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
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
// Copyright 2015 The Servo Project Developers. See the
// COPYRIGHT file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! 3.3.3 Preparations for Implicit Processing
//!
//! <http://www.unicode.org/reports/tr9/#Preparations_for_Implicit_Processing>

use alloc::vec::Vec;
use core::cmp::max;
use core::ops::Range;

use super::level::Level;
use super::BidiClass::{self, *};

/// A maximal substring of characters with the same embedding level.
///
/// Represented as a range of byte indices.
pub type LevelRun = Range<usize>;

/// Output of `isolating_run_sequences` (steps X9-X10)
#[derive(Debug, PartialEq)]
pub struct IsolatingRunSequence {
    pub runs: Vec<LevelRun>,
    pub sos: BidiClass, // Start-of-sequence type.
    pub eos: BidiClass, // End-of-sequence type.
}

/// Compute the set of isolating run sequences.
///
/// An isolating run sequence is a maximal sequence of level runs such that for all level runs
/// except the last one in the sequence, the last character of the run is an isolate initiator
/// whose matching PDI is the first character of the next level run in the sequence.
///
/// Note: This function does *not* return the sequences in order by their first characters.
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn isolating_run_sequences(
    para_level: Level,
    original_classes: &[BidiClass],
    levels: &[Level],
) -> Vec<IsolatingRunSequence> {
    let runs = level_runs(levels, original_classes);

    // Compute the set of isolating run sequences.
    // <http://www.unicode.org/reports/tr9/#BD13>
    let mut sequences = Vec::with_capacity(runs.len());

    // When we encounter an isolate initiator, we push the current sequence onto the
    // stack so we can resume it after the matching PDI.
    let mut stack = vec![Vec::new()];

    for run in runs {
        assert!(run.len() > 0);
        assert!(!stack.is_empty());

        let start_class = original_classes[run.start];
        // > In rule X10, [..] skip over any BNs when [..].
        // > Do the same when determining if the last character of the sequence is an isolate initiator.
        //
        // <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>
        let end_class = original_classes[run.start..run.end]
            .iter()
            .copied()
            .rev()
            .filter(not_removed_by_x9)
            .next()
            .unwrap_or(start_class);

        let mut sequence = if start_class == PDI && stack.len() > 1 {
            // Continue a previous sequence interrupted by an isolate.
            stack.pop().unwrap()
        } else {
            // Start a new sequence.
            Vec::new()
        };

        sequence.push(run);

        if let RLI | LRI | FSI = end_class {
            // Resume this sequence after the isolate.
            stack.push(sequence);
        } else {
            // This sequence is finished.
            sequences.push(sequence);
        }
    }
    // Pop any remaning sequences off the stack.
    sequences.extend(stack.into_iter().rev().filter(|seq| !seq.is_empty()));

    // Determine the `sos` and `eos` class for each sequence.
    // <http://www.unicode.org/reports/tr9/#X10>
    sequences
        .into_iter()
        .map(|sequence: Vec<LevelRun>| {
            assert!(!sequence.is_empty());

            let mut result = IsolatingRunSequence {
                runs: sequence,
                sos: L,
                eos: L,
            };

            let start_of_seq = result.runs[0].start;
            let runs_len = result.runs.len();
            let end_of_seq = result.runs[runs_len - 1].end;

            // > (not counting characters removed by X9)
            let seq_level = result
                .iter_forwards_from(start_of_seq, 0)
                .filter(|i| not_removed_by_x9(&original_classes[*i]))
                .map(|i| levels[i])
                .next()
                .unwrap_or(levels[start_of_seq]);

            // XXXManishearth the spec talks of a start and end level,
            // but for a given IRS the two should be equivalent, yes?
            let end_level = result
                .iter_backwards_from(end_of_seq, runs_len - 1)
                .filter(|i| not_removed_by_x9(&original_classes[*i]))
                .map(|i| levels[i])
                .next()
                .unwrap_or(levels[end_of_seq - 1]);

            #[cfg(test)]
            for run in result.runs.clone() {
                for idx in run {
                    if not_removed_by_x9(&original_classes[idx]) {
                        assert_eq!(seq_level, levels[idx]);
                    }
                }
            }

            // Get the level of the last non-removed char before the runs.
            let pred_level = match original_classes[..start_of_seq]
                .iter()
                .rposition(not_removed_by_x9)
            {
                Some(idx) => levels[idx],
                None => para_level,
            };

            // Get the last non-removed character to check if it is an isolate initiator.
            // The spec calls for an unmatched one, but matched isolate initiators
            // will never be at the end of a level run (otherwise there would be more to the run).
            // We unwrap_or(BN) because BN marks removed classes and it won't matter for the check.
            let last_non_removed = original_classes[..end_of_seq]
                .iter()
                .copied()
                .rev()
                .find(not_removed_by_x9)
                .unwrap_or(BN);

            // Get the level of the next non-removed char after the runs.
            let succ_level = if let RLI | LRI | FSI = last_non_removed {
                para_level
            } else {
                match original_classes[end_of_seq..]
                    .iter()
                    .position(not_removed_by_x9)
                {
                    Some(idx) => levels[end_of_seq + idx],
                    None => para_level,
                }
            };

            result.sos = max(seq_level, pred_level).bidi_class();
            result.eos = max(end_level, succ_level).bidi_class();
            result
        })
        .collect()
}

impl IsolatingRunSequence {
    /// Given a text-relative position `pos` and an index of the level run it is in,
    /// produce an iterator of all characters after and pos (`pos..`) that are in this
    /// run sequence
    pub(crate) fn iter_forwards_from(
        &self,
        pos: usize,
        level_run_index: usize,
    ) -> impl Iterator<Item = usize> + '_ {
        let runs = &self.runs[level_run_index..];

        // Check that it is in range
        // (we can't use contains() since we want an inclusive range)
        #[cfg(feature = "std")]
        debug_assert!(runs[0].start <= pos && pos <= runs[0].end);

        (pos..runs[0].end).chain(runs[1..].iter().flat_map(Clone::clone))
    }

    /// Given a text-relative position `pos` and an index of the level run it is in,
    /// produce an iterator of all characters before and excludingpos (`..pos`) that are in this
    /// run sequence
    pub(crate) fn iter_backwards_from(
        &self,
        pos: usize,
        level_run_index: usize,
    ) -> impl Iterator<Item = usize> + '_ {
        let prev_runs = &self.runs[..level_run_index];
        let current = &self.runs[level_run_index];

        // Check that it is in range
        // (we can't use contains() since we want an inclusive range)
        #[cfg(feature = "std")]
        debug_assert!(current.start <= pos && pos <= current.end);

        (current.start..pos)
            .rev()
            .chain(prev_runs.iter().rev().flat_map(Clone::clone))
    }
}

/// Finds the level runs in a paragraph.
///
/// <http://www.unicode.org/reports/tr9/#BD7>
fn level_runs(levels: &[Level], original_classes: &[BidiClass]) -> Vec<LevelRun> {
    assert_eq!(levels.len(), original_classes.len());

    let mut runs = Vec::new();
    if levels.is_empty() {
        return runs;
    }

    let mut current_run_level = levels[0];
    let mut current_run_start = 0;
    for i in 1..levels.len() {
        if !removed_by_x9(original_classes[i]) && levels[i] != current_run_level {
            // End the last run and start a new one.
            runs.push(current_run_start..i);
            current_run_level = levels[i];
            current_run_start = i;
        }
    }
    runs.push(current_run_start..levels.len());

    runs
}

/// Should this character be ignored in steps after X9?
///
/// <http://www.unicode.org/reports/tr9/#X9>
pub fn removed_by_x9(class: BidiClass) -> bool {
    match class {
        RLE | LRE | RLO | LRO | PDF | BN => true,
        _ => false,
    }
}

// For use as a predicate for `position` / `rposition`
pub fn not_removed_by_x9(class: &BidiClass) -> bool {
    !removed_by_x9(*class)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_level_runs() {
        assert_eq!(level_runs(&Level::vec(&[]), &[]), &[]);
        assert_eq!(
            level_runs(&Level::vec(&[0, 0, 0, 1, 1, 2, 0, 0]), &[L; 8]),
            &[0..3, 3..5, 5..6, 6..8]
        );
    }

    // From <http://www.unicode.org/reports/tr9/#BD13>
    #[rustfmt::skip]
    #[test]
    fn test_isolating_run_sequences() {

        // == Example 1 ==
        // text1·RLE·text2·PDF·RLE·text3·PDF·text4
        // index        0    1  2    3    4  5    6  7
        let classes = &[L, RLE, L, PDF, RLE, L, PDF, L];
        let levels =  &[0,   1, 1,   1,   1, 1,   1, 0];
        let para_level = Level::ltr();
        let mut sequences = isolating_run_sequences(para_level, classes, &Level::vec(levels));
        sequences.sort_by(|a, b| a.runs[0].clone().cmp(b.runs[0].clone()));
        assert_eq!(
            sequences.iter().map(|s| s.runs.clone()).collect::<Vec<_>>(),
            vec![vec![0..2], vec![2..7], vec![7..8]]
        );

        // == Example 2 ==
        // text1·RLI·text2·PDI·RLI·text3·PDI·text4
        // index        0    1  2    3    4  5    6  7
        let classes = &[L, RLI, L, PDI, RLI, L, PDI, L];
        let levels =  &[0,   0, 1,   0,   0, 1,   0, 0];
        let para_level = Level::ltr();
        let mut sequences = isolating_run_sequences(para_level, classes, &Level::vec(levels));
        sequences.sort_by(|a, b| a.runs[0].clone().cmp(b.runs[0].clone()));
        assert_eq!(
            sequences.iter().map(|s| s.runs.clone()).collect::<Vec<_>>(),
            vec![vec![0..2, 3..5, 6..8], vec![2..3], vec![5..6]]
        );

        // == Example 3 ==
        // text1·RLI·text2·LRI·text3·RLE·text4·PDF·text5·PDI·text6·PDI·text7
        // index        0    1  2    3  4    5  6    7  8    9  10  11  12
        let classes = &[L, RLI, L, LRI, L, RLE, L, PDF, L, PDI, L, PDI,  L];
        let levels =  &[0,   0, 1,   1, 2,   3, 3,   3, 2,   1, 1,   0,  0];
        let para_level = Level::ltr();
        let mut sequences = isolating_run_sequences(para_level, classes, &Level::vec(levels));
        sequences.sort_by(|a, b| a.runs[0].clone().cmp(b.runs[0].clone()));
        assert_eq!(
            sequences.iter().map(|s| s.runs.clone()).collect::<Vec<_>>(),
            vec![vec![0..2, 11..13], vec![2..4, 9..11], vec![4..6], vec![6..8], vec![8..9]]
        );
    }

    // From <http://www.unicode.org/reports/tr9/#X10>
    #[rustfmt::skip]
    #[test]
    fn test_isolating_run_sequences_sos_and_eos() {

        // == Example 1 ==
        // text1·RLE·text2·LRE·text3·PDF·text4·PDF·RLE·text5·PDF·text6
        // index        0    1  2    3  4    5  6    7    8  9   10  11
        let classes = &[L, RLE, L, LRE, L, PDF, L, PDF, RLE, L, PDF,  L];
        let levels =  &[0,   1, 1,   2, 2,   2, 1,   1,   1, 1,   1,  0];
        let para_level = Level::ltr();
        let mut sequences = isolating_run_sequences(para_level, classes, &Level::vec(levels));
        sequences.sort_by(|a, b| a.runs[0].clone().cmp(b.runs[0].clone()));

        // text1
        assert_eq!(
            &sequences[0],
            &IsolatingRunSequence {
                runs: vec![0..2],
                sos: L,
                eos: R,
            }
        );

        // text2
        assert_eq!(
            &sequences[1],
            &IsolatingRunSequence {
                runs: vec![2..4],
                sos: R,
                eos: L,
            }
        );

        // text3
        assert_eq!(
            &sequences[2],
            &IsolatingRunSequence {
                runs: vec![4..6],
                sos: L,
                eos: L,
            }
        );

        // text4 text5
        assert_eq!(
            &sequences[3],
            &IsolatingRunSequence {
                runs: vec![6..11],
                sos: L,
                eos: R,
            }
        );

        // text6
        assert_eq!(
            &sequences[4],
            &IsolatingRunSequence {
                runs: vec![11..12],
                sos: R,
                eos: L,
            }
        );

        // == Example 2 ==
        // text1·RLI·text2·LRI·text3·PDI·text4·PDI·RLI·text5·PDI·text6
        // index        0    1  2    3  4    5  6    7    8  9   10  11
        let classes = &[L, RLI, L, LRI, L, PDI, L, PDI, RLI, L, PDI,  L];
        let levels =  &[0,   0, 1,   1, 2,   1, 1,   0,   0, 1,   0,  0];
        let para_level = Level::ltr();
        let mut sequences = isolating_run_sequences(para_level, classes, &Level::vec(levels));
        sequences.sort_by(|a, b| a.runs[0].clone().cmp(b.runs[0].clone()));

        // text1·RLI·PDI·RLI·PDI·text6
        assert_eq!(
            &sequences[0],
            &IsolatingRunSequence {
                runs: vec![0..2, 7..9, 10..12],
                sos: L,
                eos: L,
            }
        );

        // text2·LRI·PDI·text4
        assert_eq!(
            &sequences[1],
            &IsolatingRunSequence {
                runs: vec![2..4, 5..7],
                sos: R,
                eos: R,
            }
        );

        // text3
        assert_eq!(
            &sequences[2],
            &IsolatingRunSequence {
                runs: vec![4..5],
                sos: L,
                eos: L,
            }
        );

        // text5
        assert_eq!(
            &sequences[3],
            &IsolatingRunSequence {
                runs: vec![9..10],
                sos: R,
                eos: R,
            }
        );
    }

    #[test]
    fn test_removed_by_x9() {
        let rem_classes = &[RLE, LRE, RLO, LRO, PDF, BN];
        let not_classes = &[L, RLI, AL, LRI, PDI];
        for x in rem_classes {
            assert_eq!(removed_by_x9(*x), true);
        }
        for x in not_classes {
            assert_eq!(removed_by_x9(*x), false);
        }
    }

    #[test]
    fn test_not_removed_by_x9() {
        let non_x9_classes = &[L, R, AL, EN, ES, ET, AN, CS, NSM, B, S, WS, ON, LRI, RLI, FSI, PDI];
        for x in non_x9_classes {
            assert_eq!(not_removed_by_x9(&x), true);
        }
    }
}