// Copyright 2014 The Chromium Authors. All rights reserved.
// Copyright (C) 2016 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:
//
//    * 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.
//    * Neither the name of Google Inc. nor the names of its
// 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
// "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 THE COPYRIGHT
// OWNER 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 "CSSSelectorParser.h"

#include "CSSParserContext.h"
#include "CSSSelectorList.h"
#include "StyleSheetContents.h"
#include <memory>

namespace WebCore {

CSSSelectorList CSSSelectorParser::parseSelector(CSSParserTokenRange range, const CSSParserContext& context, StyleSheetContents* styleSheet)
{
    CSSSelectorParser parser(context, styleSheet);
    range.consumeWhitespace();
    CSSSelectorList result = parser.consumeComplexSelectorList(range);
    if (!range.atEnd())
        return CSSSelectorList();
    return result;
}

CSSSelectorParser::CSSSelectorParser(const CSSParserContext& context, StyleSheetContents* styleSheet)
    : m_context(context)
    , m_styleSheet(styleSheet)
{
}

CSSSelectorList CSSSelectorParser::consumeComplexSelectorList(CSSParserTokenRange& range)
{
    Vector<std::unique_ptr<CSSParserSelector>> selectorList;
    std::unique_ptr<CSSParserSelector> selector = consumeComplexSelector(range);
    if (!selector)
        return CSSSelectorList();
    selectorList.append(WTFMove(selector));
    while (!range.atEnd() && range.peek().type() == CommaToken) {
        range.consumeIncludingWhitespace();
        selector = consumeComplexSelector(range);
        if (!selector)
            return CSSSelectorList();
        selectorList.append(WTFMove(selector));
    }

    if (m_failedParsing)
        return { };
    return CSSSelectorList { WTFMove(selectorList) };
}

CSSSelectorList CSSSelectorParser::consumeCompoundSelectorList(CSSParserTokenRange& range)
{
    Vector<std::unique_ptr<CSSParserSelector>> selectorList;
    std::unique_ptr<CSSParserSelector> selector = consumeCompoundSelector(range);
    range.consumeWhitespace();
    if (!selector)
        return CSSSelectorList();
    selectorList.append(WTFMove(selector));
    while (!range.atEnd() && range.peek().type() == CommaToken) {
        range.consumeIncludingWhitespace();
        selector = consumeCompoundSelector(range);
        range.consumeWhitespace();
        if (!selector)
            return CSSSelectorList();
        selectorList.append(WTFMove(selector));
    }

    if (m_failedParsing)
        return { };
    return CSSSelectorList { WTFMove(selectorList) };
}

static bool consumeLangArgumentList(std::unique_ptr<Vector<AtomString>>& argumentList, CSSParserTokenRange& range)
{
    const CSSParserToken& ident = range.consumeIncludingWhitespace();
    if (ident.type() != IdentToken && ident.type() != StringToken)
        return false;
    StringView string = ident.value();
    if (string.startsWith("--"))
        return false;
    argumentList->append(string.toAtomString());
    while (!range.atEnd() && range.peek().type() == CommaToken) {
        range.consumeIncludingWhitespace();
        const CSSParserToken& ident = range.consumeIncludingWhitespace();
        if (ident.type() != IdentToken && ident.type() != StringToken)
            return false;
        StringView string = ident.value();
        if (string.startsWith("--"))
            return false;
        argumentList->append(string.toAtomString());
    }
    return range.atEnd();
}

namespace {

enum CompoundSelectorFlags {
    HasPseudoElementForRightmostCompound = 1 << 0,
    HasContentPseudoElement = 1 << 1
};

unsigned extractCompoundFlags(const CSSParserSelector& simpleSelector, CSSParserMode parserMode)
{
    if (simpleSelector.match() != CSSSelector::PseudoElement)
        return 0;
    
    // FIXME: https://bugs.webkit.org/show_bug.cgi?id=161747
    // The UASheetMode check is a work-around to allow this selector in mediaControls(New).css:
    // input[type="range" i]::-webkit-media-slider-container > div {
    if (parserMode == UASheetMode && simpleSelector.pseudoElementType() == CSSSelector::PseudoElementWebKitCustom)
        return 0;
    return HasPseudoElementForRightmostCompound;
}

} // namespace

static bool isDescendantCombinator(CSSSelector::RelationType relation)
{
    return relation == CSSSelector::DescendantSpace;
}

std::unique_ptr<CSSParserSelector> CSSSelectorParser::consumeComplexSelector(CSSParserTokenRange& range)
{
    std::unique_ptr<CSSParserSelector> selector = consumeCompoundSelector(range);
    if (!selector)
        return nullptr;

    unsigned previousCompoundFlags = 0;

    for (CSSParserSelector* simple = selector.get(); simple && !previousCompoundFlags; simple = simple->tagHistory())
        previousCompoundFlags |= extractCompoundFlags(*simple, m_context.mode);

    while (auto combinator = consumeCombinator(range)) {
        std::unique_ptr<CSSParserSelector> nextSelector = consumeCompoundSelector(range);
        if (!nextSelector)
            return isDescendantCombinator(combinator) ? WTFMove(selector) : nullptr;
        if (previousCompoundFlags & HasPseudoElementForRightmostCompound)
            return nullptr;
        CSSParserSelector* end = nextSelector.get();
        unsigned compoundFlags = extractCompoundFlags(*end, m_context.mode);
        while (end->tagHistory()) {
            end = end->tagHistory();
            compoundFlags |= extractCompoundFlags(*end, m_context.mode);
        }
        end->setRelation(combinator);
        previousCompoundFlags = compoundFlags;
        end->setTagHistory(WTFMove(selector));

        selector = WTFMove(nextSelector);
    }

    return selector;
}

namespace {

bool isScrollbarPseudoClass(CSSSelector::PseudoClassType pseudo)
{
    switch (pseudo) {
    case CSSSelector::PseudoClassEnabled:
    case CSSSelector::PseudoClassDisabled:
    case CSSSelector::PseudoClassHover:
    case CSSSelector::PseudoClassActive:
    case CSSSelector::PseudoClassHorizontal:
    case CSSSelector::PseudoClassVertical:
    case CSSSelector::PseudoClassDecrement:
    case CSSSelector::PseudoClassIncrement:
    case CSSSelector::PseudoClassStart:
    case CSSSelector::PseudoClassEnd:
    case CSSSelector::PseudoClassDoubleButton:
    case CSSSelector::PseudoClassSingleButton:
    case CSSSelector::PseudoClassNoButton:
    case CSSSelector::PseudoClassCornerPresent:
    case CSSSelector::PseudoClassWindowInactive:
        return true;
    default:
        return false;
    }
}

bool isUserActionPseudoClass(CSSSelector::PseudoClassType pseudo)
{
    switch (pseudo) {
    case CSSSelector::PseudoClassHover:
    case CSSSelector::PseudoClassFocus:
    case CSSSelector::PseudoClassActive:
    case CSSSelector::PseudoClassFocusWithin:
        return true;
    default:
        return false;
    }
}

bool isPseudoClassValidAfterPseudoElement(CSSSelector::PseudoClassType pseudoClass, CSSSelector::PseudoElementType compoundPseudoElement)
{
    switch (compoundPseudoElement) {
    case CSSSelector::PseudoElementPart:
        return !isTreeStructuralPseudoClass(pseudoClass);
    case CSSSelector::PseudoElementResizer:
    case CSSSelector::PseudoElementScrollbar:
    case CSSSelector::PseudoElementScrollbarCorner:
    case CSSSelector::PseudoElementScrollbarButton:
    case CSSSelector::PseudoElementScrollbarThumb:
    case CSSSelector::PseudoElementScrollbarTrack:
    case CSSSelector::PseudoElementScrollbarTrackPiece:
        return isScrollbarPseudoClass(pseudoClass);
    case CSSSelector::PseudoElementSelection:
        return pseudoClass == CSSSelector::PseudoClassWindowInactive;
    case CSSSelector::PseudoElementWebKitCustom:
    case CSSSelector::PseudoElementWebKitCustomLegacyPrefixed:
        return isUserActionPseudoClass(pseudoClass);
    default:
        return false;
    }
}

bool isSimpleSelectorValidAfterPseudoElement(const CSSParserSelector& simpleSelector, CSSSelector::PseudoElementType compoundPseudoElement)
{
    if (compoundPseudoElement == CSSSelector::PseudoElementUnknown)
        return true;
    if (compoundPseudoElement == CSSSelector::PseudoElementPart) {
        if (simpleSelector.match() == CSSSelector::PseudoElement && simpleSelector.pseudoElementType() != CSSSelector::PseudoElementPart)
            return true;
    }
    if (simpleSelector.match() != CSSSelector::PseudoClass)
        return false;
    CSSSelector::PseudoClassType pseudo = simpleSelector.pseudoClassType();
    if (pseudo == CSSSelector::PseudoClassNot) {
        ASSERT(simpleSelector.selectorList());
        ASSERT(simpleSelector.selectorList()->first());
        pseudo = simpleSelector.selectorList()->first()->pseudoClassType();
    }
    return isPseudoClassValidAfterPseudoElement(pseudo, compoundPseudoElement);
}

} // namespace

std::unique_ptr<CSSParserSelector> CSSSelectorParser::consumeCompoundSelector(CSSParserTokenRange& range)
{
    std::unique_ptr<CSSParserSelector> compoundSelector;

    AtomString namespacePrefix;
    AtomString elementName;
    CSSSelector::PseudoElementType compoundPseudoElement = CSSSelector::PseudoElementUnknown;
    if (!consumeName(range, elementName, namespacePrefix)) {
        compoundSelector = consumeSimpleSelector(range);
        if (!compoundSelector)
            return nullptr;
        if (compoundSelector->match() == CSSSelector::PseudoElement)
            compoundPseudoElement = compoundSelector->pseudoElementType();
    }

    while (std::unique_ptr<CSSParserSelector> simpleSelector = consumeSimpleSelector(range)) {
        // FIXME: https://bugs.webkit.org/show_bug.cgi?id=161747
        // The UASheetMode check is a work-around to allow this selector in mediaControls(New).css:
        // video::-webkit-media-text-track-region-container.scrolling
        if (m_context.mode != UASheetMode && !isSimpleSelectorValidAfterPseudoElement(*simpleSelector.get(), compoundPseudoElement)) {
            m_failedParsing = true;
            return nullptr;
        }
        if (simpleSelector->match() == CSSSelector::PseudoElement)
            compoundPseudoElement = simpleSelector->pseudoElementType();

        if (compoundSelector)
            compoundSelector = addSimpleSelectorToCompound(WTFMove(compoundSelector), WTFMove(simpleSelector));
        else
            compoundSelector = WTFMove(simpleSelector);
    }

    if (!compoundSelector) {
        AtomString namespaceURI = determineNamespace(namespacePrefix);
        if (namespaceURI.isNull()) {
            m_failedParsing = true;
            return nullptr;
        }
        if (namespaceURI == defaultNamespace())
            namespacePrefix = nullAtom();
        
        CSSParserSelector* rawSelector = new CSSParserSelector(QualifiedName(namespacePrefix, elementName, namespaceURI));
        std::unique_ptr<CSSParserSelector> selector = std::unique_ptr<CSSParserSelector>(rawSelector);
        return selector;
    }
    prependTypeSelectorIfNeeded(namespacePrefix, elementName, compoundSelector.get());
    return splitCompoundAtImplicitShadowCrossingCombinator(WTFMove(compoundSelector), m_context);
}

std::unique_ptr<CSSParserSelector> CSSSelectorParser::consumeSimpleSelector(CSSParserTokenRange& range)
{
    const CSSParserToken& token = range.peek();
    std::unique_ptr<CSSParserSelector> selector;
    if (token.type() == HashToken)
        selector = consumeId(range);
    else if (token.type() == DelimiterToken && token.delimiter() == '.')
        selector = consumeClass(range);
    else if (token.type() == LeftBracketToken)
        selector = consumeAttribute(range);
    else if (token.type() == ColonToken)
        selector = consumePseudo(range);
    else
        return nullptr;
    if (!selector)
        m_failedParsing = true;
    return selector;
}

bool CSSSelectorParser::consumeName(CSSParserTokenRange& range, AtomString& name, AtomString& namespacePrefix)
{
    name = nullAtom();
    namespacePrefix = nullAtom();

    const CSSParserToken& firstToken = range.peek();
    if (firstToken.type() == IdentToken) {
        name = firstToken.value().toAtomString();
        range.consume();
    } else if (firstToken.type() == DelimiterToken && firstToken.delimiter() == '*') {
        name = starAtom();
        range.consume();
    } else if (firstToken.type() == DelimiterToken && firstToken.delimiter() == '|') {
        // This is an empty namespace, which'll get assigned this value below
        name = emptyAtom();
    } else
        return false;

    if (range.peek().type() != DelimiterToken || range.peek().delimiter() != '|')
        return true;
    range.consume();

    namespacePrefix = name;
    const CSSParserToken& nameToken = range.consume();
    if (nameToken.type() == IdentToken) {
        name = nameToken.value().toAtomString();
    } else if (nameToken.type() == DelimiterToken && nameToken.delimiter() == '*')
        name = starAtom();
    else {
        name = nullAtom();
        namespacePrefix = nullAtom();
        return false;
    }

    return true;
}

std::unique_ptr<CSSParserSelector> CSSSelectorParser::consumeId(CSSParserTokenRange& range)
{
    ASSERT(range.peek().type() == HashToken);
    if (range.peek().getHashTokenType() != HashTokenId)
        return nullptr;
    std::unique_ptr<CSSParserSelector> selector = std::unique_ptr<CSSParserSelector>(new CSSParserSelector());
    selector->setMatch(CSSSelector::Id);
    
    // FIXME-NEWPARSER: Avoid having to do this, but the old parser does and we need
    // to be compatible for now.
    CSSParserToken token = range.consume();
    selector->setValue(token.value().toAtomString(), m_context.mode == HTMLQuirksMode);
    return selector;
}

std::unique_ptr<CSSParserSelector> CSSSelectorParser::consumeClass(CSSParserTokenRange& range)
{
    ASSERT(range.peek().type() == DelimiterToken);
    ASSERT(range.peek().delimiter() == '.');
    range.consume();
    if (range.peek().type() != IdentToken)
        return nullptr;
    std::unique_ptr<CSSParserSelector> selector = std::unique_ptr<CSSParserSelector>(new CSSParserSelector());
    selector->setMatch(CSSSelector::Class);
    
    // FIXME-NEWPARSER: Avoid having to do this, but the old parser does and we need
    // to be compatible for now.
    CSSParserToken token = range.consume();
    selector->setValue(token.value().toAtomString(), m_context.mode == HTMLQuirksMode);

    return selector;
}

std::unique_ptr<CSSParserSelector> CSSSelectorParser::consumeAttribute(CSSParserTokenRange& range)
{
    ASSERT(range.peek().type() == LeftBracketToken);
    CSSParserTokenRange block = range.consumeBlock();
    block.consumeWhitespace();

    AtomString namespacePrefix;
    AtomString attributeName;
    if (!consumeName(block, attributeName, namespacePrefix))
        return nullptr;
    block.consumeWhitespace();

    AtomString namespaceURI = determineNamespace(namespacePrefix);
    if (namespaceURI.isNull())
        return nullptr;

    QualifiedName qualifiedName = namespacePrefix.isNull()
        ? QualifiedName(nullAtom(), attributeName, nullAtom())
        : QualifiedName(namespacePrefix, attributeName, namespaceURI);

    std::unique_ptr<CSSParserSelector> selector = std::unique_ptr<CSSParserSelector>(new CSSParserSelector());

    if (block.atEnd()) {
        selector->setAttribute(qualifiedName, m_context.isHTMLDocument, CSSSelector::CaseSensitive);
        selector->setMatch(CSSSelector::Set);
        return selector;
    }

    selector->setMatch(consumeAttributeMatch(block));

    const CSSParserToken& attributeValue = block.consumeIncludingWhitespace();
    if (attributeValue.type() != IdentToken && attributeValue.type() != StringToken)
        return nullptr;
    selector->setValue(attributeValue.value().toAtomString());
    
    selector->setAttribute(qualifiedName, m_context.isHTMLDocument, consumeAttributeFlags(block));

    if (!block.atEnd())
        return nullptr;
    return selector;
}

static bool isOnlyPseudoClassFunction(CSSSelector::PseudoClassType pseudoClassType)
{
    switch (pseudoClassType) {
    case CSSSelector::PseudoClassNot:
    case CSSSelector::PseudoClassMatches:
    case CSSSelector::PseudoClassNthChild:
    case CSSSelector::PseudoClassNthLastChild:
    case CSSSelector::PseudoClassNthOfType:
    case CSSSelector::PseudoClassNthLastOfType:
    case CSSSelector::PseudoClassLang:
    case CSSSelector::PseudoClassAny:
#if ENABLE(CSS_SELECTORS_LEVEL4)
    case CSSSelector::PseudoClassDir:
    case CSSSelector::PseudoClassRole:
#endif
        return true;
    default:
        break;
    }
    return false;
}
    
static bool isOnlyPseudoElementFunction(CSSSelector::PseudoElementType pseudoElementType)
{
    // Note that we omit cue since it can be both an ident or a function.
    switch (pseudoElementType) {
    case CSSSelector::PseudoElementPart:
    case CSSSelector::PseudoElementSlotted:
        return true;
    default:
        break;
    }
    return false;
}

std::unique_ptr<CSSParserSelector> CSSSelectorParser::consumePseudo(CSSParserTokenRange& range)
{
    ASSERT(range.peek().type() == ColonToken);
    range.consume();

    int colons = 1;
    if (range.peek().type() == ColonToken) {
        range.consume();
        colons++;
    }

    const CSSParserToken& token = range.peek();
    if (token.type() != IdentToken && token.type() != FunctionToken)
        return nullptr;

    std::unique_ptr<CSSParserSelector> selector;
    
    if (colons == 1) {
        selector = CSSParserSelector::parsePseudoClassSelector(token.value());
        if (!selector)
            return nullptr;
        if (selector->match() == CSSSelector::PseudoClass) {
            if (m_context.mode != UASheetMode && selector->pseudoClassType() == CSSSelector::PseudoClassDirectFocus)
                return nullptr;
#if ENABLE(ATTACHMENT_ELEMENT)
            if (!m_context.attachmentEnabled && selector->pseudoClassType() == CSSSelector::PseudoClassHasAttachment)
                return nullptr;
#endif
        }
    } else {
        selector = CSSParserSelector::parsePseudoElementSelector(token.value());
#if ENABLE(VIDEO_TRACK)
        // Treat the ident version of cue as PseudoElementWebkitCustom.
        if (token.type() == IdentToken && selector && selector->match() == CSSSelector::PseudoElement && selector->pseudoElementType() == CSSSelector::PseudoElementCue)
            selector->setPseudoElementType(CSSSelector::PseudoElementWebKitCustom);
#endif
    }

    if (!selector || (selector->match() == CSSSelector::PseudoElement && m_disallowPseudoElements))
        return nullptr;

    if (token.type() == IdentToken) {
        range.consume();
        if ((selector->match() == CSSSelector::PseudoElement && (selector->pseudoElementType() == CSSSelector::PseudoElementUnknown || isOnlyPseudoElementFunction(selector->pseudoElementType())))
            || (selector->match() == CSSSelector::PseudoClass && (selector->pseudoClassType() == CSSSelector::PseudoClassUnknown || isOnlyPseudoClassFunction(selector->pseudoClassType()))))
            return nullptr;
        return selector;
    }

    CSSParserTokenRange block = range.consumeBlock();
    block.consumeWhitespace();
    if (token.type() != FunctionToken)
        return nullptr;
    
    const auto& argumentStart = block.peek();
    
    if (selector->match() == CSSSelector::PseudoClass) {
        switch (selector->pseudoClassType()) {
        case CSSSelector::PseudoClassNot: {
            DisallowPseudoElementsScope scope(this);
            std::unique_ptr<CSSSelectorList> selectorList = std::unique_ptr<CSSSelectorList>(new CSSSelectorList());
            *selectorList = consumeComplexSelectorList(block);
            if (!selectorList->first() || !block.atEnd())
                return nullptr;
            selector->setSelectorList(WTFMove(selectorList));
            return selector;
        }
        case CSSSelector::PseudoClassNthChild:
        case CSSSelector::PseudoClassNthLastChild:
        case CSSSelector::PseudoClassNthOfType:
        case CSSSelector::PseudoClassNthLastOfType: {
            std::pair<int, int> ab;
            if (!consumeANPlusB(block, ab))
                return nullptr;
            block.consumeWhitespace();
            const auto& argumentEnd = block.peek();
            auto rangeOfANPlusB = block.makeSubRange(&argumentStart, &argumentEnd);
            auto argument = rangeOfANPlusB.serialize();
            selector->setArgument(argument.stripWhiteSpace());
            if (!block.atEnd()) {
                if (block.peek().type() != IdentToken)
                    return nullptr;
                const CSSParserToken& ident = block.consume();
                if (!equalIgnoringASCIICase(ident.value(), "of"))
                    return nullptr;
                if (block.peek().type() != WhitespaceToken)
                    return nullptr;
                DisallowPseudoElementsScope scope(this);
                block.consumeWhitespace();
                std::unique_ptr<CSSSelectorList> selectorList = std::unique_ptr<CSSSelectorList>(new CSSSelectorList());
                *selectorList = consumeComplexSelectorList(block);
                if (!selectorList->first() || !block.atEnd())
                    return nullptr;
                selector->setSelectorList(WTFMove(selectorList));
            }
            selector->setNth(ab.first, ab.second);
            return selector;
        }
        case CSSSelector::PseudoClassLang: {
            // FIXME: CSS Selectors Level 4 allows :lang(*-foo)
            auto argumentList = makeUnique<Vector<AtomString>>();
            if (!consumeLangArgumentList(argumentList, block))
                return nullptr;
            selector->setArgumentList(WTFMove(argumentList));
            return selector;
        }
        case CSSSelector::PseudoClassMatches: {
            std::unique_ptr<CSSSelectorList> selectorList = std::unique_ptr<CSSSelectorList>(new CSSSelectorList());
            *selectorList = consumeComplexSelectorList(block);
            if (!selectorList->first() || !block.atEnd())
                return nullptr;
            selector->setSelectorList(WTFMove(selectorList));
            return selector;
        }
        case CSSSelector::PseudoClassAny:
        case CSSSelector::PseudoClassHost: {
            std::unique_ptr<CSSSelectorList> selectorList = std::unique_ptr<CSSSelectorList>(new CSSSelectorList());
            *selectorList = consumeCompoundSelectorList(block);
            if (!selectorList->first() || !block.atEnd())
                return nullptr;
            selector->setSelectorList(WTFMove(selectorList));
            return selector;
        }
#if ENABLE(CSS_SELECTORS_LEVEL4)
        case CSSSelector::PseudoClassDir:
        case CSSSelector::PseudoClassRole: {
            const CSSParserToken& ident = block.consumeIncludingWhitespace();
            if (ident.type() != IdentToken || !block.atEnd())
                return nullptr;
            selector->setArgument(ident.value().toAtomString());
            return selector;
        }
#endif
        default:
            break;
        }

    }
    
    if (selector->match() == CSSSelector::PseudoElement) {
        switch (selector->pseudoElementType()) {
#if ENABLE(VIDEO_TRACK)
        case CSSSelector::PseudoElementCue: {
            DisallowPseudoElementsScope scope(this);
            std::unique_ptr<CSSSelectorList> selectorList = std::unique_ptr<CSSSelectorList>(new CSSSelectorList());
            *selectorList = consumeCompoundSelectorList(block);
            if (!selectorList->isValid() || !block.atEnd())
                return nullptr;
            selector->setSelectorList(WTFMove(selectorList));
            return selector;
        }
#endif
        case CSSSelector::PseudoElementPart: {
            auto argumentList = makeUnique<Vector<AtomString>>();
            do {
                auto& ident = block.consumeIncludingWhitespace();
                if (ident.type() != IdentToken)
                    return nullptr;
                argumentList->append(ident.value().toAtomString());
            } while (!block.atEnd());

            selector->setArgumentList(WTFMove(argumentList));
            return selector;
        }
        case CSSSelector::PseudoElementSlotted: {
            DisallowPseudoElementsScope scope(this);

            std::unique_ptr<CSSParserSelector> innerSelector = consumeCompoundSelector(block);
            block.consumeWhitespace();
            if (!innerSelector || !block.atEnd())
                return nullptr;
            selector->adoptSelectorVector(Vector<std::unique_ptr<CSSParserSelector>>::from(WTFMove(innerSelector)));
            return selector;
        }
        default:
            break;
        }
    }

    return nullptr;
}

CSSSelector::RelationType CSSSelectorParser::consumeCombinator(CSSParserTokenRange& range)
{
    auto fallbackResult = CSSSelector::Subselector;
    while (range.peek().type() == WhitespaceToken) {
        range.consume();
        fallbackResult = CSSSelector::DescendantSpace;
    }

    if (range.peek().type() != DelimiterToken)
        return fallbackResult;

    UChar delimiter = range.peek().delimiter();

    if (delimiter == '+' || delimiter == '~' || delimiter == '>') {
        range.consumeIncludingWhitespace();
        if (delimiter == '+')
            return CSSSelector::DirectAdjacent;
        if (delimiter == '~')
            return CSSSelector::IndirectAdjacent;
        return CSSSelector::Child;
    }

    return fallbackResult;
}

CSSSelector::Match CSSSelectorParser::consumeAttributeMatch(CSSParserTokenRange& range)
{
    const CSSParserToken& token = range.consumeIncludingWhitespace();
    switch (token.type()) {
    case IncludeMatchToken:
        return CSSSelector::List;
    case DashMatchToken:
        return CSSSelector::Hyphen;
    case PrefixMatchToken:
        return CSSSelector::Begin;
    case SuffixMatchToken:
        return CSSSelector::End;
    case SubstringMatchToken:
        return CSSSelector::Contain;
    case DelimiterToken:
        if (token.delimiter() == '=')
            return CSSSelector::Exact;
        FALLTHROUGH;
    default:
        m_failedParsing = true;
        return CSSSelector::Exact;
    }
}

CSSSelector::AttributeMatchType CSSSelectorParser::consumeAttributeFlags(CSSParserTokenRange& range)
{
    if (range.peek().type() != IdentToken)
        return CSSSelector::CaseSensitive;
    const CSSParserToken& flag = range.consumeIncludingWhitespace();
    if (equalIgnoringASCIICase(flag.value(), "i"))
        return CSSSelector::CaseInsensitive;
    m_failedParsing = true;
    return CSSSelector::CaseSensitive;
}

bool CSSSelectorParser::consumeANPlusB(CSSParserTokenRange& range, std::pair<int, int>& result)
{
    const CSSParserToken& token = range.consume();
    if (token.type() == NumberToken && token.numericValueType() == IntegerValueType) {
        result = std::make_pair(0, static_cast<int>(token.numericValue()));
        return true;
    }
    if (token.type() == IdentToken) {
        if (equalIgnoringASCIICase(token.value(), "odd")) {
            result = std::make_pair(2, 1);
            return true;
        }
        if (equalIgnoringASCIICase(token.value(), "even")) {
            result = std::make_pair(2, 0);
            return true;
        }
    }

    // The 'n' will end up as part of an ident or dimension. For a valid <an+b>,
    // this will store a string of the form 'n', 'n-', or 'n-123'.
    String nString;

    if (token.type() == DelimiterToken && token.delimiter() == '+' && range.peek().type() == IdentToken) {
        result.first = 1;
        nString = range.consume().value().toString();
    } else if (token.type() == DimensionToken && token.numericValueType() == IntegerValueType) {
        result.first = token.numericValue();
        nString = token.value().toString();
    } else if (token.type() == IdentToken) {
        if (token.value()[0] == '-') {
            result.first = -1;
            nString = token.value().substring(1).toString();
        } else {
            result.first = 1;
            nString = token.value().toString();
        }
    }

    range.consumeWhitespace();

    if (nString.isEmpty() || !isASCIIAlphaCaselessEqual(nString[0], 'n'))
        return false;
    if (nString.length() > 1 && nString[1] != '-')
        return false;

    if (nString.length() > 2) {
        bool valid;
        result.second = nString.substring(1).toIntStrict(&valid);
        return valid;
    }

    NumericSign sign = nString.length() == 1 ? NoSign : MinusSign;
    if (sign == NoSign && range.peek().type() == DelimiterToken) {
        char delimiterSign = range.consumeIncludingWhitespace().delimiter();
        if (delimiterSign == '+')
            sign = PlusSign;
        else if (delimiterSign == '-')
            sign = MinusSign;
        else
            return false;
    }

    if (sign == NoSign && range.peek().type() != NumberToken) {
        result.second = 0;
        return true;
    }

    const CSSParserToken& b = range.consume();
    if (b.type() != NumberToken || b.numericValueType() != IntegerValueType)
        return false;
    if ((b.numericSign() == NoSign) == (sign == NoSign))
        return false;
    result.second = b.numericValue();
    if (sign == MinusSign)
        result.second = -result.second;
    return true;
}

const AtomString& CSSSelectorParser::defaultNamespace() const
{
    if (!m_styleSheet)
        return starAtom();
    return m_styleSheet->defaultNamespace();
}

const AtomString& CSSSelectorParser::determineNamespace(const AtomString& prefix)
{
    if (prefix.isNull())
        return defaultNamespace();
    if (prefix.isEmpty())
        return emptyAtom(); // No namespace. If an element/attribute has a namespace, we won't match it.
    if (prefix == starAtom())
        return starAtom(); // We'll match any namespace.
    if (!m_styleSheet)
        return nullAtom(); // Cannot resolve prefix to namespace without a stylesheet, syntax error.
    return m_styleSheet->namespaceURIFromPrefix(prefix);
}

void CSSSelectorParser::prependTypeSelectorIfNeeded(const AtomString& namespacePrefix, const AtomString& elementName, CSSParserSelector* compoundSelector)
{
    bool isShadowDOM = compoundSelector->needsImplicitShadowCombinatorForMatching();
    
    if (elementName.isNull() && defaultNamespace() == starAtom() && !isShadowDOM)
        return;

    AtomString determinedElementName = elementName.isNull() ? starAtom() : elementName;
    AtomString namespaceURI = determineNamespace(namespacePrefix);
    if (namespaceURI.isNull()) {
        m_failedParsing = true;
        return;
    }
    AtomString determinedPrefix = namespacePrefix;
    if (namespaceURI == defaultNamespace())
        determinedPrefix = nullAtom();
    QualifiedName tag = QualifiedName(determinedPrefix, determinedElementName, namespaceURI);

    // *:host never matches, so we can't discard the *,
    // otherwise we can't tell the difference between *:host and just :host.
    //
    // Also, selectors where we use a ShadowPseudo combinator between the
    // element and the pseudo element for matching (custom pseudo elements,
    // ::cue), we need a universal selector to set the combinator
    // (relation) on in the cases where there are no simple selectors preceding
    // the pseudo element.
    bool explicitForHost = compoundSelector->isHostPseudoSelector() && !elementName.isNull();
    if (tag != anyQName() || explicitForHost || isShadowDOM)
        compoundSelector->prependTagSelector(tag, determinedPrefix == nullAtom() && determinedElementName == starAtom() && !explicitForHost);
}

std::unique_ptr<CSSParserSelector> CSSSelectorParser::addSimpleSelectorToCompound(std::unique_ptr<CSSParserSelector> compoundSelector, std::unique_ptr<CSSParserSelector> simpleSelector)
{
    compoundSelector->appendTagHistory(CSSSelector::Subselector, WTFMove(simpleSelector));
    return compoundSelector;
}

std::unique_ptr<CSSParserSelector> CSSSelectorParser::splitCompoundAtImplicitShadowCrossingCombinator(std::unique_ptr<CSSParserSelector> compoundSelector, const CSSParserContext& context)
{
    // The tagHistory is a linked list that stores combinator separated compound selectors
    // from right-to-left. Yet, within a single compound selector, stores the simple selectors
    // from left-to-right.
    //
    // ".a.b > div#id" is stored in a tagHistory as [div, #id, .a, .b], each element in the
    // list stored with an associated relation (combinator or Subselector).
    //
    // ::cue, ::shadow, and custom pseudo elements have an implicit ShadowPseudo combinator
    // to their left, which really makes for a new compound selector, yet it's consumed by
    // the selector parser as a single compound selector.
    //
    // Example: input#x::-webkit-clear-button -> [ ::-webkit-clear-button, input, #x ]
    //
    CSSParserSelector* splitAfter = compoundSelector.get();
    while (splitAfter->tagHistory() && !splitAfter->tagHistory()->needsImplicitShadowCombinatorForMatching())
        splitAfter = splitAfter->tagHistory();
    
    if (!splitAfter || !splitAfter->tagHistory())
        return compoundSelector;

    // ::part() combines with other pseudo elements.
    bool isPart = splitAfter->tagHistory()->match() == CSSSelector::PseudoElement && splitAfter->tagHistory()->pseudoElementType() == CSSSelector::PseudoElementPart;

    std::unique_ptr<CSSParserSelector> secondCompound;
    if (context.mode == UASheetMode || isPart) {
        // FIXME: https://bugs.webkit.org/show_bug.cgi?id=161747
        // We have to recur, since we have rules in media controls like video::a::b. This should not be allowed, and
        // we should remove this recursion once those rules are gone.
        secondCompound = splitCompoundAtImplicitShadowCrossingCombinator(splitAfter->releaseTagHistory(), context);
    } else
        secondCompound = splitAfter->releaseTagHistory();

    secondCompound->appendTagHistory(CSSSelector::ShadowDescendant, WTFMove(compoundSelector));
    return secondCompound;
}

} // namespace WebCore