LenientExplicitOrdering.java

/**
 * This file is part of Graylog.
 *
 * Graylog is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Graylog 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Graylog.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.graylog2.utilities;

import com.google.common.collect.Maps;
import com.google.common.collect.Ordering;

import java.util.List;
import java.util.Map;

/**
 * An ordering that compares objects according to a given order, sorting unknown elements by their natural comparison or last.
 */
public class LenientExplicitOrdering<T> extends Ordering<T> {
    private final Map<T, Integer> idxMap;

    public LenientExplicitOrdering(List<T> order) {
        this.idxMap = Maps.newHashMapWithExpectedSize(order.size());
        int idx = 0;
        for (T s : order) {
            idxMap.put(s, idx);
            idx++;
        }
    }

    @Override
    public int compare(T left, T right) {
        final Integer leftIdx = idxMap.get(left);
        final Integer rightIdx = idxMap.get(right);

        if (leftIdx != null && rightIdx != null) {
            //noinspection SuspiciousNameCombination
            return Integer.compare(leftIdx, rightIdx);
        }
        if (left instanceof Comparable && leftIdx == null && rightIdx == null) {
            //noinspection unchecked
            return ((Comparable) left).compareTo(right);
        }
        if (leftIdx == null) {
            return -1;
        }
        return 1;
    }
}