/** An inequality over a CPO.

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 */
package ptolemy.graph;

import ptolemy.kernel.util.IllegalActionException;

///////////////////////////////////////////////////////////////////
//// Inequality

/**
 An inequality over a CPO.
 Each inequality consists of two <code>InequalityTerms</code>, the lesser
 term and the greater term. The relation between them is <i>less than or
 equal to</i>.  In addition, an inequality keeps a list of variables in it.
 The variables are <code>InequalityTerms</code> that consist of a single
 variable.

 @author Yuhong Xiong
 @version $Id: Inequality.java 70398 2014-10-22 23:44:32Z cxh $
 @since Ptolemy II 0.2
 @Pt.ProposedRating Green (yuhong)
 @Pt.AcceptedRating Green (kienhuis)
 @see InequalityTerm
 */
public class Inequality {
    /** Construct an inequality.
     *  @param lesserTerm An <code>InequalityTerm</code> that is less than or
     *   equal to the second argument.
     *  @param greaterTerm An <code>InequalityTerm</code> that is greater than
     *   or equal to the first argument.
     *  @exception IllegalArgumentException If the <code>lesserTerm</code> or
     *   the <code>greaterTerm</code> is <code>null</code>.
     */
    public Inequality(InequalityTerm lesserTerm, InequalityTerm greaterTerm) {
        if (lesserTerm == null) {
            throw new IllegalArgumentException("Inequality.Inequality: "
                    + "lesserTerm is null.");
        }

        if (greaterTerm == null) {
            throw new IllegalArgumentException("Inequality.Inequality: "
                    + "greaterTerm is null.");
        }

        _lesserTerm = lesserTerm;
        _greaterTerm = greaterTerm;
    }

    ///////////////////////////////////////////////////////////////////
    ////                         public methods                    ////

    /** Return true if object named by the argument is equal to
     *  this Inequality object.
     *  <p>Override to return true if the greater and lesser terms of
     *  this object are the same as the greater and lesser terms of
     *  the specified object.
     *  @param object Object to compare against.
     *  @return true If the object is an Inequality and both the
     *  greater term and lesser term are equal to the corresponding
     *  terms of this object.
     */
    @Override
    public boolean equals(Object object) {
        if (object instanceof Inequality) {
            return ((Inequality) object)._greaterTerm.equals(_greaterTerm)
                    && ((Inequality) object)._lesserTerm.equals(_lesserTerm);
        }
        return false;
    }

    /** Return the greater term of this inequality.
     *  @return An <code>InequalityTerm</code>
     */
    public InequalityTerm getGreaterTerm() {
        return _greaterTerm;
    }

    /** Return the lesser term of this inequality.
     *  @return An <code>InequalityTerm</code>
     */
    public InequalityTerm getLesserTerm() {
        return _lesserTerm;
    }

    /** Return the hashCode of this object.
     *  <p>Override to return the exclusive OR of the hashcodes
     *  of the greater and lesser terms. This ensures that two
     *  objects that return true to equals() have the same
     *  hashcode.
     *  @return The XOR of the greater and lesser terms.
     */
    @Override
    public int hashCode() {
        return _lesserTerm.hashCode() ^ _greaterTerm.hashCode();
    }

    /** Test if this inequality is satisfied with the current value
     *  of variables.
     *  @param cpo A CPO over which this inequality is defined.
     *  @return True if this inequality is satisfied;
     *  false otherwise.
     *  @exception IllegalActionException If thrown while getting
     *  the value of the terms.
     */
    public boolean isSatisfied(CPO cpo) throws IllegalActionException {
        int result = cpo.compare(_lesserTerm.getValue(),
                _greaterTerm.getValue());
        return result == CPO.LOWER || result == CPO.SAME;
    }

    /** Override the base class to describe the inequality.
     *  @return A string describing the inequality.
     */
    @Override
    public String toString() {
        return _lesserTerm.toString() + " <= " + _greaterTerm.toString();
    }

    ///////////////////////////////////////////////////////////////////
    ////                         private variables                 ////
    private InequalityTerm _lesserTerm = null;

    private InequalityTerm _greaterTerm = null;
}