// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief e+e- -> D Dbar
  class BESIII_2024_I2755997 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2755997);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(Cuts::abspid==411 or Cuts::abspid==421), "UFS");
      for(unsigned int ix=0;ix<2;++ix)
	book(_sigma[ix],ix+1, 1, 1);

      for (const string& en : _sigma[0].binning().edges<0>()) {
        const double end = std::stod(en)*GeV;
        if (isCompatibleWithSqrtS(end)) {
          _ecms = en;
          break;
        }
      }
      if(_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
    }

    void findChildren(const Particle& p,map<long,int>& nRes, int &ncount) {
      for (const Particle& child : p.children()) {
        if (child.children().empty()) {
          nRes[child.pid()]-=1;
          --ncount;
        }
        else {
          findChildren(child,nRes,ncount);
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const FinalState& fs = apply<FinalState>(event, "FS");

      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      const FinalState& ufs = apply<FinalState>(event, "UFS");
      for (unsigned int ix=0; ix<ufs.particles().size(); ++ix) {
       	const Particle& p1 = ufs.particles()[ix];
      	map<long,int> nRes = nCount;
      	int ncount = ntotal;
      	findChildren(p1,nRes,ncount);
      	bool matched=false;
       	for (unsigned int iy=ix+1; iy<ufs.particles().size(); ++iy) {
          const Particle& p2 = ufs.particles()[iy];
          if (p2.pid()!=-p1.pid()) continue;
          if (!p2.parents().empty() && p2.parents()[0].pid()==p1.pid()) continue;
          map<long,int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(p2,nRes2,ncount2);
          if (ncount2!=0) continue;
          matched=true;
          for (const auto& val : nRes2) {
            if (val.second!=0) {
              matched = false;
              break;
            }
          }
          if (matched) break;
       	}
       	if(matched) {
	  if(p1.abspid()==421) _sigma[0]->fill(_ecms);
	  else                 _sigma[1]->fill(_ecms);
	  break;
      	}
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection()/ sumOfWeights() /picobarn; 
      for(unsigned int ix=0;ix<2;++ix)
        scale(_sigma[ix],fact);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _sigma[2];
    string _ecms;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2024_I2755997);

}
