//Objective of this code is to loop over the reconstructed tracks of o2trac_its.root and get the pdgcode of the associated particles, then create a tree with this information.

void TestITS(){

    //**************************** Kinematics and MC information File ***********************************//
    // Open the .root data file with MC information
    std::unique_ptr<TFile> mcFile(TFile::Open(("o2sim_Kine.root ")));
    if (!mcFile || mcFile->IsZombie()) {
        std::cerr << "Failed to open input Kine file " << ("o2sim_Kine.root");
        return;
    }
    // Open the tree
    std::unique_ptr<TTree> mcTree((TTree*)mcFile->FindObjectAny("o2sim")); 
    if (!mcTree) {
        std::cerr << "Failed to get o2sim tree";
        return;
    }

    // init the reader from the context
    o2::steer::MCKinematicsReader reader("collisioncontext.root");

    // Create the pointers for the relevant branches of the input tree
    std::vector<o2::MCTrack>* mcTracksArray = nullptr;
    mcTree->SetBranchAddress("MCTrack", &mcTracksArray);

    //**************************** Input File ***********************************//

    // Open the .root data file with tracks
    std::unique_ptr<TFile> trackFile(TFile::Open(("o2trac_its.root ")));
    if (!trackFile || trackFile->IsZombie()) {
        std::cerr << "Failed to open input digits file " << ("o2trac_its.root");
        return;
    }
    // Open the tree
    std::unique_ptr<TTree> trackTree((TTree*)trackFile->FindObjectAny("o2sim")); 
    if (!trackTree) {
        std::cerr << "Failed to get o2sim tree";
        return;
    }

    // Create the pointers for the relevant branches of the input tree
    std::vector<o2::its::TrackITS>* itsTracksArray = nullptr;
    trackTree->SetBranchAddress("ITSTrack", &itsTracksArray);

    std::vector<o2::MCCompLabel>* mcTruthArrayPtr = nullptr;
    trackTree->SetBranchAddress("ITSTrackMCTruth", &mcTruthArrayPtr); 

    //**************************** Output File ***********************************//
    // Create new .root file to store the DCA info
    std::unique_ptr<TFile> trimmedfile(new TFile("trimmed_ITSTracks.root", "RECREATE"));
    if (!trimmedfile || trimmedfile->IsZombie()) {
        std::cerr << "Failed to open file " << ("trimmed_ITSTracks.root");
        return;
    }

    // Create Tree for output file 
    std::unique_ptr<TTree> fTreeTrimmed(new TTree("trimmed_Tree", ""));

    // Initialise Tree parameters and create tree and tree branches (//check https://github.com/AliceO2Group/AliceO2/blob/aa579dea7c83b35d30b38b22bdce1822392ccf72/Framework/Core/test/test_Root2ArrowTable.cxx)
    int trackID = -1;
    int eventID = -1;
    int sourceID = -1;
    long int pdgCode;

    fTreeTrimmed->Branch("trackID",              &trackID,            "trackID/I"                    );
    fTreeTrimmed->Branch("pdgCode",              &pdgCode,            "pdgCode/I"                    );

    //********************************** Loop over the tracks of o2trac_its.root ********************************************//

    //get or set the magnetic field, needed for the DCAFitter
    float MagField = 5; // can't find it in any o2sim.root file
 
    trackTree->GetEntry(0);
    // loop over all the tracks
    int nTracks = itsTracksArray->size();
    std::cerr << "We have " << nTracks << " tracks ";
    std::cerr << "We have " << mcTruthArrayPtr->size() << " labels ";
    for (int itrack = 0; itrack<nTracks; itrack++){
        Printf("Track number %i",itrack);
        o2::its::TrackITS itstrack = itsTracksArray->at(itrack); 

        //get the trackID, eventID and sourceID of the track
        auto& mctruth = *mcTruthArrayPtr;
        auto& label = mctruth[itrack];
        trackID = label.getTrackID();
        eventID = label.getEventID();
        sourceID = label.getSourceID();
        Printf("     trackID = %i",trackID);
        Printf("     eventID = %i",eventID);
        Printf("     sourceID = %i",sourceID);

        //get the track associated to those labels
        o2::MCTrack const* mctrack = reader.getTrack(label);

        if (!mctrack){
            Printf("     no track found");
            pdgCode = 0;
            continue;
        }
 
        pdgCode = mctrack->GetPdgCode(); //returns 0,1 or 32767 which is apparently the range of the int type: -32768 to 32767 ; didn't change when using long int -> is it a coincidence?
        Printf("     pdgCode %li", pdgCode);

        // add track to tree with: trackID, pdgCode (will eventually have more, but right now is not what is causing issues)
        fTreeTrimmed->Fill();
    }
    fTreeTrimmed->Write();
    //trimmedfile->Close();
}