yowl 0.1.0

use std::convert::TryInto;

use super::{error::ReadError, missing_character::missing_character, scanner::Scanner};
use crate::feature::Rnum;

pub fn read_rnum(scanner: &mut Scanner) -> Result<Option<Rnum>, ReadError> {
    let mut digits = String::new();

    match scanner.peek() {
        Some('0'..='9') => {
            digits.push(*scanner.pop().unwrap());
        }
        Some('%') => {
            scanner.pop();

            for _ in 0..=1 {
                match scanner.peek() {
                    Some('0'..='9') => {
                        digits.push(*scanner.pop().expect("scanner done"));
                    }
                    _ => return Err(missing_character(scanner)),
                }
            }
        }
        _ => return Ok(None),
    }

    let rnum = digits.parse::<u16>().expect("rnum to u16");

    Ok(Some(rnum.try_into().expect("u16 to rnum")))
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn percent_digit() {
        let mut scanner = Scanner::new("%0");

        assert_eq!(read_rnum(&mut scanner), Err(ReadError::EndOfLine))
    }

    #[test]
    fn zero() {
        let mut scanner = Scanner::new("0");

        assert_eq!(read_rnum(&mut scanner), Ok(Some(Rnum::new(0))))
    }

    #[test]
    fn nine() {
        let mut scanner = Scanner::new("9");

        assert_eq!(read_rnum(&mut scanner), Ok(Some(Rnum::new(9))))
    }

    #[test]
    fn percent_zero_zero() {
        let mut scanner = Scanner::new("%00");

        assert_eq!(read_rnum(&mut scanner), Ok(Some(Rnum::new(0))))
    }

    #[test]
    fn percent_nine_nine() {
        let mut scanner = Scanner::new("%99");

        assert_eq!(read_rnum(&mut scanner), Ok(Some(Rnum::new(99))))
    }
}