remove(&animation);

    // Now, if we're dealing with a CSS Transition, we remove it from the m_elementToRunningCSSTransitionByCSSPropertyID map.
    // We don't need to do this for CSS Animations because their timing can be set via CSS to end, which would cause this
    // function to be called, but they should remain associated with their owning element until this is changed via a call
    // to the JS API or changing the target element's animation-name property.
    if (is<CSSTransition>(animation))
        removeDeclarativeAnimationFromListsForOwningElement(animation);
}

static void removeCSSAnimationCreatedByMarkup(const Styleable& styleable, CSSAnimation& cssAnimation)
{
    styleable.animationsCreatedByMarkup().remove(&cssAnimation);

    if (!styleable.hasKeyframeEffects())
        return;

    auto& keyframeEffectStack = styleable.ensureKeyframeEffectStack();
    auto* cssAnimationList = keyframeEffectStack.cssAnimationList();
    if (!cssAnimationList || cssAnimationList->isEmpty())
        return;

    auto& backingAnimation = cssAnimation.backingAnimation();
    for (size_t i = 0; i < cssAnimationList->size(); ++i) {
        if (cssAnimationList->animation(i) == backingAnimation) {
            // It is important we do not make a clone of the Animation references contained
            // within cssAnimationList since sorting animations in compareCSSAnimations()
            // makes pointer comparisons to distinguish between backing animations of various
            // CSSAnimation objects.
            auto newAnimationList = cssAnimationList->shallowCopy();
            newAnimationList->remove(i);
            keyframeEffectStack.setCSSAnimationList(WTFMove(newAnimationList));
            return;
        }
    }
}

void Styleable::elementWasRemoved() const
{
    cancelDeclarativeAnimations();
}

void Styleable::willChangeRenderer() const
{
    if (auto* animations = this->animations()) {
        for (const auto& animation : *animations)
            animation->willChangeRenderer();
    }
}

void Styleable::cancelDeclarativeAnimations() const
{
    if (auto* animations = this->animations()) {
        for (auto& animation : *animations) {
            if (is<DeclarativeAnimation>(animation)) {
                if (is<CSSAnimation>(animation))
                    removeCSSAnimationCreatedByMarkup(*this, downcast<CSSAnimation>(*animation));
                downcast<DeclarativeAnimation>(*animation).cancelFromStyle();
            }
        }
    }
}

static bool keyframesRuleExistsForAnimation(Element& element, const Animation& animation, const String& animationName)
{
    auto* styleScope = Style::Scope::forOrdinal(element, animation.nameStyleScopeOrdinal());
    return styleScope && styleScope->resolver().isAnimationNameValid(animationName);
}

bool Styleable::animationListContainsNewlyValidAnimation(const AnimationList& animations) const
{
    auto& keyframeEffectStack = ensureKeyframeEffectStack();
    if (!keyframeEffectStack.hasInvalidCSSAnimationNames())
        return false;

    for (auto& animation : animations) {
        auto& name = animation->name().string;
        if (name != "none" && !name.isEmpty() && keyframeEffectStack.containsInvalidCSSAnimationName(name) && keyframesRuleExistsForAnimation(element, animation.get(), name))
            return true;
    }

    return false;
}

void Styleable::updateCSSAnimations(const RenderStyle* currentStyle, const RenderStyle& newStyle, const Style::ResolutionContext& resolutionContext) const
{
    auto& keyframeEffectStack = ensureKeyframeEffectStack();

    // In case this element is newly getting a "display: none" we need to cancel all of its animations and disregard new ones.
    if (currentStyle && currentStyle->display() != DisplayType::None && newStyle.display() == DisplayType::None) {
        for (auto& cssAnimation : animationsCreatedByMarkup())
            cssAnimation->cancelFromStyle();
        keyframeEffectStack.setCSSAnimationList(nullptr);
        return;
    }

    auto* currentAnimationList = newStyle.animations();
    auto* previousAnimationList = keyframeEffectStack.cssAnimationList();
    if (!element.hasPendingKeyframesUpdate(pseudoId) && previousAnimationList && !previousAnimationList->isEmpty() && newStyle.hasAnimations() && *(previousAnimationList) == *(newStyle.animations()) && !animationListContainsNewlyValidAnimation(*newStyle.animations()))
        return;

    CSSAnimationCollection newAnimations;
    auto& previousAnimations = animationsCreatedByMarkup();

    keyframeEffectStack.clearInvalidCSSAnimationNames();

    // https://www.w3.org/TR/css-animations-1/#animations
    // The same @keyframes rule name may be repeated within an animation-name. Changes to the animation-name update existing
    // animations by iterating over the new list of animations from last to first, and, for each animation, finding the last
    // matching animation in the list of existing animations. If a match is found, the existing animation is updated using the
    // animation properties corresponding to its position in the new list of animations, whilst maintaining its current playback
    // time as described above. The matching animation is removed from the existing list of animations such that it will not match
    // twice. If a match is not found, a new animation is created. As a result, updating animation-name from ‘a’ to ‘a, a’ will
    // cause the existing animation for ‘a’ to become the second animation in the list and a new animation will be created for the
    // first item in the list.
    if (currentAnimationList) {
        for (auto& currentAnimation : makeReversedRange(*currentAnimationList)) {
            if (!currentAnimation->isValidAnimation())
                continue;

            auto& animationName = currentAnimation->name().string;
            if (animationName == "none" || animationName.isEmpty())
                continue;

            if (!keyframesRuleExistsForAnimation(element, currentAnimation.get(), animationName)) {
                keyframeEffectStack.addInvalidCSSAnimationName(animationName);
                continue;
            }

            bool foundMatchingAnimation = false;
            for (auto& previousAnimation : previousAnimations) {
                if (previousAnimation->animationName() == animationName) {
                    // Timing properties or play state may have changed so we need to update the backing animation with
                    // the Animation found in the current style.
                    previousAnimation->setBackingAnimation(currentAnimation.get());
                    // Keyframes may have been cleared if the @keyframes rules was changed since
                    // the last style update, so we must ensure keyframes are picked up.
                    previousAnimation->updateKeyframesIfNeeded(currentStyle, newStyle, resolutionContext);
                    newAnimations.add(previousAnimation);
                    // Remove the matched animation from the list of previous animations so we may not match it again.
                    previousAnimations.remove(previousAnimation);
                    foundMatchingAnimation = true;
                    break;
                }
            }

            if (!foundMatchingAnimation)
                newAnimations.add(CSSAnimation::create(*this, currentAnimation.get(), currentStyle, newStyle, resolutionContext));
        }
    }

    // Any animation found in previousAnimations but not found in newAnimations is not longer current and should be canceled.
    for (auto& previousAnimation : previousAnimations) {
        if (!newAnimations.contains(previousAnimation)) {
            if (previousAnimation->owningElement())
                previousAnimation->cancelFromStyle();
        }
    }

    setAnimationsCreatedByMarkup(WTFMove(newAnimations));

    keyframeEffectStack.setCSSAnimationList(currentAnimationList);

    element.cssAnimationsDidUpdate(pseudoId);
}

static KeyframeEffect* keyframeEffectForElementAndProperty(const Styleable& styleable, CSSPropertyID property)
{
    if (auto* keyframeEffectStack = styleable.keyframeEffectStack()) {
        auto effects = keyframeEffectStack->sortedEffects();
        for (const auto& effect : makeReversedRange(effects)) {
            if (effect->animatesProperty(property))
                return effect.get();
        }
    }

    return nullptr;
}

static bool propertyInStyleMatchesValueForTransitionInMap(CSSPropertyID property, const RenderStyle& style, PropertyToTransitionMap& transitions)
{
    if (auto* transition = transitions.get(property)) {
        if (CSSPropertyAnimation::propertiesEqual(property, style, transition->targetStyle()))
            return true;
    }
    return false;
}

static double transitionCombinedDuration(const Animation* transition)
{
    return std::max(0.0, transition->duration()) + transition->delay();
}

static bool transitionMatchesProperty(const Animation& transition, CSSPropertyID property)
{
    if (transition.isPropertyFilled())
        return false;

    auto mode = transition.property().mode;
    if (mode == Animation::TransitionMode::None || mode == Animation::TransitionMode::UnknownProperty)
        return false;
    if (mode == Animation::TransitionMode::SingleProperty) {
        auto transitionProperty = transition.property().id;
        if (transitionProperty != property) {
            for (auto longhand : shorthandForProperty(transitionProperty)) {
                if (longhand == property)
                    return true;
            }
            return false;
        }
    }
    return true;
}

static void compileTransitionPropertiesInStyle(const RenderStyle& style, HashSet<CSSPropertyID>& transitionProperties, bool& transitionPropertiesContainAll)
{
    if (transitionPropertiesContainAll)
        return;

    auto* transitions = style.transitions();
    if (!transitions)
        return;

    for (const auto& animation : *transitions) {
        auto mode = animation->property().mode;
        if (mode == Animation::TransitionMode::SingleProperty) {
            auto property = animation->property().id;
            if (isShorthandCSSProperty(property)) {
                for (auto longhand : shorthandForProperty(property))
                    transitionProperties.add(longhand);
            } else if (property != CSSPropertyInvalid)
                transitionProperties.add(property);
        } else if (mode == Animation::TransitionMode::All) {
            transitionPropertiesContainAll = true;
            return;
        }
    }
}

static void updateCSSTransitionsForStyleableAndProperty(const Styleable& styleable, CSSPropertyID property, const RenderStyle& currentStyle, const RenderStyle& newStyle, const MonotonicTime generationTime)
{
    auto* keyframeEffect = keyframeEffectForElementAndProperty(styleable, property);
    auto* animation = keyframeEffect ? keyframeEffect->animation() : nullptr;

    bool isDeclarative = false;
    if (is<DeclarativeAnimation>(animation)) {
        if (auto owningElement = downcast<DeclarativeAnimation>(*animation).owningElement())
            isDeclarative = *owningElement == styleable;
    }

    if (animation && !isDeclarative)
        return;

    const Animation* matchingBackingAnimation = nullptr;
    if (auto* transitions = newStyle.transitions()) {
        for (auto& backingAnimation : *transitions) {
            if (transitionMatchesProperty(backingAnimation.get(), property))
                matchingBackingAnimation = backingAnimation.ptr();
        }
    }

    // A CSS Transition might have completed since the last time animations were updated so we must
    // update the running and completed transitions membership in that case.
    if (is<CSSTransition>(animation) && matchingBackingAnimation && styleable.hasRunningTransitionForProperty(property) && animation->playState() == WebAnimation::PlayState::Finished) {
        styleable.ensureCompletedTransitionsByProperty().set(property, styleable.ensureRunningTransitionsByProperty().take(property));
        animation = nullptr;
    }

    // https://drafts.csswg.org/css-transitions-1/#before-change-style
    // Define the before-change style as the computed values of all properties on the element as of the previous style change event, except with
    // any styles derived from declarative animations such as CSS Transitions, CSS Animations, and SMIL Animations updated to the current time.
    auto beforeChangeStyle = [&]() -> const RenderStyle {
        if (auto* lastStyleChangeEventStyle = styleable.lastStyleChangeEventStyle()) {
            auto style = RenderStyle::clone(*lastStyleChangeEventStyle);
            if (auto* keyframeEffectStack = styleable.keyframeEffectStack()) {
                for (const auto& effect : keyframeEffectStack->sortedEffects()) {
                    auto* effectAnimation = effect->animation();
                    bool shouldUseTimelineTimeAtCreation = is<CSSTransition>(effectAnimation) && (!effectAnimation->startTime() || *effectAnimation->startTime() == styleable.element.document().timeline().currentTime());
                    effectAnimation->resolve(style, { nullptr }, shouldUseTimelineTimeAtCreation ? downcast<CSSTransition>(*effectAnimation).timelineTimeAtCreation() : std::nullopt);
                }
            }
            return style;
        }
        return RenderStyle::clone(currentStyle);
    }();

    // https://drafts.csswg.org/css-transitions-1/#after-change-style
    // Likewise, define the after-change style as the computed values of all properties on the element based on the information known at the start
    // of that style change event, but using the computed values of the animation-* properties from the before-change style, excluding any styles
    // from CSS Transitions in the computation, and inheriting from the after-change style of the parent. Note that this means the after-change
    // style does not differ from the before-change style due to newly created or canceled CSS Animations.
    auto afterChangeStyle = [&]() -> const RenderStyle {
        if (is<CSSAnimation>(animation) && animation->isRelevant()) {
            auto animatedStyle = RenderStyle::clone(newStyle);
            animation->resolve(animatedStyle, { nullptr });
            return animatedStyle;
        }

        return RenderStyle::clone(newStyle);
    }();

    if (!styleable.hasRunningTransitionForProperty(property)
        && !CSSPropertyAnimation::propertiesEqual(property, beforeChangeStyle, afterChangeStyle)
        && CSSPropertyAnimation::canPropertyBeInterpolated(property, beforeChangeStyle, afterChangeStyle)
        && !propertyInStyleMatchesValueForTransitionInMap(property, afterChangeStyle, styleable.ensureCompletedTransitionsByProperty())
        && matchingBackingAnimation && transitionCombinedDuration(matchingBackingAnimation) > 0) {
        // 1. If all of the following are true:
        //   - the element does not have a running transition for the property,
        //   - the before-change style is different from and can be interpolated with the after-change style for that property,
        //   - the element does not have a completed transition for the property or the end value of the completed transition is different from the after-change style for the property,
        //   - there is a matching transition-property value, and
        //   - the combined duration is greater than 0s,

        // then implementations must remove the completed transition (if present) from the set of completed transitions
        styleable.ensureCompletedTransitionsByProperty().remove(property);

        // and start a transition whose:
        //   - start time is the time of the style change event plus the matching transition delay,
        //   - end time is the start time plus the matching transition duration,
        //   - start value is the value of the transitioning property in the before-change style,
        //   - end value is the value of the transitioning property in the after-change style,
        //   - reversing-adjusted start value is the same as the start value, and
        //   - reversing shortening factor is 1.
        auto delay = Seconds(matchingBackingAnimation->delay());
        auto duration = Seconds(matchingBackingAnimation->duration());
        auto& reversingAdjustedStartStyle = beforeChangeStyle;
        auto reversingShorteningFactor = 1;
        styleable.ensureRunningTransitionsByProperty().set(property, CSSTransition::create(styleable, property, generationTime, *matchingBackingAnimation, &beforeChangeStyle, afterChangeStyle, delay, duration, reversingAdjustedStartStyle, reversingShorteningFactor));
    } else if (styleable.hasCompletedTransitionForProperty(property) && !propertyInStyleMatchesValueForTransitionInMap(property, afterChangeStyle, styleable.ensureCompletedTransitionsByProperty())) {
        // 2. Otherwise, if the element has a completed transition for the property and the end value of the completed transition is different from
        //    the after-change style for the property, then implementations must remove the completed transition from the set of completed transitions.
        styleable.ensureCompletedTransitionsByProperty().remove(property);
    }

    bool hasRunningTransition = styleable.hasRunningTransitionForProperty(property);
    if ((hasRunningTransition || styleable.hasCompletedTransitionForProperty(property)) && !matchingBackingAnimation) {
        // 3. If the element has a running transition or completed transition for the property, and there is not a matching transition-property
        //    value, then implementations must cancel the running transition or remove the completed transition from the set of completed transitions.
        if (hasRunningTransition)
            styleable.ensureRunningTransitionsByProperty().take(property)->cancel();
        else
            styleable.ensureCompletedTransitionsByProperty().remove(property);
    }

    if (matchingBackingAnimation && styleable.hasRunningTransitionForProperty(property) && !propertyInStyleMatchesValueForTransitionInMap(property, afterChangeStyle, styleable.ensureRunningTransitionsByProperty())) {
        auto previouslyRunningTransition = styleable.ensureRunningTransitionsByProperty().take(property);
        auto& previouslyRunningTransitionCurrentStyle = previouslyRunningTransition->currentStyle();
        // 4. If the element has a running transition for the property, there is a matching transition-property value, and the end value of the running
        //    transition is not equal to the value of the property in the after-change style, then:
        if (CSSPropertyAnimation::propertiesEqual(property, previouslyRunningTransitionCurrentStyle, afterChangeStyle) || !CSSPropertyAnimation::canPropertyBeInterpolated(property, currentStyle, afterChangeStyle)) {
            // 1. If the current value of the property in the running transition is equal to the value of the property in the after-change style,
            //    or if these two values cannot be interpolated, then implementations must cancel the running transition.
            previouslyRunningTransition->cancelFromStyle();
        } else if (transitionCombinedDuration(matchingBackingAnimation) <= 0.0 || !CSSPropertyAnimation::canPropertyBeInterpolated(property, previouslyRunningTransitionCurrentStyle, afterChangeStyle)) {
            // 2. Otherwise, if the combined duration is less than or equal to 0s, or if the current value of the property in the running transition
            //    cannot be interpolated with the value of the property in the after-change style, then implementations must cancel the running transition.
            previouslyRunningTransition->cancelFromStyle();
        } else if (CSSPropertyAnimation::propertiesEqual(property, previouslyRunningTransition->reversingAdjustedStartStyle(), afterChangeStyle)) {
            // 3. Otherwise, if the reversing-adjusted start value of the running transition is the same as the value of the property in the after-change
            //    style (see the section on reversing of transitions for why these case exists), implementations must cancel the running transition
            //    and start a new transition whose:
            //   - reversing-adjusted start value is the end value of the running transition,
            //   - reversing shortening factor is the absolute value, clamped to the range [0, 1], of the sum of:
            //       1. the output of the timing function of the old transition at the time of the style change event, times the reversing shortening factor of the old transition
            //       2. 1 minus the reversing shortening factor of the old transition.
            //   - start time is the time of the style change event plus:
            //       1. if the matching transition delay is nonnegative, the matching transition delay, or
            //       2. if the matching transition delay is negative, the product of the new transition’s reversing shortening factor and the matching transition delay,
            //   - end time is the start time plus the product of the matching transition duration and the new transition’s reversing shortening factor,
            //   - start value is the current value of the property in the running transition,
            //   - end value is the value of the property in the after-change style
            auto& reversingAdjustedStartStyle = previouslyRunningTransition->targetStyle();
            double transformedProgress = 1;
            if (auto* effect = previouslyRunningTransition->effect()) {
                if (auto computedTimingProgress = effect->getComputedTiming().progress)
                    transformedProgress = *computedTimingProgress;
            }
            auto reversingShorteningFactor = std::max(std::min(((transformedProgress * previouslyRunningTransition->reversingShorteningFactor()) + (1 - previouslyRunningTransition->reversingShorteningFactor())), 1.0), 0.0);
            auto delay = matchingBackingAnimation->delay() < 0 ? Seconds(matchingBackingAnimation->delay()) * reversingShorteningFactor : Seconds(matchingBackingAnimation->delay());
            auto duration = Seconds(matchingBackingAnimation->duration()) * reversingShorteningFactor;

            previouslyRunningTransition->cancelFromStyle();
            styleable.ensureRunningTransitionsByProperty().set(property, CSSTransition::create(styleable, property, generationTime, *matchingBackingAnimation, &beforeChangeStyle, afterChangeStyle, delay, duration, reversingAdjustedStartStyle, reversingShorteningFactor));
        } else {
            // 4. Otherwise, implementations must cancel the running transition and start a new transition whose:
            //   - start time is the time of the style change event plus the matching transition delay,
            //   - end time is the start time plus the matching transition duration,
            //   - start value is the current value of the property in the running transition,
            //   - end value is the value of the property in the after-change style,
            //   - reversing-adjusted start value is the same as the start value, and
            //   - reversing shortening factor is 1.
            auto delay = Seconds(matchingBackingAnimation->delay());
            auto duration = Seconds(matchingBackingAnimation->duration());
            auto& reversingAdjustedStartStyle = currentStyle;
            auto reversingShorteningFactor = 1;
            previouslyRunningTransition->cancelFromStyle();
            styleable.ensureRunningTransitionsByProperty().set(property, CSSTransition::create(styleable, property, generationTime, *matchingBackingAnimation, &previouslyRunningTransitionCurrentStyle, afterChangeStyle, delay, duration, reversingAdjustedStartStyle, reversingShorteningFactor));
        }
    }
}

void Styleable::updateCSSTransitions(const RenderStyle& currentStyle, const RenderStyle& newStyle) const
{
    // In case this element is newly getting a "display: none" we need to cancel all of its transitions and disregard new ones.
    if (currentStyle.hasTransitions() && currentStyle.display() != DisplayType::None && newStyle.display() == DisplayType::None) {
        if (hasRunningTransitions()) {
            auto runningTransitions = ensureRunningTransitionsByProperty();
            for (const auto& cssTransitionsByCSSPropertyIDMapItem : runningTransitions)
                cssTransitionsByCSSPropertyIDMapItem.value->cancelFromStyle();
        }
        return;
    }

    // Section 3 "Starting of transitions" from the CSS Transitions Level 1 specification.
    // https://drafts.csswg.org/css-transitions-1/#starting

    auto generationTime = MonotonicTime::now();

    // First, let's compile the list of all CSS properties found in the current style and the after-change style.
    bool transitionPropertiesContainAll = false;
    HashSet<CSSPropertyID> transitionProperties;
    compileTransitionPropertiesInStyle(currentStyle, transitionProperties, transitionPropertiesContainAll);
    compileTransitionPropertiesInStyle(newStyle, transitionProperties, transitionPropertiesContainAll);

    if (transitionPropertiesContainAll) {
        auto numberOfProperties = CSSPropertyAnimation::getNumProperties();
        for (int propertyIndex = 0; propertyIndex < numberOfProperties; ++propertyIndex) {
            std::optional<bool> isShorthand;
            auto property = CSSPropertyAnimation::getPropertyAtIndex(propertyIndex, isShorthand);
            if (isShorthand && *isShorthand)
                continue;
            updateCSSTransitionsForStyleableAndProperty(*this, property, currentStyle, newStyle, generationTime);
        }
        return;
    }

    for (auto property : transitionProperties)
        updateCSSTransitionsForStyleableAndProperty(*this, property, currentStyle, newStyle, generationTime);
}

} // namespace WebCore