//
// ********************************************************************
// * License and Disclaimer                                           *
// *                                                                  *
// * The  Geant4 software  is  copyright of the Copyright Holders  of *
// * the Geant4 Collaboration.  It is provided  under  the terms  and *
// * conditions of the Geant4 Software License,  included in the file *
// * LICENSE and available at  http://cern.ch/geant4/license .  These *
// * include a list of copyright holders.                             *
// *                                                                  *
// * Neither the authors of this software system, nor their employing *
// * institutes,nor the agencies providing financial support for this *
// * work  make  any representation or  warranty, express or implied, *
// * regarding  this  software system or assume any liability for its *
// * use.  Please see the license in the file  LICENSE  and URL above *
// * for the full disclaimer and the limitation of liability.         *
// *                                                                  *
// * This  code  implementation is the result of  the  scientific and *
// * technical work of the GEANT4 collaboration.                      *
// * By using,  copying,  modifying or  distributing the software (or *
// * any work based  on the software)  you  agree  to acknowledge its *
// * use  in  resulting  scientific  publications,  and indicate your *
// * acceptance of all terms of the Geant4 Software license.          *
// ********************************************************************
//
// G4TMagFieldEquation
//
// Class description:
//
// Templated version of  motion of quadrupole magnetic field.
// Enables testing of inlined code for field, equation, stepper, driver,
// avoiding all virtual calls.
// Adapted from G4QuadrupoleMagField.

// Author: Josh Xie (CERN, Google Summer of Code 2014), June 2014
// Supervisors:  Sandro Wenzel, John Apostolakis (CERN)
// --------------------------------------------------------------------
#ifndef G4T_QUADRUPOLE_MAGFIELD_HH
#define G4T_QUADRUPOLE_MAGFIELD_HH

#include "G4ThreeVector.hh"
#include "G4RotationMatrix.hh"
#include "G4MagneticField.hh"

/**
 * @brief G4TQuadrupoleMagField is a templated version of G4QuadrupoleMagField.
 */

class G4TQuadrupoleMagField : public G4MagneticField 
{
  public:

    G4TQuadrupoleMagField(G4double pGradient)
    {
      fGradient = pGradient ;
      fOrigin   = G4ThreeVector( 0.0, 0.0, 0.0) ;
      fpMatrix  = &IdentityMatrix;
    }

    G4TQuadrupoleMagField(G4double pGradient, 
                          G4ThreeVector pOrigin, 
                          G4RotationMatrix* pMatrix)
    {
      fGradient    = pGradient ;
      fOrigin      = pOrigin ;
      fpMatrix     = pMatrix ;
    }

    virtual ~G4TQuadrupoleMagField() = default;

    inline void GetFieldValue(const G4double y[7],
                                    G4double B[3] ) const
    {
      G4ThreeVector r_global = G4ThreeVector(
              y[0] - fOrigin.x(), 
              y[1] - fOrigin.y(), 
              y[2] - fOrigin.z());

      G4ThreeVector r_local = G4ThreeVector(
              fpMatrix->colX() * r_global,
              fpMatrix->colY() * r_global,
              fpMatrix->colZ() * r_global);

      G4ThreeVector B_local = G4ThreeVector(
              fGradient * r_local.y(),
              fGradient * r_local.x(),
              0);

      G4ThreeVector B_global = G4ThreeVector(
              fpMatrix->inverse().rowX() * B_local,
              fpMatrix->inverse().rowY() * B_local,
              fpMatrix->inverse().rowZ() * B_local);

      B[0] = B_global.x() ;
      B[1] = B_global.y() ;
      B[2] = B_global.z() ;
    }

    G4TQuadrupoleMagField* Clone() const
    {
      //TODO: Can the fpMatrix be shared??
      return new G4TQuadrupoleMagField(this->fGradient,
                                       this->fOrigin,
                                       this->fpMatrix);
    }

  private:

    static G4RotationMatrix IdentityMatrix; 

    G4double          fGradient;
    G4ThreeVector     fOrigin;
    G4RotationMatrix* fpMatrix;
};

#endif