kashida 0.2.1

Insert Kashidas/Tatweel into Arabic text, e.g. for justification purposes.
Documentation 
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

#![allow(unused)]

use alloc::{boxed::Box, vec::Vec};
use core::iter;
use hashbrown::{hash_map::Entry, HashMap};
use itertools::Itertools;
use unicode_joining_type::{get_joining_group, JoiningGroup};

use crate::global::*;
use crate::KashidaCandidate;

fn is_alaph(c: char) -> bool {
    matches!(get_joining_group(c), JoiningGroup::Alaph)
}
fn is_lamadh(c: char) -> bool {
    matches!(get_joining_group(c), JoiningGroup::Lamadh)
}

// Useful resources: https://www.unicode.org/versions/Unicode15.0.0/ch09.pdf
//                   https://bug-attachments.documentfoundation.org/attachment.cgi?id=182206
#[must_use]
pub(crate) fn find_kashidas(input: &str) -> Box<[usize]> {
    let mut candidates: HashMap<_, KashidaCandidate> =
        HashMap::with_capacity(input.split_whitespace().count());

    let word_segmenter = icu_segmenter::WordSegmenter::new_auto(Default::default());
    let grapheme_segmenter = icu_segmenter::GraphemeClusterSegmenter::new();

    let words = word_segmenter
        .segment_str(input)
        .tuple_windows()
        .filter_map(|(wb1, wb2)| Some((&input[wb1..wb2], wb1)).filter(|s| !s.0.trim().is_empty()));

    for (word_idx, (word, word_start)) in words.enumerate() {
        let graphemes = grapheme_segmenter
            .segment_str(word)
            .tuple_windows()
            .map(|(gb1, gb2)| Some(&word[gb1..gb2]))
            .pad_using(2, |_| None)
            .tuple_windows();

        for glyph_window in graphemes {
            find_kashidas_in_glyph_run(glyph_window, input, |kc| {
                match candidates.entry(word_idx) {
                    Entry::Occupied(mut e)
                        if kc.bp_priority <= e.get().bp_priority
                            && kc.breakpoint > (word.len() / 2 + word_start) =>
                    {
                        e.insert(kc)
                    }
                    Entry::Occupied(_) => kc,
                    Entry::Vacant(e) => *e.insert(kc),
                };
            });
        }
    }

    let mut ret = candidates.into_values().collect::<Vec<_>>();
    ret.sort_unstable_by_key(|a| a.bp_priority);
    ret.into_iter().map(|kc| kc.breakpoint).collect()
}

fn find_kashidas_in_glyph_run(
    (g1, g2): (Option<&str>, Option<&str>),
    input: &str,
    mut insert_candidate: impl FnMut(KashidaCandidate),
) {
    let breakpoint = |g: &str| g.as_ptr() as usize - input.as_ptr() as usize;
    match (g1, g2) {
        // If Input contains Kashida, that's the place
        (Some(g), _) if g.chars().all(is_kashida) => {
            insert_candidate(KashidaCandidate::new(breakpoint(g) + g.len(), 0));
        }

        // deal with لا early
        (Some(lam), Some(alef)) if lam.contains(is_lamadh) && alef.contains(is_alaph) => {}

        (Some(preceding), Some(g))
            if preceding.contains(joins_following) && g.contains(joins_preceding) =>
        {
            insert_candidate(KashidaCandidate::new(breakpoint(g), 1));
        }
        _ => {}
    }
}