////////////////////////////////////////////////////////////////////////////////
/// \class RAT::DU::LightPathFitter
///
/// \brief LightPath fitter abstract interface.
////////////////////////////////////////////////////////////////////////////////
#ifndef __RAT_DU_LightPathFitter__
#define __RAT_DU_LightPathFitter__

#include <TVector3.h>
#include <RAT/LightPath.hh>

namespace RAT
{

namespace LP
{

class LightPathFitter
{
public:

  LightPathFitter() { }

  virtual ~LightPathFitter() { }

  /// Attempt to fit a light path, from the start of the given path object
  /// to the end of the path.  The starting point will be used as an exact
  /// location, but the end may not be as specified (how the end is determined
  /// if it's not the same is dependent on the algorithm).  Also, if the
  /// end point is used exactly, the ending region type is copied from the
  /// argument.
  ///
  /// @param[in] startPath The beginning and (prospective) end of the path.
  /// @param[out] startPath The path will be modified.
  /// @return A reference to the modified light path.
  virtual LightPath& Fit(LightPath& startPath) const = 0;

  /// Calculate the solid angle for this path, as subtended at the start point by the PMT
  /// at the end point of the light path.
  ///
  /// @param[in] lightPath The fitted light path. If input is invalid, a fit will be performed.
  /// @param[in] pmtNorm The PMT-bucket normal vector (pointing IN, towards the AV)
  /// @param[in] nVal The nVal-sided polygon superimposed onto the PMT bucket for the calculation.
  ///            Use nVal == 0 for spherical cap approximation, otherwise nVal must be > 2.
  /// @param[out] cosThetaAvg The average cos(theta) of the incident path on the PMT bucket face.
  //             Will be <= -999.0 for invalid path.
  ///
  /// @return Solid angle, or something < 0 for invalid path.
  virtual Double_t GetSolidAngle(const LightPath& lightPath, const TVector3& pmtNorm, UInt_t nVal, Double_t& cosThetaAvg) const = 0;

}; // class LightPathFitter

} // namespace LP

} // namespace RAT

#endif