/*******************************************************************************
* 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.minisat.orders;

import org.sat4j.minisat.core.ILits;

/**
 * @author leberre TODO To change the template for this generated type comment
 *         go to Window - Preferences - Java - Code Style - Code Templates
 */
public class PureOrder extends VarOrder<ILits> {

    /**
     * Comment for <code>serialVersionUID</code>
     */
    private static final long serialVersionUID = 1L;

    private int period;

    private int cpt;

    public PureOrder() {
        this(20);
    }

    public PureOrder(int p) {
        setPeriod(p);
    }

    public final void setPeriod(int p) {
        period = p;
        cpt = period;
    }

    public int getPeriod() {
        return period;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.sat4j.minisat.core.VarOrder#select()
     */
    @Override
    public int select() {
        // wait period branching
        if (cpt < period) {
            cpt++;
        } else {
            // try to find a pure literal
            cpt = 0;
            int nblits = 2 * lits.nVars();
            for (int i = 2; i <= nblits; i++) {
                if (lits.isUnassigned(i) && lits.attaches(i).size() > 0
                        && lits.attaches(i ^ 1).size() == 0) {
                    return i;
                }
            }
        }
        // not found: using normal order
        return super.select();
    }

    @Override
    public String toString() {
        return "tries to first branch on a single phase watched unassigned variable (pure literal if using a CB data structure) else VSIDS from MiniSAT"; //$NON-NLS-1$
    }
}