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Open-source constraint solver.
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/**
 * Copyright (c) 2016, Ecole des Mines de Nantes
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    This product includes software developed by the .
 * 4. Neither the name of the  nor the
 *    names of its contributors may be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY  ''AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL  BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.chocosolver.solver.constraints.binary;

import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.explanations.RuleStore;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.events.IEventType;
import org.chocosolver.solver.variables.events.IntEventType;
import org.chocosolver.util.ESat;

/**
 * X >= Y
 * 
 * 

 *
 * @author Charles Prud'homme
 * @since 1 oct. 2010
 */
public final class PropGreaterOrEqualX_Y extends Propagator {

    private final IntVar x;
    private final IntVar y;

    @SuppressWarnings({"unchecked"})
    public PropGreaterOrEqualX_Y(IntVar[] vars) {
        super(vars, PropagatorPriority.BINARY, true);
        this.x = vars[0];
        this.y = vars[1];
    }

    @Override
    public int getPropagationConditions(int vIdx) {
        if (vIdx == 0) {
            return IntEventType.combine(IntEventType.INSTANTIATE, IntEventType.DECUPP);
        } else {
            return IntEventType.combine(IntEventType.INSTANTIATE, IntEventType.INCLOW);
        }
    }

    @Override
    public void propagate(int evtmask) throws ContradictionException {
        x.updateLowerBound(y.getLB(), this);
        y.updateUpperBound(x.getUB(), this);
        if (x.getLB() >= y.getUB()) {
            this.setPassive();
        }
    }

    @Override
    public void propagate(int varIdx, int mask) throws ContradictionException {
        if (varIdx == 0) {
            y.updateUpperBound(x.getUB(), this);
        } else {
            x.updateLowerBound(y.getLB(), this);
        }
        if (x.getLB() >= y.getUB()) {
            this.setPassive();
        }
    }

    @Override
    public ESat isEntailed() {
        if (x.getUB() < y.getLB())
            return ESat.FALSE;
        else if (x.getLB() >= y.getUB())
            return ESat.TRUE;
        else
            return ESat.UNDEFINED;
    }


    @Override
    public String toString() {
        return "prop(" + vars[0].getName() + ".GEQ." + vars[1].getName() + ")";
    }

    @Override
    public boolean why(RuleStore ruleStore, IntVar var, IEventType evt, int value) {
        boolean newrules = ruleStore.addPropagatorActivationRule(this);
        if (var.equals(x)) {
            newrules |=ruleStore.addLowerBoundRule(y);
        } else if (var.equals(y)) {
            newrules |=ruleStore.addUpperBoundRule(x);
        } else {
            newrules |=super.why(ruleStore, var, evt, value);
        }
        return newrules;
    }

}