//! SHA-256 digests for export-set identity (no external digest crate).
#![allow(clippy::unreadable_literal)]

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,
];

#[derive(Clone)]
pub struct Sha256 {
    state: [u32; 8],
    buffer: [u8; 64],
    buffer_len: usize,
    bit_len: u64,
}

impl Default for Sha256 {
    fn default() -> Self {
        Self::new()
    }
}

impl Sha256 {
    pub fn new() -> Self {
        Self {
            state: [
                0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab,
                0x5be0cd19,
            ],
            buffer: [0; 64],
            buffer_len: 0,
            bit_len: 0,
        }
    }

    pub fn update(&mut self, data: &[u8]) {
        let mut offset = 0;
        if self.buffer_len > 0 {
            let need = 64 - self.buffer_len;
            let take = need.min(data.len());
            self.buffer[self.buffer_len..self.buffer_len + take].copy_from_slice(&data[..take]);
            self.buffer_len += take;
            offset += take;
            if self.buffer_len == 64 {
                let block = self.buffer;
                self.compress(&block);
                self.bit_len = self.bit_len.saturating_add(512);
                self.buffer_len = 0;
            }
        }
        while offset + 64 <= data.len() {
            let mut block = [0u8; 64];
            block.copy_from_slice(&data[offset..offset + 64]);
            self.compress(&block);
            self.bit_len = self.bit_len.saturating_add(512);
            offset += 64;
        }
        let rest = &data[offset..];
        if !rest.is_empty() {
            self.buffer[..rest.len()].copy_from_slice(rest);
            self.buffer_len = rest.len();
        }
    }

    pub fn finalize(mut self) -> [u8; 32] {
        let total_bits = self
            .bit_len
            .saturating_add((self.buffer_len as u64).saturating_mul(8));
        self.buffer[self.buffer_len] = 0x80;
        self.buffer_len += 1;
        if self.buffer_len > 56 {
            for b in &mut self.buffer[self.buffer_len..] {
                *b = 0;
            }
            let block = self.buffer;
            self.compress(&block);
            self.buffer = [0; 64];
            self.buffer_len = 0;
        }
        for b in &mut self.buffer[self.buffer_len..56] {
            *b = 0;
        }
        self.buffer[56..64].copy_from_slice(&total_bits.to_be_bytes());
        let block = self.buffer;
        self.compress(&block);
        let mut out = [0u8; 32];
        for (i, word) in self.state.iter().enumerate() {
            out[i * 4..(i + 1) * 4].copy_from_slice(&word.to_be_bytes());
        }
        out
    }

    fn compress(&mut self, block: &[u8; 64]) {
        let mut w = [0u32; 64];
        for (i, chunk) in block.chunks_exact(4).enumerate().take(16) {
            w[i] = u32::from_be_bytes([chunk[0], chunk[1], chunk[2], chunk[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 = self.state[0];
        let mut b = self.state[1];
        let mut c = self.state[2];
        let mut d = self.state[3];
        let mut e = self.state[4];
        let mut f = self.state[5];
        let mut g = self.state[6];
        let mut h = self.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 temp1 = 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 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);
        }
        self.state[0] = self.state[0].wrapping_add(a);
        self.state[1] = self.state[1].wrapping_add(b);
        self.state[2] = self.state[2].wrapping_add(c);
        self.state[3] = self.state[3].wrapping_add(d);
        self.state[4] = self.state[4].wrapping_add(e);
        self.state[5] = self.state[5].wrapping_add(f);
        self.state[6] = self.state[6].wrapping_add(g);
        self.state[7] = self.state[7].wrapping_add(h);
    }
}

pub fn sha256(data: &[u8]) -> [u8; 32] {
    let mut h = Sha256::new();
    h.update(data);
    h.finalize()
}

pub fn sha256_hex(data: &[u8]) -> String {
    hex(&sha256(data))
}

pub fn hex(bytes: &[u8]) -> String {
    const TABLE: &[u8; 16] = b"0123456789abcdef";
    let mut out = String::with_capacity(bytes.len() * 2);
    for &b in bytes {
        out.push(TABLE[(b >> 4) as usize] as char);
        out.push(TABLE[(b & 0xf) as usize] as char);
    }
    out
}

pub fn is_sha256_hex(value: &str) -> bool {
    value.len() == 64
        && value
            .bytes()
            .all(|b| b.is_ascii_digit() || (b'a'..=b'f').contains(&b))
}

/// Stream a regular file through SHA-256 with an explicit size ceiling.
pub fn sha256_file(path: &std::path::Path, max_bytes: u64) -> Result<String, String> {
    use std::io::Read;
    let meta = std::fs::metadata(path).map_err(|e| e.to_string())?;
    if !meta.is_file() {
        return Err("bronbestand is geen regulier bestand".into());
    }
    if meta.len() > max_bytes {
        return Err(format!("bronbestand groter dan {max_bytes} bytes"));
    }
    let mut file = std::fs::File::open(path).map_err(|e| e.to_string())?;
    let mut hasher = Sha256::new();
    let mut buf = [0u8; 64 * 1024];
    let mut total = 0u64;
    loop {
        let n = file.read(&mut buf).map_err(|e| e.to_string())?;
        if n == 0 {
            break;
        }
        total = total.saturating_add(n as u64);
        if total > max_bytes {
            return Err(format!("bronbestand groter dan {max_bytes} bytes"));
        }
        hasher.update(&buf[..n]);
    }
    Ok(hex(&hasher.finalize()))
}

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

    #[test]
    fn known_vectors() {
        assert_eq!(
            sha256_hex(b""),
            "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
        );
        assert_eq!(
            sha256_hex(b"abc"),
            "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
        );
        assert_eq!(
            sha256_hex(b"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq"),
            "248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1"
        );
    }

    #[test]
    fn streaming_matches_one_shot() {
        let data: Vec<u8> = (0..300).map(|i| i as u8).collect();
        let mut h = Sha256::new();
        h.update(&data[..100]);
        h.update(&data[100..200]);
        h.update(&data[200..]);
        assert_eq!(hex(&h.finalize()), sha256_hex(&data));
    }

    #[test]
    fn hex_validator() {
        assert!(is_sha256_hex(&sha256_hex(b"x")));
        assert!(!is_sha256_hex("abc"));
        assert!(!is_sha256_hex(&"g".repeat(64)));
    }
}