// main91.cc is a part of the PYTHIA event generator.
// Copyright (C) 2021 Torbjorn Sjostrand.
// PYTHIA is licenced under the GNU GPL v2 or later, see COPYING for details.
// Please respect the MCnet Guidelines, see GUIDELINES for details.

// Keywords: analysis; root;

// This is a simple test program.
// to use ROOT for histogramming.


// Header file to access Pythia 8 program elements.
#include "Pythia8/Pythia.h"

// ROOT, for histogramming.
#include "TH1.h"

// ROOT, for interactive graphics.
#include "TStyle.h"
#include "TVirtualPad.h"
#include "TApplication.h"
#include "TLatex.h"

// ROOT, for saving file.
#include "TFile.h"

using namespace Pythia8;

int main(int argc, char* argv[]) {

  // Create the ROOT application environment.
  TApplication theApp("hist", &argc, argv);

  // Create Pythia instance and set it up to generate hard QCD processes
  // above pTHat = 20 GeV for pp collisions at 14 TeV.
  Pythia pythia;
  pythia.readString("Top:gg2ttbar = on"); // Switch on process: ttbar production
  pythia.readString("Beams:eCM = 13000."); // 13 TeV CM energy.
  pythia.readString("PartonLevel:all = off"); // swith off showering
  pythia.readString("HadronLevel:all = off"); // switch off hadronization
  pythia.readString("Next:numberShowProcess = 5"); // print first five events
  pythia.init();

  // Create file on which histogram(s) can be saved.
  TFile* outFile = new TFile("hist.root", "RECREATE");
  gStyle->SetOptTitle(0);
  gStyle->SetOptStat(0);
  gStyle->SetPadBottomMargin(gStyle->GetPadBottomMargin()*1.5);
  gStyle->SetPadLeftMargin(gStyle->GetPadLeftMargin()*1.5);
  // Book histogram.
  TH1F *toppt = new TH1F("toppt","top pt", 20, 0, 1000.);

  // Begin event loop. Generate event; skip if generation aborted.
  for (int iEvent = 0; iEvent < 1000; ++iEvent) {
    if (!pythia.next()) continue;

    // Loop over particles in event. Find last top copy. Fill its pT.
    int iTop = -1;
    for (int i = 0; i < pythia.process.size(); ++i)
      if (pythia.process[i].id() == 6) iTop = i;

    if (iTop>-1) toppt->Fill( pythia.process[iTop].pT() );
  }

  // Statistics on event generation.
  pythia.stat();

  // Show histogram. Possibility to close it.
  toppt->Draw();
  // Decorate axes
  toppt->GetXaxis()->SetTitle("p_{T}^{top} [GeV]");
  toppt->GetXaxis()->SetTitleSize(toppt->GetXaxis()->GetTitleSize()*1.8);
  toppt->GetYaxis()->SetTitle("Entries");
  toppt->GetYaxis()->SetTitleSize(toppt->GetYaxis()->GetTitleSize()*1.8);
  // Add some text
  TLatex *p = new TLatex();
  p->DrawLatex(350,350,"Third HEP Graduate Workshop");
  p->SetTextFont(52);
  p->DrawLatex(790,320,"p p #rightarrow t #bar{t}");
  p->SetTextFont(42);
  p->DrawLatex(740,290,"#sqrt{s} = 13 TeV");
  std::cout << "\nDouble click on the histogram window to quit.\n";
  gPad->WaitPrimitive();

  // Save histogram on file and close file.
  toppt->Write();
  delete outFile;

  // Done.
  return 0;
}