/*******************************************************************************
 * Copyright (c) 2009-2013 CWI
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *
 *	 * Paul Klint - Paul.Klint@cwi.nl - CWI
 *   * Jurgen J. Vinju - Jurgen.Vinju@cwi.nl - CWI
 *   * Emilie Balland - (CWI)
 *   * Arnold Lankamp - Arnold.Lankamp@cwi.nl
*******************************************************************************/
package org.rascalmpl.interpreter.matching;

import java.util.Iterator;

import org.rascalmpl.interpreter.IEvaluatorContext;
import org.rascalmpl.value.ISet;
import org.rascalmpl.value.IValue;

/**
 * Generate all subsets of a given set
 *
 */
class SubSetGenerator implements Iterator<ISet> {
	private final IEvaluatorContext ctx;
	private ISet remainingElements;
	private Iterator<IValue> elementGen;
	private SubSetGenerator subsetGen;
	private IValue currentElement;
	private boolean hasNext;
	private boolean debug = false;

	SubSetGenerator(ISet elements, IEvaluatorContext ctx){
		this.remainingElements = elements;
		elementGen = elements.iterator();
		this.ctx = ctx;
		this.hasNext = true;
	}
	
	public boolean hasNext() {
		if(debug)System.err.println("SubSetGenerator.hasNext: " + hasNext);
		return hasNext;
	}

	public ISet next() {
		if(debug)System.err.println("SubSetGenerator.next: hasNext = " + hasNext);
		if(subsetGen == null || !subsetGen.hasNext()){
			if(elementGen.hasNext()){
				currentElement = elementGen.next();
				remainingElements = remainingElements.subtract(ctx.getValueFactory().set(currentElement));
				subsetGen = new SubSetGenerator(remainingElements, ctx);
			} else {
				hasNext = false;
				return ctx.getValueFactory().set();
			}
		}
		ISet result = subsetGen.next().insert(currentElement);
		if(debug)System.err.println("SubSetGenerator.next returns: " + result);
		return result;
	}

	public void remove() {
		throw new UnsupportedOperationException("remove in SubSetGenerator");
	}
}