/*
    * 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.checkNotNull;
  
  import com.google.common.annotations.GwtCompatible;
  import com.google.common.base.Preconditions;
  
  import java.util.List;
  
  import javax.annotation.Nullable;
  
  /**
   * Implementation of {@link ImmutableList} with exactly one element.
   *
   * @author Hayward Chan
   */
  @GwtCompatible(serializable = true, emulated = true)
  @SuppressWarnings("serial") // uses writeReplace(), not default serialization
  final class SingletonImmutableList<E> extends ImmutableList<E> {
  
    final transient E element;
  
    SingletonImmutableList(E element) {
      this.element = checkNotNull(element);
    }
  
    @Override
    public E get(int index) {
      Preconditions.checkElementIndex(index, 1);
      return element;
    }
  
    @Override public int indexOf(@Nullable Object object) {
      return element.equals(object) ? 0 : -1;
    }
  
    @Override public UnmodifiableIterator<E> iterator() {
      return Iterators.singletonIterator(element);
    }
  
    @Override public int lastIndexOf(@Nullable Object object) {
      return indexOf(object);
    }
  
    @Override
    public int size() {
      return 1;
    }
  
    @Override public ImmutableList<E> subList(int fromIndex, int toIndex) {
      Preconditions.checkPositionIndexes(fromIndex, toIndex, 1);
      return (fromIndex == toIndex) ? ImmutableList.<E>of() : this;
    }
  
    @Override public ImmutableList<E> reverse() {
      return this;
    }
  
    @Override public boolean contains(@Nullable Object object) {
      return element.equals(object);
    }
  
    @Override public boolean equals(@Nullable Object object) {
      if (object == this) {
        return true;
      }
      if (object instanceof List) {
        List<?> that = (List<?>) object;
        return that.size() == 1 && element.equals(that.get(0));
      }
      return false;
    }
  
    @Override public int hashCode() {
      // not caching hash code since it could change if the element is mutable
      // in a way that modifies its hash code.
      return 31 + element.hashCode();
    }
  
    @Override public String toString() {
      String elementToString = element.toString();
      return new StringBuilder(elementToString.length() + 2)
          .append('[')
         .append(elementToString)
         .append(']')
         .toString();
   }
 
   @Override public boolean isEmpty() {
     return false;
   }
 
   @Override boolean isPartialView() {
     return false;
   }
 
   @Override
   int copyIntoArray(Object[] dst, int offset) {
     dst[offset] = element;
     return offset + 1;
   }
 }