/*
 * ProductStatistic.java
 *
 * Copyright (C) 2002-2006 Alexei Drummond and Andrew Rambaut
 *
 * This file is part of BEAST.
 * See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership and licensing.
 *
 * BEAST 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.
 *
 *  BEAST 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 BEAST; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 * Boston, MA  02110-1301  USA
 */

package dr.inference.model;

import dr.xml.*;

/**
 * @author Andrew Rambaut
 * @author Alexei Drummond
 * @version $Id: ProductStatistic.java,v 1.2 2005/05/24 20:26:00 rambaut Exp $
 */
public class DifferenceStatistic extends Statistic.Abstract {

    public static String DIFFERENCE_STATISTIC = "differenceStatistic";
    public static String ABSOLUTE = "absolute";

    private final boolean absolute;

    public DifferenceStatistic(String name, Statistic term1, Statistic term2, boolean absolute) {
        super(name);

        this.term1 = term1;
        this.term2 = term2;

        if (term1.getDimension() != 1 &&
                term2.getDimension() != 1 &&
                term1.getDimension() != term2.getDimension()) {
            throw new IllegalArgumentException();
        }

        if (term2.getDimension() == 1) {
            dimension = term1.getDimension();
        } else {
            dimension = term2.getDimension();
        }

        this.absolute = absolute;
    }

    public int getDimension() {
        return dimension;
    }

    /**
     * @return mean of contained statistics
     */
    public double getStatisticValue(int dim) {

        double statistic;

        if (term1.getDimension() == 1) {
            statistic = term1.getStatisticValue(0) - term2.getStatisticValue(dim);
        } else if (term2.getDimension() == 1) {
            statistic = term1.getStatisticValue(dim) - term1.getStatisticValue(0);
        } else {
            statistic = term1.getStatisticValue(dim) - term2.getStatisticValue(dim);
        }
        if (absolute) statistic = Math.abs(statistic);

        return statistic;
    }

    public static XMLObjectParser PARSER = new AbstractXMLObjectParser() {

        public String[] getParserNames() {
            return new String[]{getParserName(), "difference"};
        }

        public String getParserName() {
            return DIFFERENCE_STATISTIC;
        }

        public Object parseXMLObject(XMLObject xo) throws XMLParseException {

            boolean absolute = xo.getAttribute(ABSOLUTE, false);

            Statistic term1 = (Statistic) xo.getChild(0);
            Statistic term2 = (Statistic) xo.getChild(1);

            DifferenceStatistic differenceStatistic;
            try {
                differenceStatistic = new DifferenceStatistic(DIFFERENCE_STATISTIC, term1, term2, absolute);
            } catch (IllegalArgumentException iae) {
                throw new XMLParseException("Error parsing " + getParserName() + " the left and right statistics " +
                        "should be of the same dimension or of dimension 1");
            }
            return differenceStatistic;
        }

        //************************************************************************
        // AbstractXMLObjectParser implementation
        //************************************************************************

        public String getParserDescription() {
            return "This element returns a statistic that is the difference of the 2 child statistics.";
        }

        public Class getReturnType() {
            return ProductStatistic.class;
        }

        public XMLSyntaxRule[] getSyntaxRules() {
            return rules;
        }

        private final XMLSyntaxRule[] rules = {
                AttributeRule.newBooleanRule(ABSOLUTE, true),
                new ElementRule(Statistic.class, "The two operand statistics", 2, 2)
        };
    };

    // ****************************************************************
    // Private and protected stuff
    // ****************************************************************

    private int dimension = 0;
    private Statistic term1 = null;
    private Statistic term2 = null;
}
