/*

 * Copyright (c) 2019, 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.

 *

 * 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.reactivestreams.tck.flow.support;

import java.util.NoSuchElementException;

// simplest possible version of Scala's Option type

public abstract class Optional<T> {

  private static final Optional<Object> NONE = new Optional<Object>() {

    @Override

    public Object get() {

      throw new NoSuchElementException(".get call on None!");

    }

    @Override

    public boolean isEmpty() {

      return true;

    }

  };

  private Optional() {

  }

  @SuppressWarnings("unchecked")

  public static <T> Optional<T> empty() {

    return (Optional<T>) NONE;

  }

  @SuppressWarnings("unchecked")

  public static <T> Optional<T> of(T it) {

    if (it == null) return (Optional<T>) Optional.NONE;

    else return new Some(it);

  }

  public abstract T get();

  public abstract boolean isEmpty();

  public boolean isDefined() {

    return !isEmpty();

  }

  public static class Some<T> extends Optional<T> {

    private final T value;

    Some(T value) {

      this.value = value;

    }

    @Override

    public T get() {

      return value;

    }

    @Override

    public boolean isEmpty() {

      return false;

    }

    @Override

    public String toString() {

      return String.format("Some(%s)", value);

    }

  }

  @Override

  public String toString() {

    return "None";

  }

}