/* This file is part of the KDE project
 * SPDX-FileCopyrightText: 2009 Jan Hambrecht <jaham@gmx.net>
 *
 * SPDX-License-Identifier: LGPL-2.0-or-later
 */

#include "SvgCssHelper.h"
#include <FlakeDebug.h>
#include <KoXmlReader.h>
#include <QPair>
#include <QRegularExpression>

/// Token types used for tokenizing complex selectors
enum CssTokenType {
    SelectorToken, ///< a selector token
    CombinatorToken ///< a combinator token
};

/// A token used for tokenizing complex selectors
typedef QPair<CssTokenType, QString> CssToken;

/// Selector base class, merely an interface
class CssSelectorBase
{
public:
    virtual ~CssSelectorBase() = default;
    /// Matches the given element
    virtual bool match(const KoXmlElement &) = 0;
    /// Returns string representation of selector
    virtual QString toString() const
    {
        return QString();
    }
    /**
     * Returns priority of selector
     * see http://www.w3.org/TR/1998/REC-CSS2-19980512/cascade.html#specificity
     */
    virtual int priority()
    {
        return 0;
    }
};

/// Universal selector, matching anything
class UniversalSelector : public CssSelectorBase
{
public:
    bool match(const KoXmlElement &) override
    {
        // matches always
        return true;
    }
    QString toString() const override
    {
        return "*";
    }
};

/// Type selector, matching the type of an element
class TypeSelector : public CssSelectorBase
{
public:
    TypeSelector(const QString &type)
        : m_type(type)
    {
    }
    bool match(const KoXmlElement &e) override
    {
        return e.tagName() == m_type;
    }
    QString toString() const override
    {
        return m_type;
    }
    int priority() override
    {
        return 1;
    }

private:
    QString m_type;
};

/// Id selectdor, matching the id attribute
class IdSelector : public CssSelectorBase
{
public:
    IdSelector(const QString &id)
        : m_id(id)
    {
        if (id.startsWith('#'))
            m_id = id.mid(1);
    }
    bool match(const KoXmlElement &e) override
    {
        return e.attribute("id") == m_id;
    }
    QString toString() const override
    {
        return '#' + m_id;
    }
    int priority() override
    {
        return 100;
    }

private:
    QString m_id;
};

/// Attribute selector, matching existence or content of attributes
class AttributeSelector : public CssSelectorBase
{
public:
    AttributeSelector(const QString &attribute)
        : m_type(Unknown)
    {
        QString pattern = attribute;
        if (pattern.startsWith('['))
            pattern.remove(0, 1);
        if (pattern.endsWith(']'))
            pattern.remove(pattern.length() - 1, 1);
        int equalPos = pattern.indexOf('=');
        if (equalPos == -1) {
            m_type = Exists;
            m_attribute = pattern;
        } else if (equalPos > 0) {
            if (pattern[equalPos - 1] == '~') {
                m_attribute = pattern.left(equalPos - 1);
                m_type = InList;
            } else if (pattern[equalPos - 1] == '|') {
                m_attribute = pattern.left(equalPos - 1) + '-';
                m_type = StartsWith;
            } else {
                m_attribute = pattern.left(equalPos);
                m_type = Equals;
            }
            m_value = pattern.mid(equalPos + 1);
            if (m_value.startsWith(QLatin1Char('"')))
                m_value.remove(0, 1);
            if (m_value.endsWith(QLatin1Char('"')))
                m_value.chop(1);
        }
    }

    bool match(const KoXmlElement &e) override
    {
        switch (m_type) {
        case Exists:
            return e.hasAttribute(m_attribute);
            break;
        case Equals:
            return e.attribute(m_attribute) == m_value;
            break;
        case InList: {
            QStringList tokens = e.attribute(m_attribute).split(' ', Qt::SkipEmptyParts);
            return tokens.contains(m_value);
        } break;
        case StartsWith:
            return e.attribute(m_attribute).startsWith(m_value);
            break;
        default:
            return false;
        }
    }
    QString toString() const override
    {
        QString str('[');
        str += m_attribute;
        if (m_type == Equals) {
            str += '=';
        } else if (m_type == InList) {
            str += "~=";
        } else if (m_type == StartsWith) {
            str += "|=";
        }
        str += m_value;
        str += ']';
        return str;
    }
    int priority() override
    {
        return 10;
    }

private:
    enum MatchType {
        Unknown, ///< unknown    -> error state
        Exists, ///< [att]      -> attribute exists
        Equals, ///< [att=val]  -> attribute value matches exactly val
        InList, ///< [att~=val] -> attribute is whitespace separated list where one is val
        StartsWith ///< [att|=val] -> attribute starts with val-
    };
    QString m_attribute;
    QString m_value;
    MatchType m_type;
};

/// Pseudo-class selector
class PseudoClassSelector : public CssSelectorBase
{
public:
    PseudoClassSelector(const QString &pseudoClass)
        : m_pseudoClass(pseudoClass)
    {
    }

    bool match(const KoXmlElement &e) override
    {
        if (m_pseudoClass == ":first-child") {
            KoXmlNode parent = e.parentNode();
            if (parent.isNull()) {
                return false;
            }
            KoXmlNode firstChild = parent.firstChild();
            while (!firstChild.isElement() || firstChild.isNull()) {
                firstChild = firstChild.nextSibling();
            }
            return firstChild == e;
        } else {
            return false;
        }
    }
    QString toString() const override
    {
        return m_pseudoClass;
    }
    int priority() override
    {
        return 10;
    }

private:
    QString m_pseudoClass;
};

/// A simple selector, i.e. a type/universal selector followed by attribute, id or pseudo-class selectors
class CssSimpleSelector : public CssSelectorBase
{
public:
    CssSimpleSelector(const QString &token)
        : m_token(token)
    {
        compile();
    }
    ~CssSimpleSelector() override
    {
        qDeleteAll(m_selectors);
    }

    bool match(const KoXmlElement &e) override
    {
        foreach (CssSelectorBase *s, m_selectors) {
            if (!s->match(e))
                return false;
        }

        return true;
    }

    QString toString() const override
    {
        QString str;
        foreach (CssSelectorBase *s, m_selectors) {
            str += s->toString();
        }
        return str;
    }
    int priority() override
    {
        int p = 0;
        foreach (CssSelectorBase *s, m_selectors) {
            p += s->priority();
        }
        return p;
    }

private:
    void compile()
    {
        if (m_token == "*") {
            m_selectors.append(new UniversalSelector());
            return;
        }

        enum { Start, Finish, Bad, InType, InId, InAttribute, InClassAttribute, InPseudoClass } state;

        // add terminator to string
        QString expr = m_token + QChar();
        int i = 0;
        state = Start;

        QString token;
        QString sep("#[:.");
        // split into base selectors
        while ((state != Finish) && (state != Bad) && (i < expr.length())) {
            QChar ch = expr[i];
            switch (state) {
            case Start:
                token += ch;
                if (ch == '#')
                    state = InId;
                else if (ch == '[')
                    state = InAttribute;
                else if (ch == ':')
                    state = InPseudoClass;
                else if (ch == '.')
                    state = InClassAttribute;
                else if (ch != '*')
                    state = InType;
                break;
            case InAttribute:
                if (ch.isNull()) {
                    // reset state and token string
                    state = Finish;
                    token.clear();
                    continue;
                } else {
                    token += ch;
                    if (ch == ']') {
                        m_selectors.append(new AttributeSelector(token));
                        state = Start;
                        token.clear();
                    }
                }
                break;
            case InType:
            case InId:
            case InClassAttribute:
            case InPseudoClass:
                // are we at the start of the next selector or even finished?
                if (sep.contains(ch) || ch.isNull()) {
                    if (state == InType)
                        m_selectors.append(new TypeSelector(token));
                    else if (state == InId)
                        m_selectors.append(new IdSelector(token));
                    else if (state == InClassAttribute)
                        m_selectors.append(new AttributeSelector("[class~=" + token.mid(1) + ']'));
                    else if (state == InPseudoClass) {
                        m_selectors.append(new PseudoClassSelector(token));
                    }
                    // reset state and token string
                    state = ch.isNull() ? Finish : Start;
                    token.clear();
                    continue;
                } else {
                    // append character to current token
                    if (!ch.isNull())
                        token += ch;
                }
                break;
            case Bad:
            default:
                break;
            }
            i++;
        }
    }

    QList<CssSelectorBase *> m_selectors;
    QString m_token;
};

/// Complex selector, i.e. a combination of simple selectors
class CssComplexSelector : public CssSelectorBase
{
public:
    CssComplexSelector(const QList<CssToken> &tokens)
    {
        compile(tokens);
    }
    ~CssComplexSelector() override
    {
        qDeleteAll(m_selectors);
    }
    QString toString() const override
    {
        QString str;
        int selectorCount = m_selectors.count();
        if (selectorCount) {
            for (int i = 0; i < selectorCount - 1; ++i) {
                str += m_selectors[i]->toString() + m_combinators[i];
            }
            str += m_selectors.last()->toString();
        }
        return str;
    }

    bool match(const KoXmlElement &e) override
    {
        int selectorCount = m_selectors.count();
        int combinatorCount = m_combinators.length();
        // check count of selectors and combinators
        if (selectorCount - combinatorCount != 1)
            return false;

        KoXmlElement currentElement = e;

        // match in reverse order
        for (int i = 0; i < selectorCount; ++i) {
            CssSelectorBase *curr = m_selectors[selectorCount - 1 - i];
            if (!curr->match(currentElement)) {
                return false;
            }
            // last selector and still there -> rule matched completely
            if (i == selectorCount - 1)
                return true;

            CssSelectorBase *next = m_selectors[selectorCount - 1 - i - 1];
            QChar combinator = m_combinators[combinatorCount - 1 - i];
            if (combinator == ' ') {
                bool matched = false;
                // descendant combinator
                KoXmlNode parent = currentElement.parentNode();
                while (!parent.isNull()) {
                    currentElement = parent.toElement();
                    if (next->match(currentElement)) {
                        matched = true;
                        break;
                    }
                    parent = currentElement.parentNode();
                }
                if (!matched)
                    return false;
            } else if (combinator == '>') {
                // child selector
                KoXmlNode parent = currentElement.parentNode();
                if (parent.isNull())
                    return false;
                KoXmlElement parentElement = parent.toElement();
                if (next->match(parentElement)) {
                    currentElement = parentElement;
                } else {
                    return false;
                }
            } else if (combinator == '+') {
                KoXmlNode neighbor = currentElement.previousSibling();
                while (!neighbor.isNull() && !neighbor.isElement())
                    neighbor = neighbor.previousSibling();
                if (neighbor.isNull() || !neighbor.isElement())
                    return false;
                KoXmlElement neighborElement = neighbor.toElement();
                if (next->match(neighborElement)) {
                    currentElement = neighborElement;
                } else {
                    return false;
                }
            } else {
                return false;
            }
        }
        return true;
    }
    int priority() override
    {
        int p = 0;
        foreach (CssSelectorBase *s, m_selectors) {
            p += s->priority();
        }
        return p;
    }

private:
    void compile(const QList<CssToken> &tokens)
    {
        foreach (const CssToken &token, tokens) {
            if (token.first == SelectorToken) {
                m_selectors.append(new CssSimpleSelector(token.second));
            } else {
                m_combinators += token.second;
            }
        }
    }

    QString m_combinators;
    QList<CssSelectorBase *> m_selectors;
};

/// A group of selectors (comma separated in css style sheet)
typedef QList<CssSelectorBase *> SelectorGroup;
/// A css rule consisting of group of selectors corresponding to a style
typedef QPair<SelectorGroup, QString> CssRule;

class SvgCssHelper::Private
{
public:
    ~Private()
    {
        foreach (const CssRule &rule, cssRules) {
            qDeleteAll(rule.first);
        }
    }

    SelectorGroup parsePattern(const QString &pattern)
    {
        SelectorGroup group;

        QStringList selectors = pattern.split(',', Qt::SkipEmptyParts);
        for (int i = 0; i < selectors.count(); ++i) {
            CssSelectorBase *selector = compileSelector(selectors[i].simplified());
            if (selector)
                group.append(selector);
        }
        return group;
    }

    QList<CssToken> tokenize(const QString &selector)
    {
        // add terminator to string
        QString expr = selector + QChar();
        enum { Finish, Bad, InCombinator, InSelector } state;

        QChar combinator;
        int selectorStart = 0;

        QList<CssToken> tokenList;

        QChar ch = expr[0];
        if (ch.isSpace() || ch == '>' || ch == '+') {
            debugFlake << "selector starting with combinator is not allowed:" << selector;
            return tokenList;
        } else {
            state = InSelector;
            selectorStart = 0;
        }
        int i = 1;

        // split into simple selectors and combinators
        while ((state != Finish) && (state != Bad) && (i < expr.length())) {
            QChar ch = expr[i];
            switch (state) {
            case InCombinator:
                // consume as long as there a combinator characters
                if (ch == '>' || ch == '+') {
                    if (!combinator.isSpace()) {
                        // two non whitespace combinators in sequence are not allowed
                        state = Bad;
                    } else {
                        // switch combinator
                        combinator = ch;
                    }
                } else if (!ch.isSpace()) {
                    tokenList.append(CssToken(CombinatorToken, combinator));
                    state = InSelector;
                    selectorStart = i;
                    combinator = QChar();
                }
                break;
            case InSelector:
                // consume as long as there a non combinator characters
                if (ch.isSpace() || ch == '>' || ch == '+') {
                    state = InCombinator;
                    combinator = ch;
                } else if (ch.isNull()) {
                    state = Finish;
                }
                if (state != InSelector) {
                    QString simpleSelector = selector.mid(selectorStart, i - selectorStart);
                    tokenList.append(CssToken(SelectorToken, simpleSelector));
                }
                break;
            case Bad:
            default:
                break;
            }
            i++;
        }

        return tokenList;
    }

    CssSelectorBase *compileSelector(const QString &selector)
    {
        QList<CssToken> tokenList = tokenize(selector);
        if (tokenList.isEmpty())
            return nullptr;

        if (tokenList.count() == 1) {
            // simple selector
            return new CssSimpleSelector(tokenList.first().second);
        } else if (tokenList.count() > 2) {
            // complex selector
            return new CssComplexSelector(tokenList);
        }
        return nullptr;
    }

    QMap<QString, QString> cssStyles;
    QList<CssRule> cssRules;
};

SvgCssHelper::SvgCssHelper()
    : d(new Private())
{
}

SvgCssHelper::~SvgCssHelper()
{
    delete d;
}

void SvgCssHelper::parseStylesheet(const KoXmlElement &e)
{
    QString data;

    if (e.hasChildNodes()) {
        KoXmlNode c = e.firstChild();
        if (c.isCDATASection()) {
            KoXmlCDATASection cdata = c.toCDATASection();
            data = cdata.data().simplified();
        } else if (c.isText()) {
            KoXmlText text = c.toText();
            data = text.data().simplified();
        }
    }
    if (data.isEmpty())
        return;

    // remove comments
    QRegularExpression commentExp(QStringLiteral("\\/\\*.*\\*\\/"),
                                  QRegularExpression::DotMatchesEverythingOption | QRegularExpression::InvertedGreedinessOption);
    data.remove(commentExp);

    QStringList defs = data.split('}', Qt::SkipEmptyParts);
    for (int i = 0; i < defs.count(); ++i) {
        QStringList def = defs[i].split('{');
        if (def.count() != 2)
            continue;
        QString pattern = def[0].simplified();
        if (pattern.isEmpty())
            break;
        QString style = def[1].simplified();
        if (style.isEmpty())
            break;
        QStringList selectors = pattern.split(',', Qt::SkipEmptyParts);
        for (int i = 0; i < selectors.count(); ++i) {
            QString selector = selectors[i].simplified();
            d->cssStyles[selector] = style;
        }
        SelectorGroup group = d->parsePattern(pattern);
        d->cssRules.append(CssRule(group, style));
    }
}

QStringList SvgCssHelper::matchStyles(const KoXmlElement &element) const
{
    QMap<int, QString> prioritizedRules;
    // match rules to element
    foreach (const CssRule &rule, d->cssRules) {
        foreach (CssSelectorBase *s, rule.first) {
            bool matched = s->match(element);
            if (matched)
                prioritizedRules[s->priority()] = rule.second;
        }
    }

    // css style attribute has the priority of 100
    QString styleAttribute = element.attribute("style").simplified();
    if (!styleAttribute.isEmpty())
        prioritizedRules[100] = styleAttribute;

    QStringList cssStyles;
    // add matching styles in correct order to style list
    QMapIterator<int, QString> it(prioritizedRules);
    while (it.hasNext()) {
        it.next();
        cssStyles.append(it.value());
    }

    return cssStyles;
}
