use aes_gcm::aead::{Aead, KeyInit};
use aes_gcm::{Aes256Gcm, Nonce};
use anyhow::{Context, Result};
use rand::Rng;

pub const KEY_CHECK_PLAINTEXT: &[u8] = b"secrets-v3-key-check";

pub fn decode_hex(input: &str) -> Result<Vec<u8>> {
    hex::decode(input.trim()).context("invalid hex")
}

pub fn encode_hex(input: &[u8]) -> String {
    hex::encode(input)
}

pub fn extract_key_32(input: &str) -> Result<[u8; 32]> {
    let bytes = decode_hex(input)?;
    let key: [u8; 32] = bytes
        .try_into()
        .map_err(|_| anyhow::anyhow!("expected 32-byte key"))?;
    Ok(key)
}

pub fn encrypt(key: &[u8; 32], plaintext: &[u8]) -> Result<Vec<u8>> {
    let cipher = Aes256Gcm::new_from_slice(key).context("invalid AES-256 key")?;
    let mut nonce_bytes = [0_u8; 12];
    rand::rng().fill_bytes(&mut nonce_bytes);
    let nonce = Nonce::from_slice(&nonce_bytes);
    let mut out = nonce_bytes.to_vec();
    out.extend(
        cipher
            .encrypt(nonce, plaintext)
            .map_err(|_| anyhow::anyhow!("encryption failed"))?,
    );
    Ok(out)
}

pub fn decrypt(key: &[u8; 32], ciphertext: &[u8]) -> Result<Vec<u8>> {
    if ciphertext.len() < 12 {
        anyhow::bail!("ciphertext too short");
    }
    let cipher = Aes256Gcm::new_from_slice(key).context("invalid AES-256 key")?;
    let (nonce, body) = ciphertext.split_at(12);
    cipher
        .decrypt(Nonce::from_slice(nonce), body)
        .map_err(|_| anyhow::anyhow!("decryption failed"))
}