/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 */
package org.apache.tools.ant.types.resources.comparators;

import java.util.Comparator;

import org.apache.tools.ant.types.DataType;
import org.apache.tools.ant.types.Resource;

/**
 * Abstract Resource Comparator.
 * @since Ant 1.7
 */
public abstract class ResourceComparator extends DataType implements Comparator<Resource> {

    /**
     * Compare two objects.
     * @param foo the first Object.
     * @param bar the second Object.
     * @return a negative integer, zero, or a positive integer as the first
     *         argument is less than, equal to, or greater than the second.
     * @throws ClassCastException if either argument is null.
     */
    @Override
    public final int compare(Resource foo, Resource bar) {
        dieOnCircularReference();
        ResourceComparator c = isReference() ? getRef() : this;
        return c.resourceCompare(foo, bar);
    }

    /**
     * Test for equality with this ResourceComparator.
     * @param o the Object to compare against.
     * @return true if the specified Object equals this one.
     */
    @Override
    public boolean equals(Object o) {
        if (isReference()) {
            return getRef().equals(o);
        }
        return o != null && (o == this || o.getClass().equals(getClass()));
    }

    /**
     * Hashcode based on the rules for equality.
     * @return a hashcode.
     */
    @Override
    public synchronized int hashCode() {
        if (isReference()) {
            return getRef().hashCode();
        }
        return getClass().hashCode();
    }

    /**
     * Compare two Resources.
     * @param foo the first Resource.
     * @param bar the second Resource.
     * @return a negative integer, zero, or a positive integer as the first
     *         argument is less than, equal to, or greater than the second.
     */
    protected abstract int resourceCompare(Resource foo, Resource bar);

    private ResourceComparator getRef() {
        return getCheckedRef(ResourceComparator.class);
    }
}
