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

namespace Rivet {


  /// @brief Helicity angle distributions in excited $D$ meson decays
  class LHCB_2013_I1243156 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2013_I1243156);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_D1_ctheta     , 8,1,1);
      book(_h_D2_ctheta     , 8,1,2);
      book(_h_DStar2S_ctheta, 9,1,1);
      book(_h_D3_ctheta     , 9,1,2);
      book(_h_D2S_ctheta    ,10,1,1);
      book(_h_D21D_ctheta   ,10,1,2);

    }


    /// Recursively walk the decay tree to find decay products of @a p
    void findDecayProducts(Particle mother, Particles & dstar, Particles & d0, Particles & pi,unsigned int & ncount) {
      for(const Particle & p: mother.children()) {
        if(p.abspid()==413)
          dstar.push_back(p);
        else if(p.abspid()==421)
          d0.push_back(p);
        else if(p.abspid()==211)
          pi.push_back(p);
        ncount +=1;
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const Particles usps = apply<UnstableParticles>(event, "UFS")
             .particles(Cuts::abspid==425 || Cuts::abspid==10423 || Cuts::abspid==100423 || Cuts::abspid==427||
                        Cuts::abspid==100421 || Cuts::abspid==10425 || Cuts::abspid==20425);
      for (const Particle& p : usps) {
        // decay products
        Particles dstar,d0,pi;
        unsigned int ncount=0;
        findDecayProducts(p,dstar,d0, pi,ncount);
        if (ncount!=2 || dstar.size()!=1 || pi.size()!=1 || d0.size()!=0 ) continue;
        if (dstar[0].pid()/p.pid()<0) continue;
        Particle p2 = dstar[0];
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p2.momentum().betaVec());
        Vector3 d1 = boost.transform(pi[0].momentum()).p3().unit();
        ncount=0;
        dstar.clear();
        d0.clear();
        pi.clear();
        findDecayProducts(p2,dstar,d0, pi,ncount);
        if (ncount!=2 || dstar.size()!=0 || pi.size()!=1 || d0.size()!=1 ) continue;
        if (pi[0].pid()/p2.pid()<0) continue;
        Vector3 d2 = boost.transform(pi[0].momentum()).p3().unit();
        double cTheta  = d1.dot(d2);
        // decay angles
        if (p.abspid()==425)
          _h_D2_ctheta->fill(cTheta);
        else if (p.abspid()==10423)
          _h_D1_ctheta->fill(cTheta);
        else if (p.abspid()==100423)
          _h_DStar2S_ctheta->fill(cTheta);
        else if (p.abspid()==427)
          _h_D3_ctheta->fill(cTheta);
        else if (p.abspid()==100421)
          _h_D2S_ctheta->fill(cTheta);
        else if (p.abspid()==10425 || p.abspid()==20425)
          _h_D21D_ctheta->fill(cTheta);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_D1_ctheta);
      normalize(_h_D2_ctheta);
      normalize(_h_DStar2S_ctheta);
      normalize(_h_D3_ctheta     );
      normalize(_h_D2S_ctheta    );
      normalize(_h_D21D_ctheta   );
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_D1_ctheta,_h_D2_ctheta;
    Histo1DPtr _h_DStar2S_ctheta,_h_D3_ctheta;
    Histo1DPtr _h_D2S_ctheta,_h_D21D_ctheta;
    /// @}

  };



  RIVET_DECLARE_PLUGIN(LHCB_2013_I1243156);

}
