use std::fmt::{self, Write, Alignment};

struct ExtraWidth {
    num: u32,
    width: usize,
}

impl fmt::Display for ExtraWidth {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let width = self.width + f.width().unwrap_or(0);

        let mut buff = String::new();
        write!(buff, "{}", self.num)?;

        let padding = width.saturating_sub(buff.len());
        let (pre_padding, post_padding) = match f.align() {
            None => (0, padding),
            Some(Alignment::Left) => (0, padding),
            Some(Alignment::Right) => (padding, 0),
            Some(Alignment::Center) => (padding / 2, (padding + 1) / 2),
        };

        for _ in 0..pre_padding {
            write!(f, "{}", f.fill())?;
        }

        f.write_str(&buff)?;

        for _ in 0..post_padding {
            write!(f, "{}", f.fill())?;
        }

        Ok(())
    }
}

fn main() {
    println!("{:0>2}", ExtraWidth { num: 1, width: 2 });
}