/* (c) 2014 Open Source Geospatial Foundation - all rights reserved
 * (c) 2001 - 2013 OpenPlans
 * This code is licensed under the GPL 2.0 license, available at the root
 * application directory.
 */
package org.geoserver.csw.feature.sort;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

import org.opengis.feature.Feature;
import org.opengis.filter.sort.SortBy;
import org.opengis.filter.sort.SortOrder;

/**
 * Builds comparators against complex features based on {@link SortBy} definitions
 * 
 * @author Andrea Aime - GeoSolutions
 * 
 */
public class ComplexComparatorFactory {

    /**
     * Builds a composite comparator matching the specified sortBy array
     *  
     * <ul>
     * <li>{@link SortBy#NATURAL_ORDER}: sort by feature id (acceding)</li>
     * <li>{@link SortBy#REVERSE_ORDER}: sort by feature id (descending)</li>
     * <li>sort by supplied property name, and sort order</li>
     * </ul>
     * 
     * @param sortBy sort order (defined in order of precidence)
     *
     */
    public static Comparator<Feature> buildComparator(SortBy... sortBy) {
        if (sortBy.length == 0) {
            throw new IllegalArgumentException(
                    "No way to build comparators out of an empty comparator set");
        }

        if (sortBy.length == 1) {
            return buildComparator(sortBy[0]);
        } else {
            List<Comparator<Feature>> comparators = new ArrayList<Comparator<Feature>>();
            for (SortBy curr : sortBy) {
                Comparator<Feature> comparator = buildComparator(curr);
                comparators.add(comparator);
            }

            return new CompositeComparator<Feature>(comparators);
        }
    }

    /**
     * Builds a single comparator based on the sortBy specification.
     * 
     * <ul>
     * <li>{@link SortBy#NATURAL_ORDER}: sort by feature id (acceding)</li>
     * <li>{@link SortBy#REVERSE_ORDER}: sort by feature id (descending)</li>
     * <li>sort by supplied property name, and sort order</li>
     * </ul>
     * 
     * @param sortBy indication of sort order
     * @return Comparator used to determine sort order
     */
    public static Comparator<Feature> buildComparator(SortBy sortBy) {
        if (sortBy == null) {
            throw new NullPointerException("The sortBy argument must be not null (consider SortBy.UNSORTED)");
        }

        if (sortBy == SortBy.NATURAL_ORDER) {
            return new FidComparator(true);
        } else if (sortBy == SortBy.REVERSE_ORDER) {
            return new FidComparator(false);
        } else {
            return new PropertyComparator<Feature>(sortBy.getPropertyName(),
                    sortBy.getSortOrder() == SortOrder.ASCENDING);
        }
    }
}