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use std::io;
use std::io::prelude::*;
#[derive(Copy, Clone)]
pub enum Mode {
Encrypt,
Decrypt,
}
pub fn rot13_byte(mode: Mode, byte: u8) -> u8 {
let a = if byte.is_ascii_uppercase() {
b'A'
} else {
b'a'
};
let alphabet_pos = byte - a;
let shifted_pos = match mode {
Mode::Encrypt => (alphabet_pos + 13) % 26,
Mode::Decrypt => {
if alphabet_pos < 13 {
26 - (13 - alphabet_pos)
} else {
alphabet_pos - 13
}
}
};
a + shifted_pos
}
pub fn rot13_slice(mode: Mode, input: &[u8]) -> Vec<u8> {
input
.iter()
.map(|&byte| {
if byte.is_ascii_alphabetic() {
rot13_byte(mode, byte)
} else {
byte
}
})
.collect()
}
pub fn rot13<R: Read, W: Write>(mode: Mode, input: &mut R, output: &mut W) -> io::Result<()> {
let mut buffer = [0; 1024];
loop {
let amount = input.read(&mut buffer)?;
if amount == 0 {
break;
}
output.write_all(rot13_slice(mode, &buffer[..amount]).as_ref())?;
}
Ok(())
}
#[cfg(test)]
mod tests {
#[test]
fn rot13_byte_works() {
use super::{rot13_byte, Mode};
let input = b'A';
let encrypted = rot13_byte(Mode::Encrypt, input);
let decrypted = rot13_byte(Mode::Decrypt, encrypted);
assert_eq!(input, decrypted);
}
#[test]
fn rot13_slice_works() {
use super::{rot13_slice, Mode};
let input = b"Hello, World!";
let encrypted = rot13_slice(Mode::Encrypt, input);
let decrypted = rot13_slice(Mode::Decrypt, &encrypted);
assert_eq!(input, &decrypted.as_slice())
}
}