/*
 * 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;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.truth.Truth.assertThat;
import static java.util.Arrays.asList;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.collect.testing.ListTestSuiteBuilder;
import com.google.common.collect.testing.MinimalCollection;
import com.google.common.collect.testing.SetTestSuiteBuilder;
import com.google.common.collect.testing.TestStringListGenerator;
import com.google.common.collect.testing.TestStringSetGenerator;
import com.google.common.collect.testing.features.CollectionFeature;
import com.google.common.collect.testing.features.CollectionSize;
import com.google.common.collect.testing.google.MultisetTestSuiteBuilder;
import com.google.common.collect.testing.google.TestStringMultisetGenerator;
import com.google.common.collect.testing.google.UnmodifiableCollectionTests;
import com.google.common.testing.CollectorTester;
import com.google.common.testing.EqualsTester;
import com.google.common.testing.NullPointerTester;
import com.google.common.testing.SerializableTester;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.function.BiPredicate;
import java.util.stream.Collector;
import junit.framework.Test;
import junit.framework.TestCase;
import junit.framework.TestSuite;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tests for {@link ImmutableMultiset}.
 *
 * @author Jared Levy
 */
@GwtCompatible(emulated = true)
public class ImmutableMultisetTest extends TestCase {

  @GwtIncompatible // suite // TODO(cpovirk): add to collect/gwt/suites
  public static Test suite() {
    TestSuite suite = new TestSuite();
    suite.addTestSuite(ImmutableMultisetTest.class);

    suite.addTest(
        MultisetTestSuiteBuilder.using(
                new TestStringMultisetGenerator() {
                  @Override
                  protected Multiset<String> create(String[] elements) {
                    return ImmutableMultiset.copyOf(elements);
                  }
                })
            .named("ImmutableMultiset")
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.SERIALIZABLE_INCLUDING_VIEWS,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .createTestSuite());

    suite.addTest(
        MultisetTestSuiteBuilder.using(
                new TestStringMultisetGenerator() {
                  @Override
                  protected Multiset<String> create(String[] elements) {
                    return ImmutableMultiset.<String>builder().add(elements).buildJdkBacked();
                  }
                })
            .named("ImmutableMultiset [JDK backed]")
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.SERIALIZABLE_INCLUDING_VIEWS,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .createTestSuite());

    suite.addTest(
        SetTestSuiteBuilder.using(
                new TestStringSetGenerator() {
                  @Override
                  protected Set<String> create(String[] elements) {
                    return ImmutableMultiset.copyOf(elements).elementSet();
                  }
                })
            .named("ImmutableMultiset, element set")
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.SERIALIZABLE,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .createTestSuite());

    suite.addTest(
        ListTestSuiteBuilder.using(
                new TestStringListGenerator() {
                  @Override
                  protected List<String> create(String[] elements) {
                    return ImmutableMultiset.copyOf(elements).asList();
                  }

                  @Override
                  public List<String> order(List<String> insertionOrder) {
                    List<String> order = new ArrayList<>();
                    for (String s : insertionOrder) {
                      int index = order.indexOf(s);
                      if (index == -1) {
                        order.add(s);
                      } else {
                        order.add(index, s);
                      }
                    }
                    return order;
                  }
                })
            .named("ImmutableMultiset.asList")
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.SERIALIZABLE,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .createTestSuite());

    suite.addTest(
        ListTestSuiteBuilder.using(
                new TestStringListGenerator() {
                  @Override
                  protected List<String> create(String[] elements) {
                    Set<String> set = new HashSet<>();
                    ImmutableMultiset.Builder<String> builder = ImmutableMultiset.builder();
                    for (String s : elements) {
                      checkArgument(set.add(s));
                      builder.addCopies(s, 2);
                    }
                    ImmutableSet<String> elementSet =
                        (ImmutableSet<String>) builder.build().elementSet();
                    return elementSet.asList();
                  }
                })
            .named("ImmutableMultiset.elementSet.asList")
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.REJECTS_DUPLICATES_AT_CREATION,
                CollectionFeature.SERIALIZABLE,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .createTestSuite());

    return suite;
  }

  public void testCreation_noArgs() {
    Multiset<String> multiset = ImmutableMultiset.of();
    assertTrue(multiset.isEmpty());
  }

  public void testCreation_oneElement() {
    Multiset<String> multiset = ImmutableMultiset.of("a");
    assertEquals(HashMultiset.create(asList("a")), multiset);
  }

  public void testCreation_twoElements() {
    Multiset<String> multiset = ImmutableMultiset.of("a", "b");
    assertEquals(HashMultiset.create(asList("a", "b")), multiset);
  }

  public void testCreation_threeElements() {
    Multiset<String> multiset = ImmutableMultiset.of("a", "b", "c");
    assertEquals(HashMultiset.create(asList("a", "b", "c")), multiset);
  }

  public void testCreation_fourElements() {
    Multiset<String> multiset = ImmutableMultiset.of("a", "b", "c", "d");
    assertEquals(HashMultiset.create(asList("a", "b", "c", "d")), multiset);
  }

  public void testCreation_fiveElements() {
    Multiset<String> multiset = ImmutableMultiset.of("a", "b", "c", "d", "e");
    assertEquals(HashMultiset.create(asList("a", "b", "c", "d", "e")), multiset);
  }

  public void testCreation_sixElements() {
    Multiset<String> multiset = ImmutableMultiset.of("a", "b", "c", "d", "e", "f");
    assertEquals(HashMultiset.create(asList("a", "b", "c", "d", "e", "f")), multiset);
  }

  public void testCreation_sevenElements() {
    Multiset<String> multiset = ImmutableMultiset.of("a", "b", "c", "d", "e", "f", "g");
    assertEquals(HashMultiset.create(asList("a", "b", "c", "d", "e", "f", "g")), multiset);
  }

  public void testCreation_emptyArray() {
    String[] array = new String[0];
    Multiset<String> multiset = ImmutableMultiset.copyOf(array);
    assertTrue(multiset.isEmpty());
  }

  public void testCreation_arrayOfOneElement() {
    String[] array = new String[] {"a"};
    Multiset<String> multiset = ImmutableMultiset.copyOf(array);
    assertEquals(HashMultiset.create(asList("a")), multiset);
  }

  public void testCreation_arrayOfArray() {
    String[] array = new String[] {"a"};
    Multiset<String[]> multiset = ImmutableMultiset.<String[]>of(array);
    Multiset<String[]> expected = HashMultiset.create();
    expected.add(array);
    assertEquals(expected, multiset);
  }

  public void testCreation_arrayContainingOnlyNull() {
    String[] array = new String[] {null};
    try {
      ImmutableMultiset.copyOf(array);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  public void testCopyOf_collection_empty() {
    // "<String>" is required to work around a javac 1.5 bug.
    Collection<String> c = MinimalCollection.<String>of();
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertTrue(multiset.isEmpty());
  }

  public void testCopyOf_collection_oneElement() {
    Collection<String> c = MinimalCollection.of("a");
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertEquals(HashMultiset.create(asList("a")), multiset);
  }

  public void testCopyOf_collection_general() {
    Collection<String> c = MinimalCollection.of("a", "b", "a");
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertEquals(HashMultiset.create(asList("a", "b", "a")), multiset);
  }

  public void testCopyOf_collectionContainingNull() {
    Collection<String> c = MinimalCollection.of("a", null, "b");
    try {
      ImmutableMultiset.copyOf(c);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  public void testCopyOf_multiset_empty() {
    Multiset<String> c = HashMultiset.create();
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertTrue(multiset.isEmpty());
  }

  public void testCopyOf_multiset_oneElement() {
    Multiset<String> c = HashMultiset.create(asList("a"));
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertEquals(HashMultiset.create(asList("a")), multiset);
  }

  public void testCopyOf_multiset_general() {
    Multiset<String> c = HashMultiset.create(asList("a", "b", "a"));
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertEquals(HashMultiset.create(asList("a", "b", "a")), multiset);
  }

  public void testCopyOf_multisetContainingNull() {
    Multiset<String> c = HashMultiset.create(asList("a", null, "b"));
    try {
      ImmutableMultiset.copyOf(c);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  public void testCopyOf_iterator_empty() {
    Iterator<String> iterator = Iterators.emptyIterator();
    Multiset<String> multiset = ImmutableMultiset.copyOf(iterator);
    assertTrue(multiset.isEmpty());
  }

  public void testCopyOf_iterator_oneElement() {
    Iterator<String> iterator = Iterators.singletonIterator("a");
    Multiset<String> multiset = ImmutableMultiset.copyOf(iterator);
    assertEquals(HashMultiset.create(asList("a")), multiset);
  }

  public void testCopyOf_iterator_general() {
    Iterator<String> iterator = asList("a", "b", "a").iterator();
    Multiset<String> multiset = ImmutableMultiset.copyOf(iterator);
    assertEquals(HashMultiset.create(asList("a", "b", "a")), multiset);
  }

  public void testCopyOf_iteratorContainingNull() {
    Iterator<String> iterator = asList("a", null, "b").iterator();
    try {
      ImmutableMultiset.copyOf(iterator);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  public void testToImmutableMultiset() {
    BiPredicate<ImmutableMultiset<String>, ImmutableMultiset<String>> equivalence =
        (ms1, ms2) -> ms1.equals(ms2) && ms1.entrySet().asList().equals(ms2.entrySet().asList());
    CollectorTester.of(ImmutableMultiset.<String>toImmutableMultiset(), equivalence)
        .expectCollects(ImmutableMultiset.of())
        .expectCollects(
            ImmutableMultiset.of("a", "a", "b", "c", "c", "c"), "a", "a", "b", "c", "c", "c");
  }

  public void testToImmutableMultisetCountFunction() {
    BiPredicate<ImmutableMultiset<String>, ImmutableMultiset<String>> equivalence =
        (ms1, ms2) -> ms1.equals(ms2) && ms1.entrySet().asList().equals(ms2.entrySet().asList());
    CollectorTester.of(
            ImmutableMultiset.<Multiset.Entry<String>, String>toImmutableMultiset(
                Multiset.Entry::getElement, Multiset.Entry::getCount),
            equivalence)
        .expectCollects(ImmutableMultiset.of())
        .expectCollects(
            ImmutableMultiset.of("a", "a", "b", "c", "c", "c"),
            Multisets.immutableEntry("a", 1),
            Multisets.immutableEntry("b", 1),
            Multisets.immutableEntry("a", 1),
            Multisets.immutableEntry("c", 3));
  }

  public void testToImmutableMultiset_duplicates() {
    class TypeWithDuplicates {
      final int a;
      final int b;

      TypeWithDuplicates(int a, int b) {
        this.a = a;
        this.b = b;
      }

      @Override
      public int hashCode() {
        return a;
      }

      @Override
      public boolean equals(Object obj) {
        return obj instanceof TypeWithDuplicates && ((TypeWithDuplicates) obj).a == a;
      }

      public boolean fullEquals(TypeWithDuplicates other) {
        return other != null && a == other.a && b == other.b;
      }
    }

    Collector<TypeWithDuplicates, ?, ImmutableMultiset<TypeWithDuplicates>> collector =
        ImmutableMultiset.toImmutableMultiset();
    BiPredicate<ImmutableMultiset<TypeWithDuplicates>, ImmutableMultiset<TypeWithDuplicates>>
        equivalence =
            (ms1, ms2) -> {
              if (!ms1.equals(ms2)) {
                return false;
              }
              List<TypeWithDuplicates> elements1 = ImmutableList.copyOf(ms1.elementSet());
              List<TypeWithDuplicates> elements2 = ImmutableList.copyOf(ms2.elementSet());
              for (int i = 0; i < ms1.elementSet().size(); i++) {
                if (!elements1.get(i).fullEquals(elements2.get(i))) {
                  return false;
                }
              }
              return true;
            };
    TypeWithDuplicates a = new TypeWithDuplicates(1, 1);
    TypeWithDuplicates b1 = new TypeWithDuplicates(2, 1);
    TypeWithDuplicates b2 = new TypeWithDuplicates(2, 2);
    TypeWithDuplicates c = new TypeWithDuplicates(3, 1);
    CollectorTester.of(collector, equivalence)
        .expectCollects(
            ImmutableMultiset.<TypeWithDuplicates>builder().add(a).addCopies(b1, 2).add(c).build(),
            a,
            b1,
            c,
            b2);
    collector = ImmutableMultiset.toImmutableMultiset(e -> e, e -> 1);
    CollectorTester.of(collector, equivalence)
        .expectCollects(
            ImmutableMultiset.<TypeWithDuplicates>builder().add(a).addCopies(b1, 2).add(c).build(),
            a,
            b1,
            c,
            b2);
  }

  private static class CountingIterable implements Iterable<String> {
    int count = 0;

    @Override
    public Iterator<String> iterator() {
      count++;
      return asList("a", "b", "a").iterator();
    }
  }

  public void testCopyOf_plainIterable() {
    CountingIterable iterable = new CountingIterable();
    Multiset<String> multiset = ImmutableMultiset.copyOf(iterable);
    assertEquals(HashMultiset.create(asList("a", "b", "a")), multiset);
    assertEquals(1, iterable.count);
  }

  public void testCopyOf_hashMultiset() {
    Multiset<String> iterable = HashMultiset.create(asList("a", "b", "a"));
    Multiset<String> multiset = ImmutableMultiset.copyOf(iterable);
    assertEquals(HashMultiset.create(asList("a", "b", "a")), multiset);
  }

  public void testCopyOf_treeMultiset() {
    Multiset<String> iterable = TreeMultiset.create(asList("a", "b", "a"));
    Multiset<String> multiset = ImmutableMultiset.copyOf(iterable);
    assertEquals(HashMultiset.create(asList("a", "b", "a")), multiset);
  }

  public void testCopyOf_shortcut_empty() {
    Collection<String> c = ImmutableMultiset.of();
    assertSame(c, ImmutableMultiset.copyOf(c));
  }

  public void testCopyOf_shortcut_singleton() {
    Collection<String> c = ImmutableMultiset.of("a");
    assertSame(c, ImmutableMultiset.copyOf(c));
  }

  public void testCopyOf_shortcut_immutableMultiset() {
    Collection<String> c = ImmutableMultiset.of("a", "b", "c");
    assertSame(c, ImmutableMultiset.copyOf(c));
  }

  public void testBuilderAdd() {
    ImmutableMultiset<String> multiset =
        new ImmutableMultiset.Builder<String>().add("a").add("b").add("a").add("c").build();
    assertEquals(HashMultiset.create(asList("a", "b", "a", "c")), multiset);
  }

  public void testBuilderAddAll() {
    List<String> a = asList("a", "b");
    List<String> b = asList("c", "d");
    ImmutableMultiset<String> multiset =
        new ImmutableMultiset.Builder<String>().addAll(a).addAll(b).build();
    assertEquals(HashMultiset.create(asList("a", "b", "c", "d")), multiset);
  }

  public void testBuilderAddAllHashMultiset() {
    Multiset<String> a = HashMultiset.create(asList("a", "b", "b"));
    Multiset<String> b = HashMultiset.create(asList("c", "b"));
    ImmutableMultiset<String> multiset =
        new ImmutableMultiset.Builder<String>().addAll(a).addAll(b).build();
    assertEquals(HashMultiset.create(asList("a", "b", "b", "b", "c")), multiset);
  }

  public void testBuilderAddAllImmutableMultiset() {
    Multiset<String> a = ImmutableMultiset.of("a", "b", "b");
    Multiset<String> b = ImmutableMultiset.of("c", "b");
    ImmutableMultiset<String> multiset =
        new ImmutableMultiset.Builder<String>().addAll(a).addAll(b).build();
    assertEquals(HashMultiset.create(asList("a", "b", "b", "b", "c")), multiset);
  }

  public void testBuilderAddAllTreeMultiset() {
    Multiset<String> a = TreeMultiset.create(asList("a", "b", "b"));
    Multiset<String> b = TreeMultiset.create(asList("c", "b"));
    ImmutableMultiset<String> multiset =
        new ImmutableMultiset.Builder<String>().addAll(a).addAll(b).build();
    assertEquals(HashMultiset.create(asList("a", "b", "b", "b", "c")), multiset);
  }

  public void testBuilderAddAllIterator() {
    Iterator<String> iterator = asList("a", "b", "a", "c").iterator();
    ImmutableMultiset<String> multiset =
        new ImmutableMultiset.Builder<String>().addAll(iterator).build();
    assertEquals(HashMultiset.create(asList("a", "b", "a", "c")), multiset);
  }

  public void testBuilderAddCopies() {
    ImmutableMultiset<String> multiset =
        new ImmutableMultiset.Builder<String>()
            .addCopies("a", 2)
            .addCopies("b", 3)
            .addCopies("c", 0)
            .build();
    assertEquals(HashMultiset.create(asList("a", "a", "b", "b", "b")), multiset);
  }

  public void testBuilderSetCount() {
    ImmutableMultiset<String> multiset =
        new ImmutableMultiset.Builder<String>().add("a").setCount("a", 2).setCount("b", 3).build();
    assertEquals(HashMultiset.create(asList("a", "a", "b", "b", "b")), multiset);
  }

  public void testBuilderAddHandlesNullsCorrectly() {
    ImmutableMultiset.Builder<String> builder = ImmutableMultiset.builder();
    try {
      builder.add((String) null);
      fail("expected NullPointerException");
    } catch (NullPointerException expected) {
    }
  }

  public void testBuilderAddAllHandlesNullsCorrectly() {
    ImmutableMultiset.Builder<String> builder = ImmutableMultiset.builder();
    try {
      builder.addAll((Collection<String>) null);
      fail("expected NullPointerException");
    } catch (NullPointerException expected) {
    }

    builder = ImmutableMultiset.builder();
    List<String> listWithNulls = asList("a", null, "b");
    try {
      builder.addAll(listWithNulls);
      fail("expected NullPointerException");
    } catch (NullPointerException expected) {
    }

    builder = ImmutableMultiset.builder();
    Multiset<String> multisetWithNull = LinkedHashMultiset.create(asList("a", null, "b"));
    try {
      builder.addAll(multisetWithNull);
      fail("expected NullPointerException");
    } catch (NullPointerException expected) {
    }
  }

  public void testBuilderAddCopiesHandlesNullsCorrectly() {
    ImmutableMultiset.Builder<String> builder = ImmutableMultiset.builder();
    try {
      builder.addCopies(null, 2);
      fail("expected NullPointerException");
    } catch (NullPointerException expected) {
    }
  }

  public void testBuilderAddCopiesIllegal() {
    ImmutableMultiset.Builder<String> builder = ImmutableMultiset.builder();
    try {
      builder.addCopies("a", -2);
      fail("expected IllegalArgumentException");
    } catch (IllegalArgumentException expected) {
    }
  }

  public void testBuilderSetCountHandlesNullsCorrectly() {
    ImmutableMultiset.Builder<String> builder = ImmutableMultiset.builder();
    try {
      builder.setCount(null, 2);
      fail("expected NullPointerException");
    } catch (NullPointerException expected) {
    }
  }

  public void testBuilderSetCountIllegal() {
    ImmutableMultiset.Builder<String> builder = ImmutableMultiset.builder();
    try {
      builder.setCount("a", -2);
      fail("expected IllegalArgumentException");
    } catch (IllegalArgumentException expected) {
    }
  }

  @GwtIncompatible // NullPointerTester
  public void testNullPointers() {
    NullPointerTester tester = new NullPointerTester();
    tester.testAllPublicStaticMethods(ImmutableMultiset.class);
  }

  @GwtIncompatible // SerializableTester
  public void testSerialization_empty() {
    Collection<String> c = ImmutableMultiset.of();
    assertSame(c, SerializableTester.reserialize(c));
  }

  @GwtIncompatible // SerializableTester
  public void testSerialization_multiple() {
    Collection<String> c = ImmutableMultiset.of("a", "b", "a");
    Collection<String> copy = SerializableTester.reserializeAndAssert(c);
    assertThat(copy).containsExactly("a", "a", "b").inOrder();
  }

  @GwtIncompatible // SerializableTester
  public void testSerialization_elementSet() {
    Multiset<String> c = ImmutableMultiset.of("a", "b", "a");
    Collection<String> copy = LenientSerializableTester.reserializeAndAssertLenient(c.elementSet());
    assertThat(copy).containsExactly("a", "b").inOrder();
  }

  @GwtIncompatible // SerializableTester
  public void testSerialization_entrySet() {
    Multiset<String> c = ImmutableMultiset.of("a", "b", "c");
    SerializableTester.reserializeAndAssert(c.entrySet());
  }

  public void testEquals_immutableMultiset() {
    Collection<String> c = ImmutableMultiset.of("a", "b", "a");
    assertEquals(c, ImmutableMultiset.of("a", "b", "a"));
    assertEquals(c, ImmutableMultiset.of("a", "a", "b"));
    assertThat(c).isNotEqualTo(ImmutableMultiset.of("a", "b"));
    assertThat(c).isNotEqualTo(ImmutableMultiset.of("a", "b", "c", "d"));
  }

  public void testIterationOrder() {
    Collection<String> c = ImmutableMultiset.of("a", "b", "a");
    assertThat(c).containsExactly("a", "a", "b").inOrder();
    assertThat(ImmutableMultiset.of("c", "b", "a", "c").elementSet())
        .containsExactly("c", "b", "a")
        .inOrder();
  }

  public void testMultisetWrites() {
    Multiset<String> multiset = ImmutableMultiset.of("a", "b", "a");
    UnmodifiableCollectionTests.assertMultisetIsUnmodifiable(multiset, "test");
  }

  public void testAsList() {
    ImmutableMultiset<String> multiset = ImmutableMultiset.of("a", "a", "b", "b", "b");
    ImmutableList<String> list = multiset.asList();
    assertEquals(ImmutableList.of("a", "a", "b", "b", "b"), list);
    assertEquals(2, list.indexOf("b"));
    assertEquals(4, list.lastIndexOf("b"));
  }

  @GwtIncompatible // SerializableTester
  public void testSerialization_asList() {
    ImmutableMultiset<String> multiset = ImmutableMultiset.of("a", "a", "b", "b", "b");
    SerializableTester.reserializeAndAssert(multiset.asList());
  }

  public void testEquals() {
    new EqualsTester()
        .addEqualityGroup(ImmutableMultiset.of(), ImmutableMultiset.of())
        .addEqualityGroup(ImmutableMultiset.of(1), ImmutableMultiset.of(1))
        .addEqualityGroup(ImmutableMultiset.of(1, 1), ImmutableMultiset.of(1, 1))
        .addEqualityGroup(ImmutableMultiset.of(1, 2, 1), ImmutableMultiset.of(2, 1, 1))
        .testEquals();
  }

  public void testIterationOrderThroughBuilderRemovals() {
    ImmutableMultiset.Builder<String> builder = ImmutableMultiset.builder();
    builder.addCopies("a", 2);
    builder.add("b");
    builder.add("c");
    builder.setCount("b", 0);
    ImmutableMultiset<String> multiset = builder.build();
    assertThat(multiset.elementSet()).containsExactly("a", "c").inOrder();
    builder.add("b");
    assertThat(builder.build().elementSet()).containsExactly("a", "c", "b").inOrder();
    assertThat(multiset.elementSet()).containsExactly("a", "c").inOrder();
  }

  /**
   * A Comparable wrapper around a String which executes callbacks on calls to hashCode, equals, and
   * compareTo.
   */
  private static class CountsHashCodeAndEquals implements Comparable<CountsHashCodeAndEquals> {
    private final String delegateString;
    private final Runnable onHashCode;
    private final Runnable onEquals;
    private final Runnable onCompareTo;

    CountsHashCodeAndEquals(
        String delegateString, Runnable onHashCode, Runnable onEquals, Runnable onCompareTo) {
      this.delegateString = delegateString;
      this.onHashCode = onHashCode;
      this.onEquals = onEquals;
      this.onCompareTo = onCompareTo;
    }

    @Override
    public int hashCode() {
      onHashCode.run();
      return delegateString.hashCode();
    }

    @Override
    public boolean equals(@Nullable Object other) {
      onEquals.run();
      return other instanceof CountsHashCodeAndEquals
          && delegateString.equals(((CountsHashCodeAndEquals) other).delegateString);
    }

    @Override
    public int compareTo(CountsHashCodeAndEquals o) {
      onCompareTo.run();
      return delegateString.compareTo(o.delegateString);
    }
  }

  /** A holder of counters for calls to hashCode, equals, and compareTo. */
  private static final class CallsCounter {
    long hashCode;
    long equals;
    long compareTo;

    long total() {
      return hashCode + equals + compareTo;
    }

    void zero() {
      hashCode = 0;
      equals = 0;
      compareTo = 0;
    }
  }

  /** All the ways to create an ImmutableMultiset. */
  enum ConstructionPathway {
    COPY_OF_COLLECTION {
      @Override
      ImmutableMultiset<?> create(List<?> keys) {
        return ImmutableMultiset.copyOf(keys);
      }
    },
    COPY_OF_ITERATOR {
      @Override
      ImmutableMultiset<?> create(List<?> keys) {
        return ImmutableMultiset.copyOf(keys.iterator());
      }
    },
    BUILDER_ADD_ENTRY_BY_ENTRY {
      @Override
      ImmutableMultiset<?> create(List<?> keys) {
        ImmutableMultiset.Builder<Object> builder = ImmutableMultiset.builder();
        for (Object o : keys) {
          builder.add(o);
        }
        return builder.build();
      }
    },
    BUILDER_ADD_ALL_COLLECTION {
      @Override
      ImmutableMultiset<?> create(List<?> keys) {
        ImmutableMultiset.Builder<Object> builder = ImmutableMultiset.builder();
        builder.addAll(keys);
        return builder.build();
      }
    };

    @CanIgnoreReturnValue
    abstract ImmutableMultiset<?> create(List<?> keys);
  }

  /**
   * Returns a list of objects with the same hash code, of size 2^power, counting calls to equals,
   * hashCode, and compareTo in counter.
   */
  static List<CountsHashCodeAndEquals> createAdversarialInput(int power, CallsCounter counter) {
    String str1 = "Aa";
    String str2 = "BB";
    assertEquals(str1.hashCode(), str2.hashCode());
    List<String> haveSameHashes2 = Arrays.asList(str1, str2);
    List<CountsHashCodeAndEquals> result =
        Lists.newArrayList(
            Lists.transform(
                Lists.cartesianProduct(Collections.nCopies(power, haveSameHashes2)),
                strs ->
                    new CountsHashCodeAndEquals(
                        String.join("", strs),
                        () -> counter.hashCode++,
                        () -> counter.equals++,
                        () -> counter.compareTo++)));
    assertEquals(
        result.get(0).delegateString.hashCode(),
        result.get(result.size() - 1).delegateString.hashCode());
    return result;
  }

  @GwtIncompatible
  public void testResistsHashFloodingInConstruction() {
    CallsCounter smallCounter = new CallsCounter();
    List<CountsHashCodeAndEquals> haveSameHashesSmall = createAdversarialInput(10, smallCounter);
    int smallSize = haveSameHashesSmall.size();

    CallsCounter largeCounter = new CallsCounter();
    List<CountsHashCodeAndEquals> haveSameHashesLarge = createAdversarialInput(15, largeCounter);
    int largeSize = haveSameHashesLarge.size();

    for (ConstructionPathway pathway : ConstructionPathway.values()) {
      smallCounter.zero();
      pathway.create(haveSameHashesSmall);
      long smallOps = smallCounter.total();

      largeCounter.zero();
      pathway.create(haveSameHashesLarge);
      long largeOps = largeCounter.total();

      double ratio = (double) largeOps / smallOps;
      assertThat(ratio)
          .named(
              "ratio of equals/hashCode/compareTo operations to build an ImmutableMultiset via %s"
                  + " with %s entries versus %s entries",
              pathway, largeSize, smallSize)
          .isAtMost(2 * (largeSize * Math.log(largeSize)) / (smallSize * Math.log(smallSize)));
      // allow up to 2x wobble in the constant factors
    }
  }

  @GwtIncompatible
  public void testResistsHashFloodingOnCount() {
    CallsCounter smallCounter = new CallsCounter();
    List<CountsHashCodeAndEquals> haveSameHashesSmall = createAdversarialInput(10, smallCounter);
    int smallSize = haveSameHashesSmall.size();
    ImmutableMultiset<?> smallMap =
        ConstructionPathway.COPY_OF_COLLECTION.create(haveSameHashesSmall);
    long worstCaseQuerySmall = worstCaseQueryOperations(smallMap, smallCounter);

    CallsCounter largeCounter = new CallsCounter();
    List<CountsHashCodeAndEquals> haveSameHashesLarge = createAdversarialInput(15, largeCounter);
    int largeSize = haveSameHashesLarge.size();
    ImmutableMultiset<?> largeMap =
        ConstructionPathway.COPY_OF_COLLECTION.create(haveSameHashesLarge);
    long worstCaseQueryLarge = worstCaseQueryOperations(largeMap, largeCounter);

    double ratio = (double) worstCaseQueryLarge / worstCaseQuerySmall;
    assertThat(ratio)
        .named(
            "Ratio of worst case query operations for an ImmutableMultiset of size %s versus %s",
            largeSize, smallSize)
        .isAtMost(2 * Math.log(largeSize) / Math.log(smallSize));
    // allow up to 2x wobble in the constant factors
  }

  private static long worstCaseQueryOperations(Multiset<?> multiset, CallsCounter counter) {
    long worstCalls = 0;
    for (Object k : multiset.elementSet()) {
      counter.zero();
      int unused = multiset.count(k);
      worstCalls = Math.max(worstCalls, counter.total());
    }
    return worstCalls;
  }
}
