#include <osg/Depth>
#include <osg/Geode>
#include <osg/Geometry>
#include <osg/ShapeDrawable>
#include <osg/Texture2D>
#include <osg/Transform>
#include <osg/PolygonOffset>
#include <osgDB/Registry>
#include <osgDB/ReadFile>
#include <osgUtil/CullVisitor>


class MoveHorizonWithEyePointTransform : public osg::Transform
{

public:

    // Get the transformation matrix which moves from local coords to world coords
    virtual bool computeLocalToWorldMatrix(osg::Matrix& matrix,osg::NodeVisitor* nv) const 
    {
        osgUtil::CullVisitor* cv = dynamic_cast<osgUtil::CullVisitor*>(nv);
        if (cv)
        {
            osg::Vec3 eyePointLocal = cv->getEyeLocal();
            matrix.preMult(osg::Matrix::translate(eyePointLocal));
        }
        return true;
    }

    // Get transformation matrix which moves from world coords to local coords
    virtual bool computeWorldToLocalMatrix(osg::Matrix& matrix,osg::NodeVisitor* nv) const
    {
        osgUtil::CullVisitor* cv = dynamic_cast<osgUtil::CullVisitor*>(nv);
        if (cv)
        {
            osg::Vec3 eyePointLocal = cv->getEyeLocal();
            matrix.postMult(osg::Matrix::translate(-eyePointLocal));
        }
        return true;
    }
};



osg::Transform* createSky(float radius, const std::string filename)
{
    osg::Geode* geode = new osg::Geode;
    osg::ShapeDrawable* geom = new osg::ShapeDrawable( new osg::Sphere(osg::Vec3(0,0,-radius/4.0),radius) );
    
    // set up the texture state.    
    osg::Texture2D* texture = new osg::Texture2D;
    texture->setDataVariance(osg::Object::DYNAMIC);  // protect from being optimized away as static state.
    texture->setWrap(osg::Texture::WRAP_S, osg::Texture::REPEAT);
    texture->setImage(osgDB::readImageFile(filename.c_str()));
    
    osg::StateSet* stateset = new osg::StateSet;
    stateset->setTextureAttributeAndModes( 0, texture, osg::StateAttribute::ON );
    stateset->setMode( GL_LIGHTING, osg::StateAttribute::OFF );

    // to prevent being able to push the model back through the sky, we
    // do two things (i) ensure sky is drawn first, and (ii) skip writing
    // to the depth buffer
    stateset->setRenderBinDetails( -1, "RenderBin" );
    osg::Depth* depth = new osg::Depth();
    depth->setWriteMask( false );
    stateset->setAttributeAndModes( depth, osg::StateAttribute::ON );

    geom->setStateSet( stateset );
    geom->setUseDisplayList( true );
    geode->addDrawable(geom);

    osg::Transform* transform = new MoveHorizonWithEyePointTransform;
    transform->setCullingActive( false );
    transform->addChild( geode );

    return transform;
}