////////////////////////////////////////////////////////////////////
///\class RAT::AxionGenerator
///\author Christopher Jones <christopher.jones@physics.ox.ac.uk>
///\author Esther Turner <esther.turner@physics.ox.ac.uk> -- contact person
///\date 10-Feb-2015
///\brief  Generator for Solar Axions
///\details This class implements solar axion interactions within SNO+
///
/// REVISION HISTORY:
///  - 10-Feb-2015: Christopher Jones: Doxygen fixes. First Instance of adding solar axions into RAT for SNO+
///  - 24-May-2015: Christopher Jones: Fixed bug and now all four interactions produce results.
///
///
///
////////////////////////////////////////////////////////////////////


#ifndef __RAT_VERTEXGEN_SOLARAXION__
#define __RAT_VERTEXGEN_SOLARAXION__

#include <CLHEP/Random/Randomize.h>
#include <G4ParticleDefinition.hh>
#include <G4ThreeVector.hh>
#include <G4LorentzVector.hh>
#include <RAT/GLG4VertexGen.hh>
#include <RAT/EventTime.hh>
#include <RAT/DB.hh>
#include <vector>

// ROOT headers
#include <TGraph.h>
#include <TMath.h>
#include <TRandom3.h>

class G4Event;

namespace RAT
{

  class VertexGen_Axion : public GLG4VertexGen
  {
  public:
    /** Default constructor*/
    VertexGen_Axion();

    /** Destructor */
    virtual ~VertexGen_Axion();

    /** Method for generating primary verticies in Geant4 */
    virtual void GeneratePrimaryVertex(G4Event *event, G4ThreeVector &dx, G4double dt);

    /** Defines repeatability of the generator. */
    virtual bool IsRepeatable() const { return true; };

    /** Sets the state of the generator. */
    virtual void SetState(G4String state);

    /** Getter for state of the position generator.  */
    virtual G4String GetState();

  protected:
    /** Settings of the generator that is used */
    G4String fStateStr;

    /** Interaction type within the vertex generator e.g. 'compton_axion' */
    G4String fInteractionType;

    /** Direction of the incoming solar axion */
    G4ThreeVector fAxionDirection;

    /** Direction of the sun for a given interaction */
    G4ThreeVector fSolarDirection;

    /** Average nuclear mass number of the generating material */
    double fNuclearZ;

    /** Mass of the electron */
    double fMassElectron;

    /** EventTime object to deal with the non-sequentiality of the generated events. */
    EventTime fEvTime;

    /** Kinetic energy of the axion which is emitted */
    double faxionEnergy;

    /** Mass of a solar Axion */
    double faxionMass;

  private:
    /** Gamma particle within an interaction */
    G4ParticleDefinition *fGamma;

    /** Electron within an interaction */
    G4ParticleDefinition *fElectron;

    /** ROOT TGraph for differential cross section of solar axion interaction*/
    TGraph *fDiffCrossSection;

    /**
      * Normalised probability of compton axion conversion at different interaction angles
      * \details This method calculates the probability of inverse primakoff conversion for different interaction angles using the formulation set out in
      * Avignone et al. (PRD 37, 3, p.618) .
      /param theta interaction angle
      * @return normalised probability of interaction at different interaction angles
      *
    */
    double ComptonAxionDifferentialCrossSection(double theta) const;

    /**
      * Normalised probability of inverse primakoff conversion of axions at different interaction angles
      * \details This method calculates the probability of inverse primakoff conversion for different interaction angles using the formulation set out in
      * Avignone et al. (PRD 37, 3, p.618) . Angle calculated is within the nuclear rest frame.
      /param theta interaction angle
      * @return normalised probability of interaction at different interaction angles
      *
    */
    double InversePrimakoffConversionDifferentialCrossSection(double theta) const;

    /**
      * Updates the differential cross section of several solar axion interactions in SNO+
      * \details This method draws a TGraph with 10,000 points between 0.0 and Pi radians for the compton conversion and inverse primakoff interactions of solar
      * axions in SNO+ both calculated from Avignone et al. (PRD 37, 3, p.618) .
      *
    */
    void DrawDiffCrossSection() const;

    /**
      * Samples the differential cross section for either compton conversion or inverse primakoff interactions of solar axions in SNO+
      * and returns a value for the interaction angle for the chosen process.
      * @return TGraph with differential cross section
      *
    */
    double SampleDifferentialCrossSection() const;

  };

} // namespace RAT

#endif // __RAT_VERTEXGEN_SOLARAXION__