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	/*
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF licenses this file to You 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 org.apache.commons.collections4.iterators;

	import java.util.List;
	import java.util.ListIterator;
	import java.util.NoSuchElementException;

	import org.apache.commons.collections4.ResettableListIterator;

	/**
	* A ListIterator that restarts when it reaches the end or when it
	* reaches the beginning.
	* <p>
	* The iterator will loop continuously around the provided list,
	* unless there are no elements in the collection to begin with, or
	* all of the elements have been {@link #remove removed}.
	* <p>
	* Concurrent modifications are not directly supported, and for most
	* collection implementations will throw a
	* ConcurrentModificationException.
	*
	* @since 3.2
	*/
	public class LoopingListIterator<E> implements ResettableListIterator<E> {

	/** The list to base the iterator on */
	private final List<E> list;
	/** The current list iterator */
	private ListIterator<E> iterator;

	/**
	* Constructor that wraps a list.
	* <p>
	* There is no way to reset a ListIterator instance without
	* recreating it from the original source, so the List must be
	* passed in and a reference to it held.
	*
	* @param list the list to wrap
	* @throws NullPointerException if the list it null
	*/
	public LoopingListIterator(final List<E> list) {
	if (list == null) {
	throw new NullPointerException("The list must not be null");
	}
	this.list = list;
	_reset();
	}

	/**
	* Returns whether this iterator has any more elements.
	* <p>
	* Returns false only if the list originally had zero elements, or
	* all elements have been {@link #remove removed}.
	*
	* @return <code>true</code> if there are more elements
	*/
	@Override
	public boolean hasNext() {
	return !list.isEmpty();
	}

	/**
	* Returns the next object in the list.
	* <p>
	* If at the end of the list, returns the first element.
	*
	* @return the object after the last element returned
	* @throws NoSuchElementException if there are no elements in the list
	*/
	@Override
	public E next() {
	if (list.isEmpty()) {
	throw new NoSuchElementException(
	"There are no elements for this iterator to loop on");
	}
	if (iterator.hasNext() == false) {
	reset();
	}
	return iterator.next();
	}

	/**
	* Returns the index of the element that would be returned by a
	* subsequent call to {@link #next}.
	* <p>
	* As would be expected, if the iterator is at the physical end of
	* the underlying list, 0 is returned, signifying the beginning of
	* the list.
	*
	* @return the index of the element that would be returned if next() were called
	* @throws NoSuchElementException if there are no elements in the list
	*/
	@Override
	public int nextIndex() {
	if (list.isEmpty()) {
	throw new NoSuchElementException(
	"There are no elements for this iterator to loop on");
	}
	if (iterator.hasNext() == false) {
	return 0;
	}
	return iterator.nextIndex();
	}

	/**
	* Returns whether this iterator has any more previous elements.
	* <p>
	* Returns false only if the list originally had zero elements, or
	* all elements have been {@link #remove removed}.
	*
	* @return <code>true</code> if there are more elements
	*/
	@Override
	public boolean hasPrevious() {
	return !list.isEmpty();
	}

	/**
	* Returns the previous object in the list.
	* <p>
	* If at the beginning of the list, return the last element. Note
	* that in this case, traversal to find that element takes linear time.
	*
	* @return the object before the last element returned
	* @throws NoSuchElementException if there are no elements in the list
	*/
	@Override
	public E previous() {
	if (list.isEmpty()) {
	throw new NoSuchElementException(
	"There are no elements for this iterator to loop on");
	}
	if (iterator.hasPrevious() == false) {
	E result = null;
	while (iterator.hasNext()) {
	result = iterator.next();
	}
	iterator.previous();
	return result;
	}
	return iterator.previous();
	}

	/**
	* Returns the index of the element that would be returned by a
	* subsequent call to {@link #previous}.
	* <p>
	* As would be expected, if at the iterator is at the physical
	* beginning of the underlying list, the list's size minus one is
	* returned, signifying the end of the list.
	*
	* @return the index of the element that would be returned if previous() were called
	* @throws NoSuchElementException if there are no elements in the list
	*/
	@Override
	public int previousIndex() {
	if (list.isEmpty()) {
	throw new NoSuchElementException(
	"There are no elements for this iterator to loop on");
	}
	if (iterator.hasPrevious() == false) {
	return list.size() - 1;
	}
	return iterator.previousIndex();
	}

	/**
	* Removes the previously retrieved item from the underlying list.
	* <p>
	* This feature is only supported if the underlying list's
	* {@link List#iterator iterator} method returns an implementation
	* that supports it.
	* <p>
	* This method can only be called after at least one {@link #next}
	* or {@link #previous} method call. After a removal, the remove
	* method may not be called again until another {@link #next} or
	* {@link #previous} has been performed. If the {@link #reset} is
	* called, then remove may not be called until {@link #next} or
	* {@link #previous} is called again.
	*
	* @throws UnsupportedOperationException if the remove method is
	* not supported by the iterator implementation of the underlying
	* list
	*/
	@Override
	public void remove() {
	iterator.remove();
	}

	/**
	* Inserts the specified element into the underlying list.
	* <p>
	* The element is inserted before the next element that would be
	* returned by {@link #next}, if any, and after the next element
	* that would be returned by {@link #previous}, if any.
	* <p>
	* This feature is only supported if the underlying list's
	* {@link List#listIterator} method returns an implementation
	* that supports it.
	*
	* @param obj the element to insert
	* @throws UnsupportedOperationException if the add method is not
	* supported by the iterator implementation of the underlying list
	*/
	@Override
	public void add(final E obj) {
	iterator.add(obj);
	}

	/**
	* Replaces the last element that was returned by {@link #next} or
	* {@link #previous}.
	* <p>
	* This feature is only supported if the underlying list's
	* {@link List#listIterator} method returns an implementation
	* that supports it.
	*
	* @param obj the element with which to replace the last element returned
	* @throws UnsupportedOperationException if the set method is not
	* supported by the iterator implementation of the underlying list
	*/
	@Override
	public void set(final E obj) {
	iterator.set(obj);
	}

	/**
	* Resets the iterator back to the start of the list.
	*/
	@Override
	public void reset() {
	_reset();
	}

	private void _reset() {
	iterator = list.listIterator();
	}

	/**
	* Gets the size of the list underlying the iterator.
	*
	* @return the current list size
	*/
	public int size() {
	return list.size();
	}

	}

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