#include "TFile.h"
#include "TTree.h"
#include "TBranch.h"
#include "TClonesArray.h"
#include "TLorentzVector.h"

#include <iostream>

int Analyze_LHE()
{
  TFile *lhe = new TFile("lhe.root", "READ");
  if (!(lhe && lhe->IsOpen())) { delete lhe; return -1; }
  
  TTree *tree;
  lhe->GetObject("tree", tree);
  if (!tree) { delete lhe; return -2; }
  
  tree->SetMakeClass(1); // all branches in decomposed object mode
  tree->SetBranchStatus("*", 0); // disable all branches
  
  TClonesArray *Llep0_ = new TClonesArray("TLorentzVector");
  tree->SetBranchStatus("Llep0", 1); // activate "Llep0"
  tree->GetBranch("Llep0")->SetAutoDelete(kFALSE);
  tree->SetBranchAddress("Llep0", &Llep0_);
  
  Long64_t nevent = tree->GetEntries();
  
  std::cout << "####### tree->GetEntries() = " << nevent << std::endl;
  
  for (Long64_t i = 0; i < nevent; i++) {
    if (Llep0_) Llep0_->Clear();
    tree->GetEntry(i);
    std::cout << "i = " << i << std::endl;
    
    if (!Llep0_) continue; // just a precaution
    Int_t nvectors = Llep0_->GetEntriesFast();
    std::cout << "Llep0_->GetEntriesFast() = " << nvectors << std::endl;
    
    for (Int_t j = 0; j < nvectors; j++) {
      TLorentzVector *v = ((TLorentzVector *)(Llep0_->At(j)));
      if (!v) continue; // skip an "empty slot"
      std::cout << "Pt[" << j <<  "] = " << v->Pt() << std::endl;
    }
  }
  
  tree->ResetBranchAddresses(); // "detach" from local variables
  
  delete lhe; // it will automatically delete "tree", too
  delete Llep0_; // cleanup
  
  return 0;
}