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

import java.util.functions.Factory;
import java.util.functions.Mapper;

/**
 * Optional
 *
 * @author Brian Goetz
 */
public class Optional<T> {
    private final static Optional<?> EMPTY = new Optional<>();

    private final T value;
    private final boolean present;

    public Optional(T value) {
        this.value = value;
        this.present = true;
    }

    private Optional() {
        this.value = null;
        this.present = false;
    }

    public static<T> Optional<T> empty() {
        return (Optional<T>) EMPTY;
    }

    public T get() {
        if (!present)
            throw new NoSuchElementException();
        return value;
    }

    public boolean isPresent() {
        return present;
    }

    public T orElse(T other) {
        return present ? value : other;
    }

    public T orElse(Factory<T> other) {
        return present ? value : other.make();
    }

    public<V extends Throwable> T orElseThrow(Factory<V> exceptionFactory) throws V {
        if (present)
            return value;
        else
            throw exceptionFactory.make();
    }

    public<V extends Throwable> T orElseThrow(Class<V> exceptionClass) throws V {
        if (present)
            return value;
        else
            try {
                throw exceptionClass.newInstance();
            }
            catch (InstantiationException | IllegalAccessException e) {
                throw new IllegalStateException("Unexpected exception: " + e, e);
            }
    }

    public<V> Optional<V> map(Mapper<T, V> mapper) {
        return present ? new Optional<>(mapper.map(value)) : Optional.<V>empty();
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Optional optional = (Optional) o;

        if (present != optional.present) return false;
        if (value != null ? !value.equals(optional.value) : optional.value != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = value != null ? value.hashCode() : 0;
        result = 31 * result + (present ? 1 : 0);
        return result;
    }
}