1 /**
2  * Copyright (C) 2014 Google Inc.
3  * Licensed to The Android Open Source Project.
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * You may obtain a copy of the License at
8  *
9  *      http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  */
17 
18 package com.android.mail.utils;
19 
20 import com.google.android.mail.common.base.Function;
21 import com.google.common.collect.ImmutableMap;
22 
23 import java.util.Comparator;
24 import java.util.Map;
25 
26 /**
27  * Compares objects of the type {@code T} based on predefined order of the ranks of the type
28  * {@code K}. The ranks that are not in the predefined order will be considered larger than other
29  * ranks (if this comparator is used for sorting those elements will be at the end).
30  *
31  * @param <T> Type to be compared.
32  * @param <K> Type of the ranks used for comparison.
33  */
34 public class RankedComparator<T, K> implements Comparator<T> {
35 
36     private final Map<K, Integer> mRankOrder;
37 
38     private final Function<T, K> mRankExtractorFunction;
39 
40     /**
41      * Creates a comparator that compares objects of type {@code T} by extracting the ranks of the
42      * objects using {@code rankExtractorFunction} and comparing them by their position in
43      * {@code rankOrder}. Ranks not present in {@code rankOrder} are considered larger than the
44      * ranks present in the {@code rankOrder}.
45      *
46      * @param rankOrder             Order of the ranks.
47      * @param rankExtractorFunction Function that extracts rank from the object.
48      */
RankedComparator(K[] rankOrder, Function<T, K> rankExtractorFunction)49     public RankedComparator(K[] rankOrder, Function<T, K> rankExtractorFunction) {
50         final ImmutableMap.Builder<K, Integer> orderBuilder = ImmutableMap.builder();
51         for (int i = 0; i < rankOrder.length; i++) {
52             orderBuilder.put(rankOrder[i], i);
53         }
54         mRankOrder = orderBuilder.build();
55 
56         mRankExtractorFunction = rankExtractorFunction;
57     }
58 
getOrder(T object)59     private int getOrder(T object) {
60         final K key = mRankExtractorFunction.apply(object);
61 
62         if (mRankOrder.containsKey(key)) {
63             return mRankOrder.get(key);
64         }
65         return Integer.MAX_VALUE;
66     }
67 
68     @Override
compare(T lhs, T rhs)69     public int compare(T lhs, T rhs) {
70         final int orderLhs = getOrder(lhs);
71         final int orderRhs = getOrder(rhs);
72         // Order can be Integer.MAX_VALUE so subtraction should not be used.
73         return orderLhs < orderRhs ? -1 : (orderLhs == orderRhs ? 0 : 1);
74     }
75 }
76