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.text.TextUtils;
20import android.util.Log;
21
22import java.util.HashMap;
23import java.util.Iterator;
24import 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 */
32class 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    private final Config mConfig;
41
42    // The current implementation keeps a record of those corpora that have
43    // returned zero results for some prefix of the current query. mEmptyCorpora
44    // maps from corpus to the length of the query which returned
45    // zero results.  When a query is shortened (e.g., by deleting characters)
46    // or changed entirely, mEmptyCorpora is pruned (in updateQuery)
47    private final HashMap<Corpus, Integer> mEmptyCorpora
48            = new HashMap<Corpus, Integer>();
49
50    public ShouldQueryStrategy(Config config) {
51        mConfig = config;
52    }
53
54    /**
55     * Returns whether we should query the given source for the given query.
56     */
57    public boolean shouldQueryCorpus(Corpus corpus, String query) {
58        updateQuery(query);
59        if (query.length() == 0
60                && !corpus.isWebCorpus() // always query web, to warm up connection
61                && !mConfig.showSuggestionsForZeroQuery()) {
62                return false;
63        }
64        if (query.length() >= corpus.getQueryThreshold()) {
65            if (!corpus.queryAfterZeroResults() && mEmptyCorpora.containsKey(corpus)) {
66                if (DBG) Log.i(TAG, "Not querying " + corpus + ", returned 0 after "
67                        + mEmptyCorpora.get(corpus));
68                return false;
69            }
70            return true;
71        }
72        if (DBG) Log.d(TAG, "Query too short for corpus " + corpus);
73        return false;
74    }
75
76    /**
77     * Called to notify ShouldQueryStrategy when a source reports no results for a query.
78     */
79    public void onZeroResults(Corpus corpus, String query) {
80        // Make sure this result is actually for a prefix of the current query.
81        if (mLastQuery.startsWith(query) && !corpus.queryAfterZeroResults()
82                && !TextUtils.isEmpty(query)) {
83            if (DBG) Log.d(TAG, corpus + " returned 0 results for '" + query + "'");
84            mEmptyCorpora.put(corpus, query.length());
85        }
86    }
87
88    private void updateQuery(String query) {
89        if (query.startsWith(mLastQuery)) {
90            // This is a refinement of the last query, no changes to mEmptyCorpora needed
91        } else if (mLastQuery.startsWith(query)) {
92            // This is a widening of the last query: clear out any sources
93            // that reported zero results after this query.
94            Iterator<Map.Entry<Corpus, Integer>> iter = mEmptyCorpora.entrySet().iterator();
95            while (iter.hasNext()) {
96                if (iter.next().getValue() > query.length()) {
97                    iter.remove();
98                }
99            }
100        } else {
101            // This is a completely different query, clear everything.
102            mEmptyCorpora.clear();
103        }
104        mLastQuery = query;
105    }
106}
107