//! HMAC: keyed-hash message authentication code (RFC 2104).

use crate::sha2::{Sha256, Sha384, Sha512};

/// Trait abstracting a hash function for use with HMAC.
pub trait HashFunction {
    /// Block size in bytes (64 for SHA-256, 128 for SHA-512/SHA-384).
    const BLOCK_SIZE: usize;
    /// Output digest size in bytes.
    const OUTPUT_SIZE: usize;

    fn hash_new() -> Self;
    fn hash_update(&mut self, data: &[u8]);
    fn hash_finalize(self) -> Vec<u8>;
}

impl HashFunction for Sha256 {
    const BLOCK_SIZE: usize = 64;
    const OUTPUT_SIZE: usize = 32;

    fn hash_new() -> Self {
        Sha256::new()
    }

    fn hash_update(&mut self, data: &[u8]) {
        Sha256::update(self, data);
    }

    fn hash_finalize(self) -> Vec<u8> {
        Sha256::finalize(self).to_vec()
    }
}

impl HashFunction for Sha512 {
    const BLOCK_SIZE: usize = 128;
    const OUTPUT_SIZE: usize = 64;

    fn hash_new() -> Self {
        Sha512::new()
    }

    fn hash_update(&mut self, data: &[u8]) {
        Sha512::update(self, data);
    }

    fn hash_finalize(self) -> Vec<u8> {
        Sha512::finalize(self).to_vec()
    }
}

impl HashFunction for Sha384 {
    const BLOCK_SIZE: usize = 128;
    const OUTPUT_SIZE: usize = 48;

    fn hash_new() -> Self {
        Sha384::new()
    }

    fn hash_update(&mut self, data: &[u8]) {
        Sha384::update(self, data);
    }

    fn hash_finalize(self) -> Vec<u8> {
        Sha384::finalize(self).to_vec()
    }
}

/// HMAC hasher, generic over the hash function `H`.
///
/// Implements RFC 2104: `HMAC(K, m) = H((K' ⊕ opad) ∥ H((K' ⊕ ipad) ∥ m))`
pub struct Hmac<H: HashFunction> {
    /// Inner hash, pre-seeded with `K' ⊕ ipad`.
    inner: H,
    /// Pre-computed `K' ⊕ opad` for the outer hash.
    opad_key: Vec<u8>,
}

impl<H: HashFunction> Hmac<H> {
    /// Create a new HMAC instance with the given key.
    ///
    /// Keys longer than the hash block size are hashed first.
    /// Keys shorter than the block size are zero-padded.
    pub fn new(key: &[u8]) -> Self {
        // Step 1: Derive the block-sized key K'.
        let mut key_block = vec![0u8; H::BLOCK_SIZE];
        if key.len() > H::BLOCK_SIZE {
            let mut h = H::hash_new();
            h.hash_update(key);
            let hashed = h.hash_finalize();
            key_block[..hashed.len()].copy_from_slice(&hashed);
        } else {
            key_block[..key.len()].copy_from_slice(key);
        }

        // Step 2: Compute ipad and opad keys.
        let mut ipad_key = vec![0u8; H::BLOCK_SIZE];
        let mut opad_key = vec![0u8; H::BLOCK_SIZE];
        for i in 0..H::BLOCK_SIZE {
            ipad_key[i] = key_block[i] ^ 0x36;
            opad_key[i] = key_block[i] ^ 0x5c;
        }

        // Step 3: Start the inner hash with K' ⊕ ipad.
        let mut inner = H::hash_new();
        inner.hash_update(&ipad_key);

        Self { inner, opad_key }
    }

    /// Feed data into the HMAC computation.
    pub fn update(&mut self, data: &[u8]) {
        self.inner.hash_update(data);
    }

    /// Finalize and return the HMAC digest.
    pub fn finalize(self) -> Vec<u8> {
        // Complete inner hash: H((K' ⊕ ipad) ∥ message)
        let inner_hash = self.inner.hash_finalize();

        // Compute outer hash: H((K' ⊕ opad) ∥ inner_hash)
        let mut outer = H::hash_new();
        outer.hash_update(&self.opad_key);
        outer.hash_update(&inner_hash);
        outer.hash_finalize()
    }
}

/// One-shot HMAC-SHA-256.
pub fn hmac_sha256(key: &[u8], data: &[u8]) -> [u8; 32] {
    let mut h = Hmac::<Sha256>::new(key);
    h.update(data);
    let result = h.finalize();
    let mut out = [0u8; 32];
    out.copy_from_slice(&result);
    out
}

/// One-shot HMAC-SHA-384.
pub fn hmac_sha384(key: &[u8], data: &[u8]) -> [u8; 48] {
    let mut h = Hmac::<Sha384>::new(key);
    h.update(data);
    let result = h.finalize();
    let mut out = [0u8; 48];
    out.copy_from_slice(&result);
    out
}

/// One-shot HMAC-SHA-512.
pub fn hmac_sha512(key: &[u8], data: &[u8]) -> [u8; 64] {
    let mut h = Hmac::<Sha512>::new(key);
    h.update(data);
    let result = h.finalize();
    let mut out = [0u8; 64];
    out.copy_from_slice(&result);
    out
}

// ---------------------------------------------------------------------------
// Tests — RFC 4231 test vectors
// ---------------------------------------------------------------------------

#[cfg(test)]
mod tests {
    use super::*;

    fn hex(bytes: &[u8]) -> String {
        bytes.iter().map(|b| format!("{b:02x}")).collect()
    }

    // -----------------------------------------------------------------------
    // Test Case 1: Key = 0x0b * 20, Data = "Hi There"
    // -----------------------------------------------------------------------

    #[test]
    fn rfc4231_case1_sha256() {
        let key = [0x0bu8; 20];
        assert_eq!(
            hex(&hmac_sha256(&key, b"Hi There")),
            "b0344c61d8db38535ca8afceaf0bf12b881dc200c9833da726e9376c2e32cff7"
        );
    }

    #[test]
    fn rfc4231_case1_sha384() {
        let key = [0x0bu8; 20];
        assert_eq!(
            hex(&hmac_sha384(&key, b"Hi There")),
            "afd03944d84895626b0825f4ab46907f15f9dadbe4101ec682aa034c7cebc59cfaea9ea9076ede7f4af152e8b2fa9cb6"
        );
    }

    #[test]
    fn rfc4231_case1_sha512() {
        let key = [0x0bu8; 20];
        assert_eq!(
            hex(&hmac_sha512(&key, b"Hi There")),
            "87aa7cdea5ef619d4ff0b4241a1d6cb02379f4e2ce4ec2787ad0b30545e17cdedaa833b7d6b8a702038b274eaea3f4e4be9d914eeb61f1702e696c203a126854"
        );
    }

    // -----------------------------------------------------------------------
    // Test Case 2: Key = "Jefe", Data = "what do ya want for nothing?"
    // -----------------------------------------------------------------------

    #[test]
    fn rfc4231_case2_sha256() {
        assert_eq!(
            hex(&hmac_sha256(b"Jefe", b"what do ya want for nothing?")),
            "5bdcc146bf60754e6a042426089575c75a003f089d2739839dec58b964ec3843"
        );
    }

    #[test]
    fn rfc4231_case2_sha384() {
        assert_eq!(
            hex(&hmac_sha384(b"Jefe", b"what do ya want for nothing?")),
            "af45d2e376484031617f78d2b58a6b1b9c7ef464f5a01b47e42ec3736322445e8e2240ca5e69e2c78b3239ecfab21649"
        );
    }

    #[test]
    fn rfc4231_case2_sha512() {
        assert_eq!(
            hex(&hmac_sha512(b"Jefe", b"what do ya want for nothing?")),
            "164b7a7bfcf819e2e395fbe73b56e0a387bd64222e831fd610270cd7ea2505549758bf75c05a994a6d034f65f8f0e6fdcaeab1a34d4a6b4b636e070a38bce737"
        );
    }

    // -----------------------------------------------------------------------
    // Test Case 3: Key = 0xaa * 20, Data = 0xdd * 50
    // -----------------------------------------------------------------------

    #[test]
    fn rfc4231_case3_sha256() {
        let key = [0xaau8; 20];
        let data = [0xddu8; 50];
        assert_eq!(
            hex(&hmac_sha256(&key, &data)),
            "773ea91e36800e46854db8ebd09181a72959098b3ef8c122d9635514ced565fe"
        );
    }

    #[test]
    fn rfc4231_case3_sha384() {
        let key = [0xaau8; 20];
        let data = [0xddu8; 50];
        assert_eq!(
            hex(&hmac_sha384(&key, &data)),
            "88062608d3e6ad8a0aa2ace014c8a86f0aa635d947ac9febe83ef4e55966144b2a5ab39dc13814b94e3ab6e101a34f27"
        );
    }

    #[test]
    fn rfc4231_case3_sha512() {
        let key = [0xaau8; 20];
        let data = [0xddu8; 50];
        assert_eq!(
            hex(&hmac_sha512(&key, &data)),
            "fa73b0089d56a284efb0f0756c890be9b1b5dbdd8ee81a3655f83e33b2279d39bf3e848279a722c806b485a47e67c807b946a337bee8942674278859e13292fb"
        );
    }

    // -----------------------------------------------------------------------
    // Test Case 4: Key = 0x01..0x19 (25 bytes), Data = 0xcd * 50
    // -----------------------------------------------------------------------

    #[test]
    fn rfc4231_case4_sha256() {
        let key: Vec<u8> = (0x01..=0x19).collect();
        let data = [0xcdu8; 50];
        assert_eq!(
            hex(&hmac_sha256(&key, &data)),
            "82558a389a443c0ea4cc819899f2083a85f0faa3e578f8077a2e3ff46729665b"
        );
    }

    #[test]
    fn rfc4231_case4_sha384() {
        let key: Vec<u8> = (0x01..=0x19).collect();
        let data = [0xcdu8; 50];
        assert_eq!(
            hex(&hmac_sha384(&key, &data)),
            "3e8a69b7783c25851933ab6290af6ca77a9981480850009cc5577c6e1f573b4e6801dd23c4a7d679ccf8a386c674cffb"
        );
    }

    #[test]
    fn rfc4231_case4_sha512() {
        let key: Vec<u8> = (0x01..=0x19).collect();
        let data = [0xcdu8; 50];
        assert_eq!(
            hex(&hmac_sha512(&key, &data)),
            "b0ba465637458c6990e5a8c5f61d4af7e576d97ff94b872de76f8050361ee3dba91ca5c11aa25eb4d679275cc5788063a5f19741120c4f2de2adebeb10a298dd"
        );
    }

    // -----------------------------------------------------------------------
    // Test Case 5: Truncation (Key = 0x0c * 20, Data = "Test With Truncation")
    // Verify the first 16 bytes of the full HMAC match the truncated vector.
    // -----------------------------------------------------------------------

    #[test]
    fn rfc4231_case5_sha256_truncated() {
        let key = [0x0cu8; 20];
        let result = hmac_sha256(&key, b"Test With Truncation");
        assert_eq!(hex(&result[..16]), "a3b6167473100ee06e0c796c2955552b");
    }

    #[test]
    fn rfc4231_case5_sha384_truncated() {
        let key = [0x0cu8; 20];
        let result = hmac_sha384(&key, b"Test With Truncation");
        assert_eq!(hex(&result[..16]), "3abf34c3503b2a23a46efc619baef897");
    }

    #[test]
    fn rfc4231_case5_sha512_truncated() {
        let key = [0x0cu8; 20];
        let result = hmac_sha512(&key, b"Test With Truncation");
        assert_eq!(hex(&result[..16]), "415fad6271580a531d4179bc891d87a6");
    }

    // -----------------------------------------------------------------------
    // Test Case 6: Key longer than block size (0xaa * 131)
    // Data = "Test Using Larger Than Block-Size Key - Hash Key First"
    // -----------------------------------------------------------------------

    #[test]
    fn rfc4231_case6_sha256() {
        let key = [0xaau8; 131];
        assert_eq!(
            hex(&hmac_sha256(
                &key,
                b"Test Using Larger Than Block-Size Key - Hash Key First"
            )),
            "60e431591ee0b67f0d8a26aacbf5b77f8e0bc6213728c5140546040f0ee37f54"
        );
    }

    #[test]
    fn rfc4231_case6_sha384() {
        let key = [0xaau8; 131];
        assert_eq!(
            hex(&hmac_sha384(&key, b"Test Using Larger Than Block-Size Key - Hash Key First")),
            "4ece084485813e9088d2c63a041bc5b44f9ef1012a2b588f3cd11f05033ac4c60c2ef6ab4030fe8296248df163f44952"
        );
    }

    #[test]
    fn rfc4231_case6_sha512() {
        let key = [0xaau8; 131];
        assert_eq!(
            hex(&hmac_sha512(&key, b"Test Using Larger Than Block-Size Key - Hash Key First")),
            "80b24263c7c1a3ebb71493c1dd7be8b49b46d1f41b4aeec1121b013783f8f3526b56d037e05f2598bd0fd2215d6a1e5295e64f73f63f0aec8b915a985d786598"
        );
    }

    // -----------------------------------------------------------------------
    // Test Case 7: Key longer than block size, data longer than block size
    // Key = 0xaa * 131
    // -----------------------------------------------------------------------

    const CASE7_DATA: &[u8] = b"This is a test using a larger than block-size key and a larger than block-size data. The key needs to be hashed before being used by the HMAC algorithm.";

    #[test]
    fn rfc4231_case7_sha256() {
        let key = [0xaau8; 131];
        assert_eq!(
            hex(&hmac_sha256(&key, CASE7_DATA)),
            "9b09ffa71b942fcb27635fbcd5b0e944bfdc63644f0713938a7f51535c3a35e2"
        );
    }

    #[test]
    fn rfc4231_case7_sha384() {
        let key = [0xaau8; 131];
        assert_eq!(
            hex(&hmac_sha384(&key, CASE7_DATA)),
            "6617178e941f020d351e2f254e8fd32c602420feb0b8fb9adccebb82461e99c5a678cc31e799176d3860e6110c46523e"
        );
    }

    #[test]
    fn rfc4231_case7_sha512() {
        let key = [0xaau8; 131];
        assert_eq!(
            hex(&hmac_sha512(&key, CASE7_DATA)),
            "e37b6a775dc87dbaa4dfa9f96e5e3ffddebd71f8867289865df5a32d20cdc944b6022cac3c4982b10d5eeb55c3e4de15134676fb6de0446065c97440fa8c6a58"
        );
    }

    // -----------------------------------------------------------------------
    // Streaming API tests
    // -----------------------------------------------------------------------

    #[test]
    fn streaming_matches_oneshot_sha256() {
        let key = b"secret key";
        let data = b"The quick brown fox jumps over the lazy dog";
        let expected = hmac_sha256(key, data);

        let mut h = Hmac::<Sha256>::new(key);
        h.update(&data[..10]);
        h.update(&data[10..30]);
        h.update(&data[30..]);
        let result = h.finalize();
        assert_eq!(&result[..], &expected[..]);
    }

    #[test]
    fn streaming_matches_oneshot_sha512() {
        let key = b"another secret key";
        let data = b"Some message to authenticate";
        let expected = hmac_sha512(key, data);

        let mut h = Hmac::<Sha512>::new(key);
        h.update(&data[..5]);
        h.update(&data[5..]);
        let result = h.finalize();
        assert_eq!(&result[..], &expected[..]);
    }

    #[test]
    fn empty_data() {
        let key = [0x0bu8; 20];
        let result = hmac_sha256(&key, b"");
        // Just verify it doesn't panic and produces 32 bytes.
        assert_eq!(result.len(), 32);
    }

    #[test]
    fn key_exactly_block_size_sha256() {
        // Key exactly 64 bytes (SHA-256 block size) — no hashing, no padding needed.
        let key = [0x42u8; 64];
        let result = hmac_sha256(&key, b"test");
        assert_eq!(result.len(), 32);

        // Verify streaming matches.
        let mut h = Hmac::<Sha256>::new(&key);
        h.update(b"test");
        assert_eq!(&h.finalize()[..], &result[..]);
    }
}