/*
    * 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.giraph.utils;
  
  import com.google.common.collect.Iterables;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.concurrent.ConcurrentMap;
  import org.apache.log4j.Logger;
  
  /** Helper methods for Collections */
  public class CollectionUtils {
    /** Class logger */
    private static final Logger LOG = Logger.getLogger(CollectionUtils.class);
  
    /** Do not instantiate. */
    private CollectionUtils() { }
  
    /**
     * If map already has a value associated with the key it adds values to that
     * value, otherwise it will put values to the map.  Do not reuse values.
     *
     * @param key    Key under which we are adding values
     * @param values Values we want to add
     * @param map    Map which we are adding values to
     * @param <K> Key
     * @param <V> Value
     * @param <C> Collection
     * @return New value associated with the key
     */
    public static <K, V, C extends Collection<V>> C addConcurrent(K key,
        C values, ConcurrentMap<K, C> map) {
      C currentValues = map.get(key);
      if (currentValues == null) {
        currentValues = map.putIfAbsent(key, values);
        if (currentValues == null) {
          return values;
        }
      }
      synchronized (currentValues) {
        currentValues.addAll(values);
      }
      return currentValues;
    }
  
    /**
     * Helper method to check if iterables are equal.  Supports the case
     * where the iterable next() returns a reused object.  We do assume that
     * iterator() produces the objects in the same order across repeated calls,
     * if the object doesn't change.   This is very expensive (n^2) and should
     * be used for testing only.
     *
     * @param first First iterable
     * @param second Second iterable
     * @param <T> Type to compare
     * @return True if equal, false otherwise
     */
    public static <T> boolean isEqual(Iterable<T> first, Iterable<T> second) {
      // Relies on elements from the iterator arriving in the same order.
      // For every element in first, check elements on the second iterable by
      // marking the ones seen that have been found.  Then ensure that all
      // the elements of the second have been seen as well.
      int firstSize = Iterables.size(first);
      int secondSize = Iterables.size(second);
      boolean[] usedSecondArray = new boolean[secondSize];
      Iterator<T> firstIterator = first.iterator();
      while (firstIterator.hasNext()) {
        T firstValue = firstIterator.next();
        boolean foundFirstValue = false;
        Iterator<T> secondIterator = second.iterator();
        for (int i = 0; i < usedSecondArray.length; ++i) {
          T secondValue = secondIterator.next();
          if (!usedSecondArray[i]) {
            if (firstValue.equals(secondValue)) {
              usedSecondArray[i] = true;
              foundFirstValue = true;
              break;
            }
          }
        }
  
        if (!foundFirstValue) {
          LOG.error("isEqual: Couldn't find element from first (" + firstValue +
             ") in second " + second + "(size=" + secondSize + ")");
         return false;
       }
     }
 
     Iterator<T> secondIterator = second.iterator();
     for (int i = 0; i < usedSecondArray.length; ++i) {
       T secondValue = secondIterator.next();
       if (!usedSecondArray[i]) {
         LOG.error("isEqual: Element " + secondValue + " (index " + i +
             ") in second " + second + "(size=" + secondSize +
             ") not found in " + first + " (size=" + firstSize + ")");
         return false;
       }
     }
 
     return true;
   }
 }