/*
    This file is part of jellything (https://codeberg.org/metamuffin/jellything)
    which is licensed under the GNU Affero General Public License (version 3); see /COPYING.
    Copyright (C) 2024 metamuffin <metamuffin.org>
*/
use super::SessionData;
use aes_gcm_siv::{
    aead::{generic_array::GenericArray, Aead},
    KeyInit,
};
use anyhow::anyhow;
use base64::Engine;
use chrono::{Duration, Utc};
use jellybase::SECRETS;
use jellycommon::user::PermissionSet;
use log::warn;
use std::sync::LazyLock;

static SESSION_KEY: LazyLock<[u8; 32]> = LazyLock::new(|| {
    if let Some(sk) = &SECRETS.session_key {
        let r = base64::engine::general_purpose::STANDARD
            .decode(sk)
            .expect("key invalid; should be valid base64");
        r.try_into()
            .expect("key has the wrong length; should be 32 bytes")
    } else {
        warn!("session_key not configured; generating a random one.");
        [(); 32].map(|_| rand::random())
    }
});

pub fn create(username: String, permissions: PermissionSet, expire: Duration) -> String {
    let session_data = SessionData {
        expire: Utc::now() + expire,
        username: username.to_owned(),
        permissions,
    };
    let mut plaintext =
        bincode::serde::encode_to_vec(&session_data, bincode::config::standard()).unwrap();

    while plaintext.len() % 16 == 0 {
        plaintext.push(0);
    }

    let cipher = aes_gcm_siv::Aes256GcmSiv::new_from_slice(&*SESSION_KEY).unwrap();
    let nonce = [(); 12].map(|_| rand::random());
    let mut ciphertext = cipher
        .encrypt(&GenericArray::from(nonce), plaintext.as_slice())
        .unwrap();
    ciphertext.extend(nonce);

    base64::engine::general_purpose::URL_SAFE.encode(&ciphertext)
}

pub fn validate(token: &str) -> anyhow::Result<String> {
    let ciphertext = base64::engine::general_purpose::URL_SAFE.decode(token)?;
    let cipher = aes_gcm_siv::Aes256GcmSiv::new_from_slice(&*SESSION_KEY).unwrap();
    let (ciphertext, nonce) = ciphertext.split_at(ciphertext.len() - 12);
    let plaintext = cipher
        .decrypt(nonce.into(), ciphertext)
        .map_err(|e| anyhow!("decryption failed: {e:?}"))?;

    let (session_data, _): (SessionData, _) =
        bincode::serde::decode_from_slice(&plaintext, bincode::config::standard())?;

    if session_data.expire < Utc::now() {
        Err(anyhow!("session expired"))?
    }

    Ok(session_data.username)
}

#[test]
fn test() {
    let tok = create(
        "blub".to_string(),
        jellycommon::user::PermissionSet::default(),
        Duration::days(1),
    );
    validate(&tok).unwrap();
}

#[test]
fn test_crypto() {
    let nonce = [(); 12].map(|_| rand::random());
    let cipher = aes_gcm_siv::Aes256GcmSiv::new_from_slice(&*SESSION_KEY).unwrap();
    let plaintext = b"testing stuff---";
    let ciphertext = cipher
        .encrypt(&GenericArray::from(nonce), plaintext.as_slice())
        .unwrap();
    let plaintext2 = cipher
        .decrypt((&nonce).into(), ciphertext.as_slice())
        .unwrap();
    assert_eq!(plaintext, plaintext2.as_slice());
}