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/*
 * 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.base;

import com.google.common.annotations.GwtCompatible;

import java.io.Serializable;
import java.util.Iterator;

import javax.annotation.Nullable;

@GwtCompatible(serializable = true)
final class PairwiseEquivalence extends Equivalence>
    implements Serializable {

  final Equivalence elementEquivalence;

  PairwiseEquivalence(Equivalence elementEquivalence) {
    this.elementEquivalence = Preconditions.checkNotNull(elementEquivalence);
  }

  @Override
  protected boolean doEquivalent(Iterable iterableA, Iterable iterableB) {
    Iterator iteratorA = iterableA.iterator();
    Iterator iteratorB = iterableB.iterator();

    while (iteratorA.hasNext() && iteratorB.hasNext()) {
      if (!elementEquivalence.equivalent(iteratorA.next(), iteratorB.next())) {
        return false;
      }
    }

    return !iteratorA.hasNext() && !iteratorB.hasNext();
  }

  @Override
  protected int doHash(Iterable iterable) {
    int hash = 78721;
    for (T element : iterable) {
      hash = hash * 24943 + elementEquivalence.hash(element);
    }
    return hash;
  }

  @Override
  public boolean equals(@Nullable Object object) {
    if (object instanceof PairwiseEquivalence) {
      PairwiseEquivalence that = (PairwiseEquivalence) object;
      return this.elementEquivalence.equals(that.elementEquivalence);
    }

    return false;
  }

  @Override
  public int hashCode() {
    return elementEquivalence.hashCode() ^ 0x46a3eb07;
  }

  @Override
  public String toString() {
    return elementEquivalence + ".pairwise()";
  }

  private static final long serialVersionUID = 1;
}