/*
 * Copyright (C) 2007 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 com.google.common.annotations.GwtCompatible;
import com.google.common.base.Objects;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Collection;
import java.util.Iterator;
import org.checkerframework.checker.nullness.qual.Nullable;

A collection which forwards all its method calls to another collection. Subclasses should
override one or more methods to modify the behavior of the backing collection as desired per the
decorator pattern.
Warning: The methods of ForwardingCollection forward indiscriminately to the methods of the delegate. For example, overriding add alone will not change the behavior of addAll, which can lead to unexpected behavior. In this case, you should override addAll as well, either providing your own implementation, or delegating to the provided standardAddAll method. 
default method warning: This class does not forward calls to 
default methods. Instead, it inherits their default implementations. When those implementations invoke methods, they invoke methods on the ForwardingCollection. 
The standard methods are not guaranteed to be thread-safe, even when all of the methods that they depend on are thread-safe. 
Author:
Kevin Bourrillion, Louis Wasserman
Since:
2.0/**
 * A collection which forwards all its method calls to another collection. Subclasses should
 * override one or more methods to modify the behavior of the backing collection as desired per the
 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p><b>Warning:</b> The methods of {@code ForwardingCollection} forward <b>indiscriminately</b> to
 * the methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> 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><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
 * default} methods. Instead, it inherits their default implementations. When those implementations
 * invoke methods, they invoke methods on the {@code ForwardingCollection}.
 *
 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even when all of the
 * methods that they depend on are thread-safe.
 *
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
public abstract class ForwardingCollection<E> extends ForwardingObject implements Collection<E> {
  // TODO(lowasser): identify places where thread safety is actually lost

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

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

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

  @Override
  public int size() {
    return delegate().size();
  }

  @CanIgnoreReturnValue
  @Override
  public boolean removeAll(Collection<?> collection) {
    return delegate().removeAll(collection);
  }

  @Override
  public boolean isEmpty() {
    return delegate().isEmpty();
  }

  @Override
  public boolean contains(Object object) {
    return delegate().contains(object);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean add(E element) {
    return delegate().add(element);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean remove(Object object) {
    return delegate().remove(object);
  }

  @Override
  public boolean containsAll(Collection<?> collection) {
    return delegate().containsAll(collection);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean addAll(Collection<? extends E> collection) {
    return delegate().addAll(collection);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean retainAll(Collection<?> collection) {
    return delegate().retainAll(collection);
  }

  @Override
  public void clear() {
    delegate().clear();
  }

  @Override
  public Object[] toArray() {
    return delegate().toArray();
  }

  @CanIgnoreReturnValue
  @Override
  public <T> T[] toArray(T[] array) {
    return delegate().toArray(array);
  }

  
A sensible definition of contains in terms of iterator. If you override iterator, you may wish to override contains to forward to this implementation. 
Since:
7.0/**
   * A sensible definition of {@link #contains} in terms of {@link #iterator}. If you override
   * {@link #iterator}, you may wish to override {@link #contains} to forward to this
   * implementation.
   *
   * @since 7.0
   */
  protected boolean standardContains(@Nullable Object object) {
    return Iterators.contains(iterator(), object);
  }

  
A sensible definition of containsAll in terms of contains . If you override contains, you may wish to override containsAll to forward to this implementation. 
Since:
7.0/**
   * A sensible definition of {@link #containsAll} in terms of {@link #contains} . If you override
   * {@link #contains}, you may wish to override {@link #containsAll} to forward to this
   * implementation.
   *
   * @since 7.0
   */
  protected boolean standardContainsAll(Collection<?> collection) {
    return Collections2.containsAllImpl(this, collection);
  }

  
A sensible definition of addAll in terms of add. If you override add, you may wish to override addAll to forward to this implementation. 
Since:
7.0/**
   * A sensible definition of {@link #addAll} in terms of {@link #add}. If you override {@link
   * #add}, you may wish to override {@link #addAll} to forward to this implementation.
   *
   * @since 7.0
   */
  protected boolean standardAddAll(Collection<? extends E> collection) {
    return Iterators.addAll(this, collection.iterator());
  }

  
A sensible definition of remove in terms of iterator, using the iterator's remove method. If you override iterator, you may wish to override remove to forward to this implementation. 
Since:
7.0/**
   * A sensible definition of {@link #remove} in terms of {@link #iterator}, using the iterator's
   * {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
   * #remove} to forward to this implementation.
   *
   * @since 7.0
   */
  protected boolean standardRemove(@Nullable Object object) {
    Iterator<E> iterator = iterator();
    while (iterator.hasNext()) {
      if (Objects.equal(iterator.next(), object)) {
        iterator.remove();
        return true;
      }
    }
    return false;
  }

  
A sensible definition of removeAll in terms of iterator, using the iterator's remove method. If you override iterator, you may wish to override removeAll to forward to this implementation. 
Since:
7.0/**
   * A sensible definition of {@link #removeAll} in terms of {@link #iterator}, using the iterator's
   * {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
   * #removeAll} to forward to this implementation.
   *
   * @since 7.0
   */
  protected boolean standardRemoveAll(Collection<?> collection) {
    return Iterators.removeAll(iterator(), collection);
  }

  
A sensible definition of retainAll in terms of iterator, using the iterator's remove method. If you override iterator, you may wish to override retainAll to forward to this implementation. 
Since:
7.0/**
   * A sensible definition of {@link #retainAll} in terms of {@link #iterator}, using the iterator's
   * {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
   * #retainAll} to forward to this implementation.
   *
   * @since 7.0
   */
  protected boolean standardRetainAll(Collection<?> collection) {
    return Iterators.retainAll(iterator(), collection);
  }

  
A sensible definition of clear in terms of iterator, using the iterator's remove method. If you override iterator, you may wish to override clear to forward to this implementation. 
Since:
7.0/**
   * A sensible definition of {@link #clear} in terms of {@link #iterator}, using the iterator's
   * {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
   * #clear} to forward to this implementation.
   *
   * @since 7.0
   */
  protected void standardClear() {
    Iterators.clear(iterator());
  }

  
A sensible definition of isEmpty as !iterator().hasNext. If you override isEmpty, you may wish to override isEmpty to forward to this implementation. Alternately, it may be more efficient to implement isEmpty as size() == 0. 
Since:
7.0/**
   * A sensible definition of {@link #isEmpty} as {@code !iterator().hasNext}. If you override
   * {@link #isEmpty}, you may wish to override {@link #isEmpty} to forward to this implementation.
   * Alternately, it may be more efficient to implement {@code isEmpty} as {@code size() == 0}.
   *
   * @since 7.0
   */
  protected boolean standardIsEmpty() {
    return !iterator().hasNext();
  }

  
A sensible definition of ForwardingObject.toString in terms of iterator. If you override iterator, you may wish to override ForwardingObject.toString to forward to this implementation. 
Since:
7.0/**
   * A sensible definition of {@link #toString} in terms of {@link #iterator}. If you override
   * {@link #iterator}, you may wish to override {@link #toString} to forward to this
   * implementation.
   *
   * @since 7.0
   */
  protected String standardToString() {
    return Collections2.toStringImpl(this);
  }

  
A sensible definition of toArray() in terms of toArray(Object[]). If you override toArray(Object[]), you may wish to override toArray to forward to this implementation. 
Since:
7.0/**
   * A sensible definition of {@link #toArray()} in terms of {@link #toArray(Object[])}. If you
   * override {@link #toArray(Object[])}, you may wish to override {@link #toArray} to forward to
   * this implementation.
   *
   * @since 7.0
   */
  protected Object[] standardToArray() {
    Object[] newArray = new Object[size()];
    return toArray(newArray);
  }

  
A sensible definition of toArray(Object[]) in terms of size and iterator. If you override either of these methods, you may wish to override toArray to forward to this implementation. 
Since:
7.0/**
   * A sensible definition of {@link #toArray(Object[])} in terms of {@link #size} and {@link
   * #iterator}. If you override either of these methods, you may wish to override {@link #toArray}
   * to forward to this implementation.
   *
   * @since 7.0
   */
  protected <T> T[] standardToArray(T[] array) {
    return ObjectArrays.toArrayImpl(this, array);
  }
}