//
// ********************************************************************
// * License and Disclaimer                                           *
// *                                                                  *
// * The  Geant4 software  is  copyright of the Copyright Holders  of *
// * the Geant4 Collaboration.  It is provided  under  the terms  and *
// * conditions of the Geant4 Software License,  included in the file *
// * LICENSE and available at  http://cern.ch/geant4/license .  These *
// * include a list of copyright holders.                             *
// *                                                                  *
// * Neither the authors of this software system, nor their employing *
// * institutes,nor the agencies providing financial support for this *
// * work  make  any representation or  warranty, express or implied, *
// * regarding  this  software system or assume any liability for its *
// * use.  Please see the license in the file  LICENSE  and URL above *
// * for the full disclaimer and the limitation of liability.         *
// *                                                                  *
// * This  code  implementation is the result of  the  scientific and *
// * technical work of the GEANT4 collaboration.                      *
// * By using,  copying,  modifying or  distributing the software (or *
// * any work based  on the software)  you  agree  to acknowledge its *
// * use  in  resulting  scientific  publications,  and indicate your *
// * acceptance of all terms of the Geant4 Software license.          *
// ********************************************************************
//
// G4BOptnForceFreeFlight
//
// Class Description:
//
// A G4VBiasingOperation physics-based biasing operation.
// If forces the physics process to not act on the track.
// In this implementation (meant for the ForceCollision
// operator) the free flight is done under zero weight for
// the track, and the action is meant to accumulate the weight
// change for making this uninteracting flight,
// cumulatedWeightChange.
// When the track reaches the current volume boundary, its
// weight is restored with value: initialWeight * cumulatedWeightChange
//
// Author: Marc Verderi, November 2013.
// --------------------------------------------------------------------
#ifndef G4BOptnForceFreeFlight_hh
#define G4BOptnForceFreeFlight_hh 1

#include "G4VBiasingOperation.hh"
#include "G4ForceCondition.hh"
#include "G4ParticleChange.hh" // Should add a dedicated "weight change only"
                               // particle change
class G4ILawForceFreeFlight;

class G4BOptnForceFreeFlight : public G4VBiasingOperation
{
  public:

    // -- Constructor :
    G4BOptnForceFreeFlight(const G4String& name);
    // -- destructor:
    virtual ~G4BOptnForceFreeFlight();
  
    // -- Methods from G4VBiasingOperation interface:
    // -------------------------------------------
    // -- Used:
    virtual const G4VBiasingInteractionLaw*
    ProvideOccurenceBiasingInteractionLaw( const G4BiasingProcessInterface*,
                                           G4ForceCondition& );
    virtual void AlongMoveBy( const G4BiasingProcessInterface*,
                              const G4Step*, G4double );
    virtual G4VParticleChange*
    ApplyFinalStateBiasing( const G4BiasingProcessInterface*,
                            const G4Track*, const G4Step*, G4bool& );

    // -- Unused:
    virtual G4double DistanceToApplyOperation( const G4Track*,
                            G4double, G4ForceCondition* ) { return DBL_MAX; }
    virtual G4VParticleChange* GenerateBiasingFinalState( const G4Track*,
                            const G4Step* ) { return nullptr; }

    // -- Additional methods, specific to this class:
    // ----------------------------------------------
    // -- return concrete type of interaction law:
    G4ILawForceFreeFlight* GetForceFreeFlightLaw()
    {
      return fForceFreeFlightInteractionLaw;
    }
    // -- initialization for weight:
    void ResetInitialTrackWeight(G4double w)
    {
      fInitialTrackWeight = w;
      fCumulatedWeightChange = 1.0;
    }
    G4bool OperationComplete() const
    {
      return fOperationComplete;
    }

  private:

    G4ILawForceFreeFlight* fForceFreeFlightInteractionLaw = nullptr;
    G4double  fCumulatedWeightChange = -1.0,
              fInitialTrackWeight = -1.0;
    G4ParticleChange fParticleChange;
    G4bool fOperationComplete = true;
};

#endif