/*
    * 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 static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.annotations.Beta;
  import com.google.common.annotations.GwtCompatible;
  
  import java.io.Serializable;
  
  import javax.annotation.Nullable;
  
  /**
   * Equivalence applied on functional result.
   *
   * @author Bob Lee
   * @since 10.0
   */
  @Beta
  @GwtCompatible
  final class FunctionalEquivalence<F, T> extends Equivalence<F>
      implements Serializable {
  
    private static final long serialVersionUID = 0;
  
    private final Function<F, ? extends T> function;
    private final Equivalence<T> resultEquivalence;
  
    FunctionalEquivalence(
        Function<F, ? extends T> function, Equivalence<T> resultEquivalence) {
      this.function = checkNotNull(function);
      this.resultEquivalence = checkNotNull(resultEquivalence);
    }
  
    @Override protected boolean doEquivalent(F a, F b) {
      return resultEquivalence.equivalent(function.apply(a), function.apply(b));
    }
  
    @Override protected int doHash(F a) {
      return resultEquivalence.hash(function.apply(a));
    }
  
    @Override public boolean equals(@Nullable Object obj) {
      if (obj == this) {
        return true;
      }
      if (obj instanceof FunctionalEquivalence) {
        FunctionalEquivalence<?, ?> that = (FunctionalEquivalence<?, ?>) obj;
        return function.equals(that.function)
            && resultEquivalence.equals(that.resultEquivalence);
      }
      return false;
    }
  
    @Override public int hashCode() {
      return Objects.hashCode(function, resultEquivalence);
    }
  
    @Override public String toString() {
      return resultEquivalence + ".onResultOf(" + function + ")";
    }
  }