use std::iter::once;
use std::mem;

fn find_offset(bytes: &[u8]) -> usize {
    bytes.iter().position(|b| b == &b'\n').unwrap()
}

fn moved<T>(x: T) -> T {x}
fn hor_mirror(s: String) -> String {

    let mut bytes_vec = s.into_bytes();
    let len = bytes_vec.len();
    let offset = find_offset(&bytes_vec);
    {
        let mut bytes: &mut [u8] = bytes_vec.as_mut();
        for _ in 0..(len / offset) / 2 {
            {
                let (mut slice, mut rest) = bytes.split_at_mut(offset);
                for (slice_byte, rest_byte) in slice.iter_mut().zip(rest.iter_mut().rev()) {
                    mem::swap(slice_byte, rest_byte);
                }

            }
            bytes = moved(&mut bytes[offset..]); //WHY
        }
    }
    String::from_utf8(bytes_vec).unwrap()
}

fn vert_mirror(s: String) -> String {
    let mut bytes = s.into_bytes();
    for line in bytes.split_mut(|b| b == &b'\n') {
        line.reverse();
    }
    String::from_utf8(bytes).unwrap()

}
// first parameter: dots have to be replaced by function of one variable
fn oper<F: Fn(String) -> String>(f: F, s: String) -> String {
    f(s)
}
fn testing1(s: &str, exp: &str) -> () {
    assert_eq!(oper(hor_mirror, s.to_string()), exp)
}
fn main() {
    testing1("lVHt\nJVhv\nCSbg\nyeCt", "yeCt\nCSbg\nJVhv\nlVHt");
    testing1("njMK\ndbrZ\nLPKo\ncEYz", "cEYz\nLPKo\ndbrZ\nnjMK");
    testing1("QMxo\ntmFe\nWLUG\nowoq", "owoq\nWLUG\ntmFe\nQMxo");
}