//! SHA-1 (FIPS 180-4), used only to check the `Sec-WebSocket-Accept` header of a WebSocket
//! handshake (RFC 6455, section 4.2.2). Never use it for anything that needs to resist attack.

/// The digest of `data`.
pub fn sha1(data: &[u8]) -> [u8; 20] {
    let mut h = Sha1::new();
    h.update(data);
    h.finish()
}

/// SHA-1 fed in pieces.
#[derive(Debug, Clone)]
pub struct Sha1 {
    state: [u32; 5],
    block: [u8; 64],
    filled: usize,
    length: u64,
}

impl Default for Sha1 {
    fn default() -> Self {
        Self::new()
    }
}

impl Sha1 {
    pub fn new() -> Sha1 {
        Sha1 {
            state: [
                0x6745_2301,
                0xEFCD_AB89,
                0x98BA_DCFE,
                0x1032_5476,
                0xC3D2_E1F0,
            ],
            block: [0; 64],
            filled: 0,
            length: 0,
        }
    }

    pub fn update(&mut self, mut data: &[u8]) {
        // Add 8 * data.len() to `length` (wrapping; `u64::try_from`, never `as`). Copy bytes into
        // `block` from `filled` on; each time it is full (64), `compress` it and set `filled` to 0.
        // Use `split_at` and `get_mut(..)`, no indexing that can go out of bounds.
        todo!()
    }

    pub fn finish(mut self) -> [u8; 20] {
        // Save `length`. Feed 0x80 then zeros so that 56 bytes of the block are filled (56 -
        // filled, or 120 - filled when filled >= 56), then the saved length as 8 big-endian bytes,
        // through `update`. `update` adds to `length`: put the saved value back after. Then the
        // five state words, big-endian.
        todo!()
    }

    fn compress(&mut self, block: &[u8; 64]) {
        // FIPS 180-4, section 6.1.2: w[0..16] are the block as big-endian u32s; w[i] = (w[i-3] ^
        // w[i-8] ^ w[i-14] ^ w[i-16]).rotate_left(1) for 16..80. Eighty rounds with f and k by
        // range: 0..=19 (b & c) | (!b & d), 0x5A827999; 20..=39 b ^ c ^ d, 0x6ED9EBA1; 40..=59 (b &
        // c) | (b & d) | (c & d), 0x8F1BBCDC; 60..=79 b ^ c ^ d, 0xCA62C1D6. All additions
        // wrapping. Add a..e into state.
        todo!()
    }
}