// sha256 twice in one process (makepad score_pdf's one-shot form and core_util's streaming
// form with its hardware self-check, software path): each copies a const IV into its state
// and mutates it, so a const that a mutated local aliased made every hash after the first in
// a process wrong (core_util hw::check's `let mut h = super::H0` broke every later
// Sha256::new()). Known vectors (FIPS 180-4). rustc prints the same line.
fn sha256_oneshot(data: &[u8]) -> [u8; 32] {
    const INITIAL: [u32; 8] = [
        0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
        0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
    ];
    const K: [u32; 64] = [
        0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1,
        0x923f82a4, 0xab1c5ed5, 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
        0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786,
        0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
        0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147,
        0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
        0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85, 0xa2bfe8a1, 0xa81a664b,
        0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
        0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a,
        0x5b9cca4f, 0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
        0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
    ];
    let bit_len = (data.len() as u64).wrapping_mul(8);
    let total_len = (data.len() + 9).div_ceil(64) * 64;
    let mut padded = vec![0_u8; total_len];
    padded[..data.len()].copy_from_slice(data);
    padded[data.len()] = 0x80;
    padded[total_len - 8..].copy_from_slice(&bit_len.to_be_bytes());
    let mut state = INITIAL;
    for chunk in padded.chunks_exact(64) {
        let mut words = [0_u32; 64];
        for (index, word) in chunk.chunks_exact(4).enumerate() {
            words[index] = u32::from_be_bytes([word[0], word[1], word[2], word[3]]);
        }
        for index in 16..64 {
            let s0 = words[index - 15].rotate_right(7)
                ^ words[index - 15].rotate_right(18)
                ^ (words[index - 15] >> 3);
            let s1 = words[index - 2].rotate_right(17)
                ^ words[index - 2].rotate_right(19)
                ^ (words[index - 2] >> 10);
            words[index] = words[index - 16]
                .wrapping_add(s0)
                .wrapping_add(words[index - 7])
                .wrapping_add(s1);
        }
        let [mut a, mut b, mut c, mut d, mut e, mut f, mut g, mut h] = state;
        for index in 0..64 {
            let s1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
            let choice = (e & f) ^ ((!e) & g);
            let first = h
                .wrapping_add(s1)
                .wrapping_add(choice)
                .wrapping_add(K[index])
                .wrapping_add(words[index]);
            let s0 = a.rotate_right(2) ^ a.rotate_right(13) ^ a.rotate_right(22);
            let majority = (a & b) ^ (a & c) ^ (b & c);
            let second = s0.wrapping_add(majority);
            h = g;
            g = f;
            f = e;
            e = d.wrapping_add(first);
            d = c;
            c = b;
            b = a;
            a = first.wrapping_add(second);
        }
        for (target, value) in state.iter_mut().zip([a, b, c, d, e, f, g, h]) {
            *target = target.wrapping_add(value);
        }
    }
    let mut output = [0_u8; 32];
    for (chunk, value) in output.chunks_exact_mut(4).zip(state) {
        chunk.copy_from_slice(&value.to_be_bytes());
    }
    output
}

fn hex(bytes: &[u8]) -> String {
    const DIGITS: &[u8; 16] = b"0123456789abcdef";
    let mut output = String::with_capacity(bytes.len() * 2);
    for byte in bytes {
        output.push(DIGITS[(byte >> 4) as usize] as char);
        output.push(DIGITS[(byte & 15) as usize] as char);
    }
    output
}

const K: [u32; 64] = [
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
    0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
    0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
    0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
    0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
    0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
];

const H0: [u32; 8] = [
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
];

#[derive(Clone)]
struct Sha256 {
    h: [u32; 8],
    block: [u8; 64],
    block_len: usize,
    total_len: u64,
}

impl Sha256 {
    fn new() -> Self {
        Self { h: H0, block: [0; 64], block_len: 0, total_len: 0 }
    }
    fn update(&mut self, mut data: &[u8]) {
        self.total_len = self.total_len.wrapping_add(data.len() as u64);
        if self.block_len > 0 {
            let take = (64 - self.block_len).min(data.len());
            self.block[self.block_len..self.block_len + take].copy_from_slice(&data[..take]);
            self.block_len += take;
            data = &data[take..];
            if self.block_len == 64 {
                let block = self.block;
                self.compress(&block);
                self.block_len = 0;
            }
            if data.is_empty() {
                // A still-partial buffered block must survive; the remainder
                // write below would zero block_len and drop it.
                return;
            }
        }
        let mut chunks = data.chunks_exact(64);
        for chunk in &mut chunks {
            let mut block = [0u8; 64];
            block.copy_from_slice(chunk);
            self.compress(&block);
        }
        let rest = chunks.remainder();
        self.block[..rest.len()].copy_from_slice(rest);
        self.block_len = rest.len();
    }

    fn finalize(mut self) -> [u8; 32] {
        let bit_len = self.total_len.wrapping_mul(8);
        let mut tail = [0u8; 128];
        tail[..self.block_len].copy_from_slice(&self.block[..self.block_len]);
        tail[self.block_len] = 0x80;
        // One padded block if the length fits, otherwise two.
        let tail_len = if self.block_len < 56 { 64 } else { 128 };
        tail[tail_len - 8..tail_len].copy_from_slice(&bit_len.to_be_bytes());
        let mut block = [0u8; 64];
        block.copy_from_slice(&tail[..64]);
        self.compress(&block);
        if tail_len == 128 {
            block.copy_from_slice(&tail[64..]);
            self.compress(&block);
        }
        let mut out = [0u8; 32];
        for (i, v) in self.h.iter().enumerate() {
            out[i * 4..i * 4 + 4].copy_from_slice(&v.to_be_bytes());
        }
        out
    }

    fn compress(&mut self, chunk: &[u8; 64]) {
        Self::compress_sw(&mut self.h, chunk);
    }

    fn compress_sw(h: &mut [u32; 8], chunk: &[u8; 64]) {
        let mut w = [0u32; 64];
        for (i, word) in chunk.chunks_exact(4).enumerate() {
            w[i] = u32::from_be_bytes([word[0], word[1], word[2], word[3]]);
        }
        for i in 16..64 {
            let s0 = w[i - 15].rotate_right(7) ^ w[i - 15].rotate_right(18) ^ (w[i - 15] >> 3);
            let s1 = w[i - 2].rotate_right(17) ^ w[i - 2].rotate_right(19) ^ (w[i - 2] >> 10);
            w[i] = w[i - 16]
                .wrapping_add(s0)
                .wrapping_add(w[i - 7])
                .wrapping_add(s1);
        }
        let (mut a, mut b, mut c, mut d) = (h[0], h[1], h[2], h[3]);
        let (mut e, mut f, mut g, mut hh) = (h[4], h[5], h[6], h[7]);
        for i in 0..64 {
            let s1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
            let ch = (e & f) ^ ((!e) & g);
            let t1 = hh
                .wrapping_add(s1)
                .wrapping_add(ch)
                .wrapping_add(K[i])
                .wrapping_add(w[i]);
            let s0 = a.rotate_right(2) ^ a.rotate_right(13) ^ a.rotate_right(22);
            let maj = (a & b) ^ (a & c) ^ (b & c);
            let t2 = s0.wrapping_add(maj);
            hh = g;
            g = f;
            f = e;
            e = d.wrapping_add(t1);
            d = c;
            c = b;
            b = a;
            a = t1.wrapping_add(t2);
        }
        h[0] = h[0].wrapping_add(a);
        h[1] = h[1].wrapping_add(b);
        h[2] = h[2].wrapping_add(c);
        h[3] = h[3].wrapping_add(d);
        h[4] = h[4].wrapping_add(e);
        h[5] = h[5].wrapping_add(f);
        h[6] = h[6].wrapping_add(g);
        h[7] = h[7].wrapping_add(hh);
    }
}

// core_util's hardware self-check, run once before the first hash (sha256.rs hw::check):
// the IV copied through a module path, then written through `&mut`
mod hw {
    const ABC_BLOCK: [u8; 64] = {
        let mut b = [0u8; 64];
        b[0] = b'a';
        b[1] = b'b';
        b[2] = b'c';
        b[3] = 0x80;
        b[63] = 24;
        b
    };
    const ABC_DIGEST: [u32; 8] = [
        0xba7816bf, 0x8f01cfea, 0x414140de, 0x5dae2223, 0xb00361a3, 0x96177a9c, 0xb410ff61, 0xf20015ad,
    ];
    pub fn check() -> bool {
        let mut h = super::H0;
        super::Sha256::compress_sw(&mut h, &ABC_BLOCK);
        h == ABC_DIGEST
    }
}

fn streaming(data: &[u8]) -> [u8; 32] {
    let mut s = Sha256::new();
    s.update(data);
    s.finalize()
}

#[test]
fn sha256_twice() {
    let abc = "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad";
    let two = "248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1";
    let msg2 = b"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq";
    assert!(hw::check());
    assert!(hw::check());
    for _ in 0..2 {
        assert_eq!(hex(&sha256_oneshot(b"abc")), abc);
        assert_eq!(hex(&sha256_oneshot(msg2)), two);
        assert_eq!(hex(&streaming(b"abc")), abc);
        assert_eq!(hex(&streaming(msg2)), two);
    }
    println!("{} {}", hex(&sha256_oneshot(b"abc")), hex(&streaming(msg2)));
}