/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import java.util.Iterator;
import java.util.NavigableSet;
import java.util.SortedSet;

import com.google.common.annotations.Beta;

/**
 * A navigable set which forwards all its method calls to another navigable set.
 * Subclasses should override one or more methods to modify the behavior of the
 * backing set as desired per the
 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator
 * pattern</a>.
 *
 * <p>
 * <i>Warning:</i> The methods of {@code ForwardingNavigableSet} forward
 * <i>indiscriminately</i> to the methods of the delegate. For example,
 * overriding {@link #add} alone <i>will not</i> change the behavior of
 * {@link #addAll}, which can lead to unexpected behavior. In this case, you
 * should override {@code addAll} as well, either providing your own
 * implementation, or delegating to the provided {@code standardAddAll} method.
 *
 * <p>
 * Each of the {@code standard} methods uses the set's comparator (or the
 * natural ordering of the elements, if there is no comparator) to test element
 * equality. As a result, if the comparator is not consistent with equals, some
 * of the standard implementations may violate the {@code Set} contract.
 *
 * <p>
 * The {@code standard} methods and the collection views they return are not
 * guaranteed to be thread-safe, even when all of the methods that they depend
 * on are thread-safe.
 *
 * @author Louis Wasserman
 * @since 12.0
 */
public abstract class ForwardingNavigableSet<E> extends ForwardingSortedSet<E> implements NavigableSet<E> {

	/** Constructor for use by subclasses. */
	protected ForwardingNavigableSet() {
	}

	@Override
	protected abstract NavigableSet<E> delegate();

	@Override
	public E lower(E e) {
		return delegate().lower(e);
	}

	/**
	 * A sensible definition of {@link #lower} in terms of the
	 * {@code descendingIterator} method of {@link #headSet(Object, boolean)}. If
	 * you override {@link #headSet(Object, boolean)}, you may wish to override
	 * {@link #lower} to forward to this implementation.
	 */
	protected E standardLower(E e) {
		return Iterators.getNext(headSet(e, false).descendingIterator(), null);
	}

	@Override
	public E floor(E e) {
		return delegate().floor(e);
	}

	/**
	 * A sensible definition of {@link #floor} in terms of the
	 * {@code descendingIterator} method of {@link #headSet(Object, boolean)}. If
	 * you override {@link #headSet(Object, boolean)}, you may wish to override
	 * {@link #floor} to forward to this implementation.
	 */
	protected E standardFloor(E e) {
		return Iterators.getNext(headSet(e, true).descendingIterator(), null);
	}

	@Override
	public E ceiling(E e) {
		return delegate().ceiling(e);
	}

	/**
	 * A sensible definition of {@link #ceiling} in terms of the {@code iterator}
	 * method of {@link #tailSet(Object, boolean)}. If you override
	 * {@link #tailSet(Object, boolean)}, you may wish to override {@link #ceiling}
	 * to forward to this implementation.
	 */
	protected E standardCeiling(E e) {
		return Iterators.getNext(tailSet(e, true).iterator(), null);
	}

	@Override
	public E higher(E e) {
		return delegate().higher(e);
	}

	/**
	 * A sensible definition of {@link #higher} in terms of the {@code iterator}
	 * method of {@link #tailSet(Object, boolean)}. If you override
	 * {@link #tailSet(Object, boolean)}, you may wish to override {@link #higher}
	 * to forward to this implementation.
	 */
	protected E standardHigher(E e) {
		return Iterators.getNext(tailSet(e, false).iterator(), null);
	}

	@Override
	public E pollFirst() {
		return delegate().pollFirst();
	}

	/**
	 * A sensible definition of {@link #pollFirst} in terms of the {@code iterator}
	 * method. If you override {@link #iterator} you may wish to override
	 * {@link #pollFirst} to forward to this implementation.
	 */
	protected E standardPollFirst() {
		return Iterators.pollNext(iterator());
	}

	@Override
	public E pollLast() {
		return delegate().pollLast();
	}

	/**
	 * A sensible definition of {@link #pollLast} in terms of the
	 * {@code descendingIterator} method. If you override
	 * {@link #descendingIterator} you may wish to override {@link #pollLast} to
	 * forward to this implementation.
	 */
	protected E standardPollLast() {
		return Iterators.pollNext(descendingIterator());
	}

	protected E standardFirst() {
		return iterator().next();
	}

	protected E standardLast() {
		return descendingIterator().next();
	}

	@Override
	public NavigableSet<E> descendingSet() {
		return delegate().descendingSet();
	}

	/**
	 * A sensible implementation of {@link NavigableSet#descendingSet} in terms of
	 * the other methods of {@link NavigableSet}, notably including
	 * {@link NavigableSet#descendingIterator}.
	 *
	 * <p>
	 * In many cases, you may wish to override
	 * {@link ForwardingNavigableSet#descendingSet} to forward to this
	 * implementation or a subclass thereof.
	 *
	 * @since 12.0
	 */
	@Beta
	protected class StandardDescendingSet extends Sets.DescendingSet<E> {
		/** Constructor for use by subclasses. */
		public StandardDescendingSet() {
			super(ForwardingNavigableSet.this);
		}
	}

	@Override
	public Iterator<E> descendingIterator() {
		return delegate().descendingIterator();
	}

	@Override
	public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
		return delegate().subSet(fromElement, fromInclusive, toElement, toInclusive);
	}

	/**
	 * A sensible definition of {@link #subSet(Object, boolean, Object, boolean)} in
	 * terms of the {@code headSet} and {@code tailSet} methods. In many cases, you
	 * may wish to override {@link #subSet(Object, boolean, Object, boolean)} to
	 * forward to this implementation.
	 */
	@Beta
	protected NavigableSet<E> standardSubSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
		return tailSet(fromElement, fromInclusive).headSet(toElement, toInclusive);
	}

	/**
	 * A sensible definition of {@link #subSet(Object, Object)} in terms of the
	 * {@link #subSet(Object, boolean, Object, boolean)} method. If you override
	 * {@link #subSet(Object, boolean, Object, boolean)}, you may wish to override
	 * {@link #subSet(Object, Object)} to forward to this implementation.
	 */
	@Override
	protected SortedSet<E> standardSubSet(E fromElement, E toElement) {
		return subSet(fromElement, true, toElement, false);
	}

	@Override
	public NavigableSet<E> headSet(E toElement, boolean inclusive) {
		return delegate().headSet(toElement, inclusive);
	}

	/**
	 * A sensible definition of {@link #headSet(Object)} in terms of the
	 * {@link #headSet(Object, boolean)} method. If you override
	 * {@link #headSet(Object, boolean)}, you may wish to override
	 * {@link #headSet(Object)} to forward to this implementation.
	 */
	protected SortedSet<E> standardHeadSet(E toElement) {
		return headSet(toElement, false);
	}

	@Override
	public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
		return delegate().tailSet(fromElement, inclusive);
	}

	/**
	 * A sensible definition of {@link #tailSet(Object)} in terms of the
	 * {@link #tailSet(Object, boolean)} method. If you override
	 * {@link #tailSet(Object, boolean)}, you may wish to override
	 * {@link #tailSet(Object)} to forward to this implementation.
	 */
	protected SortedSet<E> standardTailSet(E fromElement) {
		return tailSet(fromElement, true);
	}
}
