//! Symmetric cypher stuff

use ::zeroize::Zeroize;

/// Secret, used for keys.
/// Grants that on drop() we will zero out memory
#[derive(Zeroize)]
#[zeroize(drop)]
#[allow(missing_debug_implementations)]
pub struct Secret {
    secret: [u8; 32],
}

impl Secret {
    /// return a reference to the secret
    pub fn as_ref(&self) -> &[u8; 32] {
        &self.secret
    }
}
impl From<::x25519_dalek::SharedSecret> for Secret {
    fn from(shared_secret: ::x25519_dalek::SharedSecret) -> Self {
        Self {
            secret: shared_secret.to_bytes(),
        }
    }
}

/// List of possible Ciphers
#[derive(Debug, Copy, Clone, PartialEq, ::num_derive::FromPrimitive)]
#[repr(u8)]
pub enum CipherKind {
    /// Chaha20_Poly1305
    Chacha20Poly1305 = 0,
}

impl CipherKind {
    /// required length of the nonce
    pub fn nonce_len(&self) -> usize {
        ::ring::aead::CHACHA20_POLY1305.nonce_len()
    }
    /// required length of the key
    pub fn key_len(&self) -> usize {
        ::ring::aead::CHACHA20_POLY1305.key_len()
    }
    /// Length of the authentication tag
    pub fn tag_len(&self) -> usize {
        ::ring::aead::CHACHA20_POLY1305.tag_len()
    }
}

/// actual ciphers
#[derive(Debug)]
pub enum Cipher {
    /// Cipher Chaha20_Poly1305
    Chacha20Poly1305(Chacha20Poly1305),
}

impl Cipher {
    /// Build a new Cipher
    pub fn new(kind: CipherKind, secret: Secret) -> Self {
        match kind {
            CipherKind::Chacha20Poly1305 => {
                Self::Chacha20Poly1305(Chacha20Poly1305::new(secret))
            }
        }
    }
}

/// Chacha20Poly1305 cipher
#[derive(Debug)]
pub struct Chacha20Poly1305 {
    cipher: ::ring::aead::OpeningKey<Nonce>,
}

impl Chacha20Poly1305 {
    /// Initialize the cipher with the given nonce
    pub fn with_nonce(key: Secret, nonce: Nonce) -> Self {
        let unbound_key = ::ring::aead::UnboundKey::new(
            &::ring::aead::CHACHA20_POLY1305,
            key.as_ref(),
        )
        .unwrap();
        use ::ring::aead::BoundKey;
        Self {
            cipher: ::ring::aead::OpeningKey::<Nonce>::new(unbound_key, nonce),
        }
    }
    /// Initialize a new ChachaPoly20 cipher with a random nonce
    pub fn new(key: Secret) -> Self {
        Self::with_nonce(key, Nonce::new())
    }
}

#[derive(Debug, Copy, Clone)]
#[repr(C)]
#[allow(missing_debug_implementations)]
struct NonceNum {
    high: u32,
    low: u64,
}
/// Nonce with sequence for chach20_apoly1305
#[repr(C)]
pub union Nonce {
    num: NonceNum,
    // ring::aead::Nonce does not implement 'Copy'
    // even though it's just [u8;12]
    raw: ::core::mem::ManuallyDrop<::ring::aead::Nonce>,
    easy_from: [u8; 12],
}

impl ::core::fmt::Debug for Nonce {
    fn fmt(
        &self,
        f: &mut core::fmt::Formatter<'_>,
    ) -> Result<(), ::std::fmt::Error> {
        // use the Debug from NonceNum
        #[allow(unsafe_code)]
        unsafe {
            core::fmt::Debug::fmt(&self.num, f)
        }
    }
}

impl Nonce {
    // FIXME: nonces should be random!
    /// Generate a new random Nonce
    pub fn new() -> Self {
        #[allow(unsafe_code)]
        unsafe {
            Self {
                num: NonceNum { high: 42, low: 69 },
            }
        }
    }
    /// Create Nonce from array
    pub fn from_slice(raw: [u8; 12]) -> Self {
        #[allow(unsafe_code)]
        unsafe {
            Self { easy_from: raw }
        }
    }
}

impl Clone for Nonce {
    fn clone(&self) -> Self {
        #[allow(unsafe_code)]
        unsafe {
            Self { num: self.num }
        }
    }
}

impl ::ring::aead::NonceSequence for Nonce {
    fn advance(
        &mut self,
    ) -> Result<::ring::aead::Nonce, ::ring::error::Unspecified> {
        #[allow(unsafe_code)]
        unsafe {
            let old_low = self.num.low;
            self.num.low = self.num.low + 1;
            if self.num.low < old_low {
                self.num.high = self.num.high;
            }
            Ok(::core::mem::ManuallyDrop::take(&mut self.raw))
        }
    }
}