/*

 * Copyright (c) 2017, 2017, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package org.graalvm.collections;

import java.util.Objects;

/**

 * Utility class representing a pair of values.

 *

 * @since 1.0

 */

public final class Pair<L, R> {

    private static final Pair<Object, Object> EMPTY = new Pair<>(null, null);

    private final L left;

    private final R right;

    /**

     * Returns an empty pair.

     *

     * @since 1.0

     */

    @SuppressWarnings("unchecked")

    public static <L, R> Pair<L, R> empty() {

        return (Pair<L, R>) EMPTY;

    }

    /**

     * Constructs a pair with its left value being {@code left}, or returns an empty pair if

     * {@code left} is null.

     *

     * @return the constructed pair or an empty pair if {@code left} is null.

     * @since 1.0

     */

    public static <L, R> Pair<L, R> createLeft(L left) {

        if (left == null) {

            return empty();

        } else {

            return new Pair<>(left, null);

        }

    }

    /**

     * Constructs a pair with its right value being {@code right}, or returns an empty pair if

     * {@code right} is null.

     *

     * @return the constructed pair or an empty pair if {@code right} is null.

     * @since 1.0

     */

    public static <L, R> Pair<L, R> createRight(R right) {

        if (right == null) {

            return empty();

        } else {

            return new Pair<>(null, right);

        }

    }

    /**

     * Constructs a pair with its left value being {@code left}, and its right value being

     * {@code right}, or returns an empty pair if both inputs are null.

     *

     * @return the constructed pair or an empty pair if both inputs are null.

     * @since 1.0

     */

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

        if (right == null && left == null) {

            return empty();

        } else {

            return new Pair<>(left, right);

        }

    }

    private Pair(L left, R right) {

        this.left = left;

        this.right = right;

    }

    /**

     * Returns the left value of this pair.

     *

     * @since 1.0

     */

    public L getLeft() {

        return left;

    }

    /**

     * Returns the right value of this pair.

     *

     * @since 1.0

     */

    public R getRight() {

        return right;

    }

    /**

     * {@inheritDoc}

     *

     * @since 1.0

     */

    @Override

    public int hashCode() {

        return Objects.hashCode(left) + 31 * Objects.hashCode(right);

    }

    /**

     * {@inheritDoc}

     *

     * @since 1.0

     */

    @SuppressWarnings("unchecked")

    @Override

    public boolean equals(Object obj) {

        if (obj == this) {

            return true;

        }

        if (obj instanceof Pair) {

            Pair<L, R> pair = (Pair<L, R>) obj;

            return Objects.equals(left, pair.left) && Objects.equals(right, pair.right);

        }

        return false;

    }

    /**

     * {@inheritDoc}

     *

     * @since 1.0

     */

    @Override

    public String toString() {

        return String.format("(%s, %s)", left, right);

    }

}