struct RunLength<I>
where
    I: Iterator,
{
    iter: I,
    saved: Option<I::Item>,
}

impl<I> RunLength<I>
where
    I: Iterator,
{
    fn new(iter: I) -> Self {
        Self { iter, saved: None }
    }
}

impl<I> Iterator for RunLength<I>
where
    I: Iterator,
    <I as std::iter::Iterator>::Item: PartialEq,
{
    type Item = (I::Item, usize);

    fn next(&mut self) -> Option<Self::Item> {
        let c = self.saved.take().or_else(|| self.iter.next())?;

        let mut count = 1;
        while let Some(n) = self.iter.next() {
            if n == c {
                count += 1
            } else {
                self.saved = Some(n);
                break;
            }
        }

        Some((c, count))
    }
}

pub fn encode_tiny(data: &str) -> String {
    use std::fmt::Write;

    RunLength::new(data.chars()).fold(String::new(), |mut s, (c, count)| {
        match count {
            1 => s.push(c),
            n => write!(&mut s, "{}{}", n, c).unwrap(),
        }
        s
    })
}