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/// \file eventgenerator/particleGun/src/PrimaryGeneratorAction3.cc
/// \brief Implementation of the PrimaryGeneratorAction3 class
//
//
// $Id$
// 
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#include "PrimaryGeneratorAction3.hh"
#include "PrimaryGeneratorAction.hh"

#include "G4Event.hh"
#include "G4ParticleGun.hh"
#include "G4ParticleTable.hh"
#include "G4ParticleDefinition.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"

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PrimaryGeneratorAction3::PrimaryGeneratorAction3(G4ParticleGun* gun)
: fParticleGun(gun)
{    
  // direction
  //
  G4double theta = 90*deg, phi = 45*deg;
  fNewUz = G4ThreeVector(std::sin(theta)*std::cos(phi),
                         std::sin(theta)*std::sin(phi),
                         std::cos(theta));
                        
  fAlphaMax = 15*deg;                        
}

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PrimaryGeneratorAction3::~PrimaryGeneratorAction3()
{ }

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void PrimaryGeneratorAction3::GeneratePrimaries(G4Event* anEvent)
{
  //particle direction uniform around fNewUz axis
  //
  //1- in World frame      
  //cosAlpha uniform in [cos(0), cos(fAlphaMax)]
  G4double cosAlpha = 1. - G4UniformRand()*(1.- std::cos(fAlphaMax));
  G4double sinAlpha = std::sqrt(1. - cosAlpha*cosAlpha);
  G4double psi      = twopi*G4UniformRand();  //psi uniform in [0, 2*pi]  
  G4ThreeVector dir(sinAlpha*std::cos(psi),sinAlpha*std::sin(psi),cosAlpha);
  
  //2- rotate dir   (rotateUz transforms uz to fNewUz)
  dir.rotateUz(fNewUz);           

  fParticleGun->SetParticleMomentumDirection(dir);
  
  //set energy
  //
  fParticleGun->SetParticleEnergy(1*MeV);    

  //create vertex
  //   
  fParticleGun->GeneratePrimaryVertex(anEvent);
}

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