/*
 * 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 com.google.common.annotations.GwtCompatible;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * 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
@ElementTypesAreNonnullByDefault
abstract class AbstractIndexedListIterator<E extends @Nullable Object>
    extends UnmodifiableListIterator<E> {
  private final int size;
  private int position;

  /** Returns the element with the specified index. This method is called by {@link #next()}. */
  @ParametricNullness
  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
  @ParametricNullness
  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
  @ParametricNullness
  public final E previous() {
    if (!hasPrevious()) {
      throw new NoSuchElementException();
    }
    return get(--position);
  }

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