/*
    * Copyright (C) 2007 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.collect;
  
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.annotations.GwtCompatible;
  import com.google.common.base.Function;
  import com.google.common.base.Objects;
  
  import java.io.Serializable;
  
  import javax.annotation.Nullable;
  
  /**
   * An ordering that orders elements by applying an order to the result of a
   * function on those elements.
   */
  @GwtCompatible(serializable = true)
  final class ByFunctionOrdering<F, T>
      extends Ordering<F> implements Serializable {
    final Function<F, ? extends T> function;
    final Ordering<T> ordering;
  
    ByFunctionOrdering(
        Function<F, ? extends T> function, Ordering<T> ordering) {
      this.function = checkNotNull(function);
      this.ordering = checkNotNull(ordering);
    }
  
    @Override public int compare(F left, F right) {
      return ordering.compare(function.apply(left), function.apply(right));
    }
  
    @Override public boolean equals(@Nullable Object object) {
      if (object == this) {
        return true;
      }
      if (object instanceof ByFunctionOrdering) {
        ByFunctionOrdering<?, ?> that = (ByFunctionOrdering<?, ?>) object;
        return this.function.equals(that.function)
            && this.ordering.equals(that.ordering);
      }
      return false;
    }
  
    @Override public int hashCode() {
      return Objects.hashCode(function, ordering);
    }
  
    @Override public String toString() {
      return ordering + ".onResultOf(" + function + ")";
    }
  
    private static final long serialVersionUID = 0;
  }