/* Soot - a J*va Optimization Framework
 * Copyright (C) 1997-2000 Etienne Gagnon.  All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/*
 * Modified by the Sable Research Group and others 1997-1999.  
 * See the 'credits' file distributed with Soot for the complete list of
 * contributors.  (Soot is distributed at http://www.sable.mcgill.ca/soot)
 */


package soot.jimple.toolkits.typing;

import soot.*;
import java.util.*;

class StronglyConnectedComponents
{
  List<TypeVariable> variables;
  Set<TypeVariable> black;
  LinkedList<TypeVariable> finished;
  
  LinkedList<LinkedList<TypeVariable>> forest = new LinkedList<LinkedList<TypeVariable>>();
  LinkedList<TypeVariable> current_tree;
  
  private static final boolean DEBUG = false;
  
  public static void merge(List<TypeVariable> typeVariableList) throws TypeException
  {
    new StronglyConnectedComponents(typeVariableList);
  }

  private StronglyConnectedComponents(List<TypeVariable> typeVariableList) throws TypeException
  {
    variables = typeVariableList;
    
    black = new TreeSet<TypeVariable>();
    finished = new LinkedList<TypeVariable>();
    
    for (TypeVariable var : variables) {
	if(!black.contains(var))
	  {
	    black.add(var);
	    dfsg_visit(var);
	  }
      }
    
    black = new TreeSet<TypeVariable>();
    
    for (TypeVariable var : finished) {
	if(!black.contains(var))
	  {
	    current_tree = new LinkedList<TypeVariable>();
	    forest.add(current_tree);
	    black.add(var);
	    dfsgt_visit(var);
	  }
      }
    
    for(Iterator<LinkedList<TypeVariable>> i = forest.iterator(); i.hasNext();)
      {
	LinkedList list = i.next();
	TypeVariable previous = null;
	StringBuffer s = null;
	if(DEBUG)
	  {
	    s = new StringBuffer("scc:\n");
	  }
	
	for(Iterator j = list.iterator(); j.hasNext();)
	  {
	    TypeVariable current = (TypeVariable) j.next();
	   
	    if(DEBUG)
	      {
		s.append(" " + current + "\n");
	      }

	    if(previous == null)
	      {
		previous = current;
	      }
	    else
	      {
		try
		  {
		    previous = previous.union(current);
		  }
		catch(TypeException e)
		  {
		    if(DEBUG)
		      {
			G.v().out.println(s);
		      }
		    throw e;
		  }
	      }
	  }
      }
  }
  
  private void dfsg_visit(TypeVariable var)
  {
    List<TypeVariable> parents = var.parents();
    
    for (TypeVariable parent : parents) {
	if(!black.contains(parent))
	  {
	    black.add(parent);
	    dfsg_visit(parent);
	  }
      }
    
    finished.add(0, var);
  }
  
  private void dfsgt_visit(TypeVariable var)
  {
    current_tree.add(var);
    
    List<TypeVariable> children = var.children();
    
    for (TypeVariable child : children) {
	if(!black.contains(child))
	  {
	    black.add(child);
	    dfsgt_visit(child);
	  }
      }
  }
}