/* osgEarth
 * Copyright 2025 Pelican Mapping
 * MIT License
 */
#pragma once

#include <osgEarth/Common>
#include <osgEarth/Geoid>
#include <osgEarth/Units>
#include <osg/Shape>

namespace osgEarth
{
    class OSGEARTH_EXPORT GeoExtent;

    /** 
     * Reference information for vertical (height) information.
     */
    class OSGEARTH_EXPORT VerticalDatum : public osg::Object
    {
    public:
        META_Object(osgEarth, VerticalDatum);

        /**
         * Creates an vertical datum from an initialization string. This method
         * uses an internal cache so that there is only ever one instance or each
         * unique vertical datum.
         *
         * Note! This will accept either the vdatum name (e.g., "egm96") or the
         * inverse of a vdatum (e.g., "-egm96") for which all values will be
         * negated.
         */
        static VerticalDatum* get( const std::string& init );


    public: // static transform methods

        /**
         * Transforms a Z coordinate from one vertical datum to another.
         */
        static bool transform(
            const VerticalDatum* from,
            const VerticalDatum* to,
            double               lat_deg,
            double               lon_deg,
            double&              in_out_z );

        /**
         * Transforms a Z coordinate from one vertical datum to another.
         */
        static bool transform(
            const VerticalDatum* from,
            const VerticalDatum* to,
            double               lat_deg,
            double               lon_deg,
            float&               in_out_z );

        /**
         * Transforms the values in a height field from one vertical datum to another.
         */
        static bool transform(
            const VerticalDatum* from,
            const VerticalDatum* to,
            const GeoExtent&     extent,
            osg::HeightField*    hf );


    public: // raw transformations

        /**
         * Converts an MSL value (height relative to a mean sea level model) to the
         * corresponding HAE value (height above the model's reference ellipsoid)
         */
        inline double msl2hae(double lat_deg, double lon_deg, double msl) const {
            return _geoid.valid() ? msl + _geoid->getHeight(lat_deg, lon_deg, INTERP_BILINEAR) : msl;
        }

        /**
         * Converts an HAE value (height above the model's reference ellipsoid) to the
         * corresponding MSL value (height relative to a mean sea level model)
         */
        inline double hae2msl(double lat_deg, double lon_deg, double hae) const {
            return _geoid.valid() ? hae - _geoid->getHeight(lat_deg, lon_deg, INTERP_BILINEAR) : hae;
        }

    public: // properties

        /** Gets the readable name of this SRS. */
        const std::string& getName() const { return _name; }

        /** Gets the linear units of height values */
        const UnitsType& getUnits() const { return _units; }

        /** Gets the string that was used to initialize this SRS */
        const std::string& getInitString() const { return _initString; }

        /** Gets the underlying geoid */
        const Geoid* getGeoid() const { return _geoid.get(); }

        /** Tests this SRS for equivalence with another. */
        virtual bool isEquivalentTo( const VerticalDatum* rhs ) const;
        
    public:

        /** Creates a geoid-based VSRS. */
        VerticalDatum(
            const std::string& name,
            const std::string& initString,
            Geoid*             geoid =0L );

        /** Creates a simple ellipsoidal VSRS. */
        VerticalDatum( const UnitsType& units );

    protected:
        // required by META_Object, but not used.
        VerticalDatum() = default;
        VerticalDatum(const VerticalDatum& rhs, const osg::CopyOp& op) { }

        std::string         _name;
        std::string         _initString;
        osg::ref_ptr<Geoid> _geoid;
        UnitsType           _units;

        static VerticalDatum* create(const std::string& initString);
    };
}
