// SPDX-License-Identifier: CC0-1.0

//! SHA1 implementation.

use internals::slice::SliceExt;

#[cfg(bench)]
mod benches;
mod crypto;
#[cfg(bench)]
mod tests;

use core::cmp;

use crate::{incomplete_block_len, HashEngine as _};

crate::internal_macros::general_hash_type! {
    160,
    false,
    "Output of the SHA1 hash function."
}

impl Hash {
    /// Finalize a hash engine to produce a hash.
    pub fn from_engine(mut e: HashEngine) -> Self {
        // pad buffer with a single 1-bit then all 0s, until there are exactly 8 bytes remaining
        let n_bytes_hashed = e.bytes_hashed;

        let zeroes = [0; BLOCK_SIZE - 8];
        e.input(&[0x80]);
        if incomplete_block_len(&e) > zeroes.len() {
            e.input(&zeroes);
        }
        let pad_length = zeroes.len() - incomplete_block_len(&e);
        e.input(&zeroes[..pad_length]);
        debug_assert_eq!(incomplete_block_len(&e), zeroes.len());

        e.input(&(8 * n_bytes_hashed).to_be_bytes());
        debug_assert_eq!(incomplete_block_len(&e), 0);

        Hash(e.midstate())
    }
}

const BLOCK_SIZE: usize = 64;

/// Engine to compute SHA1 hash function.
#[derive(Debug, Clone)]
pub struct HashEngine {
    buffer: [u8; BLOCK_SIZE],
    h: [u32; 5],
    bytes_hashed: u64,
}

impl HashEngine {
    /// Constructs a new SHA1 hash engine.
    pub const fn new() -> Self {
        Self {
            h: [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476, 0xc3d2e1f0],
            bytes_hashed: 0,
            buffer: [0; BLOCK_SIZE],
        }
    }

    #[cfg(not(hashes_fuzz))]
    pub(crate) fn midstate(&self) -> [u8; 20] {
        let mut ret = [0; 20];
        for (val, ret_bytes) in self.h.iter().zip(ret.bitcoin_as_chunks_mut().0) {
            *ret_bytes = val.to_be_bytes();
        }
        ret
    }

    #[cfg(hashes_fuzz)]
    pub(crate) fn midstate(&self) -> [u8; 20] {
        let mut ret = [0; 20];
        ret.copy_from_slice(&self.buffer[..20]);
        ret
    }
}

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

impl crate::HashEngine for HashEngine {
    type Hash = Hash;
    type Bytes = [u8; 20];
    const BLOCK_SIZE: usize = 64;

    fn n_bytes_hashed(&self) -> u64 { self.bytes_hashed }

    crate::internal_macros::engine_input_impl!();

    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
}