use super::funejson::Value;

/// FIPS 180-4 section 4.2.2: the first 32 bits of the fractional parts of the
/// cube roots of the first 64 primes.
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,
];

/// FIPS 180-4 section 5.3.3: the initial hash value.
const H0: [u32; 8] = [
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
];

fn compress(h: &mut [u32; 8], block: &[u8]) {
    let mut w = [0u32; 64];
    for t in 0..16 {
        w[t] = u32::from_be_bytes([block[t * 4], block[t * 4 + 1], block[t * 4 + 2], block[t * 4 + 3]]);
    }
    for t in 16..64 {
        let s0 = w[t - 15].rotate_right(7) ^ w[t - 15].rotate_right(18) ^ (w[t - 15] >> 3);
        let s1 = w[t - 2].rotate_right(17) ^ w[t - 2].rotate_right(19) ^ (w[t - 2] >> 10);
        w[t] = w[t - 16].wrapping_add(s0).wrapping_add(w[t - 7]).wrapping_add(s1);
    }
    let [mut a, mut b, mut c, mut d, mut e, mut f, mut g, mut hh] = *h;
    for t 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[t]).wrapping_add(w[t]);
        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);
    }
    for (slot, v) in h.iter_mut().zip([a, b, c, d, e, f, g, hh]) {
        *slot = slot.wrapping_add(v);
    }
}

/// The SHA-256 digest of a byte string (FIPS 180-4), with the standard
/// library only.
///
/// # Panics
/// Panics if any value is outside 0-255.
pub fn sha256(bytes: &[i64]) -> Vec<i64> {
    let mut message: Vec<u8> = Vec::with_capacity(bytes.len() + 72);
    for &b in bytes {
        if !(0..=255).contains(&b) {
            panic!("bytes must be a list of integers from 0 to 255");
        }
        message.push(b as u8);
    }
    // Padding (section 5.1.1): a 1 bit, zeros, then the length in bits as a
    // 64-bit big-endian integer, to a multiple of 64 bytes.
    let bit_length = (bytes.len() as u64).wrapping_mul(8);
    message.push(0x80);
    while message.len() % 64 != 56 {
        message.push(0);
    }
    message.extend_from_slice(&bit_length.to_be_bytes());

    let mut h = H0;
    for block in message.chunks_exact(64) {
        compress(&mut h, block);
    }
    h.iter().flat_map(|word| word.to_be_bytes()).map(|b| b as i64).collect()
}

pub fn fune_vector(args: &[Value]) -> Value {
    let bytes: Vec<i64> = match &args[0] {
        Value::Arr(items) => items
            .iter()
            .map(|item| match item {
                Value::Int(i) => *i,
                _ => panic!("bytes must be a list of integers from 0 to 255"),
            })
            .collect(),
        _ => panic!("bytes must be a list of integers from 0 to 255"),
    };
    Value::Arr(sha256(&bytes).into_iter().map(Value::Int).collect())
}