/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 Robert Osfield
 *
 * This library is open source and may be redistributed and/or modified under
 * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or
 * (at your option) any later version.  The full license is in LICENSE file
 * included with this distribution, and on the openscenegraph.org website.
 *
 * This library 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
 * OpenSceneGraph Public License for more details.
*/

#ifndef OSG_OBSERVER
#define OSG_OBSERVER 1

#include <OpenThreads/Mutex>
#include <osg/Export>
#include <set>

namespace osg {

/** Observer base class for tracking when objects are unreferenced (there reference count goes to 0) and are being deleted.*/
class OSG_EXPORT Observer
{
    public:
        Observer();
        virtual ~Observer();

        /** Get the optional global observer mutex, this can be shared between all osg::Observer.*/
        static OpenThreads::Mutex* getGlobalObserverMutex();

        inline OpenThreads::Mutex* getObserverMutex() const { return osg::Observer::getGlobalObserverMutex(); }

        /** objectUnreferenced(void*) is called when the observed object's referenced count goes to zero, indicating that
        * the object will be deleted unless a new reference is made to it.  If you wish to prevent deletion of the object
        * then it's reference count should be incremented such as via taking a ref_ptr<> to it, if no refernce is taken
        * by any of the observers of the object then the object will be deleted, and objectDeleted will in turn be called.
        * return true if the Observer wishes to removed from the oberseved objects observer set.*/
        virtual bool objectUnreferenced(void*) { return false; }

        /** objectDeleted is called when the observed object is about to be deleted.  The observer will be automatically
        * removed from the observerd objects observer set so there is no need for the objectDeleted implementation
        * to call removeObserver() on the observed object. */
        virtual void objectDeleted(void*) {}

};

/** Class used by osg::Referenced to track the observers assoicated with it.*/
class OSG_EXPORT ObserverSet
{
    public:

        ObserverSet();
        ~ObserverSet();

        inline OpenThreads::Mutex* getObserverSetMutex() const { return osg::Observer::getGlobalObserverMutex(); }

        void addObserver(Observer* observer);
        void removeObserver(Observer* observer);

        void signalObjectUnreferenced(void* ptr);
        void signalObjectDeleted(void* ptr);

        typedef std::set<Observer*> Observers;
        Observers& getObservers() { return _observers; }
        const Observers& getObservers() const { return _observers; }

    protected:

        Observers _observers;
};

}

#endif