/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you 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 org.apache.hadoop.hbase.util;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.List;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  
  /**
   * Utility methods for dealing with Collections, including treating null collections as empty.
   */
  @InterfaceAudience.Private
  public class CollectionUtils {
  
    private static final List<Object> EMPTY_LIST = Collections.unmodifiableList(
      new ArrayList<Object>(0));
  
    
    @SuppressWarnings("unchecked")
    public static <T> Collection<T> nullSafe(Collection<T> in) {
      if (in == null) {
        return (Collection<T>)EMPTY_LIST;
      }
      return in;
    }
  
    /************************ size ************************************/
  
    public static <T> int nullSafeSize(Collection<T> collection) {
      if (collection == null) {
        return 0;
      }
      return collection.size();
    }
  
    public static <A, B> boolean nullSafeSameSize(Collection<A> a, Collection<B> b) {
      return nullSafeSize(a) == nullSafeSize(b);
    }
  
    /*************************** empty ****************************************/
  
    public static <T> boolean isEmpty(Collection<T> collection) {
      return collection == null || collection.isEmpty();
    }
  
    public static <T> boolean notEmpty(Collection<T> collection) {
      return !isEmpty(collection);
    }
  
    /************************ first/last **************************/
  
    public static <T> T getFirst(Collection<T> collection) {
      if (CollectionUtils.isEmpty(collection)) {
        return null;
      }
      for (T t : collection) {
        return t;
      }
      return null;
    }
    
    /**
     * @param list any list
     * @return -1 if list is empty, otherwise the max index
     */
    public static int getLastIndex(List<?> list){
      if(isEmpty(list)){
        return -1;
      }
      return list.size() - 1;
    }
    
    /**
     * @param list
     * @param index the index in question
     * @return true if it is the last index or if list is empty and -1 is passed for the index param
     */
    public static boolean isLastIndex(List<?> list, int index){
      return index == getLastIndex(list);
    }
 
   public static <T> T getLast(List<T> list) {
     if (isEmpty(list)) {
       return null;
     }
     return list.get(list.size() - 1);
   }
 }