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/*
 * 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 extends Ordering implements Serializable {
  final Ordering ordering;

  NullsFirstOrdering(Ordering 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  Ordering 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  Ordering nullsFirst() {
    return (Ordering) this;
  }

  @Override public  Ordering 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;
}