//! crypto/sha256: hand-rolled SHA-256.

use crate::types::{byte, int};

pub const Size: int = 32;
pub const BlockSize: int = 64;

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,
];

pub struct Digest {
    state: [u32; 8],
    buf: Vec<byte>,
    len: u64,
}

#[allow(non_snake_case)]
pub fn New() -> Digest {
    Digest {
        state: [
            0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
            0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
        ],
        buf: Vec::with_capacity(64),
        len: 0,
    }
}

impl Digest {
    pub fn Write(&mut self, p: &[byte]) -> (int, crate::errors::error) {
        self.len = self.len.wrapping_add(p.len() as u64);
        self.buf.extend_from_slice(p);
        while self.buf.len() >= 64 {
            let block: [u8; 64] = self.buf[..64].try_into().unwrap();
            process(&mut self.state, &block);
            self.buf.drain(..64);
        }
        (p.len() as int, crate::errors::nil)
    }

    pub fn Sum(&self, b: &[byte]) -> Vec<byte> {
        let mut state = self.state;
        let mut buf = self.buf.clone();
        let bit_len = self.len.wrapping_mul(8);
        buf.push(0x80);
        while buf.len() % 64 != 56 {
            buf.push(0);
        }
        buf.extend_from_slice(&bit_len.to_be_bytes());
        let mut i = 0;
        while i < buf.len() {
            let block: [u8; 64] = buf[i..i + 64].try_into().unwrap();
            process(&mut state, &block);
            i += 64;
        }
        let mut out = b.to_vec();
        for v in state.iter() {
            out.extend_from_slice(&v.to_be_bytes());
        }
        out
    }

    pub fn Reset(&mut self) {
        self.state = [
            0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
            0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
        ];
        self.buf.clear();
        self.len = 0;
    }
}

#[allow(non_snake_case)]
pub fn Sum256(data: &[byte]) -> [byte; 32] {
    let mut h = New();
    h.Write(data);
    let v = h.Sum(&[]);
    let mut out = [0u8; 32];
    out.copy_from_slice(&v);
    out
}

fn process(state: &mut [u32; 8], block: &[u8; 64]) {
    let mut w = [0u32; 64];
    for i in 0..16 {
        w[i] = u32::from_be_bytes([
            block[i * 4], block[i * 4 + 1], block[i * 4 + 2], block[i * 4 + 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 = 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..64 {
        let s1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
        let ch = (e & f) ^ (!e & g);
        let t1 = h.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 mj = (a & b) ^ (a & c) ^ (b & c);
        let t2 = s0.wrapping_add(mj);
        h = g;
        g = f;
        f = e;
        e = d.wrapping_add(t1);
        d = c;
        c = b;
        b = a;
        a = t1.wrapping_add(t2);
    }
    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);
}

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

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

    #[test]
    fn sha256_empty() {
        let h = Sum256(b"");
        assert_eq!(
            hex(&h),
            "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
        );
    }

    #[test]
    fn sha256_abc() {
        let h = Sum256(b"abc");
        assert_eq!(
            hex(&h),
            "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
        );
    }

    #[test]
    fn sha256_long_message() {
        let msg = b"The quick brown fox jumps over the lazy dog";
        let h = Sum256(msg);
        assert_eq!(
            hex(&h),
            "d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592"
        );
    }

    #[test]
    fn sha256_streaming_equals_single() {
        let mut a = New();
        a.Write(b"hello ");
        a.Write(b"world");
        let out_a = a.Sum(&[]);
        let out_b = Sum256(b"hello world").to_vec();
        assert_eq!(out_a, out_b);
    }
}
