/*******************************************************************************
* SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
*
* 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
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU Lesser General Public License Version 2.1 or later (the
* "LGPL"), in which case the provisions of the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of the LGPL, and not to allow others to use your version of
* this file under the terms of the EPL, indicate your decision by deleting
* the provisions above and replace them with the notice and other provisions
* required by the LGPL. If you do not delete the provisions above, a recipient
* may use your version of this file under the terms of the EPL or the LGPL.
* 
* Based on the original MiniSat specification from:
* 
* An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
* Sixth International Conference on Theory and Applications of Satisfiability
* Testing, LNCS 2919, pp 502-518, 2003.
*
* See www.minisat.se for the original solver in C++.
* 
*******************************************************************************/
package org.sat4j.tools;

import org.sat4j.core.VecInt;
import org.sat4j.specs.ContradictionException;
import org.sat4j.specs.ISolver;
import org.sat4j.specs.IVecInt;
import org.sat4j.specs.TimeoutException;

/**
 * Another solver decorator that counts the number of solutions.
 * 
 * Note that this approach is quite naive so do not expect it to work on large
 * examples. The number of solutions will be wrong if the SAT solver
 * does not provide a complete assignment. 
 * 
 * The class is expected to be used that way:
 * 
 * <pre>
 * SolutionCounter counter = new SolverCounter(SolverFactory.newDefault());
 * try {
 *     int nbSol = counter.countSolutions();
 *     // the exact number of solutions is nbSol
 *     ...
 *  } catch (TimeoutException te) {
 *     int lowerBound = counter.lowerBound();
 *     // the solver found lowerBound solutions so far.
 *     ...
 *  }
 *  </pre>
 *     
 * @author leberre
 * 
 */
public class SolutionCounter extends SolverDecorator<ISolver> {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    private int lowerBound;
    
    public SolutionCounter(ISolver solver) {
        super(solver);
    }

    /**
     * Get the number of solutions found before the timeout occurs.
     * 
     * @return the number of solutions found so far.
     */
    public int lowerBound() {
    	return lowerBound;
    }
    
    /**
     * Naive approach to count the solutions available in
     * a boolean formula: each time a solution is found, 
     * a new clause is added to prevent it to be found again.
     *  
     * @return the number of solution found.
     * @throws TimeoutException if the timeout given to the solver is reached.
     */
    public long countSolutions() throws TimeoutException {
        lowerBound = 0;
        boolean trivialfalsity = false;

        while (!trivialfalsity && isSatisfiable(true)) {
            lowerBound++;
            int[] last = model();
            IVecInt clause = new VecInt(last.length);
            for (int q : last) {
                clause.push(-q);
            }
            try {
                // System.out.println("Sol number "+nbsols+" adding " + clause);
                addClause(clause);
            } catch (ContradictionException e) {
                trivialfalsity = true;
            }
        }
        return lowerBound;
    }
}