/*
    * 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 java.util.List;
  
  import javax.annotation.Nullable;
  
  /** An ordering that compares objects according to a given order. */
  @GwtCompatible(serializable = true)
  final class ExplicitOrdering<T> extends Ordering<T> implements Serializable {
    final ImmutableMap<T, Integer> rankMap;
  
    ExplicitOrdering(List<T> valuesInOrder) {
      this(buildRankMap(valuesInOrder));
    }
  
    ExplicitOrdering(ImmutableMap<T, Integer> rankMap) {
      this.rankMap = rankMap;
    }
  
    @Override public int compare(T left, T right) {
      return rank(left) - rank(right); // safe because both are nonnegative
    }
  
    private int rank(T value) {
      Integer rank = rankMap.get(value);
      if (rank == null) {
        throw new IncomparableValueException(value);
      }
      return rank;
    }
  
    private static <T> ImmutableMap<T, Integer> buildRankMap(
        List<T> valuesInOrder) {
      ImmutableMap.Builder<T, Integer> builder = ImmutableMap.builder();
      int rank = 0;
      for (T value : valuesInOrder) {
        builder.put(value, rank++);
      }
      return builder.build();
    }
  
    @Override public boolean equals(@Nullable Object object) {
      if (object instanceof ExplicitOrdering) {
        ExplicitOrdering<?> that = (ExplicitOrdering<?>) object;
        return this.rankMap.equals(that.rankMap);
      }
      return false;
    }
  
    @Override public int hashCode() {
      return rankMap.hashCode();
    }
  
    @Override public String toString() {
      return "Ordering.explicit(" + rankMap.keySet() + ")";
    }
  
    private static final long serialVersionUID = 0;
  }