use alloc::boxed::Box;

use super::{ActiveKeyExchange, hmac};

use crate::error::Error;

use crate::version::TLS12;

/// Implements [`Prf`] using a [`hmac::Hmac`].

pub struct PrfUsingHmac<'a>(pub &'a dyn hmac::Hmac);

impl Prf for PrfUsingHmac<'_> {

    fn for_key_exchange(

        &self,

        output: &mut [u8; 48],

        kx: Box<dyn ActiveKeyExchange>,

        peer_pub_key: &[u8],

        label: &[u8],

        seed: &[u8],

    ) -> Result<(), Error> {

        prf(

            output,

            self.0

                .with_key(

                    kx.complete_for_tls_version(peer_pub_key, &TLS12)?

                        .secret_bytes(),

                )

                .as_ref(),

            label,

            seed,

        );

        Ok(())

    }

    fn for_secret(&self, output: &mut [u8], secret: &[u8], label: &[u8], seed: &[u8]) {

        prf(output, self.0.with_key(secret).as_ref(), label, seed);

    }

}

/// An instantiation of the TLS1.2 PRF with a specific, implicit hash function.

///

/// See the definition in [RFC5246 section 5](https://www.rfc-editor.org/rfc/rfc5246#section-5).

///

/// See [`PrfUsingHmac`] as a route to implementing this trait with just

/// an implementation of [`hmac::Hmac`].

pub trait Prf: Send + Sync {

    /// Computes `PRF(secret, label, seed)` using the secret from a completed key exchange.

    ///

    /// Completes the given key exchange, and then uses the resulting shared secret

    /// to compute the PRF, writing the result into `output`.

    ///

    /// The caller guarantees that `label`, `seed` are non-empty. The caller makes no

    /// guarantees about the contents of `peer_pub_key`. It must be validated by

    /// [`ActiveKeyExchange::complete`].

    fn for_key_exchange(

        &self,

        output: &mut [u8; 48],

        kx: Box<dyn ActiveKeyExchange>,

        peer_pub_key: &[u8],

        label: &[u8],

        seed: &[u8],

    ) -> Result<(), Error>;

    /// Computes `PRF(secret, label, seed)`, writing the result into `output`.

    ///

    /// The caller guarantees that `secret`, `label`, and `seed` are non-empty.

    fn for_secret(&self, output: &mut [u8], secret: &[u8], label: &[u8], seed: &[u8]);

    /// Return `true` if this is backed by a FIPS-approved implementation.

    fn fips(&self) -> bool {

        false

    }

}

pub(crate) fn prf(out: &mut [u8], hmac_key: &dyn hmac::Key, label: &[u8], seed: &[u8]) {

    // A(1)

    let mut current_a = hmac_key.sign(&[label, seed]);

    let chunk_size = hmac_key.tag_len();

    for chunk in out.chunks_mut(chunk_size) {

        // P_hash[i] = HMAC_hash(secret, A(i) + seed)

        let p_term = hmac_key.sign(&[current_a.as_ref(), label, seed]);

        chunk.copy_from_slice(&p_term.as_ref()[..chunk.len()]);

        // A(i+1) = HMAC_hash(secret, A(i))

        current_a = hmac_key.sign(&[current_a.as_ref()]);

    }

}

#[cfg(all(test, feature = "ring"))]

mod tests {

    use crate::crypto::hmac::Hmac;

    // nb: crypto::aws_lc_rs provider doesn't provide (or need) hmac,

    // so cannot be used for this test.

    use crate::crypto::ring::hmac;

    // Below known answer tests come from https://mailarchive.ietf.org/arch/msg/tls/fzVCzk-z3FShgGJ6DOXqM1ydxms/

    #[test]

    fn check_sha256() {

        let secret = b"\x9b\xbe\x43\x6b\xa9\x40\xf0\x17\xb1\x76\x52\x84\x9a\x71\xdb\x35";

        let seed = b"\xa0\xba\x9f\x93\x6c\xda\x31\x18\x27\xa6\xf7\x96\xff\xd5\x19\x8c";

        let label = b"test label";

        let expect = include_bytes!("../testdata/prf-result.1.bin");

        let mut output = [0u8; 100];

        super::prf(

            &mut output,

            &*hmac::HMAC_SHA256.with_key(secret),

            label,

            seed,

        );

        assert_eq!(expect.len(), output.len());

        assert_eq!(expect.to_vec(), output.to_vec());

    }

    #[test]

    fn check_sha512() {

        let secret = b"\xb0\x32\x35\x23\xc1\x85\x35\x99\x58\x4d\x88\x56\x8b\xbb\x05\xeb";

        let seed = b"\xd4\x64\x0e\x12\xe4\xbc\xdb\xfb\x43\x7f\x03\xe6\xae\x41\x8e\xe5";

        let label = b"test label";

        let expect = include_bytes!("../testdata/prf-result.2.bin");

        let mut output = [0u8; 196];

        super::prf(

            &mut output,

            &*hmac::HMAC_SHA512.with_key(secret),

            label,

            seed,

        );

        assert_eq!(expect.len(), output.len());

        assert_eq!(expect.to_vec(), output.to_vec());

    }

    #[test]

    fn check_sha384() {

        let secret = b"\xb8\x0b\x73\x3d\x6c\xee\xfc\xdc\x71\x56\x6e\xa4\x8e\x55\x67\xdf";

        let seed = b"\xcd\x66\x5c\xf6\xa8\x44\x7d\xd6\xff\x8b\x27\x55\x5e\xdb\x74\x65";

        let label = b"test label";

        let expect = include_bytes!("../testdata/prf-result.3.bin");

        let mut output = [0u8; 148];

        super::prf(

            &mut output,

            &*hmac::HMAC_SHA384.with_key(secret),

            label,

            seed,

        );

        assert_eq!(expect.len(), output.len());

        assert_eq!(expect.to_vec(), output.to_vec());

    }

}

#[cfg(all(bench, feature = "ring"))]

mod benchmarks {

    #[bench]

    fn bench_sha256(b: &mut test::Bencher) {

        use crate::crypto::hmac::Hmac;

        use crate::crypto::ring::hmac;

        let label = &b"extended master secret"[..];

        let seed = [0u8; 32];

        let key = &b"secret"[..];

        b.iter(|| {

            let mut out = [0u8; 48];

            super::prf(&mut out, &*hmac::HMAC_SHA256.with_key(key), &label, &seed);

            test::black_box(out);

        });

    }

}