Source/WebKit2/UIProcess/WebBackForwardList.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2010 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. AND ITS CONTRIBUTORS ``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 ITS 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 "WebBackForwardList.h"

 #include "APIArray.h"
 #include "SessionState.h"
 #include "WebPageProxy.h"
 #include <WebCore/DiagnosticLoggingClient.h>
 #include <WebCore/DiagnosticLoggingKeys.h>

 namespace WebKit {

 using namespace WebCore;

 // FIXME: Make this static once WebBackForwardListCF.cpp is no longer using it.
 uint64_t generateWebBackForwardItemID();

 uint64_t generateWebBackForwardItemID()
 {
     // These IDs exist in the UIProcess for items created by the UIProcess.
     // The IDs generated here need to never collide with the IDs created in WebBackForwardListProxy in the WebProcess.
     // We accomplish this by starting from 2, and only ever using even ids.
     static uint64_t uniqueHistoryItemID = 0;
     uniqueHistoryItemID += 2;
     return uniqueHistoryItemID;
 }

 static const unsigned DefaultCapacity = 100;

 WebBackForwardList::WebBackForwardList(WebPageProxy& page)
     : m_page(&page)
     , m_hasCurrentIndex(false)
     , m_currentIndex(0)
     , m_capacity(DefaultCapacity)
 {
 }

 WebBackForwardList::~WebBackForwardList()
 {
     // A WebBackForwardList should never be destroyed unless it's associated page has been closed or is invalid.
     ASSERT((!m_page && !m_hasCurrentIndex) || !m_page->isValid());
 }

 void WebBackForwardList::pageClosed()
 {
     // We should have always started out with an m_page and we should never close the page twice.
     ASSERT(m_page);

     if (m_page) {
         size_t size = m_entries.size();
         for (size_t i = 0; i < size; ++i) {
             ASSERT(m_entries[i]);
             if (!m_entries[i])
                 continue;

             didRemoveItem(*m_entries[i]);
         }
     }

     m_page = 0;
     m_entries.clear();
     m_hasCurrentIndex = false;
 }

 void WebBackForwardList::addItem(WebBackForwardListItem* newItem)
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     if (!m_capacity || !newItem || !m_page)
         return;

     Vector<RefPtr<WebBackForwardListItem>> removedItems;

     if (m_hasCurrentIndex) {
         m_page->recordAutomaticNavigationSnapshot();

         // Toss everything in the forward list.
         unsigned targetSize = m_currentIndex + 1;
         removedItems.reserveCapacity(m_entries.size() - targetSize);
         while (m_entries.size() > targetSize) {
             didRemoveItem(*m_entries.last());
             removedItems.append(WTFMove(m_entries.last()));
             m_entries.removeLast();
         }

         // Toss the first item if the list is getting too big, as long as we're not using it
         // (or even if we are, if we only want 1 entry).
         if (m_entries.size() == m_capacity && (m_currentIndex || m_capacity == 1)) {
             didRemoveItem(*m_entries[0]);
             removedItems.append(WTFMove(m_entries[0]));
             m_entries.remove(0);

             if (m_entries.isEmpty())
                 m_hasCurrentIndex = false;
             else
                 m_currentIndex--;
         }
     } else {
         // If we have no current item index we should also not have any entries.
         ASSERT(m_entries.isEmpty());

         // But just in case it does happen in practice we'll get back in to a consistent state now before adding the new item.
         size_t size = m_entries.size();
         for (size_t i = 0; i < size; ++i) {
             ASSERT(m_entries[i]);
             if (!m_entries[i])
                 continue;
             didRemoveItem(*m_entries[i]);
             removedItems.append(WTFMove(m_entries[i]));
         }
         m_entries.clear();
     }

     bool shouldKeepCurrentItem = true;

     if (!m_hasCurrentIndex) {
         ASSERT(m_entries.isEmpty());
         m_currentIndex = 0;
         m_hasCurrentIndex = true;
     } else {
         shouldKeepCurrentItem = m_page->shouldKeepCurrentBackForwardListItemInList(m_entries[m_currentIndex].get());
         if (shouldKeepCurrentItem)
             m_currentIndex++;
     }

     if (!shouldKeepCurrentItem) {
         // m_current should never be pointing past the end of the entries Vector.
         // If it is, something has gone wrong and we should not try to swap in the new item.
         ASSERT(m_currentIndex < m_entries.size());

         removedItems.append(m_entries[m_currentIndex]);
         m_entries[m_currentIndex] = newItem;
     } else {
         // m_current should never be pointing more than 1 past the end of the entries Vector.
         // If it is, something has gone wrong and we should not try to insert the new item.
         ASSERT(m_currentIndex <= m_entries.size());

         if (m_currentIndex <= m_entries.size())
             m_entries.insert(m_currentIndex, newItem);
     }

     m_page->didChangeBackForwardList(newItem, WTFMove(removedItems));
 }

 void WebBackForwardList::goToItem(WebBackForwardListItem* item)
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     if (!m_entries.size() || !item || !m_page || !m_hasCurrentIndex)
         return;

     size_t targetIndex = m_entries.find(item);

     // If the target item wasn't even in the list, there's nothing else to do.
     if (targetIndex == notFound)
         return;

     if (targetIndex < m_currentIndex) {
         unsigned delta = m_entries.size() - targetIndex - 1;
         String deltaValue = delta > 10 ? ASCIILiteral("over10") : String::number(delta);
         m_page->logDiagnosticMessage(WebCore::DiagnosticLoggingKeys::backNavigationDeltaKey(), deltaValue, ShouldSample::No);
     }

     // If we're going to an item different from the current item, ask the client if the current
     // item should remain in the list.
     WebBackForwardListItem* currentItem = m_entries[m_currentIndex].get();
     bool shouldKeepCurrentItem = true;
     if (currentItem != item) {
         m_page->recordAutomaticNavigationSnapshot();
         shouldKeepCurrentItem = m_page->shouldKeepCurrentBackForwardListItemInList(m_entries[m_currentIndex].get());
     }

     // If the client said to remove the current item, remove it and then update the target index.
     Vector<RefPtr<WebBackForwardListItem>> removedItems;
     if (!shouldKeepCurrentItem) {
         removedItems.append(currentItem);
         m_entries.remove(m_currentIndex);
         targetIndex = m_entries.find(item);

         ASSERT(targetIndex != notFound);
     }

     m_currentIndex = targetIndex;
     m_page->didChangeBackForwardList(nullptr, removedItems);
 }

 WebBackForwardListItem* WebBackForwardList::currentItem() const
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     return m_page && m_hasCurrentIndex ? m_entries[m_currentIndex].get() : nullptr;
 }

 WebBackForwardListItem* WebBackForwardList::backItem() const
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     return m_page && m_hasCurrentIndex && m_currentIndex ? m_entries[m_currentIndex - 1].get() : nullptr;
 }

 WebBackForwardListItem* WebBackForwardList::forwardItem() const
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     return m_page && m_hasCurrentIndex && m_entries.size() && m_currentIndex < m_entries.size() - 1 ? m_entries[m_currentIndex + 1].get() : nullptr;
 }

 WebBackForwardListItem* WebBackForwardList::itemAtIndex(int index) const
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     if (!m_hasCurrentIndex || !m_page)
         return nullptr;

     // Do range checks without doing math on index to avoid overflow.
     if (index < -backListCount())
         return nullptr;

     if (index > forwardListCount())
         return nullptr;

     return m_entries[index + m_currentIndex].get();
 }

 int WebBackForwardList::backListCount() const
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     return m_page && m_hasCurrentIndex ? m_currentIndex : 0;
 }

 int WebBackForwardList::forwardListCount() const
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     return m_page && m_hasCurrentIndex ? m_entries.size() - (m_currentIndex + 1) : 0;
 }

 Ref<API::Array> WebBackForwardList::backList() const
 {
     return backListAsAPIArrayWithLimit(backListCount());
 }

 Ref<API::Array> WebBackForwardList::forwardList() const
 {
     return forwardListAsAPIArrayWithLimit(forwardListCount());
 }

 Ref<API::Array> WebBackForwardList::backListAsAPIArrayWithLimit(unsigned limit) const
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     if (!m_page || !m_hasCurrentIndex)
         return API::Array::create();

     unsigned backListSize = static_cast<unsigned>(backListCount());
     unsigned size = std::min(backListSize, limit);
     if (!size)
         return API::Array::create();

     Vector<RefPtr<API::Object>> vector;
     vector.reserveInitialCapacity(size);

     ASSERT(backListSize >= size);
     for (unsigned i = backListSize - size; i < backListSize; ++i) {
         ASSERT(m_entries[i]);
         vector.uncheckedAppend(m_entries[i].get());
     }

     return API::Array::create(WTFMove(vector));
 }

 Ref<API::Array> WebBackForwardList::forwardListAsAPIArrayWithLimit(unsigned limit) const
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     if (!m_page || !m_hasCurrentIndex)
         return API::Array::create();

     unsigned size = std::min(static_cast<unsigned>(forwardListCount()), limit);
     if (!size)
         return API::Array::create();

     Vector<RefPtr<API::Object>> vector;
     vector.reserveInitialCapacity(size);

     unsigned last = m_currentIndex + size;
     ASSERT(last < m_entries.size());
     for (unsigned i = m_currentIndex + 1; i <= last; ++i) {
         ASSERT(m_entries[i]);
         vector.uncheckedAppend(m_entries[i].get());
     }

     return API::Array::create(WTFMove(vector));
 }

 void WebBackForwardList::removeAllItems()
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     Vector<RefPtr<WebBackForwardListItem>> removedItems;

     for (auto& entry : m_entries) {
         ASSERT(entry);
         if (!entry)
             continue;

         didRemoveItem(*entry);
         removedItems.append(WTFMove(entry));
     }

     m_entries.clear();
     m_hasCurrentIndex = false;
     m_page->didChangeBackForwardList(nullptr, WTFMove(removedItems));
 }

 void WebBackForwardList::clear()
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     size_t size = m_entries.size();
     if (!m_page || size <= 1)
         return;

     RefPtr<WebBackForwardListItem> currentItem = this->currentItem();
     Vector<RefPtr<WebBackForwardListItem>> removedItems;

     if (!currentItem) {
         // We should only ever have no current item if we also have no current item index.
         ASSERT(!m_hasCurrentIndex);

         // But just in case it does happen in practice we should get back into a consistent state now.
         for (size_t i = 0; i < size; ++i) {
             ASSERT(m_entries[i]);
             if (!m_entries[i])
                 continue;

             didRemoveItem(*m_entries[i]);
             removedItems.append(WTFMove(m_entries[i]));
         }

         m_entries.clear();
         m_hasCurrentIndex = false;
         m_page->didChangeBackForwardList(nullptr, WTFMove(removedItems));

         return;
     }

     for (size_t i = 0; i < size; ++i) {
         ASSERT(m_entries[i]);
         if (m_entries[i] && m_entries[i] != currentItem)
             didRemoveItem(*m_entries[i]);
     }

     removedItems.reserveCapacity(size - 1);
     for (size_t i = 0; i < size; ++i) {
         if (i != m_currentIndex && m_hasCurrentIndex && m_entries[i])
             removedItems.append(WTFMove(m_entries[i]));
     }

     m_currentIndex = 0;

     if (currentItem) {
         m_entries.shrink(1);
         m_entries[0] = WTFMove(currentItem);
     } else {
         m_entries.clear();
         m_hasCurrentIndex = false;
     }

     m_page->didChangeBackForwardList(nullptr, WTFMove(removedItems));
 }

 BackForwardListState WebBackForwardList::backForwardListState(const std::function<bool (WebBackForwardListItem&)>& filter) const
 {
     ASSERT(!m_hasCurrentIndex || m_currentIndex < m_entries.size());

     BackForwardListState backForwardListState;
     if (m_hasCurrentIndex)
         backForwardListState.currentIndex = m_currentIndex;

     for (size_t i = 0; i < m_entries.size(); ++i) {
         auto& entry = *m_entries[i];

         if (filter && !filter(entry)) {
             auto& currentIndex = backForwardListState.currentIndex;
             if (currentIndex && i <= currentIndex.value() && currentIndex.value())
                 --currentIndex.value();

             continue;
         }

         backForwardListState.items.append(entry.itemState());
     }

     if (backForwardListState.items.isEmpty())
         backForwardListState.currentIndex = std::nullopt;
     else if (backForwardListState.items.size() <= backForwardListState.currentIndex.value())
         backForwardListState.currentIndex = backForwardListState.items.size() - 1;

     return backForwardListState;
 }

 void WebBackForwardList::restoreFromState(BackForwardListState backForwardListState)
 {
     Vector<RefPtr<WebBackForwardListItem>> items;
     items.reserveInitialCapacity(backForwardListState.items.size());

     for (auto& backForwardListItemState : backForwardListState.items) {
         backForwardListItemState.identifier = generateWebBackForwardItemID();
         items.uncheckedAppend(WebBackForwardListItem::create(WTFMove(backForwardListItemState), m_page->pageID()));
     }
     m_hasCurrentIndex = !!backForwardListState.currentIndex;
     m_currentIndex = backForwardListState.currentIndex.value_or(0);
     m_entries = WTFMove(items);
 }

 Vector<BackForwardListItemState> WebBackForwardList::itemStates() const
 {
     Vector<BackForwardListItemState> itemStates;
     itemStates.reserveInitialCapacity(m_entries.size());

     for (const auto& entry : m_entries)
         itemStates.uncheckedAppend(entry->itemState());

     return itemStates;
 }

 void WebBackForwardList::didRemoveItem(WebBackForwardListItem& backForwardListItem)
 {
     m_page->backForwardRemovedItem(backForwardListItem.itemID());

 #if PLATFORM(COCOA)
     backForwardListItem.setSnapshot(nullptr);
 #endif
 }

 } // namespace WebKit
	/*
	* Copyright (C) 2010 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. AND ITS CONTRIBUTORS ``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 ITS 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 "WebBackForwardList.h"

	#include "APIArray.h"
	#include "SessionState.h"
	#include "WebPageProxy.h"
	#include <WebCore/DiagnosticLoggingClient.h>
	#include <WebCore/DiagnosticLoggingKeys.h>

	namespace WebKit {

	using namespace WebCore;

	// FIXME: Make this static once WebBackForwardListCF.cpp is no longer using it.
	uint64_t generateWebBackForwardItemID();

	uint64_t generateWebBackForwardItemID()
	{
	// These IDs exist in the UIProcess for items created by the UIProcess.
	// The IDs generated here need to never collide with the IDs created in WebBackForwardListProxy in the WebProcess.
	// We accomplish this by starting from 2, and only ever using even ids.
	static uint64_t uniqueHistoryItemID = 0;
	uniqueHistoryItemID += 2;
	return uniqueHistoryItemID;
	}

	static const unsigned DefaultCapacity = 100;

	WebBackForwardList::WebBackForwardList(WebPageProxy& page)
	: m_page(&page)
	, m_hasCurrentIndex(false)
	, m_currentIndex(0)
	, m_capacity(DefaultCapacity)
	{
	}

	WebBackForwardList::~WebBackForwardList()
	{
	// A WebBackForwardList should never be destroyed unless it's associated page has been closed or is invalid.
	ASSERT((!m_page && !m_hasCurrentIndex) \|\| !m_page->isValid());
	}

	void WebBackForwardList::pageClosed()
	{
	// We should have always started out with an m_page and we should never close the page twice.
	ASSERT(m_page);

	if (m_page) {
	size_t size = m_entries.size();
	for (size_t i = 0; i < size; ++i) {
	ASSERT(m_entries[i]);
	if (!m_entries[i])
	continue;

	didRemoveItem(*m_entries[i]);
	}
	}

	m_page = 0;
	m_entries.clear();
	m_hasCurrentIndex = false;
	}

	void WebBackForwardList::addItem(WebBackForwardListItem* newItem)
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	if (!m_capacity \|\| !newItem \|\| !m_page)
	return;

	Vector<RefPtr<WebBackForwardListItem>> removedItems;

	if (m_hasCurrentIndex) {
	m_page->recordAutomaticNavigationSnapshot();

	// Toss everything in the forward list.
	unsigned targetSize = m_currentIndex + 1;
	removedItems.reserveCapacity(m_entries.size() - targetSize);
	while (m_entries.size() > targetSize) {
	didRemoveItem(*m_entries.last());
	removedItems.append(WTFMove(m_entries.last()));
	m_entries.removeLast();
	}

	// Toss the first item if the list is getting too big, as long as we're not using it
	// (or even if we are, if we only want 1 entry).
	if (m_entries.size() == m_capacity && (m_currentIndex \|\| m_capacity == 1)) {
	didRemoveItem(*m_entries[0]);
	removedItems.append(WTFMove(m_entries[0]));
	m_entries.remove(0);

	if (m_entries.isEmpty())
	m_hasCurrentIndex = false;
	else
	m_currentIndex--;
	}
	} else {
	// If we have no current item index we should also not have any entries.
	ASSERT(m_entries.isEmpty());

	// But just in case it does happen in practice we'll get back in to a consistent state now before adding the new item.
	size_t size = m_entries.size();
	for (size_t i = 0; i < size; ++i) {
	ASSERT(m_entries[i]);
	if (!m_entries[i])
	continue;
	didRemoveItem(*m_entries[i]);
	removedItems.append(WTFMove(m_entries[i]));
	}
	m_entries.clear();
	}

	bool shouldKeepCurrentItem = true;

	if (!m_hasCurrentIndex) {
	ASSERT(m_entries.isEmpty());
	m_currentIndex = 0;
	m_hasCurrentIndex = true;
	} else {
	shouldKeepCurrentItem = m_page->shouldKeepCurrentBackForwardListItemInList(m_entries[m_currentIndex].get());
	if (shouldKeepCurrentItem)
	m_currentIndex++;
	}

	if (!shouldKeepCurrentItem) {
	// m_current should never be pointing past the end of the entries Vector.
	// If it is, something has gone wrong and we should not try to swap in the new item.
	ASSERT(m_currentIndex < m_entries.size());

	removedItems.append(m_entries[m_currentIndex]);
	m_entries[m_currentIndex] = newItem;
	} else {
	// m_current should never be pointing more than 1 past the end of the entries Vector.
	// If it is, something has gone wrong and we should not try to insert the new item.
	ASSERT(m_currentIndex <= m_entries.size());

	if (m_currentIndex <= m_entries.size())
	m_entries.insert(m_currentIndex, newItem);
	}

	m_page->didChangeBackForwardList(newItem, WTFMove(removedItems));
	}

	void WebBackForwardList::goToItem(WebBackForwardListItem* item)
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	if (!m_entries.size() \|\| !item \|\| !m_page \|\| !m_hasCurrentIndex)
	return;

	size_t targetIndex = m_entries.find(item);

	// If the target item wasn't even in the list, there's nothing else to do.
	if (targetIndex == notFound)
	return;

	if (targetIndex < m_currentIndex) {
	unsigned delta = m_entries.size() - targetIndex - 1;
	String deltaValue = delta > 10 ? ASCIILiteral("over10") : String::number(delta);
	m_page->logDiagnosticMessage(WebCore::DiagnosticLoggingKeys::backNavigationDeltaKey(), deltaValue, ShouldSample::No);
	}

	// If we're going to an item different from the current item, ask the client if the current
	// item should remain in the list.
	WebBackForwardListItem* currentItem = m_entries[m_currentIndex].get();
	bool shouldKeepCurrentItem = true;
	if (currentItem != item) {
	m_page->recordAutomaticNavigationSnapshot();
	shouldKeepCurrentItem = m_page->shouldKeepCurrentBackForwardListItemInList(m_entries[m_currentIndex].get());
	}

	// If the client said to remove the current item, remove it and then update the target index.
	Vector<RefPtr<WebBackForwardListItem>> removedItems;
	if (!shouldKeepCurrentItem) {
	removedItems.append(currentItem);
	m_entries.remove(m_currentIndex);
	targetIndex = m_entries.find(item);

	ASSERT(targetIndex != notFound);
	}

	m_currentIndex = targetIndex;
	m_page->didChangeBackForwardList(nullptr, removedItems);
	}

	WebBackForwardListItem* WebBackForwardList::currentItem() const
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	return m_page && m_hasCurrentIndex ? m_entries[m_currentIndex].get() : nullptr;
	}

	WebBackForwardListItem* WebBackForwardList::backItem() const
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	return m_page && m_hasCurrentIndex && m_currentIndex ? m_entries[m_currentIndex - 1].get() : nullptr;
	}

	WebBackForwardListItem* WebBackForwardList::forwardItem() const
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	return m_page && m_hasCurrentIndex && m_entries.size() && m_currentIndex < m_entries.size() - 1 ? m_entries[m_currentIndex + 1].get() : nullptr;
	}

	WebBackForwardListItem* WebBackForwardList::itemAtIndex(int index) const
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	if (!m_hasCurrentIndex \|\| !m_page)
	return nullptr;

	// Do range checks without doing math on index to avoid overflow.
	if (index < -backListCount())
	return nullptr;

	if (index > forwardListCount())
	return nullptr;

	return m_entries[index + m_currentIndex].get();
	}

	int WebBackForwardList::backListCount() const
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	return m_page && m_hasCurrentIndex ? m_currentIndex : 0;
	}

	int WebBackForwardList::forwardListCount() const
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	return m_page && m_hasCurrentIndex ? m_entries.size() - (m_currentIndex + 1) : 0;
	}

	Ref<API::Array> WebBackForwardList::backList() const
	{
	return backListAsAPIArrayWithLimit(backListCount());
	}

	Ref<API::Array> WebBackForwardList::forwardList() const
	{
	return forwardListAsAPIArrayWithLimit(forwardListCount());
	}

	Ref<API::Array> WebBackForwardList::backListAsAPIArrayWithLimit(unsigned limit) const
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	if (!m_page \|\| !m_hasCurrentIndex)
	return API::Array::create();

	unsigned backListSize = static_cast<unsigned>(backListCount());
	unsigned size = std::min(backListSize, limit);
	if (!size)
	return API::Array::create();

	Vector<RefPtr<API::Object>> vector;
	vector.reserveInitialCapacity(size);

	ASSERT(backListSize >= size);
	for (unsigned i = backListSize - size; i < backListSize; ++i) {
	ASSERT(m_entries[i]);
	vector.uncheckedAppend(m_entries[i].get());
	}

	return API::Array::create(WTFMove(vector));
	}

	Ref<API::Array> WebBackForwardList::forwardListAsAPIArrayWithLimit(unsigned limit) const
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	if (!m_page \|\| !m_hasCurrentIndex)
	return API::Array::create();

	unsigned size = std::min(static_cast<unsigned>(forwardListCount()), limit);
	if (!size)
	return API::Array::create();

	Vector<RefPtr<API::Object>> vector;
	vector.reserveInitialCapacity(size);

	unsigned last = m_currentIndex + size;
	ASSERT(last < m_entries.size());
	for (unsigned i = m_currentIndex + 1; i <= last; ++i) {
	ASSERT(m_entries[i]);
	vector.uncheckedAppend(m_entries[i].get());
	}

	return API::Array::create(WTFMove(vector));
	}

	void WebBackForwardList::removeAllItems()
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	Vector<RefPtr<WebBackForwardListItem>> removedItems;

	for (auto& entry : m_entries) {
	ASSERT(entry);
	if (!entry)
	continue;

	didRemoveItem(*entry);
	removedItems.append(WTFMove(entry));
	}

	m_entries.clear();
	m_hasCurrentIndex = false;
	m_page->didChangeBackForwardList(nullptr, WTFMove(removedItems));
	}

	void WebBackForwardList::clear()
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	size_t size = m_entries.size();
	if (!m_page \|\| size <= 1)
	return;

	RefPtr<WebBackForwardListItem> currentItem = this->currentItem();
	Vector<RefPtr<WebBackForwardListItem>> removedItems;

	if (!currentItem) {
	// We should only ever have no current item if we also have no current item index.
	ASSERT(!m_hasCurrentIndex);

	// But just in case it does happen in practice we should get back into a consistent state now.
	for (size_t i = 0; i < size; ++i) {
	ASSERT(m_entries[i]);
	if (!m_entries[i])
	continue;

	didRemoveItem(*m_entries[i]);
	removedItems.append(WTFMove(m_entries[i]));
	}

	m_entries.clear();
	m_hasCurrentIndex = false;
	m_page->didChangeBackForwardList(nullptr, WTFMove(removedItems));

	return;
	}

	for (size_t i = 0; i < size; ++i) {
	ASSERT(m_entries[i]);
	if (m_entries[i] && m_entries[i] != currentItem)
	didRemoveItem(*m_entries[i]);
	}

	removedItems.reserveCapacity(size - 1);
	for (size_t i = 0; i < size; ++i) {
	if (i != m_currentIndex && m_hasCurrentIndex && m_entries[i])
	removedItems.append(WTFMove(m_entries[i]));
	}

	m_currentIndex = 0;

	if (currentItem) {
	m_entries.shrink(1);
	m_entries[0] = WTFMove(currentItem);
	} else {
	m_entries.clear();
	m_hasCurrentIndex = false;
	}

	m_page->didChangeBackForwardList(nullptr, WTFMove(removedItems));
	}

	BackForwardListState WebBackForwardList::backForwardListState(const std::function<bool (WebBackForwardListItem&)>& filter) const
	{
	ASSERT(!m_hasCurrentIndex \|\| m_currentIndex < m_entries.size());

	BackForwardListState backForwardListState;
	if (m_hasCurrentIndex)
	backForwardListState.currentIndex = m_currentIndex;

	for (size_t i = 0; i < m_entries.size(); ++i) {
	auto& entry = *m_entries[i];

	if (filter && !filter(entry)) {
	auto& currentIndex = backForwardListState.currentIndex;
	if (currentIndex && i <= currentIndex.value() && currentIndex.value())
	--currentIndex.value();

	continue;
	}

	backForwardListState.items.append(entry.itemState());
	}

	if (backForwardListState.items.isEmpty())
	backForwardListState.currentIndex = std::nullopt;
	else if (backForwardListState.items.size() <= backForwardListState.currentIndex.value())
	backForwardListState.currentIndex = backForwardListState.items.size() - 1;

	return backForwardListState;
	}

	void WebBackForwardList::restoreFromState(BackForwardListState backForwardListState)
	{
	Vector<RefPtr<WebBackForwardListItem>> items;
	items.reserveInitialCapacity(backForwardListState.items.size());

	for (auto& backForwardListItemState : backForwardListState.items) {
	backForwardListItemState.identifier = generateWebBackForwardItemID();
	items.uncheckedAppend(WebBackForwardListItem::create(WTFMove(backForwardListItemState), m_page->pageID()));
	}
	m_hasCurrentIndex = !!backForwardListState.currentIndex;
	m_currentIndex = backForwardListState.currentIndex.value_or(0);
	m_entries = WTFMove(items);
	}

	Vector<BackForwardListItemState> WebBackForwardList::itemStates() const
	{
	Vector<BackForwardListItemState> itemStates;
	itemStates.reserveInitialCapacity(m_entries.size());

	for (const auto& entry : m_entries)
	itemStates.uncheckedAppend(entry->itemState());

	return itemStates;
	}

	void WebBackForwardList::didRemoveItem(WebBackForwardListItem& backForwardListItem)
	{
	m_page->backForwardRemovedItem(backForwardListItem.itemID());

	#if PLATFORM(COCOA)
	backForwardListItem.setSnapshot(nullptr);
	#endif
	}

	} // namespace WebKit