//------------------------------------------------------------------------------

struct MyPlots
{
  TH1 *fJetPT[2];
  TH1 *fMissingET;
  TH1 *fElectronPT;
  TH1 *fTrackChi2;
};

//------------------------------------------------------------------------------

void BookHistograms(ExRootResult *result, MyPlots *plots)
{
  THStack *stack;
  TLegend *legend;
  TPaveText *comment;

  // book 2 histograms for PT of 1st and 2nd leading jets

  plots->fJetPT[0] = result->AddHist1D("jet_pt_0", "leading jet P_{T}",
                                       "jet P_{T}, GeV/c", "number of jets",
                                       40, 0.0, 200.0);

  plots->fJetPT[1] = result->AddHist1D("jet_pt_1", "2nd leading jet P_{T}",
                                       "jet P_{T}, GeV/c", "number of jets",
                                       40, 0.0, 200.0);

  plots->fJetPT[0]->SetLineColor(kRed);
  plots->fJetPT[1]->SetLineColor(kBlue);

  // book 1 stack of 2 histograms

  stack = result->AddHistStack("jet_pt_all", "1st and 2nd jets PT");
  stack->Add(plots->fJetPT[0]);
  stack->Add(plots->fJetPT[1]);

  // book legend for stack of 2 histograms

  legend = result->AddLegend(0.72, 0.86, 0.98, 0.98);
  legend->AddEntry(plots->fJetPT[0], "leading jet", "l");
  legend->AddEntry(plots->fJetPT[1], "second jet", "l");

  // attach legend to stack (legend will be printed over stack in .eps file)

  result->Attach(stack, legend);

  // book more histograms

  plots->fMissingET = result->AddHist1D("missing_et", "Missing E_{T}",
                                        "Missing E_{T}, GeV", "number of events",
                                        60, 0.0, 300.0);

  plots->fElectronPT = result->AddHist1D("electron_pt", "electron P_{T}",
                                         "electron P_{T}, GeV/c", "number of electrons",
                                         40, 0.0, 200.0);

  plots->fTrackChi2 = result->AddHist1D("e_track_chi2", "e-track #chi^{2}",
                                        "e-track #chi^{2}", "number of tracks",
                                        100, 0.0, 10.0);
  
  
  // book general comment

  comment = result->AddComment(0.54, 0.72, 0.98, 0.98);
  comment->AddText("demonstration plot");
  comment->AddText("produced by Example.C");

  // attach comment to single histograms
  
  result->Attach(plots->fJetPT[0], comment);
  result->Attach(plots->fJetPT[1], comment);
  result->Attach(plots->fMissingET, comment);
  result->Attach(plots->fElectronPT, comment);
  result->Attach(plots->fTrackChi2, comment);
}

//------------------------------------------------------------------------------

void AnalyseEvents(ExRootTree *tree, MyPlots *plots)
{
  TClonesArray *branchJet = tree->UseBranch("JetIC5A", "TRootJet");
  TClonesArray *branchElec = tree->UseBranch("Elec", "TRootElectron");
  TClonesArray *branchTrkEP = tree->UseBranch("TrkEP", "TRootTrack");
  TClonesArray *branchMETCH = tree->UseBranch("METCH", "TRootMissingET");

  Long64_t allEntries = tree->GetEntries();

  cout << "** Chain contains " << allEntries << " events" << endl;

  TRootJet *jet[2];
  TRootMissingET *met;
  TRootElectron *electron;
  TRootTrack *track;

  TIter itElec(branchElec);
  
  Long64_t entry;

  // Loop over all events
  for(entry = 0; entry < allEntries; ++entry)
  {
    // Load selected branches with data from specified event
    tree->ReadEntry(entry);

    // Analyse two leading jets
    if(branchJet->GetEntries() >= 2)
    {
      jet[0] = (TRootJet*) branchJet->At(0);
      jet[1] = (TRootJet*) branchJet->At(1);

      plots->fJetPT[0]->Fill(jet[0]->PT);
      plots->fJetPT[1]->Fill(jet[1]->PT);
    }

    // Analyse missing ET
    if(branchMETCH->GetEntries() > 0)
    {
      met = (TRootMissingET*) branchMETCH->At(0);
      plots->fMissingET->Fill(met->MET);
    }

    // Loop over all electrons in event
    itElec.Reset();
    while(electron = (TRootElectron*) itElec.Next())
    {
      plots->fElectronPT->Fill(electron->TrkPT);

      // Get track associated with electron
      track = (TRootTrack*) electron->Trk.GetObject();

      if(track) plots->fTrackChi2->Fill(track->Chi2);
    }
  }
}

//------------------------------------------------------------------------------

void PrintHistograms(ExRootResult *result, MyPlots *plots)
{
  result->Print();
}

//------------------------------------------------------------------------------

void Example(const TString &inputFileList)
{
  TChain chain("Analysis");

  if(!FillChain(chain, inputFileList)) return;

  ExRootTree *tree = new ExRootTree(&chain);
  ExRootResult *result = new ExRootResult();

  MyPlots *plots = new MyPlots;

  BookHistograms(result, plots);

  AnalyseEvents(tree, plots);

  PrintHistograms(result, plots);

  result->Write("results.root");
  
  cout << "** Exiting..." << endl;

  delete plots;
  delete result;
  delete tree;
}

//------------------------------------------------------------------------------