    // @(#)root/tree:$Name:  $:$Id: TFriendElement.cxx,v 1.11 2004/09/24 18:22:46 brun Exp $
    // Author: Rene Brun   07/04/2001

    /*************************************************************************
     * Copyright (C) 1995-2001, Rene Brun and Fons Rademakers.               *
     * All rights reserved.                                                  *
     *                                                                       *
     * For the licensing terms see $ROOTSYS/LICENSE.                         *
     * For the list of contributors see $ROOTSYS/README/CREDITS.             *
     *************************************************************************/

    //////////////////////////////////////////////////////////////////////////
    //                                                                      //
    // TFriendElement                                                       //
    //                                                                      //
    // A TFriendElement TF describes a TTree object TF in a file.           //
    // When a TFriendElement TF is added to the the list of friends of an   //
    // existing TTree T, any variable from TF can be referenced in a query  //
    // to T.                                                                //
    //                                                                      //
    // To add a TFriendElement to an existing TTree T, do:                  //
    //       T.AddFriend("friendTreename","friendTreeFile");                //
    //                                                                      //
    //  See TTree::AddFriend for more information.                          //
    //                                                                      //
    //////////////////////////////////////////////////////////////////////////

    #include "TTree.h"
    #include "TFriendElement.h"
    #include "TFile.h"
    #include "TROOT.h"

    R__EXTERN TTree *gTree;

    ClassImp(TFriendElement)

    //______________________________________________________________________________
     TFriendElement::TFriendElement() : TNamed()
    {
    //*-*-*-*-*-*Default constructor for a friend element*-*-*-*-*-*-*-*-*-*-*-*-*
    //*-*        =======================================

       fFile       = 0;
       fTree       = 0;
       fOwnFile    = kFALSE;
       fParentTree = gTree;
    }

    //______________________________________________________________________________
     TFriendElement::TFriendElement(TTree *tree, const char *treename, const char *filename)
        :TNamed(treename,filename)
    {
    //*-*-*-*-*-*-*-*-*-*-*-*-*Create a friend element*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
    //*-*                      ======================
    //
    // If treename is of the form "a=b", an alias called "a" is created for
    // treename = "b" by default the alias name is the name of the tree.

       fFile       = 0;
       fTree       = 0;
       fOwnFile    = kTRUE;
       fParentTree = tree;
       fTreeName   = treename;
       if (strchr(treename,'=')) {
          char *temp = Compress(treename);
          char *equal = strchr(temp,'=');
          *equal=0;
          fTreeName = equal+1;
          SetName(temp);
          delete [] temp;
       }

       Connect();
    }

    //______________________________________________________________________________
     TFriendElement::TFriendElement(TTree *tree, const char *treename, TFile *file)
        :TNamed(treename,file?file->GetName():"")
    {
    //*-*-*-*-*-*-*-*-*-*-*-*-*Create a friend element*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
    //*-*                      ======================
    //
    // If treename is of the form "a=b", an alias called "a" is created for
    // treename = "b" by default the alias name is the name of the tree.
    // The passed TFile is managed by the user (i.e. user must delete the TFile).

       fFile       = file;
       fTree       = 0;
       fOwnFile    = kFALSE;
       fParentTree = tree;
       fTreeName   = treename;
       if (strchr(treename,'=')) {
          char *temp = Compress(treename);
          char *equal = strchr(temp,'=');
          *equal=0;
          fTreeName = equal+1;
          SetName(temp);
          delete [] temp;
       }

       Connect();
    }

    //______________________________________________________________________________
     TFriendElement::TFriendElement(TTree *tree, TTree* friendtree, const char *alias)
    :TNamed(friendtree?friendtree->GetName():"",
              friendtree
            ? (   friendtree->GetDirectory()
                ? (    friendtree->GetDirectory()->GetFile()
                     ? friendtree->GetDirectory()->GetFile()->GetName()
                     :  ""
                  )
                : ""
              )
            :  "")
    {
    //*-*-*-*-*-*-*-*-*-*-*-*-*Create a friend element*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
    //*-*                      ======================
    //

       fTree       = friendtree;
       fTreeName   = "";
       fFile       = 0;
       if (fTree) {
          fTreeName   = fTree->GetName();
          if (fTree->GetDirectory()) fFile = fTree->GetDirectory()->GetFile();
       }
       fOwnFile    = kFALSE;
       fParentTree = tree;
       if (alias && strlen(alias)) {
          char *temp = Compress(alias);
          SetName(temp);
          delete [] temp;
       }

       // No need to Connect.
    }

    //______________________________________________________________________________
     TFriendElement::~TFriendElement()
    {

       DisConnect();
    }

    //_______________________________________________________________________
     TTree *TFriendElement::Connect()
    {
    // Connect file and return TTree.

       GetFile();
       return GetTree();
    }

    //_______________________________________________________________________
     TTree *TFriendElement::DisConnect()
    {
    // DisConnect file and TTree.

       if (fOwnFile) delete fFile;
       fFile = 0;
       fTree = 0;
       return 0;
    }

    //_______________________________________________________________________
     TFile *TFriendElement::GetFile()
    {
    // Return pointer to TFile containing this friend TTree.

       if (fFile || IsZombie()) return fFile;
       if (strlen(GetTitle()))
          fFile = new TFile(GetTitle());
       else {
          TDirectory *dir = fParentTree->GetDirectory();
          if (dir) {
             fFile = dir->GetFile();
             fOwnFile = kFALSE;
          }
       }
       if (fFile && fFile->IsZombie()) {
          MakeZombie();
          delete fFile;
          fFile = 0;
       }
       return fFile;
    }

    //_______________________________________________________________________
     TTree *TFriendElement::GetTree()
    {
    // Return pointer to friend TTree.

       if (fTree) return fTree;
       if (!GetFile()) {
          // This could be a memory tree or chain
          fTree = (TTree*)gROOT->FindObject(GetTreeName());
          if (fTree) {
             if (!fTree->InheritsFrom(TTree::Class()) ) {
                fTree = 0;
             }
          }
          return fTree;
       }
       fTree = (TTree*)fFile->Get(GetTreeName());
       TDirectory *dir = fParentTree->GetDirectory();
       if (dir && dir != gDirectory) dir->cd();
       return fTree;
    }

    //_______________________________________________________________________
     void TFriendElement::ls(Option_t *) const
    {
    // List this friend element.

       printf(" Friend Tree: %s in file: %s\n",GetName(),GetTitle());
    }