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

#include "MyMollerBhabhaModel.hh"

#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"

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using namespace std;

MyMollerBhabhaModel::MyMollerBhabhaModel(const G4ParticleDefinition* p, const G4String& nam)
  : G4MollerBhabhaModel(p, nam)
{}

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MyMollerBhabhaModel::~MyMollerBhabhaModel() {}

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G4double MyMollerBhabhaModel::ComputeDEDXPerVolume(const G4Material* material,
                                                   const G4ParticleDefinition* p,
                                                   G4double kineticEnergy, G4double cutEnergy)
{
  if (!particle) SetParticle(p);
  // calculate the dE/dx due to the ionization by Seltzer-Berger formula

  G4double electronDensity = material->GetElectronDensity();
  G4double Zeff = electronDensity / material->GetTotNbOfAtomsPerVolume();
  G4double th = 0.25 * sqrt(Zeff) * keV;
  G4double tkin = kineticEnergy;
  G4bool lowEnergy = false;
  if (kineticEnergy < th) {
    tkin = th;
    lowEnergy = true;
  }
  G4double tau = tkin / electron_mass_c2;
  G4double gam = tau + 1.0;
  G4double gamma2 = gam * gam;
  G4double beta2 = 1. - 1. / gamma2;
  // G4double bg2   = beta2*gamma2;

  G4double eexc = material->GetIonisation()->GetMeanExcitationEnergy();
  eexc /= electron_mass_c2;
  G4double eexc2 = eexc * eexc;

  G4double d = min(cutEnergy, MaxSecondaryEnergy(p, tkin)) / electron_mass_c2;
  G4double dedx;

  // electron
  if (isElectron) {
    dedx = log(2.0 * (tau + 2.0) / eexc2) - 1.0 - beta2 + log((tau - d) * d) + tau / (tau - d)
           + (0.5 * d * d + (2.0 * tau + 1.) * log(1. - d / tau)) / gamma2;

    // positron
  }
  else {
    G4double d2 = d * d * 0.5;
    G4double d3 = d2 * d / 1.5;
    G4double d4 = d3 * d * 3.75;
    G4double y = 1.0 / (1.0 + gam);
    dedx =
      log(2.0 * (tau + 2.0) / eexc2) + log(tau * d)
      - beta2 * (tau + 2.0 * d - y * (3.0 * d2 + y * (d - d3 + y * (d2 - tau * d3 + d4)))) / tau;
  }

  // do not apply density correction
  // G4double cden  = material->GetIonisation()->GetCdensity();
  // G4double mden  = material->GetIonisation()->GetMdensity();
  // G4double aden  = material->GetIonisation()->GetAdensity();
  // G4double x0den = material->GetIonisation()->GetX0density();
  // G4double x1den = material->GetIonisation()->GetX1density();
  // G4double x     = log(bg2)/twoln10;

  // if (x >= x0den) {
  //   dedx -= twoln10*x - cden;
  //   if (x < x1den) dedx -= aden*pow(x1den-x, mden);
  // }

  // now you can compute the total ionization loss
  dedx *= twopi_mc2_rcl2 * electronDensity / beta2;
  if (dedx < 0.0) dedx = 0.0;

  // lowenergy extrapolation

  if (lowEnergy) {
    if (kineticEnergy >= lowLimit)
      dedx *= sqrt(tkin / kineticEnergy);
    else
      dedx *= sqrt(tkin * kineticEnergy) / lowLimit;
  }
  return dedx;
}

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