1/*
2 * Copyright (C) 2009 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.contacts.common;
18
19import java.util.Iterator;
20import java.util.List;
21
22/**
23 * Class used for collapsing data items into groups of similar items. The data items that should be
24 * collapsible should implement the Collapsible interface. The class also contains a utility
25 * function that takes an ArrayList of items and returns a list of the same items collapsed into
26 * groups.
27 */
28public final class Collapser {
29
30    /*
31     * This utility class cannot be instantiated.
32     */
33    private Collapser() {}
34
35    /*
36     * The Collapser uses an n^2 algorithm so we don't want it to run on
37     * lists beyond a certain size. This specifies the maximum size to collapse.
38     */
39    private static final int MAX_LISTSIZE_TO_COLLAPSE = 20;
40
41    /*
42     * Interface implemented by data types that can be collapsed into groups of similar data. This
43     * can be used for example to collapse similar contact data items into a single item.
44     */
45    public interface Collapsible<T> {
46        public void collapseWith(T t);
47        public boolean shouldCollapseWith(T t);
48    }
49
50    /**
51     * Collapses a list of Collapsible items into a list of collapsed items. Items are collapsed
52     * if {@link Collapsible#shouldCollapseWith(Object)} returns true, and are collapsed
53     * through the {@Link Collapsible#collapseWith(Object)} function implemented by the data item.
54     *
55     * @param list List of Objects of type <T extends Collapsible<T>> to be collapsed.
56     */
57    public static <T extends Collapsible<T>> void collapseList(List<T> list) {
58
59        int listSize = list.size();
60        // The algorithm below is n^2 so don't run on long lists
61        if (listSize > MAX_LISTSIZE_TO_COLLAPSE) {
62            return;
63        }
64
65        for (int i = 0; i < listSize; i++) {
66            T iItem = list.get(i);
67            if (iItem != null) {
68                for (int j = i + 1; j < listSize; j++) {
69                    T jItem = list.get(j);
70                    if (jItem != null) {
71                        if (iItem.shouldCollapseWith(jItem)) {
72                            iItem.collapseWith(jItem);
73                            list.set(j, null);
74                        } else if (jItem.shouldCollapseWith(iItem)) {
75                            jItem.collapseWith(iItem);
76                            list.set(i, null);
77                            break;
78                        }
79                    }
80                }
81            }
82        }
83
84        // Remove the null items
85        Iterator<T> itr = list.iterator();
86        while (itr.hasNext()) {
87            if (itr.next() == null) {
88                itr.remove();
89            }
90        }
91
92    }
93}
94