use std::{
    fs::File,
    io::{self, Read},
    path::Path,
};

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Checksum {
    pub algorithm: &'static str,
    pub hex: String,
}

pub fn sha256_file(path: &Path) -> io::Result<Checksum> {
    let mut file = File::open(path)?;
    let mut hasher = Sha256::new();
    let mut buffer = [0_u8; 16 * 1024];
    loop {
        let read = file.read(&mut buffer)?;
        if read == 0 {
            break;
        }
        hasher.update(&buffer[..read]);
    }
    Ok(Checksum {
        algorithm: "sha256",
        hex: hasher.finish_hex(),
    })
}

// Small, dependency-free SHA-256 implementation for packaging checksums. This
// keeps liora-packager lightweight and avoids pulling crypto crates into xtask.
struct Sha256 {
    state: [u32; 8],
    len: u64,
    buffer: [u8; 64],
    buffer_len: usize,
}

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

    fn update(&mut self, mut input: &[u8]) {
        self.len = self.len.wrapping_add((input.len() as u64) * 8);
        if self.buffer_len > 0 {
            let to_copy = (64 - self.buffer_len).min(input.len());
            self.buffer[self.buffer_len..self.buffer_len + to_copy]
                .copy_from_slice(&input[..to_copy]);
            self.buffer_len += to_copy;
            input = &input[to_copy..];
            if self.buffer_len == 64 {
                let block = self.buffer;
                self.compress(&block);
                self.buffer_len = 0;
            }
        }
        while input.len() >= 64 {
            let mut block = [0_u8; 64];
            block.copy_from_slice(&input[..64]);
            self.compress(&block);
            input = &input[64..];
        }
        if !input.is_empty() {
            self.buffer[..input.len()].copy_from_slice(input);
            self.buffer_len = input.len();
        }
    }

    fn finish_hex(mut self) -> String {
        self.buffer[self.buffer_len] = 0x80;
        self.buffer_len += 1;
        if self.buffer_len > 56 {
            for byte in &mut self.buffer[self.buffer_len..] {
                *byte = 0;
            }
            let block = self.buffer;
            self.compress(&block);
            self.buffer_len = 0;
        }
        for byte in &mut self.buffer[self.buffer_len..56] {
            *byte = 0;
        }
        self.buffer[56..].copy_from_slice(&self.len.to_be_bytes());
        let block = self.buffer;
        self.compress(&block);

        let mut out = String::with_capacity(64);
        for word in self.state {
            out.push_str(&format!("{word:08x}"));
        }
        out
    }

    fn compress(&mut self, block: &[u8; 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,
        ];
        let mut w = [0_u32; 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, mut b, mut c, mut d, mut e, mut f, mut g, mut h] = self.state;
        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);
        }
        for (slot, value) in self.state.iter_mut().zip([a, b, c, d, e, f, g, h]) {
            *slot = slot.wrapping_add(value);
        }
    }
}

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

    #[test]
    fn sha256_matches_known_empty_and_abc_vectors() {
        let mut hasher = Sha256::new();
        assert_eq!(
            hasher.finish_hex(),
            "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
        );

        hasher = Sha256::new();
        hasher.update(b"abc");
        assert_eq!(
            hasher.finish_hex(),
            "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
        );
    }
}
