kashida 0.3.1

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

use alloc::boxed::Box;
use hashbrown::HashMap;
use itertools::Itertools;

use unicode_joining_type::{JoiningType, get_joining_type};

pub(crate) fn is_kashida(c: char) -> bool {
    matches!(get_joining_type(c), JoiningType::JoinCausing)
}
pub(crate) fn joins_following(c: char) -> bool {
    matches!(get_joining_type(c), JoiningType::DualJoining | JoiningType::JoinCausing)
}
pub(crate) fn joins_preceding(c: char) -> bool {
    matches!(
        get_joining_type(c),
        JoiningType::DualJoining | JoiningType::JoinCausing | JoiningType::RightJoining
    )
}

#[must_use]
pub(crate) fn find_kashidas(input: &str) -> Box<[usize]> {
    let mut candidates: HashMap<_, usize> =
        HashMap::with_capacity(input.split_whitespace().count());

    let (word_segmenter, grapheme_segmenter) = super::get_segmenters();


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

    for (word_idx, word) in words.enumerate() {
        let graphemes = grapheme_segmenter
            .as_borrowed()
            .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, |bp| {
                candidates.insert(word_idx, bp);
            });
        }
    }

    candidates.into_values().collect()
}

fn find_kashidas_in_glyph_run(
    (g1, g2): (Option<&str>, Option<&str>),
    input: &str,
    mut insert_candidate: impl FnMut(usize),
) {
    let breakpoint = |g: &str| g.as_ptr() as usize - input.as_ptr() as usize;
    match (g1, g2) {
        (Some(preceding), Some(g))
            if preceding.contains(joins_following) && g.contains(joins_preceding) =>
        {
            insert_candidate(breakpoint(g));
        }
        _ => {}
    }
}