use alloc::boxed::Box;

use alloc::vec::Vec;

use zeroize::Zeroize;

use super::{ActiveKeyExchange, hmac};

use crate::error::Error;

use crate::version::TLS13;

/// Implementation of `HkdfExpander` via `hmac::Key`.

pub struct HkdfExpanderUsingHmac(Box<dyn hmac::Key>);

impl HkdfExpanderUsingHmac {

    fn expand_unchecked(&self, info: &[&[u8]], output: &mut [u8]) {

        let mut term = hmac::Tag::new(b"");

        for (n, chunk) in output

            .chunks_mut(self.0.tag_len())

            .enumerate()

        {

            term = self

                .0

                .sign_concat(term.as_ref(), info, &[(n + 1) as u8]);

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

        }

    }

}

impl HkdfExpander for HkdfExpanderUsingHmac {

    fn expand_slice(&self, info: &[&[u8]], output: &mut [u8]) -> Result<(), OutputLengthError> {

        if output.len() > 255 * self.0.tag_len() {

            return Err(OutputLengthError);

        }

        self.expand_unchecked(info, output);

        Ok(())

    }

    fn expand_block(&self, info: &[&[u8]]) -> OkmBlock {

        let mut tag = [0u8; hmac::Tag::MAX_LEN];

        let reduced_tag = &mut tag[..self.0.tag_len()];

        self.expand_unchecked(info, reduced_tag);

        OkmBlock::new(reduced_tag)

    }

    fn hash_len(&self) -> usize {

        self.0.tag_len()

    }

}

/// Implementation of `Hkdf` (and thence `HkdfExpander`) via `hmac::Hmac`.

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

impl Hkdf for HkdfUsingHmac<'_> {

    fn extract_from_zero_ikm(&self, salt: Option<&[u8]>) -> Box<dyn HkdfExpander> {

        let zeroes = [0u8; hmac::Tag::MAX_LEN];

        Box::new(HkdfExpanderUsingHmac(self.0.with_key(

            &self.extract_prk_from_secret(salt, &zeroes[..self.0.hash_output_len()]),

        )))

    }

    fn extract_from_secret(&self, salt: Option<&[u8]>, secret: &[u8]) -> Box<dyn HkdfExpander> {

        Box::new(HkdfExpanderUsingHmac(

            self.0

                .with_key(&self.extract_prk_from_secret(salt, secret)),

        ))

    }

    fn expander_for_okm(&self, okm: &OkmBlock) -> Box<dyn HkdfExpander> {

        Box::new(HkdfExpanderUsingHmac(self.0.with_key(okm.as_ref())))

    }

    fn hmac_sign(&self, key: &OkmBlock, message: &[u8]) -> hmac::Tag {

        self.0

            .with_key(key.as_ref())

            .sign(&[message])

    }

}

impl HkdfPrkExtract for HkdfUsingHmac<'_> {

    fn extract_prk_from_secret(&self, salt: Option<&[u8]>, secret: &[u8]) -> Vec<u8> {

        let zeroes = [0u8; hmac::Tag::MAX_LEN];

        let salt = match salt {

            Some(salt) => salt,

            None => &zeroes[..self.0.hash_output_len()],

        };

        self.0

            .with_key(salt)

            .sign(&[secret])

            .as_ref()

            .to_vec()

    }

}

/// Implementation of `HKDF-Expand` with an implicitly stored and immutable `PRK`.

pub trait HkdfExpander: Send + Sync {

    /// `HKDF-Expand(PRK, info, L)` into a slice.

    ///

    /// Where:

    ///

    /// - `PRK` is the implicit key material represented by this instance.

    /// - `L` is `output.len()`.

    /// - `info` is a slice of byte slices, which should be processed sequentially

    ///   (or concatenated if that is not possible).

    ///

    /// Returns `Err(OutputLengthError)` if `L` is larger than `255 * HashLen`.

    /// Otherwise, writes to `output`.

    fn expand_slice(&self, info: &[&[u8]], output: &mut [u8]) -> Result<(), OutputLengthError>;

    /// `HKDF-Expand(PRK, info, L=HashLen)` returned as a value.

    ///

    /// - `PRK` is the implicit key material represented by this instance.

    /// - `L := HashLen`.

    /// - `info` is a slice of byte slices, which should be processed sequentially

    ///   (or concatenated if that is not possible).

    ///

    /// This is infallible, because by definition `OkmBlock` is always exactly

    /// `HashLen` bytes long.

    fn expand_block(&self, info: &[&[u8]]) -> OkmBlock;

    /// Return what `HashLen` is for this instance.

    ///

    /// This must be no larger than [`OkmBlock::MAX_LEN`].

    fn hash_len(&self) -> usize;

}

/// A HKDF implementation oriented to the needs of TLS1.3.

///

/// See [RFC5869](https://datatracker.ietf.org/doc/html/rfc5869) for the terminology

/// used in this definition.

///

/// You can use [`HkdfUsingHmac`] which implements this trait on top of an implementation

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

pub trait Hkdf: Send + Sync {

    /// `HKDF-Extract(salt, 0_HashLen)`

    ///

    /// `0_HashLen` is a string of `HashLen` zero bytes.

    ///

    /// A `salt` of `None` should be treated as a sequence of `HashLen` zero bytes.

    fn extract_from_zero_ikm(&self, salt: Option<&[u8]>) -> Box<dyn HkdfExpander>;

    /// `HKDF-Extract(salt, secret)`

    ///

    /// A `salt` of `None` should be treated as a sequence of `HashLen` zero bytes.

    fn extract_from_secret(&self, salt: Option<&[u8]>, secret: &[u8]) -> Box<dyn HkdfExpander>;

    /// `HKDF-Extract(salt, shared_secret)` where `shared_secret` is the result of a key exchange.

    ///

    /// Custom implementations should complete the key exchange by calling

    /// `kx.complete(peer_pub_key)` and then using this as the input keying material to

    /// `HKDF-Extract`.

    ///

    /// A `salt` of `None` should be treated as a sequence of `HashLen` zero bytes.

    fn extract_from_kx_shared_secret(

        &self,

        salt: Option<&[u8]>,

        kx: Box<dyn ActiveKeyExchange>,

        peer_pub_key: &[u8],

    ) -> Result<Box<dyn HkdfExpander>, Error> {

        Ok(self.extract_from_secret(

            salt,

            kx.complete_for_tls_version(peer_pub_key, &TLS13)?

                .secret_bytes(),

        ))

    }

    /// Build a `HkdfExpander` using `okm` as the secret PRK.

    fn expander_for_okm(&self, okm: &OkmBlock) -> Box<dyn HkdfExpander>;

    /// Signs `message` using `key` viewed as a HMAC key.

    ///

    /// This should use the same hash function as the HKDF functions in this

    /// trait.

    ///

    /// See [RFC2104](https://datatracker.ietf.org/doc/html/rfc2104) for the

    /// definition of HMAC.

    fn hmac_sign(&self, key: &OkmBlock, message: &[u8]) -> hmac::Tag;

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

    fn fips(&self) -> bool {

        false

    }

}

/// An extended HKDF implementation that supports directly extracting a pseudo-random key (PRK).

///

/// The base [`Hkdf`] trait is tailored to the needs of TLS 1.3, where all extracted PRKs

/// are expanded as-is, and so can be safely encapsulated without exposing the caller

/// to the key material.

///

/// In other contexts (for example, hybrid public key encryption (HPKE)) it may be necessary

/// to use the extracted PRK directly for purposes other than an immediate expansion.

/// This trait can be implemented to offer this functionality when it is required.

pub(crate) trait HkdfPrkExtract: Hkdf {

    /// `HKDF-Extract(salt, secret)`

    ///

    /// A `salt` of `None` should be treated as a sequence of `HashLen` zero bytes.

    ///

    /// In most cases you should prefer [`Hkdf::extract_from_secret`] and using the

    /// returned [HkdfExpander] instead of handling the PRK directly.

    fn extract_prk_from_secret(&self, salt: Option<&[u8]>, secret: &[u8]) -> Vec<u8>;

}

/// `HKDF-Expand(PRK, info, L)` to construct any type from a byte array.

///

/// - `PRK` is the implicit key material represented by this instance.

/// - `L := N`; N is the size of the byte array.

/// - `info` is a slice of byte slices, which should be processed sequentially

///   (or concatenated if that is not possible).

///

/// This is infallible, because the set of types (and therefore their length) is known

/// at compile time.

pub fn expand<T, const N: usize>(expander: &dyn HkdfExpander, info: &[&[u8]]) -> T

where

    T: From<[u8; N]>,

{

    let mut output = [0u8; N];

    expander

        .expand_slice(info, &mut output)

        .expect("expand type parameter T is too large");

    T::from(output)

}

Unexecuted instantiation: rustls::crypto::tls13::expand::<[u8; 8], 8>

Unexecuted instantiation: rustls::crypto::tls13::expand::<rustls::crypto::cipher::Iv, 12>

Unexecuted instantiation: rustls::crypto::tls13::expand::<rustls::crypto::cipher::AeadKey, 32>

/// Output key material from HKDF, as a value type.

#[derive(Clone)]

pub struct OkmBlock {

    buf: [u8; Self::MAX_LEN],

    used: usize,

}

impl OkmBlock {

    /// Build a single OKM block by copying a byte slice.

    ///

    /// The slice can be up to [`OkmBlock::MAX_LEN`] bytes in length.

    pub fn new(bytes: &[u8]) -> Self {

        let mut tag = Self {

            buf: [0u8; Self::MAX_LEN],

            used: bytes.len(),

        };

        tag.buf[..bytes.len()].copy_from_slice(bytes);

        tag

    }

    /// Maximum supported HMAC tag size: supports up to SHA512.

    pub const MAX_LEN: usize = 64;

}

impl Drop for OkmBlock {

    fn drop(&mut self) {

        self.buf.zeroize();

    }

}

impl AsRef<[u8]> for OkmBlock {

    fn as_ref(&self) -> &[u8] {

        &self.buf[..self.used]

    }

}

/// An error type used for `HkdfExpander::expand_slice` when

/// the slice exceeds the maximum HKDF output length.

#[derive(Debug)]

pub struct OutputLengthError;

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

mod tests {

    use std::prelude::v1::*;

    use super::{Hkdf, HkdfUsingHmac, expand};

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

    // so cannot be used for this test.

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

    struct ByteArray<const N: usize>([u8; N]);

    impl<const N: usize> From<[u8; N]> for ByteArray<N> {

        fn from(array: [u8; N]) -> Self {

            Self(array)

        }

    }

    /// Test cases from appendix A in the RFC, minus cases requiring SHA1.

    #[test]

    fn test_case_1() {

        let hkdf = HkdfUsingHmac(&hmac::HMAC_SHA256);

        let ikm = &[0x0b; 22];

        let salt = &[

            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c,

        ];

        let info: &[&[u8]] = &[

            &[0xf0, 0xf1, 0xf2],

            &[0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9],

        ];

        let output: ByteArray<42> = expand(

            hkdf.extract_from_secret(Some(salt), ikm)

                .as_ref(),

            info,

        );

        assert_eq!(

            &output.0,

            &[

                0x3c, 0xb2, 0x5f, 0x25, 0xfa, 0xac, 0xd5, 0x7a, 0x90, 0x43, 0x4f, 0x64, 0xd0, 0x36,

                0x2f, 0x2a, 0x2d, 0x2d, 0x0a, 0x90, 0xcf, 0x1a, 0x5a, 0x4c, 0x5d, 0xb0, 0x2d, 0x56,

                0xec, 0xc4, 0xc5, 0xbf, 0x34, 0x00, 0x72, 0x08, 0xd5, 0xb8, 0x87, 0x18, 0x58, 0x65

            ]

        );

    }

    #[test]

    fn test_case_2() {

        let hkdf = HkdfUsingHmac(&hmac::HMAC_SHA256);

        let ikm: Vec<u8> = (0x00u8..=0x4f).collect();

        let salt: Vec<u8> = (0x60u8..=0xaf).collect();

        let info: Vec<u8> = (0xb0u8..=0xff).collect();

        let output: ByteArray<82> = expand(

            hkdf.extract_from_secret(Some(&salt), &ikm)

                .as_ref(),

            &[&info],

        );

        assert_eq!(

            &output.0,

            &[

                0xb1, 0x1e, 0x39, 0x8d, 0xc8, 0x03, 0x27, 0xa1, 0xc8, 0xe7, 0xf7, 0x8c, 0x59, 0x6a,

                0x49, 0x34, 0x4f, 0x01, 0x2e, 0xda, 0x2d, 0x4e, 0xfa, 0xd8, 0xa0, 0x50, 0xcc, 0x4c,

                0x19, 0xaf, 0xa9, 0x7c, 0x59, 0x04, 0x5a, 0x99, 0xca, 0xc7, 0x82, 0x72, 0x71, 0xcb,

                0x41, 0xc6, 0x5e, 0x59, 0x0e, 0x09, 0xda, 0x32, 0x75, 0x60, 0x0c, 0x2f, 0x09, 0xb8,

                0x36, 0x77, 0x93, 0xa9, 0xac, 0xa3, 0xdb, 0x71, 0xcc, 0x30, 0xc5, 0x81, 0x79, 0xec,

                0x3e, 0x87, 0xc1, 0x4c, 0x01, 0xd5, 0xc1, 0xf3, 0x43, 0x4f, 0x1d, 0x87

            ]

        );

    }

    #[test]

    fn test_case_3() {

        let hkdf = HkdfUsingHmac(&hmac::HMAC_SHA256);

        let ikm = &[0x0b; 22];

        let salt = &[];

        let info = &[];

        let output: ByteArray<42> = expand(

            hkdf.extract_from_secret(Some(salt), ikm)

                .as_ref(),

            info,

        );

        assert_eq!(

            &output.0,

            &[

                0x8d, 0xa4, 0xe7, 0x75, 0xa5, 0x63, 0xc1, 0x8f, 0x71, 0x5f, 0x80, 0x2a, 0x06, 0x3c,

                0x5a, 0x31, 0xb8, 0xa1, 0x1f, 0x5c, 0x5e, 0xe1, 0x87, 0x9e, 0xc3, 0x45, 0x4e, 0x5f,

                0x3c, 0x73, 0x8d, 0x2d, 0x9d, 0x20, 0x13, 0x95, 0xfa, 0xa4, 0xb6, 0x1a, 0x96, 0xc8

            ]

        );

    }

    #[test]

    fn test_salt_not_provided() {

        // can't use test case 7, because we don't have (or want) SHA1.

        //

        // this output is generated with cryptography.io:

        //

        // >>> hkdf.HKDF(algorithm=hashes.SHA384(), length=96, salt=None, info=b"hello").derive(b"\x0b" * 40)

        let hkdf = HkdfUsingHmac(&hmac::HMAC_SHA384);

        let ikm = &[0x0b; 40];

        let info = &[&b"hel"[..], &b"lo"[..]];

        let output: ByteArray<96> = expand(

            hkdf.extract_from_secret(None, ikm)

                .as_ref(),

            info,

        );

        assert_eq!(

            &output.0,

            &[

                0xd5, 0x45, 0xdd, 0x3a, 0xff, 0x5b, 0x19, 0x46, 0xd4, 0x86, 0xfd, 0xb8, 0xd8, 0x88,

                0x2e, 0xe0, 0x1c, 0xc1, 0xa5, 0x48, 0xb6, 0x05, 0x75, 0xe4, 0xd7, 0x5d, 0x0f, 0x5f,

                0x23, 0x40, 0xee, 0x6c, 0x9e, 0x7c, 0x65, 0xd0, 0xee, 0x79, 0xdb, 0xb2, 0x07, 0x1d,

                0x66, 0xa5, 0x50, 0xc4, 0x8a, 0xa3, 0x93, 0x86, 0x8b, 0x7c, 0x69, 0x41, 0x6b, 0x3e,

                0x61, 0x44, 0x98, 0xb8, 0xc2, 0xfc, 0x82, 0x82, 0xae, 0xcd, 0x46, 0xcf, 0xb1, 0x47,

                0xdc, 0xd0, 0x69, 0x0d, 0x19, 0xad, 0xe6, 0x6c, 0x70, 0xfe, 0x87, 0x92, 0x04, 0xb6,

                0x82, 0x2d, 0x97, 0x7e, 0x46, 0x80, 0x4c, 0xe5, 0x76, 0x72, 0xb4, 0xb8

            ]

        );

    }

    #[test]

    fn test_output_length_bounds() {

        let hkdf = HkdfUsingHmac(&hmac::HMAC_SHA256);

        let ikm = &[];

        let info = &[];

        let mut output = [0u8; 32 * 255 + 1];

        assert!(

            hkdf.extract_from_secret(None, ikm)

                .expand_slice(info, &mut output)

                .is_err()

        );

    }

}