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/**
* Copyright (C) 2014 Google Inc.
* Licensed to The Android Open Source Project.
*
* 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.android.mail.utils;
import com.google.android.mail.common.base.Function;
import com.google.common.collect.ImmutableMap;
import java.util.Comparator;
import java.util.Map;
/**
* Compares objects of the type {@code T} based on predefined order of the ranks of the type
* {@code K}. The ranks that are not in the predefined order will be considered larger than other
* ranks (if this comparator is used for sorting those elements will be at the end).
*
* @param <T> Type to be compared.
* @param <K> Type of the ranks used for comparison.
*/
public class RankedComparator<T, K> implements Comparator<T> {
private final Map<K, Integer> mRankOrder;
private final Function<T, K> mRankExtractorFunction;
/**
* Creates a comparator that compares objects of type {@code T} by extracting the ranks of the
* objects using {@code rankExtractorFunction} and comparing them by their position in
* {@code rankOrder}. Ranks not present in {@code rankOrder} are considered larger than the
* ranks present in the {@code rankOrder}.
*
* @param rankOrder Order of the ranks.
* @param rankExtractorFunction Function that extracts rank from the object.
*/
public RankedComparator(K[] rankOrder, Function<T, K> rankExtractorFunction) {
final ImmutableMap.Builder<K, Integer> orderBuilder = ImmutableMap.builder();
for (int i = 0; i < rankOrder.length; i++) {
orderBuilder.put(rankOrder[i], i);
}
mRankOrder = orderBuilder.build();
mRankExtractorFunction = rankExtractorFunction;
}
private int getOrder(T object) {
final K key = mRankExtractorFunction.apply(object);
if (mRankOrder.containsKey(key)) {
return mRankOrder.get(key);
}
return Integer.MAX_VALUE;
}
@Override
public int compare(T lhs, T rhs) {
final int orderLhs = getOrder(lhs);
final int orderRhs = getOrder(rhs);
// Order can be Integer.MAX_VALUE so subtraction should not be used.
return orderLhs < orderRhs ? -1 : (orderLhs == orderRhs ? 0 : 1);
}
}
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