/*

 * 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.commons.collections4.comparators;

import java.io.Serializable;

import java.util.Comparator;

import org.apache.commons.collections4.ComparatorUtils;

import org.apache.commons.collections4.Transformer;

/**

 * Decorates another Comparator with transformation behavior. That is, the

 * return value from the transform operation will be passed to the decorated

 * {@link Comparator#compare(Object,Object) compare} method.

 * <p>

 * This class is Serializable from Commons Collections 4.0.

 * </p>

 *

 * @param <I> the input type to the transformer

 * @param <O> the output type from the transformer

 *

 * @since 2.1

 *

 * @see org.apache.commons.collections4.Transformer

 * @see org.apache.commons.collections4.comparators.ComparableComparator

 */

public class TransformingComparator<I, O> implements Comparator<I>, Serializable {

    /** Serialization version from Collections 4.0. */

    private static final long serialVersionUID = 3456940356043606220L;

    /** The decorated comparator. */

    private final Comparator<O> decorated;

    /** The transformer being used. */

    private final Transformer<? super I, ? extends O> transformer;

    //-----------------------------------------------------------------------

    /**

     * Constructs an instance with the given Transformer and a

     * {@link ComparableComparator ComparableComparator}.

     *

     * @param transformer what will transform the arguments to <code>compare</code>

     */

    public TransformingComparator(final Transformer<? super I, ? extends O> transformer) {

        this(transformer, ComparatorUtils.NATURAL_COMPARATOR);

    }

    /**

     * Constructs an instance with the given Transformer and Comparator.

     *

     * @param transformer  what will transform the arguments to <code>compare</code>

     * @param decorated  the decorated Comparator

     */

    public TransformingComparator(final Transformer<? super I, ? extends O> transformer,

                                  final Comparator<O> decorated) {

        this.decorated = decorated;

        this.transformer = transformer;

    }

    //-----------------------------------------------------------------------

    /**

     * Returns the result of comparing the values from the transform operation.

     *

     * @param obj1  the first object to transform then compare

     * @param obj2  the second object to transform then compare

     * @return negative if obj1 is less, positive if greater, zero if equal

     */

    @Override

    public int compare(final I obj1, final I obj2) {

        final O value1 = this.transformer.transform(obj1);

        final O value2 = this.transformer.transform(obj2);

        return this.decorated.compare(value1, value2);

    }

    //-----------------------------------------------------------------------

    /**

     * Implement a hash code for this comparator that is consistent with

     * {@link #equals(Object) equals}.

     *

     * @return a hash code for this comparator.

     */

    @Override

    public int hashCode() {

        int total = 17;

        total = total*37 + (decorated == null ? 0 : decorated.hashCode());

        total = total*37 + (transformer == null ? 0 : transformer.hashCode());

        return total;

    }

    /**

     * Returns <code>true</code> iff <i>that</i> Object is

     * is a {@link Comparator} whose ordering is known to be

     * equivalent to mine.

     * <p>

     * This implementation returns <code>true</code>

     * iff <code><i>that</i></code> is a {@link TransformingComparator}

     * whose attributes are equal to mine.

     *

     * @param object  the object to compare to

     * @return true if equal

     */

    @Override

    public boolean equals(final Object object) {

        if (this == object) {

            return true;

        }

        if (null == object) {

            return false;

        }

        if (object.getClass().equals(this.getClass())) {

            final TransformingComparator<?, ?> comp = (TransformingComparator<?, ?>) object;

            return (null == decorated ? null == comp.decorated : decorated.equals(comp.decorated)) &&

                   (null == transformer ? null == comp.transformer : transformer.equals(comp.transformer));

        }

        return false;

    }

}