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

namespace Rivet {


  /// @brief Cross section for e+e- K0SK+-\pi+-\pi0 and K0SK+-pi-+eta between 3.90 to 4.60 GeV
  class BESIII_2018_I1699641 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1699641);


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

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

      // Book histograms
      for(unsigned int ix=0;ix<2;++ix)
        book(_sigma[ix], 1+ix, 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()) {
        if(isCompatibleWithSqrtS(4.085)) _ecms="4.085"s;
        else
          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;
      }
      // K K pi pi
      if(ntotal==4 && nCount[310]==1 && nCount[111]==1 &&
         ((nCount[ 321]==1 &&nCount[-211]==1) ||
          (nCount[-321]==1 &&nCount[ 211]==1) ))
        _sigma[0]->fill(_ecms);
      // eta resonance
      const FinalState& ufs = apply<FinalState>(event, "UFS");
      for (const Particle& p : ufs.particles()) {
        if(p.children().empty()) continue;
        if(p.pid()!=221) continue;
        map<long,int> nRes=nCount;
        int ncount = ntotal;
        findChildren(p,nRes,ncount);
        if(ncount!=3) continue;
        bool matched=true;
        for(auto const & val : nRes) {
          if(abs(val.first)==321 || abs(val.first)==211) {
            continue;
          }
          else if(abs(val.first)==310) {
            if(val.second!=1) {
              matched = false;
              break;
            }
          }
          else if(val.second!=0) {
            matched = false;
            break;
          }
        }
        if(matched==false) continue;
        if((nCount[ 321] == 1 && nCount[-211] ==1) ||
           (nCount[-321] == 1 && nCount[ 211] ==1))
          _sigma[1]->fill(_ecms);
      }
    }


    /// 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_2018_I1699641);


}
