1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

use crate::complex::ComplexPayloads;
use crate::indices::{Latin1Indices, Utf16Indices};
use crate::provider::*;
use crate::WordType;
use core::str::CharIndices;
use utf8_iter::Utf8CharIndices;

/// A trait allowing for RuleBreakIterator to be generalized to multiple string
/// encoding methods and granularity such as grapheme cluster, word, etc.
pub trait RuleBreakType<'l, 's> {
    /// The iterator over characters.
    type IterAttr: Iterator<Item = (usize, Self::CharType)> + Clone + core::fmt::Debug;

    /// The character type.
    type CharType: Copy + Into<u32> + core::fmt::Debug;

    fn get_current_position_character_len(iter: &RuleBreakIterator<'l, 's, Self>) -> usize;

    fn handle_complex_language(
        iter: &mut RuleBreakIterator<'l, 's, Self>,
        left_codepoint: Self::CharType,
    ) -> Option<usize>;
}

/// Implements the [`Iterator`] trait over the segmenter boundaries of the given string.
///
/// Lifetimes:
///
/// - `'l` = lifetime of the segmenter object from which this iterator was created
/// - `'s` = lifetime of the string being segmented
///
/// The [`Iterator::Item`] is an [`usize`] representing index of a code unit
/// _after_ the boundary (for a boundary at the end of text, this index is the length
/// of the [`str`] or array of code units).
#[derive(Debug)]
pub struct RuleBreakIterator<'l, 's, Y: RuleBreakType<'l, 's> + ?Sized> {
    pub(crate) iter: Y::IterAttr,
    pub(crate) len: usize,
    pub(crate) current_pos_data: Option<(usize, Y::CharType)>,
    pub(crate) result_cache: alloc::vec::Vec<usize>,
    pub(crate) data: &'l RuleBreakDataV1<'l>,
    pub(crate) complex: Option<&'l ComplexPayloads>,
    pub(crate) boundary_property: u8,
}

impl<'l, 's, Y: RuleBreakType<'l, 's> + ?Sized> Iterator for RuleBreakIterator<'l, 's, Y> {
    type Item = usize;

    fn next(&mut self) -> Option<Self::Item> {
        // If we have break point cache by previous run, return this result
        if let Some(&first_result) = self.result_cache.first() {
            let mut i = 0;
            loop {
                if i == first_result {
                    self.result_cache = self.result_cache.iter().skip(1).map(|r| r - i).collect();
                    return self.get_current_position();
                }
                i += Y::get_current_position_character_len(self);
                self.advance_iter();
                if self.is_eof() {
                    self.result_cache.clear();
                    self.boundary_property = self.data.complex_property;
                    return Some(self.len);
                }
            }
        }

        if self.is_eof() {
            self.advance_iter();
            if self.is_eof() && self.len == 0 {
                // Empty string. Since `self.current_pos_data` is always going to be empty,
                // we never read `self.len` except for here, so we can use it to mark that
                // we have already returned the single empty-string breakpoint.
                self.len = 1;
                return Some(0);
            }
            let Some(right_prop) = self.get_current_break_property() else {
                // iterator already reaches to EOT. Reset boundary property for word-like.
                self.boundary_property = 0;
                return None;
            };
            // SOT x anything
            if matches!(
                self.get_break_state_from_table(self.data.sot_property, right_prop),
                BreakState::Break | BreakState::NoMatch
            ) {
                self.boundary_property = 0; // SOT is special type
                return self.get_current_position();
            }
        }

        'a: loop {
            debug_assert!(!self.is_eof());
            let left_codepoint = self.get_current_codepoint()?;
            let left_prop = self.get_break_property(left_codepoint);
            self.advance_iter();

            let Some(right_prop) = self.get_current_break_property() else {
                self.boundary_property = left_prop;
                return Some(self.len);
            };

            // Some segmenter rules doesn't have language-specific rules, we have to use LSTM (or dictionary) segmenter.
            // If property is marked as SA, use it
            if right_prop == self.data.complex_property {
                if left_prop != self.data.complex_property {
                    // break before SA
                    self.boundary_property = left_prop;
                    return self.get_current_position();
                }
                let break_offset = Y::handle_complex_language(self, left_codepoint);
                if break_offset.is_some() {
                    return break_offset;
                }
            }

            match self.get_break_state_from_table(left_prop, right_prop) {
                BreakState::Keep => continue,
                BreakState::Break | BreakState::NoMatch => {
                    self.boundary_property = left_prop;
                    return self.get_current_position();
                }
                BreakState::Index(mut index) | BreakState::Intermediate(mut index) => {
                    // This isn't simple rule set. We need marker to restore iterator to previous position.
                    let mut previous_iter = self.iter.clone();
                    let mut previous_pos_data = self.current_pos_data;
                    let mut previous_left_prop = left_prop;

                    loop {
                        self.advance_iter();

                        let Some(prop) = self.get_current_break_property() else {
                            // Reached EOF. But we are analyzing multiple characters now, so next break may be previous point.
                            self.boundary_property = index;
                            if self.get_break_state_from_table(index, self.data.eot_property)
                                == BreakState::NoMatch
                            {
                                self.boundary_property = previous_left_prop;
                                self.iter = previous_iter;
                                self.current_pos_data = previous_pos_data;
                                return self.get_current_position();
                            }
                            // EOF
                            return Some(self.len);
                        };

                        let previous_break_state_is_cp_prop =
                            index <= self.data.last_codepoint_property;

                        match self.get_break_state_from_table(index, prop) {
                            BreakState::Keep => continue 'a,
                            BreakState::NoMatch => {
                                self.boundary_property = previous_left_prop;
                                self.iter = previous_iter;
                                self.current_pos_data = previous_pos_data;
                                return self.get_current_position();
                            }
                            BreakState::Break => return self.get_current_position(),
                            BreakState::Intermediate(i) => {
                                index = i;
                                if previous_break_state_is_cp_prop {
                                    // Move marker
                                    previous_left_prop = index;
                                }
                                previous_iter = self.iter.clone();
                                previous_pos_data = self.current_pos_data;
                            }
                            BreakState::Index(i) => {
                                index = i;
                                if previous_break_state_is_cp_prop {
                                    // Move marker
                                    previous_iter = self.iter.clone();
                                    previous_pos_data = self.current_pos_data;
                                    previous_left_prop = index;
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

impl<'l, 's, Y: RuleBreakType<'l, 's> + ?Sized> RuleBreakIterator<'l, 's, Y> {
    pub(crate) fn advance_iter(&mut self) {
        self.current_pos_data = self.iter.next();
    }

    pub(crate) fn is_eof(&self) -> bool {
        self.current_pos_data.is_none()
    }

    pub(crate) fn get_current_break_property(&self) -> Option<u8> {
        self.get_current_codepoint()
            .map(|c| self.get_break_property(c))
    }

    pub(crate) fn get_current_position(&self) -> Option<usize> {
        self.current_pos_data.map(|(pos, _)| pos)
    }

    pub(crate) fn get_current_codepoint(&self) -> Option<Y::CharType> {
        self.current_pos_data.map(|(_, codepoint)| codepoint)
    }

    fn get_break_property(&self, codepoint: Y::CharType) -> u8 {
        // Note: Default value is 0 == UNKNOWN
        self.data.property_table.get32(codepoint.into())
    }

    fn get_break_state_from_table(&self, left: u8, right: u8) -> BreakState {
        let idx = left as usize * self.data.property_count as usize + right as usize;
        // We use unwrap_or to fall back to the base case and prevent panics on bad data.
        self.data
            .break_state_table
            .get(idx)
            .unwrap_or(BreakState::Keep)
    }

    /// Return the status value of break boundary.
    /// If segmenter isn't word, always return WordType::None
    pub fn word_type(&self) -> WordType {
        if self.result_cache.first().is_some() {
            // Dictionary type (CJ and East Asian) is letter.
            return WordType::Letter;
        }
        if self.boundary_property == 0 {
            // break position is SOT / Any
            return WordType::None;
        }
        self.data
            .word_type_table
            .get((self.boundary_property - 1) as usize)
            .unwrap_or(WordType::None)
    }

    /// Return true when break boundary is word-like such as letter/number/CJK
    /// If segmenter isn't word, return false
    pub fn is_word_like(&self) -> bool {
        self.word_type().is_word_like()
    }
}

#[derive(Debug)]
pub struct RuleBreakTypeUtf8;

impl<'l, 's> RuleBreakType<'l, 's> for RuleBreakTypeUtf8 {
    type IterAttr = CharIndices<'s>;
    type CharType = char;

    fn get_current_position_character_len(iter: &RuleBreakIterator<Self>) -> usize {
        iter.get_current_codepoint().map_or(0, |c| c.len_utf8())
    }

    fn handle_complex_language(
        _: &mut RuleBreakIterator<Self>,
        _: Self::CharType,
    ) -> Option<usize> {
        unreachable!()
    }
}

#[derive(Debug)]
pub struct RuleBreakTypePotentiallyIllFormedUtf8;

impl<'l, 's> RuleBreakType<'l, 's> for RuleBreakTypePotentiallyIllFormedUtf8 {
    type IterAttr = Utf8CharIndices<'s>;
    type CharType = char;

    fn get_current_position_character_len(iter: &RuleBreakIterator<Self>) -> usize {
        iter.get_current_codepoint().map_or(0, |c| c.len_utf8())
    }

    fn handle_complex_language(
        _: &mut RuleBreakIterator<Self>,
        _: Self::CharType,
    ) -> Option<usize> {
        unreachable!()
    }
}

#[derive(Debug)]
pub struct RuleBreakTypeLatin1;

impl<'l, 's> RuleBreakType<'l, 's> for RuleBreakTypeLatin1 {
    type IterAttr = Latin1Indices<'s>;
    type CharType = u8;

    fn get_current_position_character_len(_: &RuleBreakIterator<Self>) -> usize {
        unreachable!()
    }

    fn handle_complex_language(
        _: &mut RuleBreakIterator<Self>,
        _: Self::CharType,
    ) -> Option<usize> {
        unreachable!()
    }
}

#[derive(Debug)]
pub struct RuleBreakTypeUtf16;

impl<'l, 's> RuleBreakType<'l, 's> for RuleBreakTypeUtf16 {
    type IterAttr = Utf16Indices<'s>;
    type CharType = u32;

    fn get_current_position_character_len(iter: &RuleBreakIterator<Self>) -> usize {
        match iter.get_current_codepoint() {
            None => 0,
            Some(ch) if ch >= 0x10000 => 2,
            _ => 1,
        }
    }

    fn handle_complex_language(
        _: &mut RuleBreakIterator<Self>,
        _: Self::CharType,
    ) -> Option<usize> {
        unreachable!()
    }
}