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** Copyright (C) 2016 The Qt Company Ltd.
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** This file is part of the QtXmlPatterns module of the Qt Toolkit.
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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_CachingIterator_H
#define Patternist_CachingIterator_H

#include <QList>
#include <QVector>

#include <private/qdynamiccontext_p.h>
#include <private/qitem_p.h>

QT_BEGIN_NAMESPACE

namespace QPatternist
{
    /**
     * @short An QAbstractXmlForwardIterator that gets its item from a cache unless its empty, in
     * which case it continues to populate the cache as well as deliver on its
     * own from a source QAbstractXmlForwardIterator.
     *
     * @author Frans Englich <frans.frans.englich@nokia.com>
     * @ingroup Patternist_iterators
     */
    class CachingIterator : public Item::Iterator
    {
    public:
        /**
         * We always use the same cache cell so why don't we use it directly,
         * instead of passing the slot and ItemSequenceCacheCell::Vector to
         * this class? Because the GenericDynamicContext might decide to resize
         * the vector and that would invalidate the reference.
         *
         * We intentionally pass in a non-const reference here.
         */
        CachingIterator(ItemSequenceCacheCell::Vector &cacheCells,
                        const VariableSlotID slot,
                        const DynamicContext::Ptr &context);

        virtual Item next();
        virtual Item current() const;
        virtual xsInteger position() const;
        virtual Item::Iterator::Ptr copy() const;

    private:
        Item                        m_current;
        xsInteger                   m_position;

        /**
         * This variable cannot be called m_slot, because
         * /usr/include/sys/sysmacros.h on hpuxi-acc defines it.
         */
        const VariableSlotID        m_varSlot;

        /**
         * We don't use the context. We only keep a reference such that it
         * doesn't get deleted, and m_cacheCells starts to dangle.
         */
        const DynamicContext::Ptr   m_context;

        /**
         * We intentionally store a reference here such that we are able to
         * modify the item.
         */
        ItemSequenceCacheCell::Vector &m_cacheCells;

        /**
         * Whether this CachingIterator is delivering items from
         * m_cacheCell.cacheItems or from m_cacheCell.sourceIterator.
         */
        bool m_usingCache;
    };
}

QT_END_NAMESPACE

#endif