/* -*-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/>
 */
#pragma once

#include <osgEarth/Common>
#include <osg/Matrix>

namespace osgEarth
{
    /**
     * A 2-axis ellipsoid used to approximate the shape of 
     * the Earth or other planetary body.
     */
    class OSGEARTH_EXPORT Ellipsoid
    {
    public:
        //! Construct a default WGS84 ellipsoid
        Ellipsoid();

        //! Copy
        Ellipsoid(const Ellipsoid&);

        //! Construct an ellipsoid
        //! @param semiMajorRadius Radius at the equator (meters)
        //! @param semiMinorRadius Radius Radius of the poles (meters)
        Ellipsoid(
            double semiMajorRadius,
            double semiMinorRadius);

        //! Equatorial radius
        double getSemiMajorAxis() const;
        double getRadiusEquator() const { return getSemiMajorAxis(); }
        void setSemiMajorAxis(double value);

        //! Polar radius (meters)
        double getSemiMinorAxis() const;
        double getRadiusPolar() const { return getSemiMinorAxis(); }
        void setSemiMinorAxis(double value);

        //! Name of this ellipsoid (meters)
        const std::string& getName() const { return _name; }
        void setName(const std::string& value) { _name = value; }

        //! Matrix to transform from LTP at a point to geocentric
        osg::Matrix geocentricToLocalToWorld(const osg::Vec3d& xyz) const;

        //! Get local up vector at a geocentric point
        osg::Vec3d geocentricToUpVector(const osg::Vec3d& xyz) const;

        //! Convert geocentric coords to geodetic (LL DEG + Alt M)
        osg::Vec3d geocentricToGeodetic(const osg::Vec3d& xyz) const;

        //! Convert geodetic coords to geocentric coord
        osg::Vec3d geodeticToGeocentric(const osg::Vec3d& lla) const;

        //! Get the coordinate frame at the geocentric point
        osg::Matrix geodeticToCoordFrame(const osg::Vec3d& xyz) const;

        //! Converts degrees to meters at a given latitide
        double longitudinalDegreesToMeters(double value, double lat_deg = 0.0) const;

        //! Converts meters to degrees at a given latitide
        double metersToLongitudinalDegrees(double value, double lat_deg =0.0) const;

        //! Geodesic distance in meters from one lat/long to another
        double geodesicDistance(
            const osg::Vec2d& longlat1_deg, 
            const osg::Vec2d& longlat2_deg) const;

        //! Geodesic interpolation between two lat/long points
        osg::Vec3d geodesicInterpolate(
            const osg::Vec3d& longlat1_deg,
            const osg::Vec3d& longlat2_deg,
            double t) const;

        //! Intersects a geocentric line with the ellipsoid.
        //! Upon success return true and place the first intersection
        //! point in "out".
        bool intersectGeocentricLine(
            const osg::Vec3d& p0,
            const osg::Vec3d& p1,
            osg::Vec3d& out) const;

        //! Calculate the world horizon culling point for a set of input points.
        //! @param points Points to consider, in world coordinates
        //! @return The horizon culling point, in world coordinates
        osg::Vec3d calculateHorizonCullingPoint(const std::vector<osg::Vec3d>& points) const;

        //! dtor
        ~Ellipsoid();

    private:
        void set(double er, double pr);

        std::string _name;
        osg::ref_ptr<osg::Referenced> _em;
        osg::Matrix _ellipsoidToUnitSphere;
        osg::Matrix _unitSphereToEllipsoid;
    };
}