/* osgEarth
* Copyright 2025 Pelican Mapping
* MIT License
*/
#ifndef OSGEARTH_SCENE_GRAPH_CALLBACK_H
#define OSGEARTH_SCENE_GRAPH_CALLBACK_H 1

#include <osgEarth/Common>
#include <osgEarth/Threading>
#include <osg/PagedLOD>
#include <osg/observer_ptr>

namespace osgEarth
{
    /**
     * Callback for getting notifications of scene graph events.
     * Not all methods may be invoked in all situations. It's up to
     * the implementation to call then when it wants.
     */
    class SceneGraphCallback : public osg::Referenced
    {
    public:
        //! Called before a node is added to the live scene graph, possibly from a background pager thread
        virtual void onPreMergeNode(osg::Node* node) { }
        virtual void onPreMergeNode(osg::Node* node, osg::Object* sender) { onPreMergeNode(node); }

        //! Called after a node is added to the live scene graph in the main/update thread
        virtual void onPostMergeNode(osg::Node* node) { }
        virtual void onPostMergeNode(osg::Node* node, osg::Object* sender) { onPostMergeNode(node); }

        //! Called after a node is remoevd from the live scene graph in the main/update thread
        virtual void onRemoveNode(osg::Node* node) { }
        virtual void onRemoveNode(osg::Node* node, osg::Object* sender) { onRemoveNode(node); }
    };
    typedef std::vector<osg::ref_ptr<SceneGraphCallback> > SceneGraphCallbackVector;

    /**
     * Container for scene graph callbacks. Typically an object that
     * supports scene graph callbacks will host an instance of this
     * object and use it register and fire callbacks at the appropriate times.
     */
    class OSGEARTH_EXPORT SceneGraphCallbacks : public osg::Referenced
    {
    public:
        SceneGraphCallbacks(osg::Object* sender);

    public:
        //! Add a new callback
        virtual void add(SceneGraphCallback* cb);

        //! Remove an existing callback
        virtual void remove(SceneGraphCallback* cb);

        //! Invoke all pre-merge callbacks on the provided node
        virtual void firePreMergeNode(osg::Node* node);

        //! Invoke all post-merge callbacks on the provided node
        virtual void firePostMergeNode(osg::Node* node);

        //! Invoke all remove callbacks on the provided node
        virtual void fireRemoveNode(osg::Node* node);

    private:
        SceneGraphCallbackVector _callbacks;
        Threading::RecursiveMutex _mutex;
        osg::observer_ptr<osg::Object> _sender;
    };

    namespace Util
    {
        /**
         * Extends the osg::PagedLOD class to invoke SceneGraphCallbacks
         * when nodes are added or removed from the live scene graph.
         * (Note, this object does not invoke the preMergeNode method.)
         */
        class OSGEARTH_EXPORT PagedLODWithSceneGraphCallbacks : public osg::PagedLOD
        {
        public:
            PagedLODWithSceneGraphCallbacks(SceneGraphCallbacks* host);

            /**
             * Gets the SceneGraphCallbacks.
             */
            SceneGraphCallbacks* getSceneGraphCallbacks() const;

            /**
             * Sets the SceneGraphCallbacks
             */
            void setSceneGraphCallbacks(SceneGraphCallbacks* host);

        public: // osg::Group

            virtual bool addChild(osg::Node* child);
            virtual bool insertChild(unsigned index, osg::Node* child);
            virtual bool replaceChild(osg::Node* origChild, osg::Node* newChild);
            virtual void childRemoved(unsigned pos, unsigned num);

        private:
            osg::observer_ptr<SceneGraphCallbacks> _host;
            osg::observer_ptr<osg::Object> _sender;
        };
    }
}

#endif // OSGEARTH_SCENE_GRAPH_CALLBACK_H
