use num_bigint::BigUint;
use num_traits::FromPrimitive;
use rand::Rng;

use util;

lazy_static! {
    pub static ref DH_GENERATOR: BigUint = BigUint::from_u64(0x2).unwrap();
    pub static ref DH_PRIME: BigUint = BigUint::from_bytes_be(&[
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xc9,
        0x0f, 0xda, 0xa2, 0x21, 0x68, 0xc2, 0x34, 0xc4, 0xc6,
        0x62, 0x8b, 0x80, 0xdc, 0x1c, 0xd1, 0x29, 0x02, 0x4e,
        0x08, 0x8a, 0x67, 0xcc, 0x74, 0x02, 0x0b, 0xbe, 0xa6,
        0x3b, 0x13, 0x9b, 0x22, 0x51, 0x4a, 0x08, 0x79, 0x8e,
        0x34, 0x04, 0xdd, 0xef, 0x95, 0x19, 0xb3, 0xcd, 0x3a,
        0x43, 0x1b, 0x30, 0x2b, 0x0a, 0x6d, 0xf2, 0x5f, 0x14,
        0x37, 0x4f, 0xe1, 0x35, 0x6d, 0x6d, 0x51, 0xc2, 0x45,
        0xe4, 0x85, 0xb5, 0x76, 0x62, 0x5e, 0x7e, 0xc6, 0xf4,
        0x4c, 0x42, 0xe9, 0xa6, 0x3a, 0x36, 0x20, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff ]);
}

pub struct DHLocalKeys {
    private_key: BigUint,
    public_key: BigUint,
}

impl DHLocalKeys {
    pub fn random<R: Rng>(rng: &mut R) -> DHLocalKeys {
        let key_data = util::rand_vec(rng, 95);

        let private_key = BigUint::from_bytes_be(&key_data);
        let public_key = util::powm(&DH_GENERATOR, &private_key, &DH_PRIME);

        DHLocalKeys {
            private_key: private_key,
            public_key: public_key,
        }
    }

    pub fn public_key(&self) -> Vec<u8> {
        self.public_key.to_bytes_be()
    }

    pub fn shared_secret(&self, remote_key: &[u8]) -> Vec<u8> {
        let shared_key = util::powm(
            &BigUint::from_bytes_be(remote_key),
            &self.private_key,
            &DH_PRIME,
        );
        shared_key.to_bytes_be()
    }
}