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      1 /*
      2  * Copyright (C) 2010 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.quicksearchbox;
     18 
     19 import android.text.TextUtils;
     20 import android.util.Log;
     21 
     22 import java.util.HashMap;
     23 import java.util.Iterator;
     24 import java.util.Map;
     25 
     26 /**
     27  * Decides whether a given source should be queried for a given query, taking
     28  * into account the source's query threshold and query after zero results flag.
     29  *
     30  * This class is thread safe.
     31  */
     32 class ShouldQueryStrategy {
     33 
     34     private static final boolean DBG = false;
     35     private static final String TAG = "QSB.ShouldQueryStrategy";
     36 
     37     // The last query we've seen
     38     private String mLastQuery = "";
     39 
     40     // The current implementation keeps a record of those corpora that have
     41     // returned zero results for some prefix of the current query. mEmptyCorpora
     42     // maps from corpus to the length of the query which returned
     43     // zero results.  When a query is shortened (e.g., by deleting characters)
     44     // or changed entirely, mEmptyCorpora is pruned (in updateQuery)
     45     private final HashMap<Corpus, Integer> mEmptyCorpora
     46             = new HashMap<Corpus, Integer>();
     47 
     48     /**
     49      * Returns whether we should query the given source for the given query.
     50      */
     51     public boolean shouldQueryCorpus(Corpus corpus, String query) {
     52         updateQuery(query);
     53         if (query.length() >= corpus.getQueryThreshold()) {
     54             if (!corpus.queryAfterZeroResults() && mEmptyCorpora.containsKey(corpus)) {
     55                 if (DBG) Log.i(TAG, "Not querying " + corpus + ", returned 0 after "
     56                         + mEmptyCorpora.get(corpus));
     57                 return false;
     58             }
     59             return true;
     60         }
     61         if (DBG) Log.d(TAG, "Query too short for corpus " + corpus);
     62         return false;
     63     }
     64 
     65     /**
     66      * Called to notify ShouldQueryStrategy when a source reports no results for a query.
     67      */
     68     public void onZeroResults(Corpus corpus, String query) {
     69         // Make sure this result is actually for a prefix of the current query.
     70         if (mLastQuery.startsWith(query) && !corpus.queryAfterZeroResults()
     71                 && !TextUtils.isEmpty(query)) {
     72             if (DBG) Log.d(TAG, corpus + " returned 0 results for '" + query + "'");
     73             mEmptyCorpora.put(corpus, query.length());
     74         }
     75     }
     76 
     77     private void updateQuery(String query) {
     78         if (query.startsWith(mLastQuery)) {
     79             // This is a refinement of the last query, no changes to mEmptyCorpora needed
     80         } else if (mLastQuery.startsWith(query)) {
     81             // This is a widening of the last query: clear out any sources
     82             // that reported zero results after this query.
     83             Iterator<Map.Entry<Corpus, Integer>> iter = mEmptyCorpora.entrySet().iterator();
     84             while (iter.hasNext()) {
     85                 if (iter.next().getValue() > query.length()) {
     86                     iter.remove();
     87                 }
     88             }
     89         } else {
     90             // This is a completely different query, clear everything.
     91             mEmptyCorpora.clear();
     92         }
     93         mLastQuery = query;
     94     }
     95 }
     96