/*
 * Copyright (C) 2011 Google Inc. All rights reserved.
 * Copyright (C) 2018-2022 Apple Inc. All rights reserved.
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 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * 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.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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 */

#include "config.h"

#include "MutationObserver.h"

#include "Document.h"
#include "GCReachableRef.h"
#include "HTMLSlotElement.h"
#include "InspectorInstrumentation.h"
#include "MutationCallback.h"
#include "MutationObserverRegistration.h"
#include "MutationRecord.h"
#include "WindowEventLoop.h"
#include <algorithm>
#include <wtf/IsoMallocInlines.h>
#include <wtf/MainThread.h>
#include <wtf/NeverDestroyed.h>

namespace WebCore {

WTF_MAKE_ISO_ALLOCATED_IMPL(MutationObserver);

static unsigned s_observerPriority = 0;

Ref<MutationObserver> MutationObserver::create(Ref<MutationCallback>&& callback)
{
    ASSERT(isMainThread());
    return adoptRef(*new MutationObserver(WTFMove(callback)));
}

MutationObserver::MutationObserver(Ref<MutationCallback>&& callback)
    : m_callback(WTFMove(callback))
    , m_priority(s_observerPriority++)
{
}

MutationObserver::~MutationObserver()
{
    ASSERT(m_registrations.computesEmpty());
}

bool MutationObserver::validateOptions(MutationObserverOptions options)
{
    return options.containsAny(AllMutationTypes)
        && (options.contains(OptionType::Attributes) || !options.contains(OptionType::AttributeOldValue))
        && (options.contains(OptionType::Attributes) || !options.contains(OptionType::AttributeFilter))
        && (options.contains(OptionType::CharacterData) || !options.contains(OptionType::CharacterDataOldValue));
}

ExceptionOr<void> MutationObserver::observe(Node& node, const Init& init)
{
    MutationObserverOptions options;

    if (init.childList)
        options.add(OptionType::ChildList);
    if (init.subtree)
        options.add(OptionType::Subtree);
    if (init.attributeOldValue.value_or(false))
        options.add(OptionType::AttributeOldValue);
    if (init.characterDataOldValue.value_or(false))
        options.add(OptionType::CharacterDataOldValue);

    HashSet<AtomString> attributeFilter;
    if (init.attributeFilter) {
        for (auto& value : init.attributeFilter.value())
            attributeFilter.add(value);
        options.add(OptionType::AttributeFilter);
    }

    if (init.attributes ? init.attributes.value() : options.containsAny({ OptionType::AttributeFilter, OptionType::AttributeOldValue }))
        options.add(OptionType::Attributes);

    if (init.characterData ? init.characterData.value() : options.contains(OptionType::CharacterDataOldValue))
        options.add(OptionType::CharacterData);

    if (!validateOptions(options))
        return Exception { TypeError };

    node.registerMutationObserver(*this, options, attributeFilter);

    return { };
}

auto MutationObserver::takeRecords() -> TakenRecords
{
    return { WTFMove(m_records), WTFMove(m_pendingTargets) };
}

void MutationObserver::disconnect()
{
    m_pendingTargets.clear();
    m_records.clear();
    WeakHashSet registrations { m_registrations };
    for (auto& registration : registrations) {
        Ref nodeRef { registration.node() };
        nodeRef->unregisterMutationObserver(registration);
    }
}

void MutationObserver::observationStarted(MutationObserverRegistration& registration)
{
    ASSERT(!m_registrations.contains(registration));
    m_registrations.add(registration);
}

void MutationObserver::observationEnded(MutationObserverRegistration& registration)
{
    ASSERT(m_registrations.contains(registration));
    m_registrations.remove(registration);
}

void MutationObserver::enqueueMutationRecord(Ref<MutationRecord>&& mutation)
{
    ASSERT(isMainThread());
    ASSERT(mutation->target());
    Ref document = mutation->target()->document();

    m_pendingTargets.add(*mutation->target());
    m_records.append(WTFMove(mutation));

    Ref eventLoop = document->windowEventLoop();
    eventLoop->activeMutationObservers().add(this);
    eventLoop->queueMutationObserverCompoundMicrotask();
}

void MutationObserver::enqueueSlotChangeEvent(HTMLSlotElement& slot)
{
    ASSERT(isMainThread());
    Ref eventLoop = slot.document().windowEventLoop();
    auto& list = eventLoop->signalSlotList();
    ASSERT(list.findIf([&slot](auto& entry) { return entry.ptr() == &slot; }) == notFound);
    list.append(slot);

    eventLoop->queueMutationObserverCompoundMicrotask();
}

void MutationObserver::setHasTransientRegistration(Document& document)
{
    Ref eventLoop = document.windowEventLoop();
    eventLoop->activeMutationObservers().add(this);
    eventLoop->queueMutationObserverCompoundMicrotask();
}

bool MutationObserver::isReachableFromOpaqueRoots(JSC::AbstractSlotVisitor& visitor) const
{
    for (auto& registration : m_registrations) {
        if (registration.isReachableFromOpaqueRoots(visitor))
            return true;
    }
    return false;
}

bool MutationObserver::canDeliver()
{
    return m_callback->canInvokeCallback();
}

void MutationObserver::deliver()
{
    ASSERT(canDeliver());

    // Calling takeTransientRegistrations() can modify m_registrations, so it's necessary
    // to make a copy of the transient registrations before operating on them.
    Vector<MutationObserverRegistration*, 1> transientRegistrations;
    Vector<std::unique_ptr<HashSet<GCReachableRef<Node>>>, 1> nodesToKeepAlive;
    HashSet<GCReachableRef<Node>> pendingTargets;
    pendingTargets.swap(m_pendingTargets);
    for (auto& registration : m_registrations) {
        if (registration.hasTransientRegistrations())
            transientRegistrations.append(&registration);
    }
    for (auto& registration : transientRegistrations)
        nodesToKeepAlive.append(registration->takeTransientRegistrations());

    if (m_records.isEmpty()) {
        ASSERT(m_pendingTargets.isEmpty());
        return;
    }

    Vector<Ref<MutationRecord>> records;
    records.swap(m_records);

    // FIXME: Keep mutation observer callback as long as its observed nodes are alive. See https://webkit.org/b/179224.
    if (m_callback->hasCallback()) {
        auto* context = m_callback->scriptExecutionContext();
        if (!context)
            return;

        InspectorInstrumentation::willFireObserverCallback(*context, "MutationObserver"_s);
        m_callback->handleEvent(*this, records, *this);
        InspectorInstrumentation::didFireObserverCallback(*context);
    }
}

// https://dom.spec.whatwg.org/#notify-mutation-observers
void MutationObserver::notifyMutationObservers(WindowEventLoop& eventLoop)
{
    if (!eventLoop.suspendedMutationObservers().isEmpty()) {
        for (auto& observer : copyToVector(eventLoop.suspendedMutationObservers())) {
            if (!observer->canDeliver())
                continue;

            eventLoop.suspendedMutationObservers().remove(observer);
            eventLoop.activeMutationObservers().add(observer);
        }
    }

    while (!eventLoop.activeMutationObservers().isEmpty() || !eventLoop.signalSlotList().isEmpty()) {
        // 2. Let notify list be a copy of unit of related similar-origin browsing contexts' list of MutationObserver objects.
        auto notifyList = copyToVector(eventLoop.activeMutationObservers());
        eventLoop.activeMutationObservers().clear();
        std::sort(notifyList.begin(), notifyList.end(), [](auto& lhs, auto& rhs) {
            return lhs->m_priority < rhs->m_priority;
        });

        // 3. Let signalList be a copy of unit of related similar-origin browsing contexts' signal slot list.
        // 4. Empty unit of related similar-origin browsing contexts' signal slot list.
        Vector<GCReachableRef<HTMLSlotElement>> slotList;
        if (!eventLoop.signalSlotList().isEmpty()) {
            slotList.swap(eventLoop.signalSlotList());
            for (auto& slot : slotList)
                slot->didRemoveFromSignalSlotList();
        }

        // 5. For each MutationObserver object mo in notify list, execute a compound microtask subtask
        for (auto& observer : notifyList) {
            if (observer->canDeliver())
                observer->deliver();
            else
                eventLoop.suspendedMutationObservers().add(observer);
        }

        // 6. For each slot slot in signalList, in order, fire an event named slotchange, with its bubbles attribute set to true, at slot.
        for (auto& slot : slotList)
            slot->dispatchSlotChangeEvent();
    }
}

} // namespace WebCore