// For some reason the branches
// of the tree don't get reactivated once they were
// deactivated. But strangely this is the case when only
// one tree is in the chain, it works with two trees in it.
//
// This is a minimal example.
//
// Tested in 
//  * Root 5.26/00
//  * Root 5.34/03
//
// root -l TestTTreeBranchActivation.C++
//
#include <iostream>
#include <sstream>
#include <stdlib.h>
#include <cassert>
#include "TROOT.h"
#include "TChain.h"

TTree *t;

// branches
float scanpoint;
float scanbest;
float chi2minToy;
float chi2minGlobalToy;

void open()
{
  t->SetBranchAddress("scanpoint",        &scanpoint);
  t->SetBranchAddress("scanbest",         &scanbest);
  t->SetBranchAddress("chi2minToy",       &chi2minToy);
  t->SetBranchAddress("chi2minGlobalToy", &chi2minGlobalToy);
}

///
/// Loop over the tree onece.
/// (originally to get min and max values)
///
void computeMinMaxN()
{
  t->SetBranchStatus("*", 0);
  t->SetBranchStatus("scanpoint", 1);
  Long64_t nentries = t->GetEntries();
  for (Long64_t i = 0; i < nentries; i++) t->GetEntry(i);
  t->SetBranchStatus("*", 1);
}


void TestTTreeBranchActivation()
{
  // open TTrees into a chain
  TChain *c = new TChain("plugin");
  c->Add("run1.root");
  // c->Add("run2.root"); // UNCOMMENT AND IT WILL WORK
  t = c;
  // connect branches
  open();
  // deactivate branches, loop over tree, re-activate branches
  computeMinMaxN();
  // main loop, loops over tree again
  int nentries = t->GetEntries();
  for (int i = 0; i < nentries; i++)
  {
    t->GetEntry(i);
    // print some branches
    if ( i%1000==0) printf("%5i %f %f %f %f\n", i,
      chi2minToy,chi2minGlobalToy,
      scanpoint,scanbest);
  }
}