ShouldQueryStrategy.java revision a65408ff321345557f93effa41395174640870eb 
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
17package com.android.quicksearchbox;
18
19import android.util.Log;
20
21import java.util.HashMap;
22import java.util.Iterator;
23import java.util.Map;
24
25/**
26 * Decides whether a given source should be queried for a given query, taking
27 * into account the source's query threshold and query after zero results flag.
28 *
29 * This class is thread safe.
30 */
31class ShouldQueryStrategy {
32    private static final boolean DBG = true;
33    private static final String TAG = "QSB.ShouldQueryStrategy";
34
35    // The last query we've seen
36    private String mLastQuery = "";
37
38    // The current implementation keeps a record of those corpora that have
39    // returned zero results for some prefix of the current query. mEmptyCorpora
40    // maps from corpus to the length of the query which returned
41    // zero results.  When a query is shortened (e.g., by deleting characters)
42    // or changed entirely, mEmptyCorpora is pruned (in updateQuery)
43    private final HashMap<Corpus, Integer> mEmptyCorpora
44            = new HashMap<Corpus, Integer>();
45
46    /**
47     * Returns whether we should query the given source for the given query.
48     */
49    public boolean shouldQueryCorpus(Corpus corpus, String query) {
50        updateQuery(query);
51        if (query.length() >= corpus.getQueryThreshold()) {
52            if (!corpus.queryAfterZeroResults() && mEmptyCorpora.containsKey(corpus)) {
53                if (DBG) Log.i(TAG, "Not querying " + corpus + ", returned 0 after "
54                        + mEmptyCorpora.get(corpus));
55                return false;
56            }
57            return true;
58        }
59        return false;
60    }
61
62    /**
63     * Called to notify ShouldQueryStrategy when a source reports no results for a query.
64     */
65    public void onZeroResults(Corpus corpus, String query) {
66        // Make sure this result is actually for a prefix of the current query.
67        if (mLastQuery.startsWith(query) && !corpus.queryAfterZeroResults()) {
68            if (DBG) Log.d(TAG, corpus + " returned 0 results for " + query);
69            mEmptyCorpora.put(corpus, query.length());
70        }
71    }
72
73    private void updateQuery(String query) {
74        if (query.startsWith(mLastQuery)) {
75            // This is a refinement of the last query, no changes to mEmptyCorpora needed
76        } else if (mLastQuery.startsWith(query)) {
77            // This is a widening of the last query: clear out any sources
78            // that reported zero results after this query.
79            Iterator<Map.Entry<Corpus, Integer>> iter = mEmptyCorpora.entrySet().iterator();
80            while (iter.hasNext()) {
81                if (iter.next().getValue() > query.length()) {
82                    iter.remove();
83                }
84            }
85        } else {
86            // This is a completely different query, clear everything.
87            mEmptyCorpora.clear();
88        }
89        mLastQuery = query;
90    }
91}
92