/* osgEarth - Geospatial SDK for OpenSceneGraph
* Copyright 2008-2016 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_ELEVATION_H
#define OSGEARTH_ELEVATION_H

#include <osgEarth/Common>
#include <osgEarth/Units>
#include <osgEarth/GeoData>
#include <osgEarth/TileKey>
#include <osgEarth/Math>
#include <osg/Texture2D>

namespace osgEarth
{
    constexpr int ELEVATION_TILE_SIZE = 257;

    class Map;
    class ProgressCallback;

    extern OSGEARTH_EXPORT osg::Texture* createEmptyElevationTexture();

    extern OSGEARTH_EXPORT osg::Texture* createEmptyNormalMapTexture();

    /**
     * Result of an elevation sampling query
     */
    class OSGEARTH_EXPORT ElevationSample
    {
    public:
        ElevationSample() : _e(NO_DATA_VALUE, Units::METERS), _r(0.0, Units::METERS) { }
        ElevationSample(const Distance& e, const Distance& r) : _e(e), _r(r) { }
        const Distance& elevation() const { return _e; }
        const Distance& resolution() const { return _r; }
        bool hasData() const { return _e.getValue() != NO_DATA_VALUE && _r.getValue() > 0.0f; }
    private:
        Distance _e, _r;
    };

    /**
     * Elevation grid as a texture with in optional associated normal map.
     */
    class OSGEARTH_EXPORT ElevationTexture : public osg::Texture2D
    {
    public:
        ElevationTexture(
            const TileKey& key,
            const GeoHeightField& hf,
            const std::vector<float>& resolutions);

        virtual ~ElevationTexture();

        //! Gets the elevation at the map coordinates. These coordinates must
        //! be in the SRS used to create the texture.
        ElevationSample getElevation(double x, double y) const;

        //! Gets the elevation using normalized [0..1] coordinates.
        ElevationSample getElevationUV(double u, double v) const;

        //! Extent of the texture
        const GeoExtent& getExtent() const { return _extent; }

        //! TileKey used to create this elevation grid
        const TileKey& getTileKey() const { return _tilekey; }

        //! Normal map associated with the elevation data, if available.
        osg::Texture2D* getNormalMapTexture() const;

        //! The normal at map coordinates, or (0,0,1) if the tile does not
        //! contain a normal map.
        osg::Vec3 getNormal(double x, double y) const;

        //! The packed normal at map coordinates, or (0,0,0,0) if the tile does not
        //! contain a normal map.
        void getPackedNormal(double x, double y, osg::Vec4& packed);

        //! Generates a normal map for this object.
        void generateNormalMap(const Map* map, void* workingSet, ProgressCallback* progress);

        //! Direct access to the pixel reader
        const ImageUtils::PixelReader& reader() const { return _read; }

        //! Matching list of sample resolutions
        const std::vector<float>& getResolutions() const { return _resolutions; }

        //! Get the resolution at s,t
        inline float getResolution(int s, int t) const {
            return _resolutions[t*_read.s()+s];
        }
        inline float getResolutionUV(double u, double v) const {
            return getResolution(
                (int)(u*(double)(_read.s()-1)),
                (int)(v*(double)(_read.t()-1)));
        }

        //! Ruggedness value at map coordinates (x,y)
        //! (Warning: experimental function; may go away or change without notice.)
        //! Note: currently disabled and will always return 0.
        inline float getRuggedness(double x, double y) const;

        //! The heightfield that was used to populate this object
        const osg::HeightField* getHeightField() const {
            return _heightField.get();
        }

    private:
        TileKey _tilekey;
        GeoExtent _extent;
        Distance _resolution;
        ImageUtils::PixelReader _read;
        ImageUtils::PixelReader _readNormal;
        osg::ref_ptr<osg::Texture2D> _normalTex;
        osg::ref_ptr<const osg::HeightField> _heightField;
        std::vector<float> _resolutions;
        osg::ref_ptr<osg::Image> _ruggedness;
        ImageUtils::PixelReader _readRuggedness;
        std::mutex _mutex;
    };

    /**
     * Utility class that makes normal map texture for the given tile key
     */
    class OSGEARTH_EXPORT NormalMapGenerator
    {
    public:
        osg::Texture2D* createNormalMap(
            const TileKey& key,
            const class Map* map,
            void* workingSet,
            osg::Image* ruggedness,
            ProgressCallback* progress);

        //! Packs a 3-vec normal into RG (octohedral compression)
        static void pack(const osg::Vec3& normal, osg::Vec4& packed);

        //! Unpacks the RG packed normal into a 3-vec.
        static void unpack(const osg::Vec4& packed, osg::Vec3& normal);
    };

    //! Revisioned key for elevation lookups (internal)
    namespace Internal
    {
        struct RevElevationKey
        {
            TileKey _tilekey;
            int _revision;

            inline bool operator < (const RevElevationKey& rhs) const {
                if ( _tilekey < rhs._tilekey ) return true;
                if ( rhs._tilekey < _tilekey ) return false;
                return _revision < rhs._revision;
            }
            inline bool operator == (const RevElevationKey& rhs) const {
                return 
                    _tilekey == rhs._tilekey &&
                    _revision == rhs._revision;
            }
            inline bool operator != (const RevElevationKey& rhs) const {
                return 
                    _tilekey != rhs._tilekey ||
                    _revision != rhs._revision;
            }
            inline std::size_t hash() const {
                return osgEarth::hash_value_unsigned(_tilekey.hash(), (std::size_t)_revision);
            }
        };
    }
}

namespace std {
    // std::hash specialization for Key
    template<> struct hash<osgEarth::Internal::RevElevationKey> {
        inline size_t operator()(const osgEarth::Internal::RevElevationKey& value) const {
            return value.hash();
        }
    };
}


#endif // OSGEARTH_ELEVATION_H