#ifndef WEIGHTHH
#define WEIGHTHH

#include "Evt.hh"
#include "Flux.hh"
#include "Head_util.hh"

/*! \brief Construct a function to weight the events.

 This function takes a Head object, a desired live-time and
 optionally a Flux object. It returns a function that can
 be used to compute the event weight.

 Depending on the flux and the information in Head, the weigh
 should be computed in the correct way.

 For data-files, the weighting function should always return 1.0.
 For mupage files, the weighting function will apply a simple
 scaling to the desired live-time.
 For neutrino-mc (genhen, gseagen) files, the weighting function
 will use the 'w2' and the flux to compute the correct weight.
 */

inline std::function< double (const Evt& evt) >
make_weight_function( Head& head,
                      double livetime  = -1,
                      const DiffuseFlux* flux = NULL )
{
  double mupage_livetime, ngen;

  bool have_flux     = (flux != NULL);
  bool have_livetime = (livetime != -1);
  if (!have_livetime) livetime = 365 * 24 * 3600; // default: 1 yr


  switch ( filetype( head ) )
  {

  case filetype_t::data :

    if ( !have_livetime ) fatal("livetime is specified for data file");

    return [] ( const Evt & evt ) // flux and livetime ignored
    {
      return 1;
    };
    break;


  case filetype_t::mupage :

    if ( have_flux      ) fatal("Flux is specified for mupage-file");

    mupage_livetime = head.mc_livetime();

    return [ = ] ( const Evt & evt )
    {
      return livetime / mupage_livetime;
    };
    break;


  case filetype_t::genhen :
  case filetype_t::gseagen :

    if (!have_flux) fatal("no flux specified for genhen/gseagen file");

    ngen = head.ngen() / ( 365 * 24 * 3600 ) ;

    return [ = ]( const Evt & evt )
    {


      const Trk& nu = * ( const_cast< Evt&>(evt)).primary_neutrino(); // todo: fix const stuff
      return livetime / ngen * evt.w[1] * flux->dNdEdOmega( nu ) ;
    };
    break;

  default :
    print("no weighting scheme implemented for filetype", filetype(head) );
    return []( const Evt & evt ) { print("weight function not valid.") ; return 0; };
  }

}


#endif