/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at legal-notices/CDDLv1_0.txt
 * or http://forgerock.org/license/CDDLv1.0.html.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at legal-notices/CDDLv1_0.txt.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information:
 *      Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 *
 *
 *      Copyright 2013-2014 ForgeRock AS
 */
package com.forgerock.opendj.util;

import java.util.Comparator;

/**
 * Ordered pair of arbitrary objects.
 *
 * @param <F>
 *            type of the first pair element
 * @param <S>
 *            type of the second pair element
 */
public final class Pair<F, S> {

    private static final class ComparablePairComparator
            <F extends Comparable<F>, S extends Comparable<S>>
            implements Comparator<Pair<F, S>> {
        /** {@inheritDoc} */
        @Override
        public int compare(Pair<F, S> o1, Pair<F, S> o2) {
            final int compareResult = o1.getFirst().compareTo(o2.getFirst());
            if (compareResult == 0) {
                return o1.getSecond().compareTo(o2.getSecond());
            }
            return compareResult;
        }
    }

    /** An empty Pair. */
    public static final Pair<?, ?> EMPTY = Pair.of(null, null);

    /**
     * {@link Comparator} for {@link Pair}s made of {@link Comparable} elements.
     */
    @SuppressWarnings("rawtypes")
    public static final Comparator COMPARATOR = new ComparablePairComparator();

    /** The first pair element. */
    private final F first;

    /** The second pair element. */
    private final S second;

    /**
     * Creates a pair.
     *
     * @param first
     *            the first element of the constructed pair
     * @param second
     *            the second element of the constructed pair
     */
    private Pair(F first, S second) {
        this.first = first;
        this.second = second;
    }

    /**
     * Factory method to build a new Pair.
     *
     * @param first
     *            the first element of the constructed pair
     * @param second
     *            the second element of the constructed pair
     * @param <F>
     *            type of the first pair element
     * @param <S>
     *            type of the second pair element
     * @return A new Pair built with the provided elements
     */
    public static <F, S> Pair<F, S> of(F first, S second) {
        return new Pair<F, S>(first, second);
    }

    /**
     * Returns an empty Pair matching the required types.
     *
     * @param <F>
     *            type of the first pair element
     * @param <S>
     *            type of the second pair element
     * @return An empty Pair matching the required types
     */
    @SuppressWarnings("unchecked")
    public static <F, S> Pair<F, S> empty() {
        return (Pair<F, S>) EMPTY;
    }

    /**
     * Returns a comparator for Pairs of comparable objects.
     *
     * @param <F>
     *            type of the first pair element
     * @param <S>
     *            type of the second pair element
     * @return a comparator for Pairs of comparable objects.
     */
    @SuppressWarnings("unchecked")
    public static <F extends Comparable<F>, S extends Comparable<S>>
    Comparator<Pair<F, S>> getPairComparator() {
        return COMPARATOR;
    }

    /**
     * Returns the first element of this pair.
     *
     * @return the first element of this pair
     */
    public F getFirst() {
        return first;
    }

    /**
     * Returns the second element of this pair.
     *
     * @return the second element of this pair
     */
    public S getSecond() {
        return second;
    }

    /** {@inheritDoc} */
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((first == null) ? 0 : first.hashCode());
        return prime * result + ((second == null) ? 0 : second.hashCode());
    }

    /** {@inheritDoc} */
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (!(obj instanceof Pair)) {
            return false;
        }
        Pair<?, ?> other = (Pair<?, ?>) obj;
        if (first == null) {
            if (other.first != null) {
                return false;
            }
        } else if (!first.equals(other.first)) {
            return false;
        }
        if (second == null) {
            if (other.second != null) {
                return false;
            }
        } else if (!second.equals(other.second)) {
            return false;
        }
        return true;
    }

    /** {@inheritDoc} */
    @Override
    public String toString() {
        return "Pair [" + first + ", " + second + "]";
    }

}