/*
 *   Copyright 2006-2007 Aaron Seigo <aseigo@kde.org>
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Library General Public License as
 *   published by the Free Software Foundation; either version 2, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details
 *
 *   You should have received a copy of the GNU Library General Public
 *   License along with this program; if not, write to the
 *   Free Software Foundation, Inc.,
 *   51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

#ifndef PLASMA_DATAENGINEMANAGER_H
#define PLASMA_DATAENGINEMANAGER_H

#include <plasma/dataengine.h>

namespace Plasma
{

class DataEngineManagerPrivate;

/**
 * @class DataEngineManager plasma/dataenginemanager.h <Plasma/DataEngineManager>
 *
 * @short DataEngine loader and life time manager
 *
 * Plasma::DataEngineManager provides facilities for listing, loading and
 * according to reference count unloading of DataEngines.
 **/
class DataEngineManager: public QObject
{
    Q_OBJECT
public:
    /**
     * Singleton pattern accessor.
     */
    static DataEngineManager *self();

    /**
     * Returns a data engine object if one is loaded and available.
     * On failure, the fallback NullEngine (which does nothing and
     * !isValid()) is returned.
     *
     * @param name the name of the engine
     */
    Plasma::DataEngine *engine(const QString &name) const;

    /**
     * Loads a data engine and increases the reference count on it.
     * This should be called once per object (or set of objects) using the
     * DataEngine. Afterwards, dataEngine should be used or the return
     * value cached. Call unloadDataEngine when finished with the engine.
     *
     * @param name the name of the engine
     * @return the data engine that was loaded, or the NullEngine on failure.
     */
    Plasma::DataEngine *loadEngine(const QString &name);

    /**
     * Decreases the reference count on the engine. If the count reaches
     * zero, then the engine is deleted to save resources.
     */
    void unloadEngine(const QString &name);

protected:
    /**
     * Reimplemented from QObject
     **/
    void timerEvent(QTimerEvent *event) override;

private:
    /**
     * Default constructor. The singleton method self() is the
     * preferred access mechanism.
     */
    DataEngineManager();
    ~DataEngineManager() override;

    DataEngineManagerPrivate *const d;

    friend class DataEngineManagerSingleton;
};

} // namespace Plasma

#endif // multiple inclusion guard
