/* Copyright (C) 2015
 * swift project Community / Contributors
 *
 * This file is part of swift project. It is subject to the license terms in the LICENSE file found in the top-level
 * directory of this distribution and at http://www.swift-project.org/license.html. No part of swift project,
 * including this file, may be copied, modified, propagated, or distributed except according to the terms
 * contained in the LICENSE file.
 */

//! \file

#ifndef BLACKMISC_VALUECACHE_PRIVATE_H
#define BLACKMISC_VALUECACHE_PRIVATE_H

#include "blackmisc/variantmap.h"
#include "blackmisc/statusmessage.h"
#include <QObject>
#include <QMutex>
#include <QMap>

namespace BlackMisc
{
    class CIdentifier;
    class CValueCache;

    namespace Private
    {

        /*!
         * \private QObject subclass used by CCached<T> class template for signal/slot communication with CValueCache.
         * An instance of this class is shared between all CCached<T> referring to the same CValueCache and owned by the same QObject,
         * with the latter QObject becoming parent of this instance.
         */
        class BLACKMISC_EXPORT CValuePage : public QObject
        {
            Q_OBJECT

        public:
            //! Returns a CValuePage owned by the parent and connected to the cache, creating one if it doesn't exist.
            static CValuePage &getPageFor(QObject *parent, CValueCache *cache);

            //! Opaque type holding the state of one value in the page.
            struct Element;

            //! Functor used for validating values.
            using Validator = std::function<bool(const CVariant &)>;

            //! Pointer-to-member-function type of slot to notify parent of changes.
            using NotifySlot = void (QObject:: *)();

            //! Returns a new instance of the opaque Element type for use by CCached<T> to interact with CValuePage.
            //! \param key The key string of the value in the cache.
            //! \param metaType The Qt metatype ID of the value object's expected type.
            //! \param validator Optional functor which returns true if the value is valid.
            //! \param defaultValue Optional value which is used in case the value is invalid.
            //! \param slot Optional member function of parent, will be called when value changes.
            Element &createElement(const QString &key, int metaType, Validator validator, const CVariant &defaultValue, NotifySlot slot);

            //! Read the currently paged value corresponding to the element's key.
            const CVariant &getValue(const Element &element) const;

            //! Write the value corresponding to the element's key and begin synchronizing it to any other pages.
            CStatusMessage setValue(Element &element, const CVariant &value);

            //! Synchronize with a change caused by another page.
            //! Connected to signal CValueCache::valuesChanged.
            //! \param values The new values.
            //! \param changedBy Pointer to the CValuePage which caused the change. Null if it was changed by another process.
            void setValuesFromCache(const BlackMisc::CVariantMap &values, QObject *changedBy);

            //! Put this page into batching mode.
            void beginBatch();

            //! Take this page out of batching mode and discard changes.
            void abandonBatch();

            //! Take this page out of batching mode and apply changes.
            void endBatch();

        signals:
            //! Synchronize this page's changes to other pages.
            //! Connected to slot CValueCache::changeValues.
            void valuesWantToCache(const BlackMisc::CVariantMap &values);

        private:
            using ElementPtr = QSharedPointer<Element>; // QMap doesn't support move-only types

            CValueCache *m_cache = nullptr;
            QMap<QString, ElementPtr> m_elements;
            int m_batchMode = 0;
            CVariantMap m_batchedValues;

            CValuePage(QObject *parent, CValueCache *cache);
            CStatusMessage validate(const Element &element, const CVariant &value) const;
        };

    } // namespace

} // namespace

#endif