/****************************************************************************

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** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).

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** This file is part of the QtXmlPatterns module of the Qt Toolkit.

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** No Commercial Usage

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** contained in the Technology Preview License Agreement accompanying

** this package.

**

** GNU Lesser General Public License Usage

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** General Public License version 2.1 as published by the Free Software

** Foundation and appearing in the file LICENSE.LGPL included in the

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****************************************************************************/

//

//  W A R N I N G

//  -------------

//

// This file is not part of the Qt API.  It exists purely as an

// implementation detail.  This header file may change from version to

// version without notice, or even be removed.

//

// We mean it.

#ifndef Patternist_OperandsIterator_H

#define Patternist_OperandsIterator_H

#include <QPair>

#include <QStack>

#include "qexpression_p.h"

QT_BEGIN_HEADER

QT_BEGIN_NAMESPACE

namespace QPatternist

{

    /**

     * @short A helper class that iterates a tree of Expression instances. It

     * is not a sub-class of QAbstractXmlForwardIterator.

     *

     * The OperandsIterator delivers all Expression instances that are children at any

     * depth of the Expression passed in the constructor.

     * The order is delivered in a defined way, from left to right and depth

     * first.

     *

     * @author Frans Englich <frans.englich@nokia.com>

     */

    class OperandsIterator

    {

        /**

         * The second value, the int, is the current position in the first.

         */

        typedef QPair<Expression::List, int> Level;

    public:

        enum TreatParent

        {

            ExcludeParent,

            IncludeParent

        };

        /**

         * if @p treatParent is @c IncludeParent, @p start is excluded.

         *

         * @p start must be a valid Expression.

         */

        inline OperandsIterator(const Expression::Ptr &start,

                                const TreatParent treatParent)

        {

            Q_ASSERT(start);

            if(treatParent == IncludeParent)

            {

                Expression::List l;

                l.append(start);

                m_exprs.push(qMakePair(l, -1));

            }

            m_exprs.push(qMakePair(start->operands(), -1));

        }

        /**

         * @short Returns the current Expression and advances the iterator.

         *

         * If the end has been reached, a default constructed pointer is

         * returned.

         *

         * We intentionally return by reference.

         */

        inline Expression::Ptr next()

        {

            if(m_exprs.isEmpty())

                return Expression::Ptr();

            Level &lvl = m_exprs.top();

            ++lvl.second;

            if(lvl.second == lvl.first.size())

            {

                /* Resume iteration above us. */

                m_exprs.pop();

                if(m_exprs.isEmpty())

                    return Expression::Ptr();

                while(true)

                {

                    Level &previous = m_exprs.top();

                    ++previous.second;

                    if(previous.second < previous.first.count())

                    {

                        const Expression::Ptr &op = previous.first.at(previous.second);

                        m_exprs.push(qMakePair(op->operands(), -1));

                        return op;

                    }

                    else

                    {

                        // We have already reached the end of this level.

                        m_exprs.pop();

                        if(m_exprs.isEmpty())

                            return Expression::Ptr();

                    }

                }

            }

            else

            {

                const Expression::Ptr &op = lvl.first.at(lvl.second);

                m_exprs.push(qMakePair(op->operands(), -1));

                return op;

            }

        }

        /**

         * Advances this iterator by the current expression and its operands.

         */

        Expression::Ptr skipOperands()

        {

            if(m_exprs.isEmpty())

                return Expression::Ptr();

            Level &lvl = m_exprs.top();

            ++lvl.second;

            if(lvl.second == lvl.first.size())

            {

                /* We've reached the end of this level, at least. */

                m_exprs.pop();

            }

            return next();

        }

    private:

        Q_DISABLE_COPY(OperandsIterator)

        QStack<Level> m_exprs;

    };

}

QT_END_NAMESPACE

QT_END_HEADER

#endif