aoc-rs-2021/src/parsing.rs

use num::Num;
use yap::{IntoTokens, Tokens};
pub fn space(tokens: &mut impl Tokens<Item = char>) -> bool {
    tokens.token(' ')
}

pub fn newline(tokens: &mut impl Tokens<Item = char>) -> bool {
    tokens.tokens("\r\n".into_tokens()) || tokens.token('\n')
}

pub fn parse_number<T: Num>(tokens: &mut impl Tokens<Item = char>) -> Option<T> {
    parse_number_with_radix(tokens, 10, None)
}

pub fn parse_digit<T: Num>(tokens: &mut impl Tokens<Item = char>) -> Option<T> {
    parse_number_with_radix(tokens, 10, Some(1))
}

pub fn parse_number_with_radix<T: Num>(
    tokens: &mut impl Tokens<Item = char>,
    base: u32,
    limit: Option<usize>,
) -> Option<T> {
    tokens.skip_tokens_while(|t| *t == ' ');
    let mut remaining = limit.map(|x| x as isize).unwrap_or(isize::MAX);
    let digits: String = tokens
        .tokens_while(|c| {
            remaining -= 1;
            c.is_digit(base) && remaining >= 0
        })
        .collect();
    if !digits.is_empty() {
        T::from_str_radix(&digits, base).ok()
    } else {
        None
    }
}

#[cfg(test)]
mod test {
    use yap::IntoTokens;

    #[test]
    fn parse_digit() {
        let mut tokens = "1234".into_tokens();
        assert_eq!(Some(1), super::parse_digit(&mut tokens));
        assert_eq!(Some(2), super::parse_digit(&mut tokens));
        assert_eq!(Some(3), super::parse_digit(&mut tokens));
        assert_eq!(Some(4), super::parse_digit(&mut tokens));
    }
}