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.util;
  
  import com.google.common.collect.ImmutableMap;
  import com.google.common.collect.ImmutableSortedMap;
  
  import java.util.AbstractMap;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.HashMap;
  import java.util.Map;
  import java.util.SortedMap;
  import java.util.TreeMap;
  
  /**
   * An immutable map that may contain null values.
   *
   * <p>If the map cannot contain null values, use {@link ImmutableMap}.
   *
   * @param <K> Key type
   * @param <V> Value type
   */
  public abstract class ImmutableNullableMap<K, V> extends AbstractMap<K, V> {
  
    private static final Map<Integer, Integer> SINGLETON_MAP =
        Collections.singletonMap(0, 0);
  
    private ImmutableNullableMap() {
    }
  
    /**
     * Returns an immutable map containing the given elements.
     *
     * <p>Behavior is as {@link ImmutableMap#copyOf(Iterable)}
     * except that this map allows nulls.
     */
    @SuppressWarnings({"JdkObsolete", "unchecked", "rawtypes"})
    public static <K, V> Map<K, V> copyOf(Map<? extends K, ? extends V> map) {
      if (map instanceof ImmutableNullableMap
          || map instanceof ImmutableMap
          || map == Collections.emptyMap()
          || map == Collections.emptyNavigableMap()
          || map.getClass() == SINGLETON_MAP.getClass()) {
        return (Map<K, V>) map;
      }
      if (map instanceof SortedMap) {
        final SortedMap<K, V> sortedMap = (SortedMap) map;
        try {
          Comparator<? super K> comparator = sortedMap.comparator();
          if (comparator == null) {
            return ImmutableSortedMap.copyOf(sortedMap);
          } else {
            return ImmutableSortedMap.copyOf(sortedMap, comparator);
          }
        } catch (NullPointerException e) {
          // Make an effectively immutable map by creating a mutable copy
          // and wrapping it to prevent modification. Unfortunately, if we see
          // it again we will not recognize that it is immutable and we will make
          // another copy.
          return Collections.unmodifiableNavigableMap(new TreeMap<>(sortedMap));
        }
      } else {
        try {
          return ImmutableMap.copyOf(map);
        } catch (NullPointerException e) {
          // Make an effectively immutable map by creating a mutable copy
          // and wrapping it to prevent modification. Unfortunately, if we see
          // it again we will not recognize that it is immutable and we will make
          // another copy.
          return Collections.unmodifiableMap(new HashMap<>(map));
        }
      }
    }
  
    /**
     * Returns an immutable navigable map containing the given entries.
     *
     * <p>Behavior is as {@link ImmutableSortedMap#copyOf(Map)}
     * except that this map allows nulls.
     */
    @SuppressWarnings({"JdkObsolete", "unchecked", "rawtypes"})
    public static <K, V> Map<K, V> copyOf(
        SortedMap<? extends K, ? extends V> map) {
      if (map instanceof ImmutableNullableMap
          || map instanceof ImmutableMap
          || map == Collections.emptyMap()
          || map == Collections.emptyNavigableMap()) {
        return (Map<K, V>) map;
      }
      final SortedMap<K, V> sortedMap = (SortedMap) map;
      try {
        Comparator<? super K> comparator = sortedMap.comparator();
        if (comparator == null) {
          return ImmutableSortedMap.copyOf(sortedMap);
        } else {
          return ImmutableSortedMap.copyOf(sortedMap, comparator);
        }
      } catch (NullPointerException e) {
        // Make an effectively immutable map by creating a mutable copy
        // and wrapping it to prevent modification. Unfortunately, if we see
        // it again we will not recognize that it is immutable and we will make
        // another copy.
        return Collections.unmodifiableNavigableMap(new TreeMap<>(sortedMap));
      }
    }
  }
  