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 android.content.Context;
20
21import java.util.Iterator;
22import java.util.List;
23
24/**
25 * Class used for collapsing data items into groups of similar items. The data items that should be
26 * collapsible should implement the Collapsible interface. The class also contains a utility
27 * function that takes an ArrayList of items and returns a list of the same items collapsed into
28 * groups.
29 */
30public final class Collapser {
31
32    /*
33     * This utility class cannot be instantiated.
34     */
35    private Collapser() {}
36
37    /*
38     * The Collapser uses an n^2 algorithm so we don't want it to run on
39     * lists beyond a certain size. This specifies the maximum size to collapse.
40     */
41    private static final int MAX_LISTSIZE_TO_COLLAPSE = 20;
42
43    /*
44     * Interface implemented by data types that can be collapsed into groups of similar data. This
45     * can be used for example to collapse similar contact data items into a single item.
46     */
47    public interface Collapsible<T> {
48        public void collapseWith(T t);
49        public boolean shouldCollapseWith(T t, Context context);
50
51    }
52
53    /**
54     * Collapses a list of Collapsible items into a list of collapsed items. Items are collapsed
55     * if {@link Collapsible#shouldCollapseWith(Object)} returns true, and are collapsed
56     * through the {@Link Collapsible#collapseWith(Object)} function implemented by the data item.
57     *
58     * @param list List of Objects of type <T extends Collapsible<T>> to be collapsed.
59     */
60    public static <T extends Collapsible<T>> void collapseList(List<T> list, Context context) {
61
62        int listSize = list.size();
63        // The algorithm below is n^2 so don't run on long lists
64        if (listSize > MAX_LISTSIZE_TO_COLLAPSE) {
65            return;
66        }
67
68        for (int i = 0; i < listSize; i++) {
69            T iItem = list.get(i);
70            if (iItem != null) {
71                for (int j = i + 1; j < listSize; j++) {
72                    T jItem = list.get(j);
73                    if (jItem != null) {
74                        if (iItem.shouldCollapseWith(jItem, context)) {
75                            iItem.collapseWith(jItem);
76                            list.set(j, null);
77                        } else if (jItem.shouldCollapseWith(iItem, context)) {
78                            jItem.collapseWith(iItem);
79                            list.set(i, null);
80                            break;
81                        }
82                    }
83                }
84            }
85        }
86
87        // Remove the null items
88        Iterator<T> itr = list.iterator();
89        while (itr.hasNext()) {
90            if (itr.next() == null) {
91                itr.remove();
92            }
93        }
94
95    }
96}
97