Source/WebCore/page/IntersectionObserver.cpp

/*
 * Copyright (C) 2016-2022 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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#include "config.h"

#include "IntersectionObserver.h"

#include "CSSParserTokenRange.h"
#include "CSSPropertyParserHelpers.h"
#include "CSSTokenizer.h"
#include "DOMWindow.h"
#include "Element.h"
#include "InspectorInstrumentation.h"
#include "IntersectionObserverCallback.h"
#include "IntersectionObserverEntry.h"
#include "Performance.h"
#include <JavaScriptCore/AbstractSlotVisitorInlines.h>
#include <wtf/Vector.h>

namespace WebCore {

static ExceptionOr<LengthBox> parseRootMargin(String& rootMargin)
{
    CSSTokenizer tokenizer(rootMargin);
    auto tokenRange = tokenizer.tokenRange();
    Vector<Length, 4> margins;
    while (!tokenRange.atEnd()) {
        if (margins.size() == 4)
            return Exception { SyntaxError, "Failed to construct 'IntersectionObserver': Extra text found at the end of rootMargin." };
        RefPtr<CSSPrimitiveValue> parsedValue = CSSPropertyParserHelpers::consumeLengthOrPercent(tokenRange, HTMLStandardMode, ValueRange::All);
        if (!parsedValue || parsedValue->isCalculated())
            return Exception { SyntaxError, "Failed to construct 'IntersectionObserver': rootMargin must be specified in pixels or percent." };
        if (parsedValue->isPercentage())
            margins.append(Length(parsedValue->doubleValue(), LengthType::Percent));
        else if (parsedValue->isPx())
            margins.append(Length(parsedValue->intValue(), LengthType::Fixed));
        else
            return Exception { SyntaxError, "Failed to construct 'IntersectionObserver': rootMargin must be specified in pixels or percent." };
    }
    switch (margins.size()) {
    case 0:
        for (unsigned i = 0; i < 4; ++i)
            margins.append(Length(0, LengthType::Fixed));
        break;
    case 1:
        for (unsigned i = 0; i < 3; ++i)
            margins.append(margins[0]);
        break;
    case 2:
        margins.append(margins[0]);
        margins.append(margins[1]);
        break;
    case 3:
        margins.append(margins[1]);
        break;
    case 4:
        break;
    default:
        ASSERT_NOT_REACHED();
    }

    return LengthBox(WTFMove(margins[0]), WTFMove(margins[1]), WTFMove(margins[2]), WTFMove(margins[3]));
}

ExceptionOr<Ref<IntersectionObserver>> IntersectionObserver::create(Document& document, Ref<IntersectionObserverCallback>&& callback, IntersectionObserver::Init&& init)
{
    RefPtr<ContainerNode> root;
    if (init.root) {
        WTF::switchOn(*init.root, [&root] (RefPtr<Element> element) {
            root = element.get();
        }, [&root] (RefPtr<Document> document) {
            root = document.get();
        });
    }

    auto rootMarginOrException = parseRootMargin(init.rootMargin);
    if (rootMarginOrException.hasException())
        return rootMarginOrException.releaseException();

    Vector<double> thresholds;
    WTF::switchOn(init.threshold, [&thresholds] (double initThreshold) {
        thresholds.reserveInitialCapacity(1);
        thresholds.uncheckedAppend(initThreshold);
    }, [&thresholds] (Vector<double>& initThresholds) {
        thresholds = WTFMove(initThresholds);
    });

    for (auto threshold : thresholds) {
        if (!(threshold >= 0 && threshold <= 1))
            return Exception { RangeError, "Failed to construct 'IntersectionObserver': all thresholds must lie in the range [0.0, 1.0]." };
    }

    return adoptRef(*new IntersectionObserver(document, WTFMove(callback), root.get(), rootMarginOrException.releaseReturnValue(), WTFMove(thresholds)));
}

IntersectionObserver::IntersectionObserver(Document& document, Ref<IntersectionObserverCallback>&& callback, ContainerNode* root, LengthBox&& parsedRootMargin, Vector<double>&& thresholds)
    : m_associatedDocument(&document)
    , m_root(root)
    , m_rootMargin(WTFMove(parsedRootMargin))
    , m_thresholds(WTFMove(thresholds))
    , m_callback(WTFMove(callback))
{
    if (is<Document>(root)) {
        auto& observerData = downcast<Document>(*root).ensureIntersectionObserverData();
        observerData.observers.append(*this);
    } else if (root) {
        auto& observerData = downcast<Element>(*root).ensureIntersectionObserverData();
        observerData.observers.append(*this);
    } else if (auto* frame = document.frame())
        m_implicitRootDocument = frame->mainFrame().document();

    std::sort(m_thresholds.begin(), m_thresholds.end());
}

IntersectionObserver::~IntersectionObserver()
{
    RefPtr root = m_root.get();
    if (is<Document>(root))
        downcast<Document>(*root).intersectionObserverDataIfExists()->observers.removeFirst(this);
    else if (root)
        downcast<Element>(*root).intersectionObserverDataIfExists()->observers.removeFirst(this);
    disconnect();
}

String IntersectionObserver::rootMargin() const
{
    StringBuilder stringBuilder;
    for (auto side : allBoxSides) {
        auto& length = m_rootMargin.at(side);
        stringBuilder.append(length.intValue(), length.isPercent() ? "%" : "px", side != BoxSide::Left ? " " : "");
    }
    return stringBuilder.toString();
}

bool IntersectionObserver::isObserving(const Element& element) const
{
    return m_observationTargets.findIf([&](auto& target) {
        return target.get() == &element;
    }) != notFound;
}

void IntersectionObserver::observe(Element& target)
{
    if (!trackingDocument() || !m_callback || isObserving(target))
        return;

    target.ensureIntersectionObserverData().registrations.append({ *this, std::nullopt });
    bool hadObservationTargets = hasObservationTargets();
    m_observationTargets.append(target);

    // Per the specification, we should dispatch at least one observation for the target. For this reason, we make sure to keep the
    // target alive until this first observation. This, in turn, will keep the IntersectionObserver's JS wrapper alive via
    // isReachableFromOpaqueRoots(), so the callback stays alive.
    m_targetsWaitingForFirstObservation.append(target);

    auto* document = trackingDocument();
    if (!hadObservationTargets)
        document->addIntersectionObserver(*this);
    document->scheduleInitialIntersectionObservationUpdate();
}

void IntersectionObserver::unobserve(Element& target)
{
    if (!removeTargetRegistration(target))
        return;

    bool removed = m_observationTargets.removeFirst(&target);
    ASSERT_UNUSED(removed, removed);
    m_targetsWaitingForFirstObservation.removeFirstMatching([&](auto& pendingTarget) { return pendingTarget.ptr() == &target; });

    if (!hasObservationTargets()) {
        if (auto* document = trackingDocument())
            document->removeIntersectionObserver(*this);
    }
}

void IntersectionObserver::disconnect()
{
    if (!hasObservationTargets())
        return;

    removeAllTargets();
    if (auto* document = trackingDocument())
        document->removeIntersectionObserver(*this);
}

auto IntersectionObserver::takeRecords() -> TakenRecords
{
    return { WTFMove(m_queuedEntries), WTFMove(m_pendingTargets) };
}

void IntersectionObserver::targetDestroyed(Element& target)
{
    m_observationTargets.removeFirst(&target);
    m_targetsWaitingForFirstObservation.removeFirstMatching([&](auto& pendingTarget) { return pendingTarget.ptr() == &target; });
    if (!hasObservationTargets()) {
        if (auto* document = trackingDocument())
            document->removeIntersectionObserver(*this);
    }
}

bool IntersectionObserver::removeTargetRegistration(Element& target)
{
    auto* observerData = target.intersectionObserverDataIfExists();
    if (!observerData)
        return false;

    auto& registrations = observerData->registrations;
    return registrations.removeFirstMatching([this](auto& registration) {
        return registration.observer.get() == this;
    });
}

void IntersectionObserver::removeAllTargets()
{
    for (auto& target : m_observationTargets) {
        bool removed = removeTargetRegistration(*target);
        ASSERT_UNUSED(removed, removed);
    }
    m_observationTargets.clear();
    m_targetsWaitingForFirstObservation.clear();
}

void IntersectionObserver::rootDestroyed()
{
    ASSERT(m_root);
    disconnect();
    m_root = nullptr;
}

std::optional<ReducedResolutionSeconds> IntersectionObserver::nowTimestamp() const
{
    if (auto* document = m_associatedDocument.get()) {
        if (auto* window = document->domWindow())
            return window->frozenNowTimestamp();
    }
    
    return std::nullopt;
}

void IntersectionObserver::appendQueuedEntry(Ref<IntersectionObserverEntry>&& entry)
{
    ASSERT(entry->target());
    m_pendingTargets.append(*entry->target());
    m_queuedEntries.append(WTFMove(entry));
}

void IntersectionObserver::notify()
{
    if (m_queuedEntries.isEmpty()) {
        ASSERT(m_pendingTargets.isEmpty());
        return;
    }

    auto takenRecords = takeRecords();
    auto targetsWaitingForFirstObservation = std::exchange(m_targetsWaitingForFirstObservation, { });

    // FIXME: The JSIntersectionObserver wrapper should be kept alive as long as the intersection observer can fire events.
    ASSERT(m_callback->hasCallback());
    if (!m_callback->hasCallback())
        return;

    auto* context = m_callback->scriptExecutionContext();
    if (!context)
        return;

    InspectorInstrumentation::willFireObserverCallback(*context, "IntersectionObserver"_s);
    m_callback->handleEvent(*this, WTFMove(takenRecords.records), *this);
    InspectorInstrumentation::didFireObserverCallback(*context);
}

bool IntersectionObserver::isReachableFromOpaqueRoots(JSC::AbstractSlotVisitor& visitor) const
{
    for (auto& target : m_observationTargets) {
        if (auto* element = target.get(); element && visitor.containsOpaqueRoot(element->opaqueRoot()))
            return true;
    }
    for (auto& target : m_pendingTargets) {
        if (visitor.containsOpaqueRoot(target->opaqueRoot()))
            return true;
    }
    return !m_targetsWaitingForFirstObservation.isEmpty();
}

} // namespace WebCore