extern crate num;
extern crate num_bigint;
extern crate num_traits;

use tiny_keccak::Keccak;

use num_bigint::{BigInt, Sign};
use num_traits::Zero;

const SEED: &str = "mimc";

pub struct Constants {
    seed_hash: BigInt,
    iv: BigInt,
    r: BigInt,
    n_rounds: i64,
    cts: Vec<BigInt>,
}

pub fn modulus(a: &BigInt, m: &BigInt) -> BigInt {
    ((a % m) + m) % m
}

pub fn generate_constants() -> Constants {
    let r: BigInt = BigInt::parse_bytes(
        b"21888242871839275222246405745257275088548364400416034343698204186575808495617",
        10,
    )
    .unwrap();

    let mut keccak = Keccak::new_keccak256();
    let mut h = [0u8; 32];
    keccak.update(SEED.as_bytes());
    keccak.finalize(&mut h);
    let mut keccak = Keccak::new_keccak256();
    let mut h_iv = [0u8; 32];
    let seed_iv = format!("{}{}", SEED, "_iv");
    keccak.update(seed_iv.as_bytes());
    keccak.finalize(&mut h_iv);

    let seed_hash: BigInt = BigInt::from_bytes_be(Sign::Plus, &h);
    let c: BigInt = BigInt::from_bytes_be(Sign::Plus, &h_iv);
    let iv: BigInt = c % &r;
    let n_rounds: i64 = 91;
    let cts = get_constants(&r, SEED, n_rounds);

    Constants {
        seed_hash: seed_hash,
        iv: iv,
        r: r,
        n_rounds: n_rounds,
        cts: cts,
    }
}

pub fn get_constants(r: &BigInt, seed: &str, n_rounds: i64) -> Vec<BigInt> {
    let mut cts: Vec<BigInt> = Vec::new();
    cts.push(Zero::zero());

    let mut keccak = Keccak::new_keccak256();
    let mut h = [0u8; 32];
    keccak.update(seed.as_bytes());
    keccak.finalize(&mut h);

    let mut c = BigInt::from_bytes_be(Sign::Plus, &h);
    for _ in 1..n_rounds {
        let mut keccak = Keccak::new_keccak256();
        let mut h = [0u8; 32];
        let (_, c_bytes) = c.to_bytes_be();
        keccak.update(&c_bytes[..]);
        keccak.finalize(&mut h);
        c = BigInt::from_bytes_be(Sign::Plus, &h);
        let n = modulus(&c, &r);
        cts.push(n);
    }
    cts
}

pub fn mimc7_hash_generic(r: &BigInt, x_in: &BigInt, k: &BigInt, n_rounds: i64) -> BigInt {
    let cts = get_constants(r, SEED, n_rounds);
    let mut h: BigInt = Zero::zero();
    for i in 0..n_rounds as usize {
        let mut t: BigInt;
        if i == 0 {
            t = x_in + k;
        } else {
            t = h + k + &cts[i];
        }
        t = modulus(&t, &r);
        let t2 = &t * &t;
        let t4 = &t2 * &t2;
        h = (t4 * t2) * t;
        h = modulus(&h, &r);
    }
    modulus(&(h + k), &r)
}

pub fn hash_generic(iv: BigInt, arr: Vec<BigInt>, r: BigInt, n_rounds: i64) -> BigInt {
    let mut h: BigInt = iv;
    for i in 0..arr.len() {
        h = mimc7_hash_generic(&r, &h, &arr[i], n_rounds);
    }
    h
}

pub struct Mimc7 {
    constants: Constants,
}

impl Mimc7 {
    pub fn new() -> Mimc7 {
        Mimc7 {
            constants: generate_constants(),
        }
    }

    pub fn hash(&self, arr: Vec<BigInt>) -> BigInt {
        // TODO check if arr elements are inside the Finite Field over R
        let mut h: BigInt = Zero::zero();
        for i in 0..arr.len() {
            h = &h + &arr[i] + self.mimc7_hash(&arr[i], &h);
            h = modulus(&h, &self.constants.r)
        }
        modulus(&h, &self.constants.r)
    }

    pub fn mimc7_hash(&self, x_in: &BigInt, k: &BigInt) -> BigInt {
        let mut h: BigInt = Zero::zero();
        for i in 0..self.constants.n_rounds as usize {
            let t: BigInt;
            if i == 0 {
                t = x_in + k;
            } else {
                t = h + k + &self.constants.cts[i];
            }
            let t2 = &t * &t;
            let t4 = &t2 * &t2;
            h = (t4 * t2) * t;
            h = modulus(&h, &self.constants.r);
        }
        modulus(&(h + k), &self.constants.r)
    }
}

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

    #[test]
    fn test_sha3() {
        let mut keccak = Keccak::new_keccak256();
        let mut res = [0u8; 32];
        keccak.update(SEED.as_bytes());
        keccak.finalize(&mut res);
        assert_eq!(
            res.to_hex(),
            "b6e489e6b37224a50bebfddbe7d89fa8fdcaa84304a70bd13f79b5d9f7951e9e"
        );

        let mut keccak = Keccak::new_keccak256();
        let mut res = [0u8; 32];
        keccak.update(SEED.as_bytes());
        keccak.finalize(&mut res);
        let c = BigInt::from_bytes_be(Sign::Plus, &res);
        assert_eq!(
            c.to_string(),
            "82724731331859054037315113496710413141112897654334566532528783843265082629790"
        );
    }
    #[test]
    fn test_generate_constants() {
        let constants = generate_constants();
        assert_eq!(
            "20888961410941983456478427210666206549300505294776164667214940546594746570981",
            constants.cts[1].to_string()
        );
    }

    #[test]
    fn test_mimc7_generic() {
        let b1: BigInt = BigInt::parse_bytes(b"1", 10).unwrap();
        let b2: BigInt = BigInt::parse_bytes(b"2", 10).unwrap();
        let constants = generate_constants();
        let h1 = mimc7_hash_generic(&constants.r, &b1, &b2, 91);
        assert_eq!(
            h1.to_string(),
            "10594780656576967754230020536574539122676596303354946869887184401991294982664"
        );
    }
    #[test]
    fn test_mimc7() {
        let b12: BigInt = BigInt::parse_bytes(b"12", 10).unwrap();
        let b45: BigInt = BigInt::parse_bytes(b"45", 10).unwrap();
        let b78: BigInt = BigInt::parse_bytes(b"78", 10).unwrap();
        let b41: BigInt = BigInt::parse_bytes(b"41", 10).unwrap();

        let mut big_arr1: Vec<BigInt> = Vec::new();
        big_arr1.push(b12.clone());
        let mimc7 = Mimc7::new();
        let h1 = mimc7.hash(big_arr1);
        let (_, h1_bytes) = h1.to_bytes_be();
        assert_eq!(
            h1_bytes.to_hex(),
            "237c92644dbddb86d8a259e0e923aaab65a93f1ec5758b8799988894ac0958fd"
        );

        let mh2 = mimc7.mimc7_hash(&b12, &b45);
        let (_, mh2_bytes) = mh2.to_bytes_be();
        assert_eq!(
            mh2_bytes.to_hex(),
            "2ba7ebad3c6b6f5a20bdecba2333c63173ca1a5f2f49d958081d9fa7179c44e4"
        );

        let mut big_arr2: Vec<BigInt> = Vec::new();
        big_arr2.push(b78.clone());
        big_arr2.push(b41.clone());
        let h2 = mimc7.hash(big_arr2);
        let (_, h2_bytes) = h2.to_bytes_be();
        assert_eq!(
            h2_bytes.to_hex(),
            "067f3202335ea256ae6e6aadcd2d5f7f4b06a00b2d1e0de903980d5ab552dc70"
        );

        let mut big_arr2: Vec<BigInt> = Vec::new();
        big_arr2.push(b12.clone());
        big_arr2.push(b45.clone());
        let h1 = mimc7.hash(big_arr2);
        let (_, h1_bytes) = h1.to_bytes_be();
        assert_eq!(
            h1_bytes.to_hex(),
            "15ff7fe9793346a17c3150804bcb36d161c8662b110c50f55ccb7113948d8879"
        );

        let mut big_arr1: Vec<BigInt> = Vec::new();
        big_arr1.push(b12.clone());
        big_arr1.push(b45.clone());
        big_arr1.push(b78.clone());
        big_arr1.push(b41.clone());
        let mimc7 = Mimc7::new();
        let h1 = mimc7.hash(big_arr1);
        let (_, h1_bytes) = h1.to_bytes_be();
        assert_eq!(
            h1_bytes.to_hex(),
            "284bc1f34f335933a23a433b6ff3ee179d682cd5e5e2fcdd2d964afa85104beb"
        );
    }
}