#include <cstdio>
#include <iostream>
#include <fstream>
#include <TH1F.h>
#include <TH1D.h>
#include <TROOT.h>
#include <TRandom.h>
#include <TTree.h>
#include <TFile.h>

void correlation() {

    // Create a file 
    TFile outf("new_output_new.root","RECREATE");

    std::cout << "creating output ..." <<std::endl;

    // Style of the plot
    gStyle->SetOptStat(0);
    gStyle->SetOptTitle(0);
    
    // Create new histograms

    TH2D* h_top_pt = new TH2D("top_pt",";Reconstructed p_{T}(top);Truth p_{T}(top) ",4,0.,600.,4, 0., 600.);
    TH2D* h_top_eta = new TH2D("top_eta",";Reconstructed #eta(top);Truth #eta(top) ",4,0.,5.,4, 0., 5.);

	//Get the old files and trees
    TFile *reco_file= new TFile("/RootFiles/test_files/input_selection/reco.root","READ");
    TFile *truth_file= new TFile("/RootFiles/test_files/input_selection/truth.root","READ");
   
    TTree *reco= (TTree*)reco_file->Get("Loop_reco");
    TTree *truth= (TTree*)truth_file->Get("Loop_truth");

    // Declaring the type of vaiables of the branches
    float reco_eventnumber, reco_runnumber, reco_t_pt, reco_t_eta;
    float truth_eventnumber, truth_runnumber, truth_t_pt, truth_t_eta;
    Long64_t nentries, nentries1, nentries2;

    // List ofthe branches in the reco tree
    reco->SetBranchAddress("reco_eventnumber",&reco_eventnumber);
    reco->SetBranchAddress("reco_runnumber",&reco_runnumber);
    reco->SetBranchAddress("reco_t_pt",&reco_t_pt);
    reco->SetBranchAddress("reco_t_eta",&reco_t_eta);

    // List ofthe branches in the truth tree
    truth->SetBranchAddress("truth_eventnumber",&truth_runnumber);
    truth->SetBranchAddress("truth_runnumber",&truth_runnumber);
    truth->SetBranchAddress("truth_t_pt",&truth_t_pt);
    truth->SetBranchAddress("truth_t_eta",&truth_t_eta);
    
    nentries1= reco->GetEntries();
    nentries2= truth->GetEntries();

    nentries= nentries1;
  
    // Running over the entries of the branches
    for (int i=0; i<nentries; i++)
         {
              truth->GetEntry(i); 
	          reco->GetEntry(i);
              
	      h_top_pt->Fill(reco_t_pt,reco_t_pt);
	      h_top_eta->Fill(reco_t_eta, truth_t_eta);

         }
    // correlation
    float cor = h_top_pt->GetCorrelationFactor();
    std::cout<<"The correlation is: "<<cor<<std::endl;

   
   // Writing the histogram in the root files
    outf.Write();
}