1// Copyright 2014 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// This module computes snippets of queries based on hits in the documents
6// for display in history search results.
7
8#ifndef COMPONENTS_QUERY_PARSER_SNIPPET_H__
9#define COMPONENTS_QUERY_PARSER_SNIPPET_H__
10
11#include <vector>
12
13#include "base/strings/string16.h"
14
15namespace query_parser {
16
17class Snippet {
18 public:
19  // Each MatchPosition is the [begin, end) positions of a match within a
20  // string.
21  typedef std::pair<size_t, size_t> MatchPosition;
22  typedef std::vector<MatchPosition> MatchPositions;
23
24  // Parses an offsets string as returned from a sqlite full text index. An
25  // offsets string encodes information about why a row matched a text query.
26  // The information is encoded in the string as a set of matches, where each
27  // match consists of the column, term-number, location, and length of the
28  // match. Each element of the match is separated by a space, as is each match
29  // from other matches.
30  //
31  // This method adds the start and end of each match whose column is
32  // column_num to match_positions. The pairs are ordered based on first,
33  // with no overlapping elements.
34  //
35  // NOTE: the positions returned are in terms of UTF8 encoding. To convert the
36  // offsets to UTF-16, use ConvertMatchPositionsToWide
37  static void ExtractMatchPositions(const std::string& offsets_str,
38                                    const std::string& column_num,
39                                    MatchPositions* match_positions);
40
41  // Converts match positions as returned from ExtractMatchPositions to be in
42  // terms of a UTF-16 2-byte code unit.
43  static void ConvertMatchPositionsToWide(
44      const std::string& utf8_string,
45      Snippet::MatchPositions* match_positions);
46
47  Snippet();
48  ~Snippet();
49
50  // Given |matches|, the match positions within |document|, compute the snippet
51  // for the document.
52  // Note that |document| is UTF-8 and the offsets in |matches| are byte
53  // offsets.
54  void ComputeSnippet(const MatchPositions& matches,
55                      const std::string& document);
56
57  const base::string16& text() const { return text_; }
58  const MatchPositions& matches() const { return matches_; }
59
60  // Efficiently swaps the contents of this snippet with the other.
61  void Swap(Snippet* other);
62
63 private:
64  // The text of the snippet.
65  base::string16 text_;
66
67  // The matches within text_.
68  MatchPositions matches_;
69};
70
71}  // namespace query_parser
72
73#endif  // COMPONENTS_QUERY_PARSER_SNIPPET_H__
74