use std::str::FromStr;

#[derive(Debug, PartialEq, Eq)]
enum Rotation {
    Left(u16),
    Right(u16),
}

struct ParseRotationError(String);

impl FromStr for Rotation {
    type Err = ParseRotationError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let err = || ParseRotationError(s.into());

        let mut chars = s.chars();
        let lr = chars.next().ok_or_else(err)?;
        let n: u16 = chars.collect::<String>().parse().map_err(|_| err())?;

        match lr {
            'L' => Ok(Self::Left(n)),
            'R' => Ok(Self::Right(n)),
            _ => Err(err()),
        }
    }
}

fn main() {
    println!("Hello, world!");
}

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

    #[test]
    fn parse_rotation() {
        assert!("L2"
            .parse::<Rotation>()
            .is_ok_and(|rot| rot == Rotation::Left(2)));

        assert!("R929"
            .parse::<Rotation>()
            .is_ok_and(|rot| rot == Rotation::Right(929)));

        assert!("M1".parse::<Rotation>().is_err());
        assert!("L".parse::<Rotation>().is_err());
        assert!("2".parse::<Rotation>().is_err());
    }
}