//! Implementation of crypto primitives using the Windows CNG (Cryptographic API: Next Generation).

use crate::types::*;

use win_crypto_ng::random::RandomNumberGenerator;

pub mod aead;
pub mod asymmetric;
pub mod ecdh;
pub mod hash;
pub mod symmetric;

/// Returns a short, human-readable description of the backend.
pub fn backend() -> String {
    // XXX: can we include features and the version?
    "Windows CNG".to_string()
}

/// Fills the given buffer with random data.
pub fn random(buf: &mut [u8]) {
    RandomNumberGenerator::system_preferred()
        .gen_random(buf)
        .expect("system-preferred RNG not to fail")
}

impl PublicKeyAlgorithm {
    pub(crate) fn is_supported_by_backend(&self) -> bool {
        use PublicKeyAlgorithm::*;
        #[allow(deprecated)]
        match &self {
            RSAEncryptSign | RSAEncrypt | RSASign | DSA | ECDH | ECDSA | EdDSA
                => true,
            ElGamalEncrypt | ElGamalEncryptSign | Private(_) | Unknown(_)
                => false,
        }
    }
}

impl Curve {
    pub(crate) fn is_supported_by_backend(&self) -> bool {
        use self::Curve::*;
        match &self {
            NistP256 | NistP384 | NistP521 | Ed25519 | Cv25519
                => true,
            BrainpoolP256 | BrainpoolP512 | Unknown(_)
                => false,
        }
    }
}

impl AEADAlgorithm {
    /// Returns the best AEAD mode supported by the backend.
    ///
    /// This SHOULD return OCB, which is the mandatory-to-implement
    /// algorithm and the most performing one, but fall back to any
    /// supported algorithm.
    pub(crate) const fn const_default() -> AEADAlgorithm {
        AEADAlgorithm::EAX
    }

    pub(crate) fn is_supported_by_backend(&self) -> bool {
        use self::AEADAlgorithm::*;
        match &self {
            EAX
                => true,
            OCB | Private(_) | Unknown(_)
                => false,
        }
    }

    #[cfg(test)]
    pub(crate) fn supports_symmetric_algo(&self, algo: &SymmetricAlgorithm) -> bool {
        match &self {
            AEADAlgorithm::EAX =>
                match algo {
                    SymmetricAlgorithm::AES128 |
                    SymmetricAlgorithm::AES192 |
                    SymmetricAlgorithm::AES256 |
                    SymmetricAlgorithm::Twofish |
                    SymmetricAlgorithm::Camellia128 |
                    SymmetricAlgorithm::Camellia192 |
                    SymmetricAlgorithm::Camellia256 => true,
                    _ => false,
                },
            _ => false
        }
    }
}