/*
    * 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 com.google.common.annotations.GwtCompatible;
  
  import java.io.Serializable;
  
  import javax.annotation.Nullable;
  
  /** An ordering that treats {@code null} as less than all other values. */
  @GwtCompatible(serializable = true)
  final class NullsFirstOrdering<T> extends Ordering<T> implements Serializable {
    final Ordering<? super T> ordering;
  
    NullsFirstOrdering(Ordering<? super T> ordering) {
      this.ordering = ordering;
    }
  
    @Override public int compare(@Nullable T left, @Nullable T right) {
      if (left == right) {
        return 0;
      }
      if (left == null) {
        return RIGHT_IS_GREATER;
      }
      if (right == null) {
        return LEFT_IS_GREATER;
      }
      return ordering.compare(left, right);
    }
  
    @Override public <S extends T> Ordering<S> reverse() {
      // ordering.reverse() might be optimized, so let it do its thing
      return ordering.reverse().nullsLast();
    }
  
    @SuppressWarnings("unchecked") // still need the right way to explain this
    @Override public <S extends T> Ordering<S> nullsFirst() {
      return (Ordering<S>) this;
    }
  
    @Override public <S extends T> Ordering<S> nullsLast() {
      return ordering.nullsLast();
    }
  
    @Override public boolean equals(@Nullable Object object) {
      if (object == this) {
        return true;
      }
      if (object instanceof NullsFirstOrdering) {
        NullsFirstOrdering<?> that = (NullsFirstOrdering<?>) object;
        return this.ordering.equals(that.ordering);
      }
      return false;
    }
  
    @Override public int hashCode() {
      return ordering.hashCode() ^ 957692532; // meaningless
    }
  
    @Override public String toString() {
      return ordering + ".nullsFirst()";
    }
  
    private static final long serialVersionUID = 0;
  }