use std::io::Read;
struct RotDecoder<R: Read> {
input: R,
rot: u8,
}
impl<R: Read> Read for RotDecoder<R> {
fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
let size = self.input.read(buf)?;
for b in &mut buf[..size] {
if b.is_ascii_alphabetic() {
let base = if b.is_ascii_uppercase() { 'A' } else { 'a' } as u8;
*b = (*b - base + self.rot) % 26 + base;
}
}
Ok(size)
}
}
fn main() {
let mut rot =
RotDecoder { input: "Gb trg gb gur bgure fvqr!".as_bytes(), rot: 13 };
let mut result = String::new();
rot.read_to_string(&mut result).unwrap();
println!("{}", result);
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn joke() {
let mut rot =
RotDecoder { input: "Gb trg gb gur bgure fvqr!".as_bytes(), rot: 13 };
let mut result = String::new();
rot.read_to_string(&mut result).unwrap();
assert_eq!(&result, "To get to the other side!");
}
#[test]
fn binary() {
let input: Vec<u8> = (0..=255u8).collect();
let mut rot = RotDecoder::<&[u8]> { input: input.as_ref(), rot: 13 };
let mut buf = [0u8; 256];
assert_eq!(rot.read(&mut buf).unwrap(), 256);
for i in 0..=255 {
if input[i] != buf[i] {
assert!(input[i].is_ascii_alphabetic());
assert!(buf[i].is_ascii_alphabetic());
}
}
}
}