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/*
 * This file is part of choco-solver, http://choco-solver.org/
 *
 * Copyright (c) 2022, IMT Atlantique. All rights reserved.
 *
 * Licensed under the BSD 4-clause license.
 *
 * See LICENSE file in the project root for full license information.
 */
package org.chocosolver.solver.constraints.unary;

import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.learn.ExplanationForSignedClause;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.util.ESat;

/**
 * Unary propagator ensuring:
 * 

 * X = C, where X is a variable and C is a constant
 * 
 * 

 *
 * @author Charles Prud'homme
 * @since 16/06/11
 */
public class PropEqualXC extends Propagator {

    private final int constant;

    public PropEqualXC(IntVar var, int cste) {
        super(new IntVar[]{var}, PropagatorPriority.UNARY, false);
        this.constant = cste;
    }

    @Override
    public void propagate(int evtmask) throws ContradictionException {
        vars[0].instantiateTo(constant, this);
    }

    @Override
    public ESat isEntailed() {
        if (vars[0].isInstantiatedTo(constant)) {
            return ESat.TRUE;
        } else if (vars[0].contains(constant)) {
            return ESat.UNDEFINED;
        }
        return ESat.FALSE;
    }

    /**
     * @implSpec
     * 

     *     Consider that v1 has been modified by propagation of this.
     *     Before the propagation, the domains were like:
     * 
     *         (v1 ∈ D1)
     *     
     * Then this propagates v1 = c, then:
     *      *         (v1 ∈ D1) → v1 = c
     *     
     * Converting to DNF:
     *      *         (v1 ∈ (U \ D1) ∪ {c})
     *     
     * 
     */
    @Override
    public void explain(int p, ExplanationForSignedClause explanation) {
        vars[0].intersectLit(constant, explanation);
    }

    @Override
    public String toString() {
        return vars[0].getName() + " = " + constant;
    }

}