// Copyright 2015-2019 Parity Technologies (UK) Ltd.
// This file is part of Parity Ethereum.

// Parity Ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity Ethereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity Ethereum.  If not, see <http://www.gnu.org/licenses/>.

use bytes::Bytes;
use crypto;
use ethereum_types::{H256, H512};
use ethkey::{self, math, Generator, Public, Random, Secret};
use jsonrpc_core::Error;
use rand::{OsRng, Rng};
use std::collections::BTreeSet;
use tiny_keccak::Keccak;
use v1::{helpers::errors, types::EncryptedDocumentKey};

/// Initialization vector length.
const INIT_VEC_LEN: usize = 16;

/// Generate document key to store in secret store.
pub fn generate_document_key(
    account_public: Public,
    server_key_public: Public,
) -> Result<EncryptedDocumentKey, Error> {
    // generate random plain document key
    let document_key = Random.generate().map_err(errors::encryption)?;

    // encrypt document key using server key
    let (common_point, encrypted_point) =
        encrypt_secret(document_key.public(), &server_key_public)?;

    // ..and now encrypt document key with account public
    let encrypted_key = ethkey::crypto::ecies::encrypt(
        &account_public,
        &crypto::DEFAULT_MAC,
        document_key.public(),
    )
    .map_err(errors::encryption)?;

    Ok(EncryptedDocumentKey {
        common_point: common_point.into(),
        encrypted_point: encrypted_point.into(),
        encrypted_key: encrypted_key.into(),
    })
}

/// Encrypt document with distributely generated key.
pub fn encrypt_document(key: Bytes, document: Bytes) -> Result<Bytes, Error> {
    // make document key
    let key = into_document_key(key)?;

    // use symmetric encryption to encrypt document
    let iv = initialization_vector();
    let mut encrypted_document = vec![0; document.len() + iv.len()];
    {
        let (mut encryption_buffer, iv_buffer) = encrypted_document.split_at_mut(document.len());

        crypto::aes::encrypt_128_ctr(&key, &iv, &document, &mut encryption_buffer)
            .map_err(errors::encryption)?;
        iv_buffer.copy_from_slice(&iv);
    }

    Ok(encrypted_document)
}

/// Decrypt document with distributely generated key.
pub fn decrypt_document(key: Bytes, mut encrypted_document: Bytes) -> Result<Bytes, Error> {
    // initialization vector takes INIT_VEC_LEN bytes
    let encrypted_document_len = encrypted_document.len();
    if encrypted_document_len < INIT_VEC_LEN {
        return Err(errors::invalid_params(
            "encrypted_document",
            "invalid encrypted data",
        ));
    }

    // make document key
    let key = into_document_key(key)?;

    // use symmetric decryption to decrypt document
    let iv = encrypted_document.split_off(encrypted_document_len - INIT_VEC_LEN);
    let mut document = vec![0; encrypted_document_len - INIT_VEC_LEN];
    crypto::aes::decrypt_128_ctr(&key, &iv, &encrypted_document, &mut document)
        .map_err(errors::encryption)?;

    Ok(document)
}

/// Decrypt document given secret shadow.
pub fn decrypt_document_with_shadow(
    decrypted_secret: Public,
    common_point: Public,
    shadows: Vec<Secret>,
    encrypted_document: Bytes,
) -> Result<Bytes, Error> {
    let key = decrypt_with_shadow_coefficients(decrypted_secret, common_point, shadows)?;
    decrypt_document(key.to_vec(), encrypted_document)
}

/// Calculate Keccak(ordered servers set)
pub fn ordered_servers_keccak(servers_set: BTreeSet<H512>) -> H256 {
    let mut servers_set_keccak = Keccak::new_keccak256();
    for server in servers_set {
        servers_set_keccak.update(&server.0);
    }

    let mut servers_set_keccak_value = [0u8; 32];
    servers_set_keccak.finalize(&mut servers_set_keccak_value);

    servers_set_keccak_value.into()
}

fn into_document_key(key: Bytes) -> Result<Bytes, Error> {
    // key is a previously distributely generated Public
    if key.len() != 64 {
        return Err(errors::invalid_params("key", "invalid public key length"));
    }

    // use x coordinate of distributely generated point as encryption key
    Ok(key[..INIT_VEC_LEN].into())
}

fn initialization_vector() -> [u8; INIT_VEC_LEN] {
    let mut result = [0u8; INIT_VEC_LEN];
    let mut rng = OsRng::new().unwrap();
    rng.fill_bytes(&mut result);
    result
}

fn decrypt_with_shadow_coefficients(
    mut decrypted_shadow: Public,
    mut common_shadow_point: Public,
    shadow_coefficients: Vec<Secret>,
) -> Result<Public, Error> {
    let mut shadow_coefficients_sum = shadow_coefficients[0].clone();
    for shadow_coefficient in shadow_coefficients.iter().skip(1) {
        shadow_coefficients_sum
            .add(shadow_coefficient)
            .map_err(errors::encryption)?;
    }

    math::public_mul_secret(&mut common_shadow_point, &shadow_coefficients_sum)
        .map_err(errors::encryption)?;
    math::public_add(&mut decrypted_shadow, &common_shadow_point).map_err(errors::encryption)?;
    Ok(decrypted_shadow)
}

fn encrypt_secret(secret: &Public, joint_public: &Public) -> Result<(Public, Public), Error> {
    // TODO: it is copypaste of `encrypt_secret` from secret_store/src/key_server_cluster/math.rs
    // use shared version from SS math library, when it'll be available

    let key_pair = Random.generate().map_err(errors::encryption)?;

    // k * T
    let mut common_point = math::generation_point();
    math::public_mul_secret(&mut common_point, key_pair.secret()).map_err(errors::encryption)?;

    // M + k * y
    let mut encrypted_point = joint_public.clone();
    math::public_mul_secret(&mut encrypted_point, key_pair.secret()).map_err(errors::encryption)?;
    math::public_add(&mut encrypted_point, secret).map_err(errors::encryption)?;

    Ok((common_point, encrypted_point))
}

#[cfg(test)]
mod tests {
    use super::{decrypt_document, decrypt_document_with_shadow, encrypt_document};
    use bytes::Bytes;
    use rustc_hex::FromHex;

    #[test]
    fn encrypt_and_decrypt_document() {
        let document_key: Bytes = "cac6c205eb06c8308d65156ff6c862c62b000b8ead121a4455a8ddeff7248128d895692136f240d5d1614dc7cc4147b1bd584bd617e30560bb872064d09ea325".from_hex().unwrap();
        let document: Bytes = b"Hello, world!!!"[..].into();

        let encrypted_document = encrypt_document(document_key.clone(), document.clone()).unwrap();
        assert!(document != encrypted_document);

        let decrypted_document =
            decrypt_document(document_key.clone(), encrypted_document).unwrap();
        assert_eq!(decrypted_document, document);
    }

    #[test]
    fn encrypt_and_shadow_decrypt_document() {
        let document: Bytes = "deadbeef".from_hex().unwrap();
        let encrypted_document = "2ddec1f96229efa2916988d8b2a82a47ef36f71c"
            .from_hex()
            .unwrap();
        let decrypted_secret = "843645726384530ffb0c52f175278143b5a93959af7864460f5a4fec9afd1450cfb8aef63dec90657f43f55b13e0a73c7524d4e9a13c051b4e5f1e53f39ecd91".parse().unwrap();
        let common_point = "07230e34ebfe41337d3ed53b186b3861751f2401ee74b988bba55694e2a6f60c757677e194be2e53c3523cc8548694e636e6acb35c4e8fdc5e29d28679b9b2f3".parse().unwrap();
        let shadows = vec![
            "46f542416216f66a7d7881f5a283d2a1ab7a87b381cbc5f29d0b093c7c89ee31"
                .parse()
                .unwrap(),
        ];
        let decrypted_document = decrypt_document_with_shadow(
            decrypted_secret,
            common_point,
            shadows,
            encrypted_document,
        )
        .unwrap();
        assert_eq!(decrypted_document, document);
    }
}