com.google.eclipse.protobuf.cdt/src/com/google/eclipse/protobuf/cdt/util/ExtendedListIterator.java

/*
 * Copyright (c) 2012 Google Inc.
 *
 * All rights reserved. This program and the accompanying materials are made available under the terms of the Eclipse
 * Public License v1.0 which accompanies this distribution, and is available at
 *
 * http://www.eclipse.org/legal/epl-v10.html
 */
package com.google.eclipse.protobuf.cdt.util;

import static java.util.Collections.emptyList;
import static java.util.Collections.unmodifiableList;

import static com.google.common.collect.Lists.newArrayList;

import java.util.List;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.AbstractIterator;

/**
 * {@code Iterator} for {@code List}s. This implementation keeps track of the index of the current element to be able
 * to:
 * <ul>
 * <li>Retrieve the elements that have not been visited yet</li>
 * <li>Check whether we are visiting the last element of the {@code List}</li>
 * @param <T> the generic type of the iterator.
 *
 * @author alruiz@google.com (Alex Ruiz)
 */
public class ExtendedListIterator<T> extends AbstractIterator<T> implements ExtendedIterator<T> {
  private static final ExtendedIterator<Object> EMPTY = newIterator(emptyList());
  private static final int NOT_STARTED = -1;

  private final List<T> list;

  private int index = NOT_STARTED;

  /**
   * Creates a new <code>{@link ExtendedListIterator}</code>.
   * @param elements the elements of the {@code Iterator} to create.
   * @return the created {@code ListIterator}.
   */
  public static <T> ExtendedIterator<T> newIterator(T...elements) {
    return new ExtendedListIterator<T>(newArrayList(elements));
  }

  /**
   * Creates a new <code>{@link ExtendedListIterator}</code>.
   * @param list the {@code List} to iterate.
   * @return the created {@code ListIterator}.
   * @throws NullPointerException if the given {@code List} is {@code null}.
   */
  public static <T> ExtendedIterator<T> newIterator(List<T> list) {
    if (list == null) {
      throw new NullPointerException("The list to iterate should not be null");
    }
    return new ExtendedListIterator<T>(list);
  }

  @VisibleForTesting ExtendedListIterator(List<T> list) {
    this.list = list;
  }

  /** {@inheritDoc} */
  @SuppressWarnings("unchecked")
  @Override public ExtendedIterator<T> notRetrievedYet() {
    int listSize = list.size();
    if (listSize == 0) {
      return (ExtendedIterator<T>) EMPTY;
    }
    List<T> remaining = list.subList(index + 1, listSize);
    return newIterator(remaining);
  }

  /** {@inheritDoc} */
  @Override public boolean wasLastListElementRetrieved() {
    if (index == NOT_STARTED) {
      return false;
    }
    int listSize = list.size();
    return listSize > 0 && index == listSize - 1;
  }

  /** {@inheritDoc} */
  @Override public ExtendedIterator<T> copy() {
    return new ExtendedListIterator<T>(list);
  }

  @Override protected T computeNext() {
    int listSize = list.size();
    if (index + 1 < listSize && listSize > 0) {
      return list.get(++index);
    }
    return endOfData();
  }

  @Override public String toString() {
    return list.toString();
  }

  @VisibleForTesting List<T> contents() {
    return unmodifiableList(list);
  }
}