extern crate rand;

use rand::{ Rng };

mod tests {
    use super::SecretData;
    #[test]
    fn it_works() {
    }

    #[test]
    fn it_generates_coefficients() {
        let secret_data = SecretData::with_secret(&"Hello, world!"[..], 3);
        assert_eq!(secret_data.coefficients.len(), 13);
    }

    #[test]
    #[should_panic]
    fn it_rejects_share_id_under_1() {
        let secret_data = SecretData::with_secret(&"Hello, world!"[..], 3);
        let _ = secret_data.get_share(0);
    }

    #[test]
    fn it_issues_shares() {
        let secret_data = SecretData::with_secret(&"Hello, world!"[..], 3);

        let s1 = secret_data.get_share(1);
        println!("Share: {:?}", s1);
        assert!(secret_data.is_valid_share(&s1));
    }

    #[test]
    fn it_repeatedly_issues_shares() {
        let secret_data = SecretData::with_secret(&"Hello, world!"[..], 3);

        let s1 = secret_data.get_share(1);
        println!("Share: {:?}", s1);
        assert!(secret_data.is_valid_share(&s1));

        let s2 = secret_data.get_share(1);
        assert_eq!(s1, s2);
    }

    #[test]
    fn it_can_recover_secret() {
        // let secret_data = SecretData::with_secret(&"Hello, world!"[..], 3);

        // let s1 = secret_data.get_share(1);
        // let s2 = secret_data.get_share(2);
        // let s3 = secret_data.get_share(3);

        let s1 = vec![1, 184, 190, 251, 87, 232, 39, 47, 17, 4, 36, 190, 245];
        let s2 = vec![2, 231, 107, 52, 138, 34, 221, 9, 221, 67, 79, 33, 16];
        let s3 = vec![3, 23, 176, 163, 177, 165, 218, 113, 163, 53, 7, 251, 196];

        let new_secret = SecretData::recover_secret(3, vec![s1, s2, s3]).unwrap();

        assert_eq!(&new_secret[..], "Hello World!");
    }

    #[test]
    fn it_can_recover_a_generated_secret() {
        let secret_data = SecretData::with_secret(&"Hello, world!"[..], 3);

        let s1 = secret_data.get_share(1);
        println!("s1: {:?}", s1);
        let s2 = secret_data.get_share(2);
        println!("s2: {:?}", s2);
        let s3 = secret_data.get_share(3);
        println!("s3: {:?}", s3);

        let new_secret = SecretData::recover_secret(3, vec![s1, s2, s3]).unwrap();

        assert_eq!(&new_secret[..], "Hello, world!");
    }
}

pub struct SecretData {
    // threshold: u8,
    pub secret_data: Option<String>,
    pub coefficients: Vec<Vec<u8>>,
}

impl SecretData {
    pub fn with_secret(secret: &str, threshold: u8) -> SecretData {
        let mut coefficients: Vec<Vec<u8>> = vec![];
        let mut rng = rand::thread_rng();
        let mut rand_container = [0u8, threshold - 1];
        for c in secret.as_bytes() {
            rng.fill_bytes(&mut rand_container);
            let mut coef: Vec<u8> = vec![*c];
            for r in rand_container.iter() {
                coef.push(*r);
            }
            coefficients.push(coef);
        }

        SecretData {
            secret_data: Some(secret.to_string()),
            // threshold: threshold,
            coefficients: coefficients,
        }
    }

    pub fn get_share(&self, id: u8) -> Vec<u8> {
        if id < 1 { // Don't need to check for id > 255 because u8 can't be
            panic!("share id must be between 1 and 255");
        }
        let mut share_bytes: Vec<u8> = vec![];
        let coefficients = self.coefficients.clone();
        for coefficient in coefficients {
            share_bytes.push(SecretData::accumulate_share_bytes(id, coefficient));
        }

        share_bytes.insert(0, id);
        share_bytes
    }

    pub fn is_valid_share( &self, share: &Vec<u8> ) -> bool {
        let id = share[0];
        // let share2 = share[1..];
        *share == self.get_share(id)
    }

    pub fn recover_secret(threshold: u8, shares: Vec<Vec<u8>>) -> Option<String> {
        if threshold as usize > shares.len() {
            println!("Number of shares is below the threshold");
            return None;
        }
        let mut xs: Vec<u8> = vec![];

        for share in shares.iter() {
            if xs.contains(&share[0]) {
                println!("Multiple shares with the same first byte");
                return None;
            }

            if share.len() != shares[0].len() {
                println!("Shares have different lengths");
                return None;
            }

            xs.push(share[0].clone());
        }
        // println!("xs is {:?}", xs);
        let mut mycoefficients: Vec<String> = vec![];
        // let mut mysecretdata = String::from("");
        let mut mysecretdata: Vec<u8> = vec![];
        let rounds = shares[0].len() - 1;

        for byte_to_use in 0..rounds {
            let mut fxs: Vec<u8> = vec![];
            for share in shares.clone() {
                fxs.push(share[1..][byte_to_use].clone());
            }
            // println!("fxs is {:?}", fxs);
            let resulting_poly: Vec<u8> = SecretData::full_lagrange(&xs, &fxs);
            // println!("resulting_poly = {:?}", resulting_poly);
            // let mut t = vec![&resulting_poly[0..(threshold - 1) as usize]];
            // let mut t = &resulting_poly[0..threshold - 1];
            // let mut t = slice[0..threshold - 1];
            // if slice[0..threshold - 1]
            // let right_side = shares.len() - threshold as usize;
            // let l = [0; shares.len() - (threshold as usize)];
            // t.append(&mut vec!(&l));
            // if resulting_poly[0..threshold-1 as usize].append([0; end as usize]) != resulting_poly {
                // raise "Share do not match. Cannot decode"
            // }
            mycoefficients.push(String::from_utf8_lossy(&resulting_poly[..]).to_string());
            mysecretdata.push(resulting_poly[0]);
        }

        match String::from_utf8(mysecretdata) {
            Ok(s) => Some(s),
            Err(e) => {
                println!("{:?}", e);
                None
            },
        }
        // Some(mysecretdata)
    }

    fn accumulate_share_bytes(id: u8, coefficient_bytes: Vec<u8>) -> u8 {
        if id < 1 { // Don't need to check for id > 255 because u8 can't be
            panic!("share id must be between 1 and 255");
        }
        let mut accumulator: u8 = 0;

        let mut x_i: u8 = 1;

        for c in coefficient_bytes {
            accumulator = SecretData::gf256_add(&accumulator, &SecretData::gf256_mul(&c, &x_i));
            x_i = SecretData::gf256_mul(&x_i, &id);
        }

        accumulator
    }

    fn full_lagrange(xs: &Vec<u8>, fxs: &Vec<u8>) -> Vec<u8> {
        let mut returned_coefficients: Vec<u8> = vec![];
        let len = fxs.len();
        for i in 0..len {
            let mut this_polynomial: Vec<u8> = vec![1];

            for j in 0..len {
                if i == j {
                    continue;
                }

                let denominator = SecretData::gf256_sub(&xs[i], &xs[j]);
                let this_term = vec![SecretData::gf256_div(&xs[j], &denominator), SecretData::gf256_div(&1, &denominator)];

                this_polynomial = SecretData::multiply_polynomials(&this_polynomial, &this_term);
                // panic!("wait");
            }
            if fxs.len() + 1 >= i {
                this_polynomial = SecretData::multiply_polynomials(&this_polynomial, &vec![fxs[i]])
            }
            // this_polynomial = _multiply_polynomials(this_polynomial, [fxs[i]]) if fxs[i]
            returned_coefficients = SecretData::add_polynomials(&returned_coefficients, &this_polynomial);
            // returnedcoefficients = _add_polynomials(returnedcoefficients, this_polynomial)
        }
        returned_coefficients
    }

    #[inline]
    fn gf256_add(a: &u8, b: &u8) -> u8 {
        a ^ b
    }

    #[inline]
    fn gf256_sub(a: &u8, b: &u8) -> u8 {
        SecretData::gf256_add(a, b)
    }

    #[inline]
    fn gf256_mul(a: &u8, b: &u8) -> u8 {
        if *a == 0 || *b == 0 {
            0
        } else {
            GF256_EXP[( (GF256_LOG[*a as usize] as u16 + GF256_LOG[*b as usize] as u16) % 255) as usize]
        }
    }

    #[inline]
    fn gf256_div(a: &u8, b: &u8) -> u8 {
        if *a == 0 {
            0
        } else if *b == 0 {
            panic!("Divide by 0");
        } else {
            let a_log = GF256_LOG[*a as usize] as i16;
            let b_log = GF256_LOG[*b as usize] as i16;

            let mut diff = a_log - b_log;

            if diff < 0 {
                diff = 255 + diff;
            }
            GF256_EXP[( diff % 255 ) as usize]
        }
    }

    fn multiply_polynomials(a: &Vec<u8>, b: &Vec<u8>) -> Vec<u8> {
        let mut resultterms: Vec<u8> = vec![];

        let mut termpadding: Vec<u8> = vec![];

        for bterm in b {
            let mut thisvalue = termpadding.clone();
            for aterm in a {
                thisvalue.push(SecretData::gf256_mul(&aterm, &bterm));
            }
            resultterms = SecretData::add_polynomials(&resultterms, &thisvalue);
            termpadding.push(0);
        }
        resultterms
    }

    fn add_polynomials(a: &Vec<u8>, b: &Vec<u8>) -> Vec<u8> {
        let mut a = a.clone();
        let mut b = b.clone();
        if a.len() < b.len() {
            let mut t = vec![0; (b.len() - a.len())];
            a.append(&mut t);
        } else if a.len() > b.len() {
            let mut t = vec![0; (a.len() - b.len())];
            b.append(&mut t);
        }
        let mut results: Vec<u8> = vec![];

        for i in 0..a.len() {
            results.push(SecretData::gf256_add(&a[i], &b[i]));
        }
        results
    }
}
static GF256_EXP: [u8; 256] = [
   0x01, 0x03, 0x05, 0x0f, 0x11, 0x33, 0x55, 0xff,
   0x1a, 0x2e, 0x72, 0x96, 0xa1, 0xf8, 0x13, 0x35,
   0x5f, 0xe1, 0x38, 0x48, 0xd8, 0x73, 0x95, 0xa4,
   0xf7, 0x02, 0x06, 0x0a, 0x1e, 0x22, 0x66, 0xaa,
   0xe5, 0x34, 0x5c, 0xe4, 0x37, 0x59, 0xeb, 0x26,
   0x6a, 0xbe, 0xd9, 0x70, 0x90, 0xab, 0xe6, 0x31,
   0x53, 0xf5, 0x04, 0x0c, 0x14, 0x3c, 0x44, 0xcc,
   0x4f, 0xd1, 0x68, 0xb8, 0xd3, 0x6e, 0xb2, 0xcd,
   0x4c, 0xd4, 0x67, 0xa9, 0xe0, 0x3b, 0x4d, 0xd7,
   0x62, 0xa6, 0xf1, 0x08, 0x18, 0x28, 0x78, 0x88,
   0x83, 0x9e, 0xb9, 0xd0, 0x6b, 0xbd, 0xdc, 0x7f,
   0x81, 0x98, 0xb3, 0xce, 0x49, 0xdb, 0x76, 0x9a,
   0xb5, 0xc4, 0x57, 0xf9, 0x10, 0x30, 0x50, 0xf0,
   0x0b, 0x1d, 0x27, 0x69, 0xbb, 0xd6, 0x61, 0xa3,
   0xfe, 0x19, 0x2b, 0x7d, 0x87, 0x92, 0xad, 0xec,
   0x2f, 0x71, 0x93, 0xae, 0xe9, 0x20, 0x60, 0xa0,
   0xfb, 0x16, 0x3a, 0x4e, 0xd2, 0x6d, 0xb7, 0xc2,
   0x5d, 0xe7, 0x32, 0x56, 0xfa, 0x15, 0x3f, 0x41,
   0xc3, 0x5e, 0xe2, 0x3d, 0x47, 0xc9, 0x40, 0xc0,
   0x5b, 0xed, 0x2c, 0x74, 0x9c, 0xbf, 0xda, 0x75,
   0x9f, 0xba, 0xd5, 0x64, 0xac, 0xef, 0x2a, 0x7e,
   0x82, 0x9d, 0xbc, 0xdf, 0x7a, 0x8e, 0x89, 0x80,
   0x9b, 0xb6, 0xc1, 0x58, 0xe8, 0x23, 0x65, 0xaf,
   0xea, 0x25, 0x6f, 0xb1, 0xc8, 0x43, 0xc5, 0x54,
   0xfc, 0x1f, 0x21, 0x63, 0xa5, 0xf4, 0x07, 0x09,
   0x1b, 0x2d, 0x77, 0x99, 0xb0, 0xcb, 0x46, 0xca,
   0x45, 0xcf, 0x4a, 0xde, 0x79, 0x8b, 0x86, 0x91,
   0xa8, 0xe3, 0x3e, 0x42, 0xc6, 0x51, 0xf3, 0x0e,
   0x12, 0x36, 0x5a, 0xee, 0x29, 0x7b, 0x8d, 0x8c,
   0x8f, 0x8a, 0x85, 0x94, 0xa7, 0xf2, 0x0d, 0x17,
   0x39, 0x4b, 0xdd, 0x7c, 0x84, 0x97, 0xa2, 0xfd,
   0x1c, 0x24, 0x6c, 0xb4, 0xc7, 0x52, 0xf6, 0x01];

  static GF256_LOG: [u8;256] = [
    0x00, 0x00, 0x19, 0x01, 0x32, 0x02, 0x1a, 0xc6,
    0x4b, 0xc7, 0x1b, 0x68, 0x33, 0xee, 0xdf, 0x03,
    0x64, 0x04, 0xe0, 0x0e, 0x34, 0x8d, 0x81, 0xef,
    0x4c, 0x71, 0x08, 0xc8, 0xf8, 0x69, 0x1c, 0xc1,
    0x7d, 0xc2, 0x1d, 0xb5, 0xf9, 0xb9, 0x27, 0x6a,
    0x4d, 0xe4, 0xa6, 0x72, 0x9a, 0xc9, 0x09, 0x78,
    0x65, 0x2f, 0x8a, 0x05, 0x21, 0x0f, 0xe1, 0x24,
    0x12, 0xf0, 0x82, 0x45, 0x35, 0x93, 0xda, 0x8e,
    0x96, 0x8f, 0xdb, 0xbd, 0x36, 0xd0, 0xce, 0x94,
    0x13, 0x5c, 0xd2, 0xf1, 0x40, 0x46, 0x83, 0x38,
    0x66, 0xdd, 0xfd, 0x30, 0xbf, 0x06, 0x8b, 0x62,
    0xb3, 0x25, 0xe2, 0x98, 0x22, 0x88, 0x91, 0x10,
    0x7e, 0x6e, 0x48, 0xc3, 0xa3, 0xb6, 0x1e, 0x42,
    0x3a, 0x6b, 0x28, 0x54, 0xfa, 0x85, 0x3d, 0xba,
    0x2b, 0x79, 0x0a, 0x15, 0x9b, 0x9f, 0x5e, 0xca,
    0x4e, 0xd4, 0xac, 0xe5, 0xf3, 0x73, 0xa7, 0x57,
    0xaf, 0x58, 0xa8, 0x50, 0xf4, 0xea, 0xd6, 0x74,
    0x4f, 0xae, 0xe9, 0xd5, 0xe7, 0xe6, 0xad, 0xe8,
    0x2c, 0xd7, 0x75, 0x7a, 0xeb, 0x16, 0x0b, 0xf5,
    0x59, 0xcb, 0x5f, 0xb0, 0x9c, 0xa9, 0x51, 0xa0,
    0x7f, 0x0c, 0xf6, 0x6f, 0x17, 0xc4, 0x49, 0xec,
    0xd8, 0x43, 0x1f, 0x2d, 0xa4, 0x76, 0x7b, 0xb7,
    0xcc, 0xbb, 0x3e, 0x5a, 0xfb, 0x60, 0xb1, 0x86,
    0x3b, 0x52, 0xa1, 0x6c, 0xaa, 0x55, 0x29, 0x9d,
    0x97, 0xb2, 0x87, 0x90, 0x61, 0xbe, 0xdc, 0xfc,
    0xbc, 0x95, 0xcf, 0xcd, 0x37, 0x3f, 0x5b, 0xd1,
    0x53, 0x39, 0x84, 0x3c, 0x41, 0xa2, 0x6d, 0x47,
    0x14, 0x2a, 0x9e, 0x5d, 0x56, 0xf2, 0xd3, 0xab,
    0x44, 0x11, 0x92, 0xd9, 0x23, 0x20, 0x2e, 0x89,
    0xb4, 0x7c, 0xb8, 0x26, 0x77, 0x99, 0xe3, 0xa5,
    0x67, 0x4a, 0xed, 0xde, 0xc5, 0x31, 0xfe, 0x18,
    0x0d, 0x63, 0x8c, 0x80, 0xc0, 0xf7, 0x70, 0x07];