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//
// $Id: G4SamplingPostStepAction.cc,v 1.3 2008/04/21 09:10:29 ahoward Exp $
// GEANT4 tag $Name: geant4-09-03 $
//
// ----------------------------------------------------------------------
// GEANT 4 class source file
//
// G4SamplingPostStepAction.cc
//
// ----------------------------------------------------------------------

#include "G4SamplingPostStepAction.hh"
#include "G4Track.hh"
#include "G4ParticleChange.hh"
#include "G4VImportanceSplitExaminer.hh"
#include "G4Nsplit_Weight.hh"
#include "G4VTrackTerminator.hh"
#include <sstream>

G4SamplingPostStepAction::
G4SamplingPostStepAction(const G4VTrackTerminator &TrackTerminator)
  : fTrackTerminator(TrackTerminator)
{
}

G4SamplingPostStepAction::~G4SamplingPostStepAction()
{
}

void G4SamplingPostStepAction::DoIt(const G4Track& aTrack, 
                                          G4ParticleChange *aParticleChange,
                                    const G4Nsplit_Weight &nw)
{  
  // evaluate results from sampler
  if (nw.fN>1)
  {
    // split track 
    Split(aTrack, nw, aParticleChange);
  }
  else if (nw.fN==1)
  {
    // don't split, but weight may be changed ! 
    aParticleChange->ProposeWeight(nw.fW);
  }
  else if (nw.fN==0)
  {
    // kill track
    fTrackTerminator.KillTrack();
  }
  else
  {
    // wrong answer
    std::ostringstream os;
    os << "Sampler returned nw = "
       << nw
       << "\n";
    G4String m = os.str();
    
    G4Exception("G4SamplingPostStepAction::DoIt()",
                "InvalidCondition", FatalException, m);
  }
}

void G4SamplingPostStepAction::Split(const G4Track &aTrack,
                                     const G4Nsplit_Weight &nw,
                                           G4ParticleChange *aParticleChange)
{
  aParticleChange->ProposeWeight(nw.fW);
  aParticleChange->SetNumberOfSecondaries(nw.fN-1);
  
  for (G4int i=1;i<nw.fN;i++)
  {
    G4Track *ptrack = new G4Track(aTrack);
    
    //    ptrack->SetCreatorProcess(aTrack.GetCreatorProcess());
    ptrack->SetWeight(nw.fW);
    
    if (ptrack->GetMomentumDirection() != aTrack.GetMomentumDirection())
    {
      G4Exception("G4SamplingPostStepAction::Split()", "InvalidCondition",
                  FatalException, "Track with same momentum !");
    }
    aParticleChange->AddSecondary(ptrack);
  }
  return;
}