////////////////////////////////////////////////////////////////////
/// \class RAT::DU::GroupVelocity
///
/// \brief  Return the total transit time using group velocities
///
/// \author Phil G Jones <p.jones22@physics.ox.ac.uk>
///
/// REVISION HISTORY:\n
///  - 21 July 2011 : New File.\n
///  - 2014-03-01 : P G Jones - refactor as part of ds review, moved from ds.
///  - 2014-07-14   J.R.Wilson - change name of scint volume to inner_av
///  - 2014-04-02 : M Mottram - updated to work with partial fill.
///  - 2015-04-16 : K Majumdar - will first attempt to find explicit group velocities in Optics files, otherwise will calculate them internally
///  - 2015-05-13 : R Stainforth - Added PMT bucket time calculation.
///
///
/// \details As Brief
///
////////////////////////////////////////////////////////////////////
#ifndef __RAT_DU_GroupVelocity__
#define __RAT_DU_GroupVelocity__

#include <RAT/DB.hh>

#include <TGraph.h>
#include <TObject.h>

namespace RAT
{
namespace DU
{

class GroupVelocity : public TObject
{
public:
  /// Called at the start of a run, loads from the database
  void BeginOfRun();
  /// Calculate the transit time by distance
  inline double CalcByDistance( const double distInInnerAV, const double distInAV, const double distInWater ) const;
  /// Calculate the transit time by distance, for a photon of specified energy
  inline double CalcByDistance( const double distInInnerAV, const double distInAV, const double distInWater, const double energy ) const;
  /// Calculate the approximate time a photon spends inside the PMT bucket region
  /// before hitting the cathode
  double PMTBucketTime( double incidentAngle ) const;

  // This ROOT macro adds dictionary methods to this class.
  // The number is 0 as this class is never, and should never be written to disc.
  // It assumes this class has no virtual methods, use ClassDef if change this.
  ClassDefNV( GroupVelocity, 0 );
private:
  /// Helper function to load the group velocity from the table into TGraph
  ///
  /// @param[in] dbTable to load the group velocity from
  /// @param[out] property graph
  void LoadGroupVelocity( DBLinkPtr dbTable, TGraph& property );

  TGraph fInnerAVGroupVelocity; ///< Group Velocity as a function of energy in scintillator
  TGraph fAVGroupVelocity; ///< Group Velocity as a function of energy in av
  TGraph fWaterGroupVelocity; ///< Group Velocity as a function of energy in water
};

double
GroupVelocity::CalcByDistance( const double distInInnerAV,
                               const double distInAV,
                               const double distInWater ) const
{
  return CalcByDistance( distInInnerAV, distInAV, distInWater, 3.103125 * 1e-6 ); //400nm
}

double
GroupVelocity::CalcByDistance( const double distInInnerAV,
                               const double distInAV,
                               const double distInWater,
                               const double energy ) const
{
  return distInInnerAV / fInnerAVGroupVelocity.Eval( energy ) + distInAV / fAVGroupVelocity.Eval( energy ) + distInWater / fWaterGroupVelocity.Eval( energy );
}

} // namespace DU

} // namespace RAT

#endif