//! RC4 (used by PDF security handler revisions 2–4). Encryption and decryption are the same.

pub fn rc4(key: &[u8], data: &[u8]) -> Vec<u8> {
    if key.is_empty() {
        return data.to_vec();
    }
    let mut s: [u8; 256] = std::array::from_fn(|i| i as u8);
    let mut j: u8 = 0;
    for i in 0..256 {
        j = j.wrapping_add(s[i]).wrapping_add(key[i % key.len()]);
        s.swap(i, j as usize);
    }
    let (mut i, mut j) = (0u8, 0u8);
    data.iter()
        .map(|b| {
            i = i.wrapping_add(1);
            j = j.wrapping_add(s[i as usize]);
            s.swap(i as usize, j as usize);
            b ^ s[s[i as usize].wrapping_add(s[j as usize]) as usize]
        })
        .collect()
}