#ifndef __JPHYSICS__JDISPERSIONINTERFACE__
#define __JPHYSICS__JDISPERSIONINTERFACE__

#include <cmath>


/**
 * \author mdejong
 */

namespace JPHYSICS {}
namespace JPP { using namespace JPHYSICS; }

namespace JPHYSICS {

  /**
   * Light dispersion inteface.
   */
  class JDispersionInterface {
  public:
    /**
     * Virtual destructor.
     */
    virtual ~JDispersionInterface()
    {}


    /**
     * Index of refraction for phase velocity.
     *
     * \param  lambda     wavelenth [nm]
     * \return            index of refraction
     */
    virtual double getIndexOfRefractionPhase(const double lambda) const = 0;


    /**
     * Dispersion of light for phase velocity.
     *
     * \param  lambda     wavelength of light [nm]
     * \return            dn/dlambda
     */
    virtual double getDispersionPhase(const double lambda) const = 0;


    /**
     * Index of refraction for group velocity.
     *
     * \param  lambda     wavelenth [nm]
     * \return            index of refraction
     */
    virtual double getIndexOfRefractionGroup(const double lambda) const 
    {
      const double n = getIndexOfRefractionPhase(lambda);
      const double y = getDispersionPhase(lambda);
      
      return n / (1.0 + y*lambda/n);
    }


    /**
     * Dispersion of light for group velocity.
     *
     * \param  lambda     wavelength of light [nm]
     * \return            dn/dlambda
     */
    virtual double getDispersionGroup(const double lambda) const = 0;    


    /**
     * Get effective index of refraction for muon light.
     *
     * \param  lambda     wavelength of light [nm]
     * \return            index of refraction
     */
    double getKappa(const double lambda) const 
    {
      const double n  = getIndexOfRefractionPhase(lambda);
      const double ng = getIndexOfRefractionGroup(lambda);

      return (ng * n - 1.0) / sqrt(n*n - 1.0);
    }


    /**
     * Get smallest index of refraction for Bremsstrahlung light (i.e.\ point at which dt/dz = 0).
     *
     * \param  lambda     wavelength of light [nm]
     * \return            index of refraction
     */
    double getKmin(const double lambda) const 
    {
      const double ng = getIndexOfRefractionGroup(lambda);

      return sqrt(ng*ng - 1.0);
    }
  };
}

#endif