Source/WebCore/style/ChildChangeInvalidation.cpp

/*
 * Copyright (C) 2021 Apple Inc. All rights reserved.
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#include "config.h"
#include "ChildChangeInvalidation.h"

#include "ElementTraversal.h"
#include "NodeRenderStyle.h"
#include "ShadowRoot.h"
#include "SlotAssignment.h"

namespace WebCore::Style {

ChildChangeInvalidation::ChildChangeInvalidation(ContainerNode& container, const ContainerNode::ChildChange& childChange)
    : m_parentElement(is<Element>(container) ? downcast<Element>(&container) : nullptr)
    , m_isEnabled(m_parentElement ? m_parentElement->needsStyleInvalidation() : false)
    , m_childChange(childChange)
{
    // FIXME: Do smarter invalidation similar to ClassChangeInvalidation.
}

ChildChangeInvalidation::~ChildChangeInvalidation()
{
    if (!m_isEnabled)
        return;

    invalidateAfterChange();
}

static void checkForEmptyStyleChange(Element& element)
{
    if (!element.styleAffectedByEmpty())
        return;

    auto* style = element.renderStyle();
    if (!style || (!style->emptyState() || element.hasChildNodes()))
        element.invalidateStyleForSubtree();
}

static void invalidateForForwardPositionalRules(Element& parent, Element* elementAfterChange)
{
    bool childrenAffected = parent.childrenAffectedByForwardPositionalRules();
    bool descendantsAffected = parent.descendantsAffectedByForwardPositionalRules();

    if (!childrenAffected && !descendantsAffected)
        return;

    for (auto* sibling = elementAfterChange; sibling; sibling = sibling->nextElementSibling()) {
        if (childrenAffected)
            sibling->invalidateStyleInternal();
        if (descendantsAffected) {
            for (auto* siblingChild = sibling->firstElementChild(); siblingChild; siblingChild = siblingChild->nextElementSibling())
                siblingChild->invalidateStyleForSubtreeInternal();
        }
    }
}

static void invalidateForBackwardPositionalRules(Element& parent, Element* elementBeforeChange)
{
    bool childrenAffected = parent.childrenAffectedByBackwardPositionalRules();
    bool descendantsAffected = parent.descendantsAffectedByBackwardPositionalRules();

    if (!childrenAffected && !descendantsAffected)
        return;

    for (auto* sibling = elementBeforeChange; sibling; sibling = sibling->previousElementSibling()) {
        if (childrenAffected)
            sibling->invalidateStyleInternal();
        if (descendantsAffected) {
            for (auto* siblingChild = sibling->firstElementChild(); siblingChild; siblingChild = siblingChild->nextElementSibling())
                siblingChild->invalidateStyleForSubtreeInternal();
        }
    }
}

static void invalidateForFirstChildState(Element& child, bool state)
{
    auto* style = child.renderStyle();
    if (!style || style->firstChildState() == state)
        child.invalidateStyleForSubtreeInternal();
}

static void invalidateForLastChildState(Element& child, bool state)
{
    auto* style = child.renderStyle();
    if (!style || style->lastChildState() == state)
        child.invalidateStyleForSubtreeInternal();
}

void ChildChangeInvalidation::invalidateAfterChange()
{
    checkForEmptyStyleChange(parentElement());

    if (m_childChange.source == ContainerNode::ChildChange::Source::Parser)
        return;

    checkForSiblingStyleChanges();
}

void ChildChangeInvalidation::invalidateAfterFinishedParsingChildren(Element& parent)
{
    if (!parent.needsStyleInvalidation())
        return;

    checkForEmptyStyleChange(parent);

    auto* lastChildElement = ElementTraversal::lastChild(parent);
    if (!lastChildElement)
        return;

    if (parent.childrenAffectedByLastChildRules())
        invalidateForLastChildState(*lastChildElement, false);

    invalidateForBackwardPositionalRules(parent, lastChildElement);
}

void ChildChangeInvalidation::checkForSiblingStyleChanges()
{
    auto& parent = parentElement();
    auto* elementBeforeChange = m_childChange.previousSiblingElement;
    auto* elementAfterChange = m_childChange.nextSiblingElement;

    // :first-child. In the parser callback case, we don't have to check anything, since we were right the first time.
    // In the DOM case, we only need to do something if |afterChange| is not 0.
    // |afterChange| is 0 in the parser case, so it works out that we'll skip this block.
    if (parent.childrenAffectedByFirstChildRules() && elementAfterChange) {
        // Find our new first child.
        RefPtr<Element> newFirstElement = ElementTraversal::firstChild(parent);

        // This is the insert/append case.
        if (newFirstElement != elementAfterChange)
            invalidateForFirstChildState(*elementAfterChange, true);

        // We also have to handle node removal.
        if (m_childChange.type == ContainerNode::ChildChange::Type::ElementRemoved && newFirstElement == elementAfterChange)
            invalidateForFirstChildState(*newFirstElement, false);
    }

    // :last-child. In the parser callback case, we don't have to check anything, since we were right the first time.
    // In the DOM case, we only need to do something if |afterChange| is not 0.
    if (parent.childrenAffectedByLastChildRules() && elementBeforeChange) {
        // Find our new last child.
        RefPtr<Element> newLastElement = ElementTraversal::lastChild(parent);

        if (newLastElement != elementBeforeChange)
            invalidateForLastChildState(*elementBeforeChange, true);

        // We also have to handle node removal.
        if (m_childChange.type == ContainerNode::ChildChange::Type::ElementRemoved && newLastElement == elementBeforeChange)
            invalidateForLastChildState(*newLastElement, false);
    }

    invalidateForSiblingCombinators(elementAfterChange);

    invalidateForForwardPositionalRules(parent, elementAfterChange);
    invalidateForBackwardPositionalRules(parent, elementBeforeChange);
}

}