Korean jeongseong replace (한글 종성 변경) in Rust

main.rs

use std::collections::HashMap;

fn get_jongseong_index(jongseong: char) -> Option<u16> {
    let jongseong_map: HashMap<char, u16> = [
        (' ', 0), ('ㄱ', 1), ('ㄲ', 2), ('ㄳ', 3), 
        ('ㄴ', 4), ('ㄵ', 5), ('ㄶ', 6), ('ㄷ', 7), 
        ('ㄹ', 8), ('ㄺ', 9), ('ㄻ', 10), ('ㄼ', 11),
        ('ㄽ', 12), ('ㄾ', 13), ('ㄿ', 14), ('ㅀ', 15),
        ('ㅁ', 16), ('ㅂ', 17), ('ㅄ', 18), ('ㅅ', 19),
        ('ㅆ', 20), ('ㅇ', 21), ('ㅈ', 22), ('ㅊ', 23),
        ('ㅋ', 24), ('ㅌ', 25), ('ㅍ', 26), ('ㅎ', 27),
    ].iter().cloned().collect();

    jongseong_map.get(&jongseong).cloned()
}


fn replace_jongseong(s: &str, original: char, replacement: char) -> String {
    let original_index = get_jongseong_index(original).unwrap();
    let replacement_index = get_jongseong_index(replacement).unwrap();
    
    s.chars()
        .map(|c| {
            let code = c as u32;
            // Check if it's a Hangul syllable
            if 0xAC00 <= code && code <= 0xD7A3 {
                // Decompose the syllable
                let syllable_index = code - 0xAC00;
                let jongseong_index = syllable_index as u16 % 28;
                if jongseong_index == original_index {
                    // If the jongseong matches the original, replace it
                    let new_code = code - (original_index as u32) + (replacement_index as u32);
                    std::char::from_u32(new_code).unwrap()
                } else {
                    // If the jongseong doesn't match, leave it alone
                    c
                }
            } else {
                // If it's not a Hangul syllable, leave it alone
                c
            }
        })
        .collect()
}

fn main() {
    let hey = "깔깘깎꾼";
    let result = replace_jongseong(hey, 'ㄽ', 'ㅋ');
    let result = replace_jongseong(&result, 'ㄲ', 'ㄴ');
    println!("{result}"); // 깔깤깐꾼
    
}