/*
    * Copyright (C) 2008 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.testing.testers;
  
  import static com.google.common.collect.testing.features.MapFeature.ALLOWS_NULL_KEYS;
  import static com.google.common.collect.testing.features.MapFeature.ALLOWS_NULL_VALUES;
  
  import com.google.common.annotations.GwtCompatible;
  import com.google.common.collect.testing.AbstractMapTester;
  import com.google.common.collect.testing.features.CollectionSize;
  import com.google.common.collect.testing.features.MapFeature;
  
  import java.util.Collection;
  import java.util.Map;
  
  /**
   * Tests {@link java.util.Map#hashCode}.
   *
   * @author George van den Driessche
   * @author Chris Povirk
   */
  @GwtCompatible
  public class MapHashCodeTester<K, V> extends AbstractMapTester<K, V> {
    public void testHashCode() {
      int expectedHashCode = 0;
      for (Map.Entry<K, V> entry : getSampleEntries()) {
        expectedHashCode += hash(entry);
      }
      assertEquals(
          "A Map's hashCode() should be the sum of those of its entries.",
          expectedHashCode, getMap().hashCode());
    }
  
    @CollectionSize.Require(absent = CollectionSize.ZERO)
    @MapFeature.Require(ALLOWS_NULL_KEYS)
    public void testHashCode_containingNullKey() {
      Map.Entry<K, V> entryWithNull = entry(null, samples.e3.getValue());
      runEntryWithNullTest(entryWithNull);
    }
  
    @CollectionSize.Require(absent = CollectionSize.ZERO)
    @MapFeature.Require(ALLOWS_NULL_VALUES)
    public void testHashCode_containingNullValue() {
      Map.Entry<K, V> entryWithNull = entry(samples.e3.getKey(), null);
      runEntryWithNullTest(entryWithNull);
    }
  
    private void runEntryWithNullTest(Map.Entry<K, V> entryWithNull) {
      Collection<Map.Entry<K, V>> entries = getSampleEntries(getNumEntries() - 1);
  
      entries.add(entryWithNull);
  
      int expectedHashCode = 0;
      for (Map.Entry<K, V> entry : entries) {
        expectedHashCode += hash(entry);
      }
  
      resetContainer(getSubjectGenerator().create(entries.toArray()));
      assertEquals(
          "A Map's hashCode() should be the sum of those of its entries (where "
              + "a null element in an entry counts as having a hash of zero).",
          expectedHashCode, getMap().hashCode());
    }
  
    private static int hash(Map.Entry<?, ?> e) {
      return (e.getKey() == null ? 0 : e.getKey().hashCode())
          ^ (e.getValue() == null ? 0 : e.getValue().hashCode());
    }
  }