//! SHA-512 hash function (FIPS 180-4).
//!
//! 512-bit output, 1024-bit (128-byte) blocks, operates on 64-bit
//! words. Same Merkle-Damgård / round-mixer structure as
//! [`super::sha256`], with 80 rounds and 64-bit additions
//! throughout.
//!
//! # Side-channel posture
//!
//! Unkeyed → not SCA-sensitive. Same CDPA caveat as SHA-256
//! when consumed by Ed25519 nonce derivation (`r =
//! H(prefix ‖ M) mod ℓ`), HMAC-SHA-512, or RFC 6979 HMAC-DRBG-512:
//! the carry chain inside each 64-bit add is exploitable per
//! `belenky2023_cdpa_hmac_sha2`. Roadmap item `T2-D` ships a
//! masked variant when the `sca-protected` feature is enabled
//! (see `arcana/doc/sca/countermeasures/hmac.rst`).

use crate::Hasher;

pub(crate) const H0_512: [u64; 8] = [
    0x6a09e667f3bcc908,
    0xbb67ae8584caa73b,
    0x3c6ef372fe94f82b,
    0xa54ff53a5f1d36f1,
    0x510e527fade682d1,
    0x9b05688c2b3e6c1f,
    0x1f83d9abfb41bd6b,
    0x5be0cd19137e2179,
];

const K: [u64; 80] = [
    0x428a2f98d728ae22,
    0x7137449123ef65cd,
    0xb5c0fbcfec4d3b2f,
    0xe9b5dba58189dbbc,
    0x3956c25bf348b538,
    0x59f111f1b605d019,
    0x923f82a4af194f9b,
    0xab1c5ed5da6d8118,
    0xd807aa98a3030242,
    0x12835b0145706fbe,
    0x243185be4ee4b28c,
    0x550c7dc3d5ffb4e2,
    0x72be5d74f27b896f,
    0x80deb1fe3b1696b1,
    0x9bdc06a725c71235,
    0xc19bf174cf692694,
    0xe49b69c19ef14ad2,
    0xefbe4786384f25e3,
    0x0fc19dc68b8cd5b5,
    0x240ca1cc77ac9c65,
    0x2de92c6f592b0275,
    0x4a7484aa6ea6e483,
    0x5cb0a9dcbd41fbd4,
    0x76f988da831153b5,
    0x983e5152ee66dfab,
    0xa831c66d2db43210,
    0xb00327c898fb213f,
    0xbf597fc7beef0ee4,
    0xc6e00bf33da88fc2,
    0xd5a79147930aa725,
    0x06ca6351e003826f,
    0x142929670a0e6e70,
    0x27b70a8546d22ffc,
    0x2e1b21385c26c926,
    0x4d2c6dfc5ac42aed,
    0x53380d139d95b3df,
    0x650a73548baf63de,
    0x766a0abb3c77b2a8,
    0x81c2c92e47edaee6,
    0x92722c851482353b,
    0xa2bfe8a14cf10364,
    0xa81a664bbc423001,
    0xc24b8b70d0f89791,
    0xc76c51a30654be30,
    0xd192e819d6ef5218,
    0xd69906245565a910,
    0xf40e35855771202a,
    0x106aa07032bbd1b8,
    0x19a4c116b8d2d0c8,
    0x1e376c085141ab53,
    0x2748774cdf8eeb99,
    0x34b0bcb5e19b48a8,
    0x391c0cb3c5c95a63,
    0x4ed8aa4ae3418acb,
    0x5b9cca4f7763e373,
    0x682e6ff3d6b2b8a3,
    0x748f82ee5defb2fc,
    0x78a5636f43172f60,
    0x84c87814a1f0ab72,
    0x8cc702081a6439ec,
    0x90befffa23631e28,
    0xa4506cebde82bde9,
    0xbef9a3f7b2c67915,
    0xc67178f2e372532b,
    0xca273eceea26619c,
    0xd186b8c721c0c207,
    0xeada7dd6cde0eb1e,
    0xf57d4f7fee6ed178,
    0x06f067aa72176fba,
    0x0a637dc5a2c898a6,
    0x113f9804bef90dae,
    0x1b710b35131c471b,
    0x28db77f523047d84,
    0x32caab7b40c72493,
    0x3c9ebe0a15c9bebc,
    0x431d67c49c100d4c,
    0x4cc5d4becb3e42b6,
    0x597f299cfc657e2a,
    0x5fcb6fab3ad6faec,
    0x6c44198c4a475817,
];

pub(crate) fn compress(state: &mut [u64; 8], block: &[u8]) {
    let mut w = [0u64; 80];
    for i in 0..16 {
        w[i] = u64::from_be_bytes([
            block[8 * i],
            block[8 * i + 1],
            block[8 * i + 2],
            block[8 * i + 3],
            block[8 * i + 4],
            block[8 * i + 5],
            block[8 * i + 6],
            block[8 * i + 7],
        ]);
    }
    for i in 16..80 {
        let s0 = w[i - 15].rotate_right(1) ^ w[i - 15].rotate_right(8) ^ (w[i - 15] >> 7);
        let s1 = w[i - 2].rotate_right(19) ^ w[i - 2].rotate_right(61) ^ (w[i - 2] >> 6);
        w[i] = w[i - 16].wrapping_add(s0).wrapping_add(w[i - 7]).wrapping_add(s1);
    }

    let mut a = state[0];
    let mut b = state[1];
    let mut c = state[2];
    let mut d = state[3];
    let mut e = state[4];
    let mut f = state[5];
    let mut g = state[6];
    let mut h = state[7];

    for i in 0..80 {
        let s1 = e.rotate_right(14) ^ e.rotate_right(18) ^ e.rotate_right(41);
        let ch = (e & f) ^ ((!e) & g);
        let temp1 = h
            .wrapping_add(s1)
            .wrapping_add(ch)
            .wrapping_add(K[i])
            .wrapping_add(w[i]);
        let s0 = a.rotate_right(28) ^ a.rotate_right(34) ^ a.rotate_right(39);
        let maj = (a & b) ^ (a & c) ^ (b & c);
        let temp2 = s0.wrapping_add(maj);

        h = g;
        g = f;
        f = e;
        e = d.wrapping_add(temp1);
        d = c;
        c = b;
        b = a;
        a = temp1.wrapping_add(temp2);
    }

    state[0] = state[0].wrapping_add(a);
    state[1] = state[1].wrapping_add(b);
    state[2] = state[2].wrapping_add(c);
    state[3] = state[3].wrapping_add(d);
    state[4] = state[4].wrapping_add(e);
    state[5] = state[5].wrapping_add(f);
    state[6] = state[6].wrapping_add(g);
    state[7] = state[7].wrapping_add(h);
}

/// SHA-512 hasher (FIPS 180-4). 512-bit output, 128-byte blocks.
///
/// 64-bit oriented sibling of SHA-256, with twice the security level
/// and roughly twice the throughput on 64-bit hardware. Used as the
/// internal hash of Ed25519 (RFC 8032), as the canonical P-521 ECDSA
/// hash (FIPS 186-5), and in TLS 1.3 / IPsec for the high-security
/// tier.
#[derive(Clone)]
pub struct Sha512 {
    pub(crate) state: [u64; 8],
    buf: [u8; 128],
    buf_len: usize,
    total_len: u128,
}

impl Sha512 {
    pub(crate) fn new_with_iv(iv: [u64; 8]) -> Self {
        Self {
            state: iv,
            buf: [0u8; 128],
            buf_len: 0,
            total_len: 0,
        }
    }
}

impl Hasher for Sha512 {
    const OUTPUT_LEN: usize = 64;
    const BLOCK_LEN: usize = 128;

    fn new() -> Self {
        Self::new_with_iv(H0_512)
    }

    fn update(&mut self, data: &[u8]) {
        let mut pos = 0;
        self.total_len += data.len() as u128;

        if self.buf_len > 0 {
            let need = 128 - self.buf_len;
            let take = need.min(data.len());
            self.buf[self.buf_len..self.buf_len + take].copy_from_slice(&data[..take]);
            self.buf_len += take;
            pos = take;
            if self.buf_len == 128 {
                let block = self.buf;
                compress(&mut self.state, &block);
                self.buf_len = 0;
            }
        }

        while pos + 128 <= data.len() {
            compress(&mut self.state, &data[pos..pos + 128]);
            pos += 128;
        }

        if pos < data.len() {
            let remaining = data.len() - pos;
            self.buf[..remaining].copy_from_slice(&data[pos..]);
            self.buf_len = remaining;
        }
    }

    fn finalize(self) -> Vec<u8> {
        let mut out = vec![0u8; 64];
        self.finalize_into(&mut out);
        out
    }

    fn finalize_into(mut self, out: &mut [u8]) {
        let bit_len = self.total_len * 8;
        let mut pad = [0u8; 136]; // max padding needed
        pad[0] = 0x80;
        let pad_len = if self.buf_len < 112 {
            112 - self.buf_len
        } else {
            240 - self.buf_len
        };
        self.update(&pad[..pad_len]);
        // SHA-512 uses 128-bit length field (big-endian)
        self.update(&(bit_len as u128).to_be_bytes());

        for (i, word) in self.state.iter().enumerate() {
            let bytes = word.to_be_bytes();
            let start = i * 8;
            if start + 8 <= out.len() {
                out[start..start + 8].copy_from_slice(&bytes);
            } else if start < out.len() {
                let end = out.len() - start;
                out[start..].copy_from_slice(&bytes[..end]);
            }
        }
    }
}

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

    #[test]
    fn test_sha512_empty() {
        let digest = Sha512::hash(b"");
        let expected: [u8; 64] = [
            0xcf, 0x83, 0xe1, 0x35, 0x7e, 0xef, 0xb8, 0xbd, 0xf1, 0x54, 0x28, 0x50, 0xd6, 0x6d, 0x80, 0x07, 0xd6, 0x20,
            0xe4, 0x05, 0x0b, 0x57, 0x15, 0xdc, 0x83, 0xf4, 0xa9, 0x21, 0xd3, 0x6c, 0xe9, 0xce, 0x47, 0xd0, 0xd1, 0x3c,
            0x5d, 0x85, 0xf2, 0xb0, 0xff, 0x83, 0x18, 0xd2, 0x87, 0x7e, 0xec, 0x2f, 0x63, 0xb9, 0x31, 0xbd, 0x47, 0x41,
            0x7a, 0x81, 0xa5, 0x38, 0x32, 0x7a, 0xf9, 0x27, 0xda, 0x3e,
        ];
        assert_eq!(&digest[..], &expected[..]);
    }

    #[test]
    fn test_sha512_abc() {
        let digest = Sha512::hash(b"abc");
        let expected: [u8; 64] = [
            0xdd, 0xaf, 0x35, 0xa1, 0x93, 0x61, 0x7a, 0xba, 0xcc, 0x41, 0x73, 0x49, 0xae, 0x20, 0x41, 0x31, 0x12, 0xe6,
            0xfa, 0x4e, 0x89, 0xa9, 0x7e, 0xa2, 0x0a, 0x9e, 0xee, 0xe6, 0x4b, 0x55, 0xd3, 0x9a, 0x21, 0x92, 0x99, 0x2a,
            0x27, 0x4f, 0xc1, 0xa8, 0x36, 0xba, 0x3c, 0x23, 0xa3, 0xfe, 0xeb, 0xbd, 0x45, 0x4d, 0x44, 0x23, 0x64, 0x3c,
            0xe8, 0x0e, 0x2a, 0x9a, 0xc9, 0x4f, 0xa5, 0x4c, 0xa4, 0x9f,
        ];
        assert_eq!(&digest[..], &expected[..]);
    }
}
