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use num_bigint::{BigUint, RandBigInt};
use std::ops::Shl;

use crate::SshResult;

use super::{HashType, KeyExchange};

#[cfg(feature = "deprecated-dh-group1-sha1")]
const GROUP1: [u8; 128] = [
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xc9, 0xf, 0xda, 0xa2, 0x21, 0x68, 0xc2, 0x34,
    0xc4, 0xc6, 0x62, 0x8b, 0x80, 0xdc, 0x1c, 0xd1, 0x29, 0x2, 0x4e, 0x8, 0x8a, 0x67, 0xcc, 0x74,
    0x2, 0xb, 0xbe, 0xa6, 0x3b, 0x13, 0x9b, 0x22, 0x51, 0x4a, 0x8, 0x79, 0x8e, 0x34, 0x4, 0xdd,
    0xef, 0x95, 0x19, 0xb3, 0xcd, 0x3a, 0x43, 0x1b, 0x30, 0x2b, 0xa, 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, 0x37, 0xed, 0x6b, 0xb, 0xff, 0x5c, 0xb6, 0xf4, 0x6, 0xb7, 0xed,
    0xee, 0x38, 0x6b, 0xfb, 0x5a, 0x89, 0x9f, 0xa5, 0xae, 0x9f, 0x24, 0x11, 0x7c, 0x4b, 0x1f, 0xe6,
    0x49, 0x28, 0x66, 0x51, 0xec, 0xe6, 0x53, 0x81, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
];

const GROUP14: [u8; 256] = [
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xc9, 0xf, 0xda, 0xa2, 0x21, 0x68, 0xc2, 0x34,
    0xc4, 0xc6, 0x62, 0x8b, 0x80, 0xdc, 0x1c, 0xd1, 0x29, 0x2, 0x4e, 0x8, 0x8a, 0x67, 0xcc, 0x74,
    0x2, 0xb, 0xbe, 0xa6, 0x3b, 0x13, 0x9b, 0x22, 0x51, 0x4a, 0x8, 0x79, 0x8e, 0x34, 0x4, 0xdd,
    0xef, 0x95, 0x19, 0xb3, 0xcd, 0x3a, 0x43, 0x1b, 0x30, 0x2b, 0xa, 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, 0x37, 0xed, 0x6b, 0xb, 0xff, 0x5c, 0xb6, 0xf4, 0x6, 0xb7, 0xed,
    0xee, 0x38, 0x6b, 0xfb, 0x5a, 0x89, 0x9f, 0xa5, 0xae, 0x9f, 0x24, 0x11, 0x7c, 0x4b, 0x1f, 0xe6,
    0x49, 0x28, 0x66, 0x51, 0xec, 0xe4, 0x5b, 0x3d, 0xc2, 0x0, 0x7c, 0xb8, 0xa1, 0x63, 0xbf, 0x5,
    0x98, 0xda, 0x48, 0x36, 0x1c, 0x55, 0xd3, 0x9a, 0x69, 0x16, 0x3f, 0xa8, 0xfd, 0x24, 0xcf, 0x5f,
    0x83, 0x65, 0x5d, 0x23, 0xdc, 0xa3, 0xad, 0x96, 0x1c, 0x62, 0xf3, 0x56, 0x20, 0x85, 0x52, 0xbb,
    0x9e, 0xd5, 0x29, 0x7, 0x70, 0x96, 0x96, 0x6d, 0x67, 0xc, 0x35, 0x4e, 0x4a, 0xbc, 0x98, 0x4,
    0xf1, 0x74, 0x6c, 0x8, 0xca, 0x18, 0x21, 0x7c, 0x32, 0x90, 0x5e, 0x46, 0x2e, 0x36, 0xce, 0x3b,
    0xe3, 0x9e, 0x77, 0x2c, 0x18, 0xe, 0x86, 0x3, 0x9b, 0x27, 0x83, 0xa2, 0xec, 0x7, 0xa2, 0x8f,
    0xb5, 0xc5, 0x5d, 0xf0, 0x6f, 0x4c, 0x52, 0xc9, 0xde, 0x2b, 0xcb, 0xf6, 0x95, 0x58, 0x17, 0x18,
    0x39, 0x95, 0x49, 0x7c, 0xea, 0x95, 0x6a, 0xe5, 0x15, 0xd2, 0x26, 0x18, 0x98, 0xfa, 0x5, 0x10,
    0x15, 0x72, 0x8e, 0x5a, 0x8a, 0xac, 0xaa, 0x68, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
];

struct DhGroup {
    prime: &'static [u8],
    generator: usize,
    exp_size: u64,
}

#[cfg(feature = "deprecated-dh-group1-sha1")]
const DH_GROUP1: DhGroup = DhGroup {
    prime: &GROUP1,
    generator: 2,
    exp_size: 256,
};

const DH_GROUP14: DhGroup = DhGroup {
    prime: &GROUP14,
    generator: 2,
    exp_size: 256,
};

fn biguint_to_mpint(biguint: &BigUint) -> Vec<u8> {
    let mut mpint = Vec::new();
    let bytes = biguint.to_bytes_be();
    if let Some(b) = bytes.first() {
        if b > &0x7f {
            mpint.push(0);
        }
    }
    mpint.extend(&bytes);
    mpint
}

macro_rules! create_dh_with_group {
    ($name: ident, $group: expr, $hash: expr) => {
        pub(super) struct $name {
            prime: BigUint,
            private_key: BigUint,
            public_key: Vec<u8>,
        }

        impl KeyExchange for $name {
            fn new() -> SshResult<Self> {
                let mut rng = rand::thread_rng();
                let group = &($group);
                let prime = BigUint::from_bytes_be(&group.prime);
                let private_key = rng.gen_biguint((group.exp_size * 8) - 2u64).shl(1);
                let public_key =
                    biguint_to_mpint(&BigUint::from(group.generator).modpow(&private_key, &prime));

                Ok(Self {
                    prime,
                    private_key,
                    public_key,
                })
            }

            fn get_public_key(&self) -> &[u8] {
                &self.public_key
            }

            fn get_shared_secret(&self, puk: Vec<u8>) -> SshResult<Vec<u8>> {
                let other_pub = BigUint::from_bytes_be(&puk);
                let shared_secret = other_pub.modpow(&self.private_key, &self.prime);
                Ok(biguint_to_mpint(&shared_secret))
            }

            fn get_hash_type(&self) -> HashType {
                $hash
            }
        }
    };
}

#[cfg(feature = "deprecated-dh-group1-sha1")]
create_dh_with_group!(DiffieHellmanGroup1Sha1, DH_GROUP1, HashType::SHA1);
create_dh_with_group!(DiffieHellmanGroup14Sha1, DH_GROUP14, HashType::SHA1);
create_dh_with_group!(DiffieHellmanGroup14Sha256, DH_GROUP14, HashType::SHA256);