/*

 * Copyright (c) 2012, 2015, 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

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 * questions.

 */

package java.util;

import java.util.function.LongConsumer;

import java.util.function.LongSupplier;

import java.util.function.Supplier;

import java.util.stream.LongStream;

/**

 *

 * <p>Additional methods that depend on the presence or absence of a contained

 * value are provided, such as {@link #orElse(long) orElse()}

 *

 * <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>

 * class; use of identity-sensitive operations (including reference equality

 * ({@code ==}), identity hash code, or synchronization) on instances of

 * {@code OptionalLong} may have unpredictable results and should be avoided.

 *

 * @since 1.8

 */

public final class OptionalLong {

    /**

     * Common instance for {@code empty()}.

     */

    private static final OptionalLong EMPTY = new OptionalLong();

    /**

     * If true then the value is present, otherwise indicates no value is present

     */

    private final boolean isPresent;

    private final long value;

    /**

     * Construct an empty instance.

     *

     * @implNote generally only one empty instance, {@link OptionalLong#EMPTY},

     * should exist per VM.

     */

    private OptionalLong() {

        this.isPresent = false;

        this.value = 0;

    }

    /**

     *

     * Instead, use {@link #isPresent()}.

     *

     */

    public static OptionalLong empty() {

        return EMPTY;

    }

    /**

     *

     */

    private OptionalLong(long value) {

        this.isPresent = true;

        this.value = value;

    }

    /**

     *

     * @return an {@code OptionalLong} with the value present

     */

    public static OptionalLong of(long value) {

        return new OptionalLong(value);

    }

    /**

     *

     * @see OptionalLong#isPresent()

     */

    public long getAsLong() {

        if (!isPresent) {

            throw new NoSuchElementException("No value present");

        }

        return value;

    }

    /**

     *

     */

    public boolean isPresent() {

        return isPresent;

    }

    /**

     *

     */

    public void ifPresent(LongConsumer action) {

        if (isPresent) {

            action.accept(value);

        }

    }

    /**

     *

     */

    public void ifPresentOrElse(LongConsumer action, Runnable emptyAction) {

        if (isPresent) {

            action.accept(value);

        } else {

            emptyAction.run();

        }

    }

    /**

     *

     * <pre>{@code

     *     Stream<OptionalLong> os = ..

     *     LongStream s = os.flatMapToLong(OptionalLong::stream)

     * }</pre>

     *

     */

    public LongStream stream() {

        if (isPresent) {

            return LongStream.of(value);

        } else {

            return LongStream.empty();

        }

    }

    /**

     *

     * @return the value, if present, otherwise {@code other}

     */

    public long orElse(long other) {

        return isPresent ? value : other;

    }

    /**

     *

     */

    }

    /**

     *

     * {@code IllegalStateException::new}

     *

     * @param <X> Type of the exception to be thrown

     */

    public<X extends Throwable> long orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {

        if (isPresent) {

            return value;

        } else {

            throw exceptionSupplier.get();

        }

    }

    /**

     * <ul>

     * <li>it is also an {@code OptionalLong} and;

     * <li>both instances have no value present or;

     * <li>the present values are "equal to" each other via {@code ==}.

     * </ul>

     *

     * @param obj an object to be tested for equality

     * @return {@code true} if the other object is "equal to" this object

     */

    @Override

    public boolean equals(Object obj) {

        if (this == obj) {

            return true;

        }

        if (!(obj instanceof OptionalLong)) {

            return false;

        }

        OptionalLong other = (OptionalLong) obj;

        return (isPresent && other.isPresent)

                ? value == other.value

                : isPresent == other.isPresent;

    }

    /**

     *

     */

    @Override

    public int hashCode() {

        return isPresent ? Long.hashCode(value) : 0;

    }

    /**

     *

     * unambiguously differentiable.

     *

     * @return the string representation of this instance

     */

    @Override

    public String toString() {

        return isPresent

                ? String.format("OptionalLong[%s]", value)

                : "OptionalLong.empty";

    }

}