/* -*-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 <osgEarth/SpatialReference>
#include <osg/NodeCallback>
#include <osg/Vec3d>
#include <osg/Shape>
#include <osg/observer_ptr>
#include <osg/Version>
#include <osg/ValueObject>
#include <osg/MatrixTransform>

namespace osgEarth
{
    /**
     * Horizon operations (for a geocentric map).
     */
    class OSGEARTH_EXPORT Horizon : public osg::Object
    {
    public:
        META_Object(osgEarth, Horizon);

    public:
        //! Construct a horizon using a default WGS84 ellipsoid model
        Horizon();

        //! Construct a horizon providing the ellipsoid model
        Horizon(const Ellipsoid& ellipsoid);

        //! Construct a horizon from a spatial reference
        Horizon(const SpatialReference* srs);

        //! Copy
        Horizon(const Horizon& rhs, const osg::CopyOp& op = osg::CopyOp::DEEP_COPY_ALL);

        //! Ellipsoid model to use for occlusion testing
        void setEllipsoid(const Ellipsoid& ellipsoid);
        const Ellipsoid& getEllipsoid() const { return _em; }

        //! Minimum allowable height-above-ellipsoid to consider when doing visibility testing
        void setMinHAE(double meters);
        double getMinHAE() const { return _minHAE; }

        //! Eye position to use when testing for occlusion
        //! @return true if the value changed; false if it was the same
        bool setEye(const osg::Vec3d& eyeECEF, const osg::RefMatrix* proj =nullptr);
        const osg::Vec3d& getEye() const { return _eye; }
        
        //! Whether a point is potentially visible over the horizon.
        //! Specify an optional radius to test a sphere
        bool isVisible(const osg::Vec3d& point, double radius =0.0) const;
                
        //! Whether a bounding sphere is potentially visible over the horizon.
        inline bool isVisible(const osg::BoundingSphere& bs) const {
            return isVisible(bs.center(), bs.radius());
        }

        //! Whether the horizon occludes a point/sphere.
        bool occludes(const osg::Vec3d& point, double radius =0.0) const {
            return !isVisible(point, radius);
        }

        //! Sets the output variable to the horizon plane plane with its
        //! normal pointing at the eye. 
        bool getPlane(osg::Plane& out_plane) const;

        //! Caclulate distance from eye to visible horizon
        double getDistanceToVisibleHorizon() const;

        //! Radius of the ellipsoid under the eye
        double getRadius() const;
        
    protected:

        Ellipsoid  _em;
        bool       _valid = false;
        bool       _orthographic = false;
        osg::Vec3d _eye;
        osg::Vec3d _eyeUnit;
        osg::Vec3d _VC;       
        double     _VCmag = 0;    // distance from eye to center (scaled)
        double     _VCmag2 = 0;   // distance from eye to center squared (scaled)
        double     _VHmag2 = 0;   // distance from eye to horizon squared (scaled)
        double     _coneCos = 0;  // cosine of half-cone
        double     _coneTan = 0;  // tangent of half-cone

        osg::Vec3d _scale;
        osg::Vec3d _scaleInv;
        double     _minVCmag = 0;
        double     _minHAE = 0;
    };


    /**
     * Cull callback that culls a node if it is occluded by the horizon.
     */
    class OSGEARTH_EXPORT HorizonCullCallback : public osg::NodeCallback
    {
    public:
        /** Construct the callback with a default Horizon model. */
        HorizonCullCallback();

        //! Whether to cull by the center point only, or by the bounding sphere
        void setCullByCenterPointOnly(bool value) { _centerOnly = value; }
        bool getCullByCenterPointOnly() const { return _centerOnly; }

        //! Enable or disable the culler
        void setEnabled(bool value) { _enabled = value; }
        bool getEnabled() const { return _enabled; }

        //! Sets an alternate node whose bounds will be used to perform
        //! the culling test. By default, the culling test is performed
        //! against the node to which this callback is attached.
        void setProxyNode(osg::Node* node) { _proxy = node; }
        osg::observer_ptr<osg::Node>& getProxyNode() { return _proxy; }
        const osg::observer_ptr<osg::Node>& getProxyNode() const { return _proxy; }

        //! Custom ellipsoid to cull against.
        //! Normally this object will automatically detect the active ellipsoid
        //! from the NodeVisitor, but if you want to use a custom one you 
        //! can do so here.
        void setEllipsoid(const Ellipsoid& em);
        const Ellipsoid& getEllipsoid() const { return _customEllipsoid; }

    public: // osg::NodeCallback
        void operator()(osg::Node* node, osg::NodeVisitor* nv) override;

    protected:
        bool isVisible(osg::Node* node, osg::NodeVisitor* nv);

    private:
        bool _centerOnly;
        bool _enabled;
        Ellipsoid _customEllipsoid;
        bool _customEllipsoidSet;
        osg::observer_ptr<osg::Node> _proxy;
    };
}