/*

  * 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.lang3.tuple;

 import java.io.Serializable;

 import java.util.Map;

 import org.apache.commons.lang3.ObjectUtils;

 import org.apache.commons.lang3.builder.CompareToBuilder;

 /**

  * <p>A pair consisting of two elements.</p>

  * 

  * <p>This class is an abstract implementation defining the basic API.

  * It refers to the elements as 'left' and 'right'. It also implements the

  * {@code Map.Entry} interface where the key is 'left' and the value is 'right'.</p>

  * 

  * <p>Subclass implementations may be mutable or immutable.

  * However, there is no restriction on the type of the stored objects that may be stored.

  * If mutable objects are stored in the pair, then the pair itself effectively becomes mutable.</p>

  *

  * @param <L> the left element type

  * @param <R> the right element type

  *

  * @since Lang 3.0

  * @version $Id: Pair.java 1436770 2013-01-22 07:09:45Z ggregory $

  */

 public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L, R>>, Serializable {

     /** Serialization version */

     private static final long serialVersionUID = 4954918890077093841L;

     /**

      * <p>Obtains an immutable pair of from two objects inferring the generic types.</p>

      * 

      * <p>This factory allows the pair to be created using inference to

      * obtain the generic types.</p>

      * 

      * @param <L> the left element type

      * @param <R> the right element type

      * @param left  the left element, may be null

      * @param right  the right element, may be null

      * @return a pair formed from the two parameters, not null

      */

     public static <L, R> Pair<L, R> of(final L left, final R right) {

         return new ImmutablePair<L, R>(left, right);

     }

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

     /**

      * <p>Gets the left element from this pair.</p>

      * 

      * <p>When treated as a key-value pair, this is the key.</p>

      * 

      * @return the left element, may be null

      */

     public abstract L getLeft();

     /**

      * <p>Gets the right element from this pair.</p>

      * 

      * <p>When treated as a key-value pair, this is the value.</p>

      * 

      * @return the right element, may be null

      */

     public abstract R getRight();

     /**

      * <p>Gets the key from this pair.</p>

      * 

      * <p>This method implements the {@code Map.Entry} interface returning the

      * left element as the key.</p>

      * 

      * @return the left element as the key, may be null

      */

     @Override

     public final L getKey() {

         return getLeft();

     }

     /**

      * <p>Gets the value from this pair.</p>

      * 

      * <p>This method implements the {@code Map.Entry} interface returning the

      * right element as the value.</p>

      * 

      * @return the right element as the value, may be null

      */

     @Override

     public R getValue() {

         return getRight();

     }

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

     /**

      * <p>Compares the pair based on the left element followed by the right element.

      * The types must be {@code Comparable}.</p>

      * 

      * @param other  the other pair, not null

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

      */

     @Override

     public int compareTo(final Pair<L, R> other) {

       return new CompareToBuilder().append(getLeft(), other.getLeft())

               .append(getRight(), other.getRight()).toComparison();

     }

     /**

      * <p>Compares this pair to another based on the two elements.</p>

      * 

      * @param obj  the object to compare to, null returns false

      * @return true if the elements of the pair are equal

      */

     @Override

     public boolean equals(final Object obj) {

         if (obj == this) {

             return true;

         }

         if (obj instanceof Map.Entry<?, ?>) {

             final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;

             return ObjectUtils.equals(getKey(), other.getKey())

                     && ObjectUtils.equals(getValue(), other.getValue());

         }

         return false;

     }

     /**

      * <p>Returns a suitable hash code.

      * The hash code follows the definition in {@code Map.Entry}.</p>

      * 

      * @return the hash code

      */

     @Override

     public int hashCode() {

         // see Map.Entry API specification

         return (getKey() == null ? 0 : getKey().hashCode()) ^

                 (getValue() == null ? 0 : getValue().hashCode());

     }

     /**

      * <p>Returns a String representation of this pair using the format {@code ($left,$right)}.</p>

      * 

      * @return a string describing this object, not null

      */

     @Override

     public String toString() {

         return new StringBuilder().append('(').append(getLeft()).append(',').append(getRight()).append(')').toString();

     }

     /**

      * <p>Formats the receiver using the given format.</p>

      * 

      * <p>This uses {@link java.util.Formattable} to perform the formatting. Two variables may

      * be used to embed the left and right elements. Use {@code %1$s} for the left

      * element (key) and {@code %2$s} for the right element (value).

      * The default format used by {@code toString()} is {@code (%1$s,%2$s)}.</p>

      * 

      * @param format  the format string, optionally containing {@code %1$s} and {@code %2$s}, not null

      * @return the formatted string, not null

      */

     public String toString(final String format) {

         return String.format(format, getLeft(), getRight());

     }

 }