/*
    * 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<T> extends Equivalence<Iterable<T>>
      implements Serializable {
  
    final Equivalence<? super T> elementEquivalence;
  
    PairwiseEquivalence(Equivalence<? super T> elementEquivalence) {
      this.elementEquivalence = Preconditions.checkNotNull(elementEquivalence);
    }
  
    @Override
    protected boolean doEquivalent(Iterable<T> iterableA, Iterable<T> iterableB) {
      Iterator<T> iteratorA = iterableA.iterator();
      Iterator<T> 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<T> 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;
  }