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/// \file PrimaryGeneratorAction3.cc
/// \brief Implementation of the PrimaryGeneratorAction3 class

#include "PrimaryGeneratorAction3.hh"

#include "PrimaryGeneratorAction.hh"

#include "G4Event.hh"
#include "G4ParticleDefinition.hh"
#include "G4ParticleGun.hh"
#include "G4ParticleTable.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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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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