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
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
// 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.

//! 3.3.4 - 3.3.6. Resolve implicit levels and types.

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

use super::char_data::BidiClass::{self, *};
use super::level::Level;
use super::prepare::{not_removed_by_x9, removed_by_x9, IsolatingRunSequence};
use super::BidiDataSource;

/// 3.3.4 Resolving Weak Types
///
/// <http://www.unicode.org/reports/tr9/#Resolving_Weak_Types>
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn resolve_weak(
    text: &str,
    sequence: &IsolatingRunSequence,
    processing_classes: &mut [BidiClass],
) {
    // Note: The spec treats these steps as individual passes that are applied one after the other
    // on the entire IsolatingRunSequence at once. We instead collapse it into a single iteration,
    // which is straightforward for rules that are based on the state of the current character, but not
    // for rules that care about surrounding characters. To deal with them, we retain additional state
    // about previous character classes that may have since been changed by later rules.

    // The previous class for the purposes of rule W4/W6, not tracking changes made after or during W4.
    let mut prev_class_before_w4 = sequence.sos;
    // The previous class for the purposes of rule W5.
    let mut prev_class_before_w5 = sequence.sos;
    // The previous class for the purposes of rule W1, not tracking changes from any other rules.
    let mut prev_class_before_w1 = sequence.sos;
    let mut last_strong_is_al = false;
    let mut et_run_indices = Vec::new(); // for W5
    let mut bn_run_indices = Vec::new(); // for W5 +  <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>

    for (run_index, level_run) in sequence.runs.iter().enumerate() {
        for i in &mut level_run.clone() {
            if processing_classes[i] == BN {
                // <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>
                // Keeps track of bn runs for W5 in case we see an ET.
                bn_run_indices.push(i);
                // BNs aren't real, skip over them.
                continue;
            }

            // Store the processing class of all rules before W2/W1.
            // Used to keep track of the last strong character for W2. W3 is able to insert new strong
            // characters, so we don't want to be misled by it.
            let mut w2_processing_class = processing_classes[i];

            // <http://www.unicode.org/reports/tr9/#W1>
            //

            if processing_classes[i] == NSM {
                processing_classes[i] = match prev_class_before_w1 {
                    RLI | LRI | FSI | PDI => ON,
                    _ => prev_class_before_w1,
                };
                // W1 occurs before W2, update this.
                w2_processing_class = processing_classes[i];
            }

            prev_class_before_w1 = processing_classes[i];

            // <http://www.unicode.org/reports/tr9/#W2>
            // <http://www.unicode.org/reports/tr9/#W3>
            //
            match processing_classes[i] {
                EN => {
                    if last_strong_is_al {
                        // W2. If previous strong char was AL, change EN to AN.
                        processing_classes[i] = AN;
                    }
                }
                // W3.
                AL => processing_classes[i] = R,
                _ => {}
            }

            // update last_strong_is_al.
            match w2_processing_class {
                L | R => {
                    last_strong_is_al = false;
                }
                AL => {
                    last_strong_is_al = true;
                }
                _ => {}
            }

            let class_before_w456 = processing_classes[i];

            // <http://www.unicode.org/reports/tr9/#W4>
            // <http://www.unicode.org/reports/tr9/#W5>
            // <http://www.unicode.org/reports/tr9/#W6> (separators only)
            // (see below for W6 terminator code)
            //
            match processing_classes[i] {
                // <http://www.unicode.org/reports/tr9/#W6>
                EN => {
                    // W5. If a run of ETs is adjacent to an EN, change the ETs to EN.
                    for j in &et_run_indices {
                        processing_classes[*j] = EN;
                    }
                    et_run_indices.clear();
                }

                // <http://www.unicode.org/reports/tr9/#W4>
                // <http://www.unicode.org/reports/tr9/#W6>
                ES | CS => {
                    // See https://github.com/servo/unicode-bidi/issues/86 for improving this.
                    // We want to make sure we check the correct next character by skipping past the rest
                    // of this one.
                    if let Some(ch) = text.get(i..).and_then(|s| s.chars().next()) {
                        let mut next_class = sequence
                            .iter_forwards_from(i + ch.len_utf8(), run_index)
                            .map(|j| processing_classes[j])
                            // <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>
                            .find(not_removed_by_x9)
                            .unwrap_or(sequence.eos);
                        if next_class == EN && last_strong_is_al {
                            // Apply W2 to next_class. We know that last_strong_is_al
                            // has no chance of changing on this character so we can still assume its value
                            // will be the same by the time we get to it.
                            next_class = AN;
                        }
                        processing_classes[i] =
                            match (prev_class_before_w4, processing_classes[i], next_class) {
                                // W4
                                (EN, ES, EN) | (EN, CS, EN) => EN,
                                // W4
                                (AN, CS, AN) => AN,
                                // W6 (separators only)
                                (_, _, _) => ON,
                            };

                        // W6 + <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>
                        // We have to do this before W5 gets its grubby hands on these characters and thinks
                        // they're part of an ET run.
                        // We check for ON to ensure that we had hit the W6 branch above, since this `ES | CS` match
                        // arm handles both W4 and W6.
                        if processing_classes[i] == ON {
                            for idx in sequence.iter_backwards_from(i, run_index) {
                                let class = &mut processing_classes[idx];
                                if *class != BN {
                                    break;
                                }
                                *class = ON;
                            }
                            for idx in sequence.iter_forwards_from(i + ch.len_utf8(), run_index) {
                                let class = &mut processing_classes[idx];
                                if *class != BN {
                                    break;
                                }
                                *class = ON;
                            }
                        }
                    } else {
                        // We're in the middle of a character, copy over work done for previous bytes
                        // since it's going to be the same answer.
                        processing_classes[i] = processing_classes[i - 1];
                    }
                }
                // <http://www.unicode.org/reports/tr9/#W5>
                ET => {
                    match prev_class_before_w5 {
                        EN => processing_classes[i] = EN,
                        _ => {
                            // <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>
                            // If there was a BN run before this, that's now a part of this ET run.
                            et_run_indices.extend(&bn_run_indices);

                            // In case this is followed by an EN.
                            et_run_indices.push(i);
                        }
                    }
                }
                _ => {}
            }

            // Common loop iteration code
            //

            // <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>
            // BN runs would have already continued the loop, clear them before we get to the next one.
            bn_run_indices.clear();

            // W6 above only deals with separators, so it doesn't change anything W5 cares about,
            // so we still can update this after running that part of W6.
            prev_class_before_w5 = processing_classes[i];

            // <http://www.unicode.org/reports/tr9/#W6> (terminators only)
            // (see above for W6 separator code)
            //
            if prev_class_before_w5 != ET {
                // W6. If we didn't find an adjacent EN, turn any ETs into ON instead.
                for j in &et_run_indices {
                    processing_classes[*j] = ON;
                }
                et_run_indices.clear();
            }

            // We stashed this before W4/5/6 could get their grubby hands on it, and it's not
            // used in the W6 terminator code below so we can update it now.
            prev_class_before_w4 = class_before_w456;
        }
    }
    // Rerun this check in case we ended with a sequence of BNs (i.e., we'd never
    // hit the end of the for loop above).
    // W6. If we didn't find an adjacent EN, turn any ETs into ON instead.
    for j in &et_run_indices {
        processing_classes[*j] = ON;
    }
    et_run_indices.clear();

    // W7. If the previous strong char was L, change EN to L.
    let mut last_strong_is_l = sequence.sos == L;
    for run in &sequence.runs {
        for i in run.clone() {
            match processing_classes[i] {
                EN if last_strong_is_l => {
                    processing_classes[i] = L;
                }
                L => {
                    last_strong_is_l = true;
                }
                R | AL => {
                    last_strong_is_l = false;
                }
                // <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>
                // Already scanning past BN here.
                _ => {}
            }
        }
    }
}

/// 3.3.5 Resolving Neutral Types
///
/// <http://www.unicode.org/reports/tr9/#Resolving_Neutral_Types>
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn resolve_neutral<D: BidiDataSource>(
    text: &str,
    data_source: &D,
    sequence: &IsolatingRunSequence,
    levels: &[Level],
    original_classes: &[BidiClass],
    processing_classes: &mut [BidiClass],
) {
    // e = embedding direction
    let e: BidiClass = levels[sequence.runs[0].start].bidi_class();
    let not_e = if e == BidiClass::L {
        BidiClass::R
    } else {
        BidiClass::L
    };
    // N0. Process bracket pairs.

    // > Identify the bracket pairs in the current isolating run sequence according to BD16.
    // We use processing_classes, not original_classes, due to BD14/BD15
    let bracket_pairs = identify_bracket_pairs(text, data_source, sequence, processing_classes);

    // > For each bracket-pair element in the list of pairs of text positions
    //
    // Note: Rust ranges are interpreted as [start..end), be careful using `pair` directly
    // for indexing as it will include the opening bracket pair but not the closing one.
    for pair in bracket_pairs {
        #[cfg(feature = "std")]
        debug_assert!(
            pair.start < processing_classes.len(),
            "identify_bracket_pairs returned a range that is out of bounds!"
        );
        #[cfg(feature = "std")]
        debug_assert!(
            pair.end < processing_classes.len(),
            "identify_bracket_pairs returned a range that is out of bounds!"
        );
        let mut found_e = false;
        let mut found_not_e = false;
        let mut class_to_set = None;

        let start_len_utf8 = text[pair.start..].chars().next().unwrap().len_utf8();
        // > Inspect the bidirectional types of the characters enclosed within the bracket pair.
        //
        // `pair` is [start, end) so we will end up processing the opening character but not the closing one.
        //
        for enclosed_i in sequence.iter_forwards_from(pair.start + start_len_utf8, pair.start_run) {
            if enclosed_i >= pair.end {
                #[cfg(feature = "std")]
                debug_assert!(
                    enclosed_i == pair.end,
                    "If we skipped past this, the iterator is broken"
                );
                break;
            }
            let class = processing_classes[enclosed_i];
            if class == e {
                found_e = true;
            } else if class == not_e {
                found_not_e = true;
            } else if class == BidiClass::EN || class == BidiClass::AN {
                // > Within this scope, bidirectional types EN and AN are treated as R.
                if e == BidiClass::L {
                    found_not_e = true;
                } else {
                    found_e = true;
                }
            }

            // If we have found a character with the class of the embedding direction
            // we can bail early.
            if found_e {
                break;
            }
        }
        // > If any strong type (either L or R) matching the embedding direction is found
        if found_e {
            // > .. set the type for both brackets in the pair to match the embedding direction
            class_to_set = Some(e);
        // > Otherwise, if there is a strong type it must be opposite the embedding direction
        } else if found_not_e {
            // > Therefore, test for an established context with a preceding strong type by
            // > checking backwards before the opening paired bracket
            // > until the first strong type (L, R, or sos) is found.
            // (see note above about processing_classes and character boundaries)
            let mut previous_strong = sequence
                .iter_backwards_from(pair.start, pair.start_run)
                .map(|i| processing_classes[i])
                .find(|class| {
                    *class == BidiClass::L
                        || *class == BidiClass::R
                        || *class == BidiClass::EN
                        || *class == BidiClass::AN
                })
                .unwrap_or(sequence.sos);

            // > Within this scope, bidirectional types EN and AN are treated as R.
            if previous_strong == BidiClass::EN || previous_strong == BidiClass::AN {
                previous_strong = BidiClass::R;
            }

            // > If the preceding strong type is also opposite the embedding direction,
            // > context is established,
            // > so set the type for both brackets in the pair to that direction.
            // AND
            // > Otherwise set the type for both brackets in the pair to the embedding direction.
            // > Either way it gets set to previous_strong
            //
            // Both branches amount to setting the type to the strong type.
            class_to_set = Some(previous_strong);
        }

        if let Some(class_to_set) = class_to_set {
            // Update all processing classes corresponding to the start and end elements, as requested.
            // We should include all bytes of the character, not the first one.
            let end_len_utf8 = text[pair.end..].chars().next().unwrap().len_utf8();
            for class in &mut processing_classes[pair.start..pair.start + start_len_utf8] {
                *class = class_to_set;
            }
            for class in &mut processing_classes[pair.end..pair.end + end_len_utf8] {
                *class = class_to_set;
            }
            // <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>
            for idx in sequence.iter_backwards_from(pair.start, pair.start_run) {
                let class = &mut processing_classes[idx];
                if *class != BN {
                    break;
                }
                *class = class_to_set;
            }
            // > Any number of characters that had original bidirectional character type NSM prior to the application of
            // > W1 that immediately follow a paired bracket which changed to L or R under N0 should change to match the type of their preceding bracket.

            // This rule deals with sequences of NSMs, so we can just update them all at once, we don't need to worry
            // about character boundaries. We do need to be careful to skip the full set of bytes for the parentheses characters.
            let nsm_start = pair.start + start_len_utf8;
            for idx in sequence.iter_forwards_from(nsm_start, pair.start_run) {
                let class = original_classes[idx];
                if class == BidiClass::NSM || processing_classes[idx] == BN {
                    processing_classes[idx] = class_to_set;
                } else {
                    break;
                }
            }
            let nsm_end = pair.end + end_len_utf8;
            for idx in sequence.iter_forwards_from(nsm_end, pair.end_run) {
                let class = original_classes[idx];
                if class == BidiClass::NSM || processing_classes[idx] == BN {
                    processing_classes[idx] = class_to_set;
                } else {
                    break;
                }
            }
        }
        // > Otherwise, there are no strong types within the bracket pair
        // > Therefore, do not set the type for that bracket pair
    }

    // N1 and N2.
    // Indices of every byte in this isolating run sequence
    let mut indices = sequence.runs.iter().flat_map(Clone::clone);
    let mut prev_class = sequence.sos;
    while let Some(mut i) = indices.next() {
        // Process sequences of NI characters.
        let mut ni_run = Vec::new();
        // The BN is for <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>
        if is_NI(processing_classes[i]) || processing_classes[i] == BN {
            // Consume a run of consecutive NI characters.
            ni_run.push(i);
            let mut next_class;
            loop {
                match indices.next() {
                    Some(j) => {
                        i = j;
                        next_class = processing_classes[j];
                        // The BN is for <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters>
                        if is_NI(next_class) || next_class == BN {
                            ni_run.push(i);
                        } else {
                            break;
                        }
                    }
                    None => {
                        next_class = sequence.eos;
                        break;
                    }
                };
            }
            // N1-N2.
            //
            // <http://www.unicode.org/reports/tr9/#N1>
            // <http://www.unicode.org/reports/tr9/#N2>
            let new_class = match (prev_class, next_class) {
                (L, L) => L,
                (R, R)
                | (R, AN)
                | (R, EN)
                | (AN, R)
                | (AN, AN)
                | (AN, EN)
                | (EN, R)
                | (EN, AN)
                | (EN, EN) => R,
                (_, _) => e,
            };
            for j in &ni_run {
                processing_classes[*j] = new_class;
            }
            ni_run.clear();
        }
        prev_class = processing_classes[i];
    }
}

struct BracketPair {
    /// The text-relative index of the opening bracket.
    start: usize,
    /// The text-relative index of the closing bracket.
    end: usize,
    /// The index of the run (in the run sequence) that the opening bracket is in.
    start_run: usize,
    /// The index of the run (in the run sequence) that the closing bracket is in.
    end_run: usize,
}
/// 3.1.3 Identifying Bracket Pairs
///
/// Returns all paired brackets in the source, as indices into the
/// text source.
///
/// <https://www.unicode.org/reports/tr9/#BD16>
fn identify_bracket_pairs<D: BidiDataSource>(
    text: &str,
    data_source: &D,
    run_sequence: &IsolatingRunSequence,
    original_classes: &[BidiClass],
) -> Vec<BracketPair> {
    let mut ret = vec![];
    let mut stack = vec![];

    for (run_index, level_run) in run_sequence.runs.iter().enumerate() {
        let slice = if let Some(slice) = text.get(level_run.clone()) {
            slice
        } else {
            #[cfg(feature = "std")]
            std::debug_assert!(
                false,
                "Found broken indices in level run: found indices {}..{} for string of length {}",
                level_run.start,
                level_run.end,
                text.len()
            );
            return ret;
        };

        for (i, ch) in slice.char_indices() {
            let actual_index = level_run.start + i;
            // All paren characters are ON.
            // From BidiBrackets.txt:
            // > The Unicode property value stability policy guarantees that characters
            // > which have bpt=o or bpt=c also have bc=ON and Bidi_M=Y
            if original_classes[level_run.start + i] != BidiClass::ON {
                continue;
            }

            if let Some(matched) = data_source.bidi_matched_opening_bracket(ch) {
                if matched.is_open {
                    // > If an opening paired bracket is found ...

                    // > ... and there is no room in the stack,
                    // > stop processing BD16 for the remainder of the isolating run sequence.
                    if stack.len() >= 63 {
                        break;
                    }
                    // > ... push its Bidi_Paired_Bracket property value and its text position onto the stack
                    stack.push((matched.opening, actual_index, run_index))
                } else {
                    // > If a closing paired bracket is found, do the following

                    // > Declare a variable that holds a reference to the current stack element
                    // > and initialize it with the top element of the stack.
                    // AND
                    // > Else, if the current stack element is not at the bottom of the stack
                    for (stack_index, element) in stack.iter().enumerate().rev() {
                        // > Compare the closing paired bracket being inspected or its canonical
                        // > equivalent to the bracket in the current stack element.
                        if element.0 == matched.opening {
                            // > If the values match, meaning the two characters form a bracket pair, then

                            // > Append the text position in the current stack element together with the
                            // > text position of the closing paired bracket to the list.
                            let pair = BracketPair {
                                start: element.1,
                                end: actual_index,
                                start_run: element.2,
                                end_run: run_index,
                            };
                            ret.push(pair);

                            // > Pop the stack through the current stack element inclusively.
                            stack.truncate(stack_index);
                            break;
                        }
                    }
                }
            }
        }
    }
    // > Sort the list of pairs of text positions in ascending order based on
    // > the text position of the opening paired bracket.
    ret.sort_by_key(|r| r.start);
    ret
}

/// 3.3.6 Resolving Implicit Levels
///
/// Returns the maximum embedding level in the paragraph.
///
/// <http://www.unicode.org/reports/tr9/#Resolving_Implicit_Levels>
#[cfg_attr(feature = "flame_it", flamer::flame)]
pub fn resolve_levels(original_classes: &[BidiClass], levels: &mut [Level]) -> Level {
    let mut max_level = Level::ltr();
    assert_eq!(original_classes.len(), levels.len());
    for i in 0..levels.len() {
        match (levels[i].is_rtl(), original_classes[i]) {
            (false, AN) | (false, EN) => levels[i].raise(2).expect("Level number error"),
            (false, R) | (true, L) | (true, EN) | (true, AN) => {
                levels[i].raise(1).expect("Level number error")
            }
            // <https://www.unicode.org/reports/tr9/#Retaining_Explicit_Formatting_Characters> handled here
            (_, _) => {}
        }
        max_level = max(max_level, levels[i]);
    }

    max_level
}

/// Neutral or Isolate formatting character (B, S, WS, ON, FSI, LRI, RLI, PDI)
///
/// <http://www.unicode.org/reports/tr9/#NI>
#[allow(non_snake_case)]
fn is_NI(class: BidiClass) -> bool {
    match class {
        B | S | WS | ON | FSI | LRI | RLI | PDI => true,
        _ => false,
    }
}