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

namespace Rivet {


  /// @brief e+ e- > sigma+ sigmabar-
  class BESIII_2024_I2748736 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2748736);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(Cuts::abspid==3222), "UFS");
      book(_sigma_plus ,1,1,1);

      for (const string& en : _sigma_plus.binning().edges<0>()) {
        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");
      // total hadronic and muonic cross sections
      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      // find the Sigmas
      const FinalState& ufs = apply<UnstableParticles>(event, "UFS");
      for (unsigned int ix=0;ix<ufs.particles().size();++ix) {
      	const Particle& p1 = ufs.particles()[ix];
      	bool matched = false;
       	// check fs
       	bool fs = true;
      	for (const Particle& child : p1.children()) {
      	  if (child.pid()==p1.pid()) {
      	    fs = false;
      	    break;
      	  }
      	}
      	if (!fs) continue;
        // find the children
        map<long,int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p1,nRes,ncount);
        for (unsigned int iy=ix+1; iy<ufs.particles().size(); ++iy) {
       	  const Particle& p2 = ufs.particles()[iy];
       	  if (p2.pid() != -p1.pid()) continue;
       	  // check fs
      	  bool fs = true;
      	  for (const Particle& child : p2.children()) {
      	    if (child.pid()==p2.pid()) {
      	      fs = false;
      	      break;
      	    }
      	  }
      	  if (!fs) 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) {
	    _sigma_plus->fill(_ecms);
	    break;
	  }
      	}
        if (matched) break;
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_sigma_plus, crossSection()/ sumOfWeights() /femtobarn);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _sigma_plus;
    string _ecms;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2024_I2748736);

}
