/*
 * Copyright (C) 2011 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.testing;

import static com.google.common.base.Preconditions.checkNotNull;
import static junit.framework.Assert.assertEquals;
import static junit.framework.Assert.assertTrue;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Equivalence;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.testing.RelationshipTester.ItemReporter;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.List;

/**
 * Tester for {@link Equivalence} relationships between groups of objects.
 *
 * <p>To use, create a new {@link EquivalenceTester} and add equivalence groups where each group
 * contains objects that are supposed to be equal to each other. Objects of different groups are
 * expected to be unequal. For example:
 *
 * <pre>{@code
 * EquivalenceTester.of(someStringEquivalence)
 *     .addEquivalenceGroup("hello", "h" + "ello")
 *     .addEquivalenceGroup("world", "wor" + "ld")
 *     .test();
 * }</pre>
 *
 * <p>Note that testing {@link Object#equals(Object)} is more simply done using the {@link
 * EqualsTester}. It includes an extra test against an instance of an arbitrary class without having
 * to explicitly add another equivalence group.
 *
 * @author Gregory Kick
 * @since 10.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public final class EquivalenceTester<T> {
  private static final int REPETITIONS = 3;

  private final Equivalence<? super T> equivalence;
  private final RelationshipTester<T> delegate;
  private final List<T> items = Lists.newArrayList();

  private EquivalenceTester(Equivalence<? super T> equivalence) {
    this.equivalence = checkNotNull(equivalence);
    this.delegate = new RelationshipTester<>(equivalence, "equivalent", "hash", new ItemReporter());
  }

  public static <T> EquivalenceTester<T> of(Equivalence<? super T> equivalence) {
    return new EquivalenceTester<>(equivalence);
  }

  /**
   * Adds a group of objects that are supposed to be equivalent to each other and not equivalent to
   * objects in any other equivalence group added to this tester.
   */
  @CanIgnoreReturnValue
  public EquivalenceTester<T> addEquivalenceGroup(T first, T... rest) {
    addEquivalenceGroup(Lists.asList(first, rest));
    return this;
  }

  @CanIgnoreReturnValue
  public EquivalenceTester<T> addEquivalenceGroup(Iterable<T> group) {
    delegate.addRelatedGroup(group);
    items.addAll(ImmutableList.copyOf(group));
    return this;
  }

  /** Run tests on equivalence methods, throwing a failure on an invalid test */
  @CanIgnoreReturnValue
  public EquivalenceTester<T> test() {
    for (int run = 0; run < REPETITIONS; run++) {
      testItems();
      delegate.test();
    }
    return this;
  }

  private void testItems() {
    for (T item : items) {
      /*
       * TODO(cpovirk): consider no longer running these equivalent() tests on every Equivalence,
       * since the Equivalence base type now implements this logic itself
       */
      assertTrue(item + " must be inequivalent to null", !equivalence.equivalent(item, null));
      assertTrue("null must be inequivalent to " + item, !equivalence.equivalent(null, item));
      assertTrue(item + " must be equivalent to itself", equivalence.equivalent(item, item));
      assertEquals(
          "the hash of " + item + " must be consistent",
          equivalence.hash(item),
          equivalence.hash(item));
    }
  }
}
