/*
 * Copyright (C) 2009 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 static com.google.common.base.Preconditions.checkPositionIndex;

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

import com.google.common.annotations.GwtCompatible;

/**
 * This class provides a skeletal implementation of the {@link ListIterator}
 * interface across a fixed number of elements that may be retrieved by
 * position. It does not support {@link #remove}, {@link #set}, or {@link #add}.
 *
 * @author Jared Levy
 */
@GwtCompatible
abstract class AbstractIndexedListIterator<E> extends UnmodifiableListIterator<E> {
	private final int size;
	private int position;

	/**
	 * Returns the element with the specified index. This method is called by
	 * {@link #next()}.
	 */
	protected abstract E get(int index);

	/**
	 * Constructs an iterator across a sequence of the given size whose initial
	 * position is 0. That is, the first call to {@link #next()} will return the
	 * first element (or throw {@link NoSuchElementException} if {@code size} is
	 * zero).
	 *
	 * @throws IllegalArgumentException if {@code size} is negative
	 */
	protected AbstractIndexedListIterator(int size) {
		this(size, 0);
	}

	/**
	 * Constructs an iterator across a sequence of the given size with the given
	 * initial position. That is, the first call to {@link #nextIndex()} will return
	 * {@code position}, and the first call to {@link #next()} will return the
	 * element at that index, if available. Calls to {@link #previous()} can
	 * retrieve the preceding {@code position} elements.
	 *
	 * @throws IndexOutOfBoundsException if {@code position} is negative or is
	 *                                   greater than {@code size}
	 * @throws IllegalArgumentException  if {@code size} is negative
	 */
	protected AbstractIndexedListIterator(int size, int position) {
		checkPositionIndex(position, size);
		this.size = size;
		this.position = position;
	}

	@Override
	public final boolean hasNext() {
		return position < size;
	}

	@Override
	public final E next() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		return get(position++);
	}

	@Override
	public final int nextIndex() {
		return position;
	}

	@Override
	public final boolean hasPrevious() {
		return position > 0;
	}

	@Override
	public final E previous() {
		if (!hasPrevious()) {
			throw new NoSuchElementException();
		}
		return get(--position);
	}

	@Override
	public final int previousIndex() {
		return position - 1;
	}
}
