1// Copyright (c) 2011 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#ifndef BASE_I18N_BREAK_ITERATOR_H_
6#define BASE_I18N_BREAK_ITERATOR_H_
7
8#include "base/basictypes.h"
9#include "base/i18n/base_i18n_export.h"
10#include "base/strings/string16.h"
11
12// The BreakIterator class iterates through the words, word breaks, and
13// line breaks in a UTF-16 string.
14//
15// It provides several modes, BREAK_WORD, BREAK_LINE, and BREAK_NEWLINE,
16// which modify how characters are aggregated into the returned string.
17//
18// Under BREAK_WORD mode, once a word is encountered any non-word
19// characters are not included in the returned string (e.g. in the
20// UTF-16 equivalent of the string " foo bar! ", the word breaks are at
21// the periods in ". .foo. .bar.!. .").
22// Note that Chinese/Japanese/Thai do not use spaces between words so that
23// boundaries can fall in the middle of a continuous run of non-space /
24// non-punctuation characters.
25//
26// Under BREAK_LINE mode, once a line breaking opportunity is encountered,
27// any non-word  characters are included in the returned string, breaking
28// only when a space-equivalent character or a line breaking opportunity
29// is encountered (e.g. in the UTF16-equivalent of the string " foo bar! ",
30// the breaks are at the periods in ". .foo .bar! .").
31//
32// Note that lines can be broken at any character/syllable/grapheme cluster
33// boundary in Chinese/Japanese/Korean and at word boundaries in Thai
34// (Thai does not use spaces between words). Therefore, this is NOT the same
35// as breaking only at space-equivalent characters where its former
36// name (BREAK_SPACE) implied.
37//
38// Under BREAK_NEWLINE mode, all characters are included in the returned
39// string, breaking only when a newline-equivalent character is encountered
40// (eg. in the UTF-16 equivalent of the string "foo\nbar!\n\n", the line
41// breaks are at the periods in ".foo\n.bar\n.\n.").
42//
43// To extract the words from a string, move a BREAK_WORD BreakIterator
44// through the string and test whether IsWord() is true. E.g.,
45//   BreakIterator iter(str, BreakIterator::BREAK_WORD);
46//   if (!iter.Init())
47//     return false;
48//   while (iter.Advance()) {
49//     if (iter.IsWord()) {
50//       // Region [iter.prev(), iter.pos()) contains a word.
51//       VLOG(1) << "word: " << iter.GetString();
52//     }
53//   }
54
55namespace base {
56namespace i18n {
57
58class BASE_I18N_EXPORT BreakIterator {
59 public:
60  enum BreakType {
61    BREAK_WORD,
62    BREAK_LINE,
63    // TODO(jshin): Remove this after reviewing call sites.
64    // If call sites really need break only on space-like characters
65    // implement it separately.
66    BREAK_SPACE = BREAK_LINE,
67    BREAK_NEWLINE,
68    BREAK_CHARACTER,
69    // But don't remove this one!
70    RULE_BASED,
71  };
72
73  // Requires |str| to live as long as the BreakIterator does.
74  BreakIterator(const string16& str, BreakType break_type);
75  // Make a rule-based iterator. BreakType == RULE_BASED is implied.
76  // TODO(andrewhayden): This signature could easily be misinterpreted as
77  // "(const string16& str, const string16& locale)". We should do something
78  // better.
79  BreakIterator(const string16& str, const string16& rules);
80  ~BreakIterator();
81
82  // Init() must be called before any of the iterators are valid.
83  // Returns false if ICU failed to initialize.
84  bool Init();
85
86  // Advance to the next break.  Returns false if we've run past the end of
87  // the string.  (Note that the very last "break" is after the final
88  // character in the string, and when we advance to that position it's the
89  // last time Advance() returns true.)
90  bool Advance();
91
92  // Updates the text used by the iterator, resetting the iterator as if
93  // if Init() had been called again. Any old state is lost. Returns true
94  // unless there is an error setting the text.
95  bool SetText(const base::char16* text, const size_t length);
96
97  // Under BREAK_WORD mode, returns true if the break we just hit is the
98  // end of a word. (Otherwise, the break iterator just skipped over e.g.
99  // whitespace or punctuation.)  Under BREAK_LINE and BREAK_NEWLINE modes,
100  // this distinction doesn't apply and it always returns false.
101  bool IsWord() const;
102
103  // Under BREAK_WORD mode, returns true if |position| is at the end of word or
104  // at the start of word. It always returns false under BREAK_LINE and
105  // BREAK_NEWLINE modes.
106  bool IsEndOfWord(size_t position) const;
107  bool IsStartOfWord(size_t position) const;
108
109  // Under BREAK_CHARACTER mode, returns whether |position| is a Unicode
110  // grapheme boundary.
111  bool IsGraphemeBoundary(size_t position) const;
112
113  // Returns the string between prev() and pos().
114  // Advance() must have been called successfully at least once for pos() to
115  // have advanced to somewhere useful.
116  string16 GetString() const;
117
118  // Returns the value of pos() returned before Advance() was last called.
119  size_t prev() const { return prev_; }
120
121  // Returns the current break position within the string,
122  // or BreakIterator::npos when done.
123  size_t pos() const { return pos_; }
124
125 private:
126  // ICU iterator, avoiding ICU ubrk.h dependence.
127  // This is actually an ICU UBreakiterator* type, which turns out to be
128  // a typedef for a void* in the ICU headers. Using void* directly prevents
129  // callers from needing access to the ICU public headers directory.
130  void* iter_;
131
132  // The string we're iterating over. Can be changed with SetText(...)
133  const string16& string_;
134
135  // Rules for our iterator. Mutually exclusive with break_type_.
136  const string16 rules_;
137
138  // The breaking style (word/space/newline). Mutually exclusive with rules_
139  BreakType break_type_;
140
141  // Previous and current iterator positions.
142  size_t prev_, pos_;
143
144  DISALLOW_COPY_AND_ASSIGN(BreakIterator);
145};
146
147}  // namespace i18n
148}  // namespace base
149
150#endif  // BASE_I18N_BREAK_ITERATOR_H_
151