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