use crate::{Error, Precompile, PrecompileResult, PrecompileWithAddress};
use revm_primitives::Bytes;

const F_ROUND: u64 = 1;
const INPUT_LENGTH: usize = 213;

pub const FUN: PrecompileWithAddress =
    PrecompileWithAddress(crate::u64_to_address(9), Precompile::Standard(run));

/// reference: <https://eips.ethereum.org/EIPS/eip-152>
/// input format:
/// [4 bytes for rounds][64 bytes for h][128 bytes for m][8 bytes for t_0][8 bytes for t_1][1 byte for f]
fn run(input: &Bytes, gas_limit: u64) -> PrecompileResult {
    let input = &input[..];

    if input.len() != INPUT_LENGTH {
        return Err(Error::Blake2WrongLength);
    }

    let f = match input[212] {
        1 => true,
        0 => false,
        _ => return Err(Error::Blake2WrongFinalIndicatorFlag),
    };

    // rounds 4 bytes
    let rounds = u32::from_be_bytes(input[..4].try_into().unwrap()) as usize;
    let gas_used = rounds as u64 * F_ROUND;
    if gas_used > gas_limit {
        return Err(Error::OutOfGas);
    }

    let mut h = [0u64; 8];
    let mut m = [0u64; 16];

    for (i, pos) in (4..68).step_by(8).enumerate() {
        h[i] = u64::from_le_bytes(input[pos..pos + 8].try_into().unwrap());
    }
    for (i, pos) in (68..196).step_by(8).enumerate() {
        m[i] = u64::from_le_bytes(input[pos..pos + 8].try_into().unwrap());
    }
    let t = [
        u64::from_le_bytes(input[196..196 + 8].try_into().unwrap()),
        u64::from_le_bytes(input[204..204 + 8].try_into().unwrap()),
    ];

    algo::compress(rounds, &mut h, m, t, f);

    let mut out = [0u8; 64];
    for (i, h) in (0..64).step_by(8).zip(h.iter()) {
        out[i..i + 8].copy_from_slice(&h.to_le_bytes());
    }

    Ok((gas_used, out.into()))
}

mod algo {
    /// SIGMA from spec: <https://datatracker.ietf.org/doc/html/rfc7693#section-2.7>
    const SIGMA: [[usize; 16]; 10] = [
        [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15],
        [14, 10, 4, 8, 9, 15, 13, 6, 1, 12, 0, 2, 11, 7, 5, 3],
        [11, 8, 12, 0, 5, 2, 15, 13, 10, 14, 3, 6, 7, 1, 9, 4],
        [7, 9, 3, 1, 13, 12, 11, 14, 2, 6, 5, 10, 4, 0, 15, 8],
        [9, 0, 5, 7, 2, 4, 10, 15, 14, 1, 11, 12, 6, 8, 3, 13],
        [2, 12, 6, 10, 0, 11, 8, 3, 4, 13, 7, 5, 15, 14, 1, 9],
        [12, 5, 1, 15, 14, 13, 4, 10, 0, 7, 6, 3, 9, 2, 8, 11],
        [13, 11, 7, 14, 12, 1, 3, 9, 5, 0, 15, 4, 8, 6, 2, 10],
        [6, 15, 14, 9, 11, 3, 0, 8, 12, 2, 13, 7, 1, 4, 10, 5],
        [10, 2, 8, 4, 7, 6, 1, 5, 15, 11, 9, 14, 3, 12, 13, 0],
    ];

    /// got IV from: <https://en.wikipedia.org/wiki/BLAKE_(hash_function)>
    const IV: [u64; 8] = [
        0x6a09e667f3bcc908,
        0xbb67ae8584caa73b,
        0x3c6ef372fe94f82b,
        0xa54ff53a5f1d36f1,
        0x510e527fade682d1,
        0x9b05688c2b3e6c1f,
        0x1f83d9abfb41bd6b,
        0x5be0cd19137e2179,
    ];

    #[inline(always)]
    #[allow(clippy::many_single_char_names)]
    /// G function: <https://tools.ietf.org/html/rfc7693#section-3.1>
    fn g(v: &mut [u64], a: usize, b: usize, c: usize, d: usize, x: u64, y: u64) {
        v[a] = v[a].wrapping_add(v[b]).wrapping_add(x);
        v[d] = (v[d] ^ v[a]).rotate_right(32);
        v[c] = v[c].wrapping_add(v[d]);
        v[b] = (v[b] ^ v[c]).rotate_right(24);
        v[a] = v[a].wrapping_add(v[b]).wrapping_add(y);
        v[d] = (v[d] ^ v[a]).rotate_right(16);
        v[c] = v[c].wrapping_add(v[d]);
        v[b] = (v[b] ^ v[c]).rotate_right(63);
    }

    // Compression function F takes as an argument the state vector "h",
    // message block vector "m" (last block is padded with zeros to full
    // block size, if required), 2w-bit offset counter "t", and final block
    // indicator flag "f".  Local vector v[0..15] is used in processing.  F
    // returns a new state vector.  The number of rounds, "r", is 12 for
    // BLAKE2b and 10 for BLAKE2s.  Rounds are numbered from 0 to r - 1.
    #[allow(clippy::many_single_char_names)]
    pub fn compress(rounds: usize, h: &mut [u64; 8], m: [u64; 16], t: [u64; 2], f: bool) {
        let mut v = [0u64; 16];
        v[..h.len()].copy_from_slice(h); // First half from state.
        v[h.len()..].copy_from_slice(&IV); // Second half from IV.

        v[12] ^= t[0];
        v[13] ^= t[1];

        if f {
            v[14] = !v[14] // Invert all bits if the last-block-flag is set.
        }
        for i in 0..rounds {
            // Message word selection permutation for this round.
            let s = &SIGMA[i % 10];
            g(&mut v, 0, 4, 8, 12, m[s[0]], m[s[1]]);
            g(&mut v, 1, 5, 9, 13, m[s[2]], m[s[3]]);
            g(&mut v, 2, 6, 10, 14, m[s[4]], m[s[5]]);
            g(&mut v, 3, 7, 11, 15, m[s[6]], m[s[7]]);

            g(&mut v, 0, 5, 10, 15, m[s[8]], m[s[9]]);
            g(&mut v, 1, 6, 11, 12, m[s[10]], m[s[11]]);
            g(&mut v, 2, 7, 8, 13, m[s[12]], m[s[13]]);
            g(&mut v, 3, 4, 9, 14, m[s[14]], m[s[15]]);
        }

        for i in 0..8 {
            h[i] ^= v[i] ^ v[i + 8];
        }
    }
}
