/*
    * 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.Beta;
  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 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
   *
   * TODO(gak): turn this into a test suite so that each test can fail
   * independently
   */
  @Beta
  @GwtCompatible 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<T>(
          equivalence, "equivalent", "hash", new ItemReporter());
    }
  
    public static <T> EquivalenceTester<T> of(Equivalence<? super T> equivalence) {
      return new EquivalenceTester<T>(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.
     */
    public EquivalenceTester<T> addEquivalenceGroup(T first, T... rest) {
      addEquivalenceGroup(Lists.asList(first, rest));
      return this;
    }
  
    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 */
    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));
     }
   }
 }