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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.reification;

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.BoolVar;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.events.IEventType;
import org.chocosolver.util.ESat;

/**
 * A propagator dedicated to express in a compact way: (x < c) ⇔ b
 *
 * @author Charles Prud'homme
 * @since 03/05/2016.
 */
public class PropXltCReif extends Propagator {

    IntVar var;
    int cste;
    BoolVar r;

    public PropXltCReif(IntVar x, int c, BoolVar r) {
        super(new IntVar[]{x, r}, PropagatorPriority.BINARY, false);
        this.cste = c;
        this.var = x;
        this.r = r;
    }

    @Override
    public void propagate(int evtmask) throws ContradictionException {
        if (r.getLB() == 1) {
            setPassive();
            var.updateUpperBound(cste - 1, this);
        } else if (r.getUB() == 0) {
            setPassive();
            var.updateLowerBound(cste, this);
        } else {
            if (var.getUB() < cste) {
                setPassive();
                r.setToTrue(this);
            } else if (var.getLB() >= cste) {
                setPassive();
                r.setToFalse(this);
            }
        }
    }

    @Override
    public ESat isEntailed() {
        if(isCompletelyInstantiated()){
            if(r.isInstantiatedTo(1)){
                return ESat.eval(var.getUB() < cste);
            }else{
                return ESat.eval(var.getLB() >= cste);
            }
        }
        return ESat.UNDEFINED;
    }

    @Override
    public boolean why(RuleStore ruleStore, IntVar var, IEventType evt, int value) {
        boolean nrules = ruleStore.addPropagatorActivationRule(this);
        if (var == vars[1]) { // r
            if (vars[1].isInstantiatedTo(1)) {
                nrules |= ruleStore.addUpperBoundRule(vars[0]);
            } else {
                nrules |= ruleStore.addLowerBoundRule(vars[0]);
            }
        } else { //
            nrules |= ruleStore.addFullDomainRule(vars[1]);
        }
        return nrules;
    }

    @Override
    public String toString() {
        return "(" + var.getName() +" < " + cste + ") <=> "+r.getName();
    }
}