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const HEADERS: [&[u8]; 3] = [b"asd", b"adf", b"ads"];
const HOME_RIGHT: [u8; 4] = [b'a',b's',b'd',b'f'];
const HOME_LEFT: [u8; 4] = [b'h',b'j',b'k',b'l'];
const ABOVE_RIGHT: [u8; 4] = [b'w',b'e',b'r',b't'];
const ABOVE_LEFT: [u8; 4] = [b'u',b'i',b'o',b'p'];
pub fn encode(buf: &[u8]) -> Vec<u8> {
let mut out = Vec::new();
let h = HEADERS[fastrand::usize(..HEADERS.len())];
for s in h {
out.push(*s);
}
for byte in buf {
let stuff = encode_byte(*byte);
for b in stuff {
out.push(b);
}
}
out
}
fn encode_byte(byte: u8) -> [u8; 4] {
[some_dict()[((byte & 0b11000000) >> 6) as usize],
some_dict()[((byte & 0b00110000) >> 4) as usize],
some_dict()[((byte & 0b00001100) >> 2) as usize],
some_dict()[(byte & 0b00000011) as usize]
]
}
fn some_dict() -> &'static [u8; 4] {
let q = fastrand::usize(0..10);
if q < 4 {
return &HOME_RIGHT
}
if q < 8 {
return &HOME_LEFT
}
if q < 9 {
return &ABOVE_RIGHT
}
return &ABOVE_LEFT
}
pub fn decode(buf: &[u8]) -> Vec<u8> {
let buf = &buf[3..];
let mut out = Vec::new();
for pair in buf.chunks(4) {
if pair.len() != 4 {
continue;
}
match (decode_sym(pair[0]), decode_sym(pair[1]), decode_sym(pair[2]), decode_sym(pair[3])) {
(Some(zero), Some(one), Some(two), Some(three)) => out.push((zero << 6) + (one << 4) + (two << 2) + three),
(_, _, _, _) => {
// U+FFFD � REPLACEMENT CHARACTER
out.push(0xFF);
out.push(0xFD);
}
}
}
out
}
pub fn decode_sym(sym: u8) -> Option<u8> {
let find = |d: &[u8; 4]| -> Option<u8> {
d.iter().enumerate().find(|s| s.1 == &sym).map(|s| s.0 as u8)
};
find(&HOME_RIGHT)
.or_else(|| find(&HOME_LEFT))
.or_else(|| find(&ABOVE_RIGHT))
.or_else(|| find(&ABOVE_LEFT))
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn it_works() {
let hello = b"hello, world!";
assert_eq!(&hello[..], &decode(&encode(hello)));
}
#[test]
fn random() {
for _ in 0..1000 {
let mut buf = vec![0; fastrand::usize(..1000)];
buf.iter_mut().for_each(|s| *s = fastrand::u8(..));
assert_eq!(&buf[..], &decode(&encode(&buf)));
}
}
}
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