/* -*-c++-*- */
/* osgEarth - Geospatial SDK for OpenSceneGraph
 * Copyright 2020 Pelican Mapping
 * http://osgearth.org
 *
 * osgEarth is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2 of the License, 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 */

#ifndef OSGEARTH_PATCH_LAYER_H
#define OSGEARTH_PATCH_LAYER_H 1

#include <osgEarth/VisibleLayer>
#include <osgEarth/TerrainTileNode>
#include <osg/RenderInfo>
#include <osg/Texture>

namespace osgEarth
{
    class TileBatch;
    class TileRenderer;

    /**
     * PatchLayer is a layer that can render terrain tiles using either
     * a geometry shader patch (GL_PATCHES) or a custom draw callback.
     */
    class OSGEARTH_EXPORT PatchLayer : public VisibleLayer
    {
    public: // serialization
        class OSGEARTH_EXPORT Options : public VisibleLayer::Options {
        public:
            META_LayerOptions(osgEarth, Options, VisibleLayer::Options);
            virtual Config getConfig() const;
        private:
            void fromConfig(const Config& conf);
        };

    public:
        META_Layer(osgEarth, PatchLayer, Options, VisibleLayer, Patch);

        //! API providing access to patch geometry 
        class OSGEARTH_EXPORT TileInfoProvider
        {
        public:
            //! Bounding box of the actual tile geometry (could be cropped by a mask)
            virtual const osg::BoundingBox& getGeomBoundingBox() const = 0;

            //! Bounding box of the full tile
            virtual const osg::BoundingBox& getTileBoundingBox() const = 0;
        };

        /**
         * Callback that the terrain engine will call to decide whether to 
         * render a tile in this layer.
         */
        struct AcceptCallback : public osg::Referenced
        {
            /** Whether to accept the entire layer. Invoked during Cull. */
            virtual bool acceptLayer(osg::NodeVisitor& nv, const osg::Camera* camera) const { return true; }

            /** Whether to accept a specific tile. Invoked during Cull. */
            virtual bool acceptKey(const TileKey& key) const { return true; }
        };

    public:

        //! Static bounding box buffer that the culling engine will use to
        //! expand the corresponding terrain tile's axis-asligned bbox
        //! during culling. This is necessary to account for the geometry that
        //! may exist in the patch tile before it gets created.
        const osg::BoundingBox& getBuffer() {
            return _buffer;
        }

        virtual void cull(
            const TileKey& key,
            osg::NodeVisitor& nv) const { }

        virtual void cull(
            const TileBatch& batch,
            osg::NodeVisitor& nv) const { }

        virtual void draw(
            osg::RenderInfo& ri) const { }

        virtual TileRenderer* getRenderer() const {
            return nullptr;
        }

        //! Callback that decides which tiles to accept for rendering
        void setAcceptCallback(AcceptCallback* value) { _acceptCallback = value; }
        AcceptCallback* getAcceptCallback() const { return _acceptCallback.get(); }


    protected:

        // default destructor
        virtual ~PatchLayer() { }

        //! post-ctor initialization, chain to super/subclasses.
        virtual void init();

        //! Culling buffer to account for layer geometry.
        osg::BoundingBox _buffer = { 0,0,0,0,0,0 };

    private:
        osg::ref_ptr<AcceptCallback> _acceptCallback;
    };

    using PatchLayerVector = std::vector<osg::ref_ptr<PatchLayer>>;


    /**
     * Interface for a patchlayer to access information and state
     * about a terrain tile
     */
    class TileState
    {
    public:
        virtual const TileKey& getKey() const = 0;

        virtual int getRevision() const = 0;

        virtual const osg::BoundingBox& getBBox() const = 0;

        virtual const osg::Matrix& getModelViewMatrix() const = 0;

        virtual const osg::Matrix& getLocalToWorld() const = 0;

        virtual int getSequence() const = 0;

        virtual float getMorphStartRange() const = 0;

        virtual float getMorphEndRange() const = 0;

        virtual bool apply(
            osg::RenderInfo& ri,
            void* implData) const = 0;

        virtual void debug(
            osg::RenderInfo& ri,
            void* implData) const { }

    };

    /**
     * Collection of tiles for a patchlayer to render
     */
    class TileBatch
    {
    public:
        TileBatch(void* env) : _env(env) { }

        const std::vector<const TileState*>& tiles() const { return _tiles; }
        void* env() const { return _env; }

        std::vector<const TileState*> _tiles;
        void* _env;
    };

    /**
     * Interface for rendering a tile batch (patchlayer)
     */
    class TileRenderer
    {
    public:
        virtual void draw(
            osg::RenderInfo& ri,
            const TileBatch& tiles) = 0;
    };

} // namespace osgEarth

#endif // OSGEARTH_PATCH_LAYER_H