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

namespace Rivet {


  /// @brief Xi- Xibar+ cross section
  class BESIII_2020_I1823448 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1823448);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_nXi, 1, 1, 4);

      for (const string& en : _nXi.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");
      // 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 Xis
      const FinalState& ufs = apply<UnstableParticles>(event, "UFS");
      for(unsigned int ix=0;ix<ufs.particles().size();++ix) {
	const Particle& p1 = ufs.particles()[ix];
	if(abs(p1.pid())!=3312) continue;
	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(abs(p2.pid())!=3312) 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(auto const & val : nRes2) {
	    if(val.second!=0) {
	      matched = false;
	      break;
	    }
	  }
	  if(matched) {
	    _nXi->fill(_ecms);
	    break;
	  }
	}
	if(matched) break;
      }
    }


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

    ///@}


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


  };


  RIVET_DECLARE_PLUGIN(BESIII_2020_I1823448);

}
