/*
 * Copyright (C) 1999-2004 <a href="mailto:mandarax@jbdietrich.com">Jens Dietrich</a>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
package org.mandarax.lib.date;

import java.util.Calendar;
import org.mandarax.kernel.Term;
import org.mandarax.kernel.Session;

/**
 * Abstract superclass for binary date (better: calendar) predicates.
 * @author <A HREF="mailto:mandarax@jbdietrich.com">Jens Dietrich</A>
 * @version 3.3.1 <9 August 2004>
 * @since 1.4
 */
public abstract class BinaryDatePredicate extends org.mandarax.lib.AbstractPredicate {

    private static Class[] structure = { Calendar.class, Calendar.class };

    /**
     * Get the structure of the function.
     * @return the structure of the function
     */
    public Class[] getStructure() {
        return structure;
    }

    /**
     * Perform the predicate using an array of terms as parameters.
     * @return the result of the computation
     * @param parameter an array of terms
     * @param session a session object
     * @throws java.lang.UnsupportedOperationException
     * @throws java.lang.IllegalArgumentException
     */
    public Object perform(Term[] parameter,Session session) throws IllegalArgumentException, UnsupportedOperationException {
        Calendar c1,c2 = null;

        try {
            c1 = (Calendar) (parameter[0].resolve (session));
            c2 = (Calendar) (parameter[1].resolve (session));
        } catch(Exception x) {
            throw new IllegalArgumentException ();
        }

        return new Boolean (compute (c1, c2));
    }

    /**
     * Compare calendars.
     * @return the result
     * @param c1 a date
     * @param c2 another date
     */
    protected abstract boolean compute(Calendar c1, Calendar c2);
}
