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//
// G4AdjointPosOnPhysVolGenerator
//
// Class description:
//
// This class is responsible for the generation of primary adjoint particles
// on the external surface of a user selected volume.
// The particles are generated uniformly on the surface with the angular
// distribution set to a cosine law relative to normal of the surface.
// It is equivalent to the flux going in from the surface if an isotropic flux
// is considered outside. 
// It uses ray tracking technique and can be applied to all kind of convex
// volumes. Using the ray tracking technique the area of the external surface
// is also computed. The area is needed to fix the weight of the primary
// adjoint particle.  
// At the time of the development of this class, generation of points on
// volume surface and computation of surface was limited in Geant4, therefore
// the general ray tracking technique was adopted. The direct method in
// G4VSolid could be now (2009) used instead.

// Author: L. Desorgher, SpaceIT GmbH - 01.06.2006
// Contract: ESA contract 21435/08/NL/AT
// Customer: ESA/ESTEC
// --------------------------------------------------------------------
#ifndef G4AdjointPosOnPhysVolGenerator_hh
#define G4AdjointPosOnPhysVolGenerator_hh 1

#include "G4VPhysicalVolume.hh"
#include "G4AffineTransform.hh"
#include "G4ThreeVector.hh"

class G4VSolid;

class G4AdjointPosOnPhysVolGenerator 
{
//---------   
  public:
//---------   

    static  G4AdjointPosOnPhysVolGenerator* GetInstance();
   
    G4VPhysicalVolume* DefinePhysicalVolume(const G4String& aName);
    void DefinePhysicalVolume1(const G4String& aName);
    G4double ComputeAreaOfExtSurface();
    G4double ComputeAreaOfExtSurface(G4int NStat);
    G4double ComputeAreaOfExtSurface(G4double epsilon);
    G4double ComputeAreaOfExtSurface(G4VSolid* aSolid);
    G4double ComputeAreaOfExtSurface(G4VSolid* aSolid,G4int NStat);
    G4double ComputeAreaOfExtSurface(G4VSolid* aSolid,G4double epsilon);
 
    void GenerateAPositionOnTheExtSurfaceOfASolid(G4VSolid* aSolid,
                                                  G4ThreeVector& p,
                                                  G4ThreeVector& direction);
    void GenerateAPositionOnTheExtSurfaceOfTheSolid(G4ThreeVector& p,
                                                    G4ThreeVector& direction);
    void GenerateAPositionOnTheExtSurfaceOfThePhysicalVolume(G4ThreeVector& p,
                                                    G4ThreeVector& direction);
    void GenerateAPositionOnTheExtSurfaceOfThePhysicalVolume(G4ThreeVector& p,
                                                    G4ThreeVector& direction,
                                                    G4double& costh_to_normal);

    inline void SetSolid(G4VSolid* aSolid)
      { theSolid=aSolid; }
    inline G4double GetAreaOfExtSurfaceOfThePhysicalVolume()
      { return AreaOfExtSurfaceOfThePhysicalVolume; }
    inline G4double GetCosThDirComparedToNormal()
      { return CosThDirComparedToNormal; }
  
//---------   
  private:   // private methods
//---------  
    G4AdjointPosOnPhysVolGenerator() = default;
   ~G4AdjointPosOnPhysVolGenerator() = default;
    G4double ComputeAreaOfExtSurfaceStartingFromSphere(G4VSolid* aSolid,
                                                       G4int NStat);
    G4double ComputeAreaOfExtSurfaceStartingFromBox(G4VSolid* aSolid,
                                                    G4int NStat);
    void GenerateAPositionOnASolidBoundary(G4VSolid* aSolid,
                                           G4ThreeVector& p,
                                           G4ThreeVector& direction);
    G4double GenerateAPositionOnASphereBoundary(G4VSolid* aSolid,
                                                G4ThreeVector& p,
                                                G4ThreeVector& direction);
    G4double GenerateAPositionOnABoxBoundary(G4VSolid* aSolid,
                                             G4ThreeVector& p,
                                             G4ThreeVector& direction);
    void ComputeTransformationFromPhysVolToWorld();

//---------   
  private:   // attributes
//---------   

   static G4ThreadLocal G4AdjointPosOnPhysVolGenerator* theInstance;
   G4VSolid* theSolid = nullptr;
   G4VPhysicalVolume* thePhysicalVolume = nullptr;

   G4bool UseSphere{true};
   G4String ModelOfSurfaceSource{"OnSolid"};
   G4AffineTransform theTransformationFromPhysVolToWorld;
   G4double AreaOfExtSurfaceOfThePhysicalVolume{0.};
   G4double CosThDirComparedToNormal{0.};
};

#endif