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      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 
     17 package com.android.contacts.common;
     18 
     19 import android.content.Context;
     20 import java.util.Iterator;
     21 import 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  */
     29 public 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