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 * Copyright (c) 2012, 2013, 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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 */
package java.util;

import java.util.function.IntConsumer;
import java.util.function.IntSupplier;
import java.util.function.Supplier;

/**
 * A container object which may or may not contain a {@code int} value.
 * If a value is present, {@code isPresent()} will return {@code true} and
 * {@code get()} will return the value.
 *
 * <p>Additional methods that depend on the presence or absence of a contained
 * value are provided, such as {@link #orElse(java.lang.Object) orElse()}
 * (return a default value if value not present) and
 * {@link #ifPresent(java.util.function.Consumer) ifPresent()} (execute a block
 * of code if the value is present.)
 *
 * @since 1.8
 */
public final class OptionalInt {
    /**
     * Common instance for {@code empty()}.
     */
    private final static OptionalInt EMPTY = new OptionalInt();

    /**
     * If true then the value is present, otherwise indicates no value is present
     */
    private final boolean isPresent;
    private final int value;

    /**
     * Construct a non-empty instance
     *
     * @param value the int value to be present.
     */
    private OptionalInt(int value) {
        this.isPresent = true;
        this.value = value;
    }

    /**
     * Construct an empty instance.
     *
     * @implNote generally only one empty instance, {@link OptionalInt#EMPTY},
     * should exist per VM.
     */
    private OptionalInt() {
        this.isPresent = false;
        this.value = 0;
    }

    /**
     * Return an empty {@code OptionalInt}.  No value is present for this Optional.
     *
     * @apiNote Though it may be tempting to do so, avoid testing if an object
     * is empty by comparing with {@code ==} against instances returned
     * {@code Option.empty()}. There is no guarantee that it is a singleton.
     * Instead, use {@code isPresent()}.
     *
     *  @return an empty {@code OptionalInt}.
     */
    @SuppressWarnings("unchecked")
    public static OptionalInt empty() {
        return EMPTY;
    }

    /**
     * Create a new {@code OptionalInt} with a present value
     * @param value The int value
     * @param value new {@code OptionalInt} with a present value.
     */
    public static OptionalInt of(int value) {
        return new OptionalInt(value);
    }

    /**
     * If a value is present in this {@code OptionalInt}, returns the value,
     * otherwise throws {@code NoSuchElementException}.
     *
     * @return the value held by this {@code OptionalInt}.
     * @throws NoSuchElementException if there is no value present.
     *
     * @see OptionalInt#isPresent()
     */
    public int getAsInt() {
        if (!isPresent) {
            throw new NoSuchElementException("No value present");
        }
        return value;
    }

    /**
     * Return {@code true} if there is a value present, otherwise {@code false}.
     *
     * @return {@code true} if there is a value present, otherwise {@code false}.
     */
    public boolean isPresent() {
        return isPresent;
    }

    /**
     * Execute the specified consumer with the value if a value is present,
     * otherwise do nothing.
     *
     * @param consumer block to be executed if a value is present.
     * @throws NullPointerException if value is present and {@code consumer} is
     * null.
     */
    public void ifPresent(IntConsumer consumer) {
        if (isPresent)
            consumer.accept(value);
    }

    /**
     * Return the value if present, otherwise return {@code other}.
     *
     * @param other value to be returned if there is no value present.
     * @return the value, if present, otherwise {@code other}.
     */
    public int orElse(int other) {
        return isPresent ? value : other;
    }

    /**
     * Return the value if present, otherwise invoke {@code other} and return
     * the result of that invocation.
     *
     * @param other {@code IntSupplier} who's result is returned if there is no
     * value present.
     * @return the value if present otherwise return result of {@code other}.
     * @throws NullPointerException if value is absent and {@code other} is null.
     */
    public int orElseGet(IntSupplier other) {
        return isPresent ? value : other.getAsInt();
    }

    /**
     * Return the contained value, if present, otherwise throw an exception
     * to be created by the provided supplier.
     *
     * @param <V> Type of the exception to be thrown.
     * @param exceptionSupplier The supplier which will return the exception to
     * be thrown.
     * @return the value.
     * @throws V if there is no value present.
     * @throws NullPointerException if value is absent and
     * {@code exceptionSupplier} is null.
     */
    public<V extends Throwable> int orElseThrow(Supplier<V> exceptionSupplier) throws V {
        if (isPresent) {
            return value;
        } else {
            throw exceptionSupplier.get();
        }
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }

        if (!(o instanceof OptionalInt)) {
            return false;
        }

        OptionalInt other = (OptionalInt) o;
        return (isPresent && other.isPresent) ? value == other.value : isPresent == other.isPresent;
    }

    @Override
    public int hashCode() {
        return Integer.hashCode(value);
    }

    @Override
    public String toString() {
        return isPresent
			? String.format("IntOptional[%s]", value)
			: "IntOptional.empty";
    }
}