//! Cryptographic operations.

pub mod aead;
pub mod keys;

pub use seq::{SeqId, SeqIdGen};
use sha2::digest::{typenum::Unsigned, OutputSizeUser};

trait TlsHasher: OutputSizeUser {
    const ZEROED: &'static [u8];
    fn expand(ikm: &[u8], label: &[u8], okm: &mut [u8]) -> Result<(), hkdf::InvalidLength>;
    fn extract(salt: &[u8], ikm: &[u8]) -> Vec<u8>;
}
macro_rules! impl_hkdf_hasher {
    () => {
        const ZEROED: &'static [u8] =
            &[0; <<Self as OutputSizeUser>::OutputSize as Unsigned>::USIZE];
        fn expand(ikm: &[u8], label: &[u8], okm: &mut [u8]) -> Result<(), hkdf::InvalidLength> {
            hkdf::Hkdf::<Self>::new(None, ikm).expand(&label, okm)
        }
        fn extract(salt: &[u8], ikm: &[u8]) -> Vec<u8> {
            hkdf::Hkdf::<Self>::extract(Some(salt), ikm)
                .0
                .as_slice()
                .to_vec()
        }
    };
}
impl TlsHasher for sha2::Sha256 {
    impl_hkdf_hasher!();
}
impl TlsHasher for sha2::Sha384 {
    impl_hkdf_hasher!();
}

pub struct CryptoProvider {
    zeroed_of_hash_size: &'static [u8],
    hkdf_extract: fn(salt: &[u8], ikm: &[u8]) -> Vec<u8>,
}
impl CryptoProvider {
    fn new<H: TlsHasher>() -> Self {
        CryptoProvider {
            zeroed_of_hash_size: H::ZEROED,
            hkdf_extract: H::extract,
        }
    }
}

mod seq {
    use std::cell::Cell;

    use super::aead::{Nonce, TlsNonce};

    /// The sequence ID generator.
    /// There is a separate one maintained for reading and writing.
    pub struct SeqIdGen {
        next: Cell<u64>,
    }
    impl SeqIdGen {
        pub fn new() -> SeqIdGen {
            SeqIdGen { next: Cell::new(0) }
        }
        pub fn next(&self) -> SeqId {
            let next = self.next.get();
            self.next.set(next.checked_add(1).unwrap());
            SeqId(next)
        }
    }
    // Don't implement `Clone` to ensure every seq id is only used once.
    pub struct SeqId(u64);
    impl SeqId {
        pub fn to_nonce(self) -> TlsNonce {
            // <https://datatracker.ietf.org/doc/html/rfc8446#section-5.3>
            // 1. The 64-bit record sequence number is encoded in network byte
            //    order and padded to the left with zeros to iv_length.
            let mut nonce = [0; 12];
            nonce[4..12].copy_from_slice(&self.0.to_be_bytes());
            let nonce = Nonce::from(nonce);

            TlsNonce::new(nonce)
        }
    }
}

#[allow(dead_code)]
pub struct TlsInnerPlaintext {
    /// The `TLSPlaintext.fragment`` value
    pub content: Vec<u8>,
    /// The `TLSPlaintext.type` value
    pub content_type: u8,
    pub padding_len: u16,
}