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use anyhow::ensure;

use crate::error::Result;

/// Encodes plaintext by elementwise xoring with the passed in key.
pub fn encode(key: &[u8], plaintext: &[u8]) -> Result<Vec<u8>> {
    xor(key, plaintext)
}

/// Decodes ciphertext by elementwise xoring with the passed in key.
pub fn decode(key: &[u8], ciphertext: &[u8]) -> Result<Vec<u8>> {
    xor(key, ciphertext)
}

fn xor(key: &[u8], input: &[u8]) -> Result<Vec<u8>> {
    let key_len = key.len();
    ensure!(key_len == 32, "Key must be 32 bytes.");

    Ok(input
        .iter()
        .enumerate()
        .map(|(i, byte)| byte ^ key[i % key_len])
        .collect())
}

#[cfg(test)]
mod tests {
    use super::*;

    use rand::{Rng, SeedableRng};
    use rand_xorshift::XorShiftRng;

    use crate::TEST_SEED;

    #[test]
    fn test_xor() {
        let mut rng = XorShiftRng::from_seed(TEST_SEED);

        for i in 0..10 {
            let key: Vec<u8> = (0..32).map(|_| rng.gen()).collect();
            let plaintext: Vec<u8> = (0..(i + 1) * 32).map(|_| rng.gen()).collect();

            let ciphertext =
                encode(key.as_slice(), plaintext.as_slice()).expect("failed to encode");

            assert_ne!(
                plaintext, ciphertext,
                "plaintext and ciphertext are identical"
            );
            assert_eq!(plaintext.len(), ciphertext.len());

            let roundtrip =
                decode(key.as_slice(), ciphertext.as_slice()).expect("failed to decode");
            assert_eq!(plaintext, roundtrip, "failed to roundtrip");
        }
    }
}