/*

  This macro will add histograms from a list of root files and write them
  to a target root file. The target file is newly created and must not be
  identical to one of the source files.

  Author: Sven A. Schmidt, sven.schmidt@cern.ch
  Date:   13.2.2001

  This code is based on the hadd.C example by Rene Brun and Dirk Geppert,
  which had a problem with directories more than one level deep.
  (see macro hadd_old.C for this previous implementation).
  
  To use this macro, modify the file names in function hadd.
  
  NB: This macro is provided as a tutorial.
      Use $ROOTSYS/bin/hadd to merge many histogram files

 */


#include "TFile.h"
#include "TH1.h"
#include "TTree.h"
#include "TKey.h"
#include <string.h>
#include <iostream.h>

TList *FileList;
TFile *Target;

void MergeRootfile( TDirectory *target, TList *sourcelist );


void hadd() {
   // in an interactive ROOT session, edit the file names
   // Target and FileList, then
   // root > .L hadd.C
   // root > hadd()
   
  Target = TFile::Open( "result.root", "RECREATE" );
  
  FileList = new TList();
  FileList->Add( TFile::Open("hsimple1.root") );
  FileList->Add( TFile::Open("hsimple2.root") );
  
  MergeRootfile( Target, FileList );

}   

void MergeRootfile( TDirectory *target, TList *sourcelist ) {
// Merge all files from sourcelist into the target directory.
// The directory level (depth) is determined by the target directory's
// current level

  //  cout << "Target path: " << target->GetPath() << endl;
  TString path( (char*)strstr( target->GetPath(), ":" ) );
  path.Remove( 0, 2 );

  TFile *first_source = (TFile*)sourcelist->First();
  first_source->cd( path );
  TDirectory *current_sourcedir = gDirectory;

  // loop over all keys in this directory
  TIter nextkey( current_sourcedir->GetListOfKeys() );
  TKey *key;
  while ( key = (TKey*)nextkey() ) {

    // read object from first source file
    first_source->cd( path );
    TObject *obj = key->ReadObj();

    if ( obj->IsA()->InheritsFrom( "TH1" ) ) {
      // descendant of TH1 -> merge it

      //      cout << "Merging histogram " << obj->GetName() << endl;
      TH1 *h1 = (TH1*)obj;

      // loop over all source files and add the content of the
      // correspondant histogram to the one pointed to by "h1"
      TFile *nextsource = (TFile*)sourcelist->After( first_source );
      while ( nextsource ) {
        
        // make sure we are at the correct directory level by cd'ing to path
        nextsource->cd( path );
        TH1 *h2 = (TH1*)gDirectory->Get( h1->GetName() );
        if ( h2 ) {
          h1->Add( h2 );
          delete h2; // don't know if this is necessary, i.e. if 
                     // h2 is created by the call to gDirectory above.
        }

        nextsource = (TFile*)sourcelist->After( nextsource );
      }

    } else if ( obj->IsA()->InheritsFrom( "TDirectory" ) ) {
      // it's a subdirectory

      cout << "Found subdirectory " << obj->GetName() << endl;

      // create a new subdir of same name and title in the target file
      target->cd();
      TDirectory *newdir = target->mkdir( obj->GetName(), obj->GetTitle() );

      // newdir is now the starting point of another round of merging
      // newdir still knows its depth within the target file via
      // GetPath(), so we can still figure out where we are in the recursion
      MergeRootfile( newdir, sourcelist );

    } else {
      // object is of no type that we know or can handle
      cout << "Unknown object type, name: " 
           << obj->GetName() << " title: " << obj->GetTitle() << endl;
    }

    // now write the merged histogram (which is "in" obj) to the target file
    // note that this will just store obj in the current directory level,
    // which is not persistent until the complete directory itself is stored
    // by "target->Write()" below
    if ( obj ) {
      target->cd();
      obj->Write( key->GetName() );
    }

  } // while ( ( TKey *key = (TKey*)nextkey() ) )

  // save modifications to target file
  target->Write();

}