content: /*
   * 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.calcite.runtime;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.List;
  
  /**
   * Map that allows you to partition values into lists according to a common
   * key, and then convert those lists into an iterator of sorted arrays.
   *
   * @param <K> Key type
   * @param <V> Value type
   */
  public class SortedMultiMap<K, V> extends HashMap<K, List<V>> {
    public void putMulti(K key, V value) {
      List<V> list = put(key, Collections.singletonList(value));
      if (list == null) {
        return;
      }
      if (list.size() == 1) {
        list = new ArrayList<>(list);
      }
      list.add(value);
      put(key, list);
    }
  
    public Iterator<V[]> arrays(final Comparator<V> comparator) {
      final Iterator<List<V>> iterator = values().iterator();
      return new Iterator<V[]>() {
        @Override public boolean hasNext() {
          return iterator.hasNext();
        }
  
        @Override public V[] next() {
          List<V> list = iterator.next();
          @SuppressWarnings("unchecked")
          final V[] vs = (V[]) list.toArray();
          Arrays.sort(vs, comparator);
          return vs;
        }
  
        @Override public void remove() {
          throw new UnsupportedOperationException();
        }
      };
    }
  
    /** Shortcut method if the partition key is empty. We know that we would end
     * up with a map with just one entry, so save ourselves the trouble of all
     * that hashing. */
    public static <V> Iterator<V[]> singletonArrayIterator(
        Comparator<V> comparator, List<V> list) {
      final SortedMultiMap<Object, V> multiMap =
          new SortedMultiMap<>();
      multiMap.put("x", list);
      return multiMap.arrays(comparator);
    }
  }
  