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//! Adapter for pure Rust implementation of the secp256k1 curve and fast ECDSA signatures
//!

use base64::decode_config;
use serde::{de::Deserializer, Deserialize, Serialize, Serializer};

use crate::identifier;
use identifier::error::Error;

use super::{create_seed, BaseKeyPair, KeyGenerator, KeyMaterial, KeyPair, Payload, DHKE, DSA};
use libsecp256k1::{Message, PublicKey, SecretKey, Signature};
use sha2::{Digest, Sha256};

/// Secp256k1 cryptographic key pair
pub type Secp256k1KeyPair = BaseKeyPair<PublicKey, SecretKey>;

/// Defines constants
pub const SECRET_KEY_LENGTH: usize = 32;
pub const KEYPAIR_LENGTH: usize = 97;

/// Keys generation
impl KeyGenerator for Secp256k1KeyPair {
    fn from_seed(seed: &[u8]) -> Self {
        let secret_seed = create_seed(seed).expect("invalid seed");
        let sk = SecretKey::parse(&secret_seed).expect("Couldn't create key");
        let pk = PublicKey::from_secret_key(&sk);
        Secp256k1KeyPair {
            public_key: pk,
            secret_key: Some(sk),
        }
    }

    fn from_public_key(pk: &[u8]) -> Self {
        let pk = PublicKey::parse_slice(pk, None).expect("Could not parse public key");

        Secp256k1KeyPair {
            secret_key: None,
            public_key: pk,
        }
    }

    fn from_secret_key(secret_key: &[u8]) -> Self {
        let sk = SecretKey::parse_slice(secret_key).unwrap();
        let pk = PublicKey::from_secret_key(&sk);

        Secp256k1KeyPair {
            public_key: pk,
            secret_key: Some(sk),
        }
    }
}

impl KeyMaterial for Secp256k1KeyPair {
    fn public_key_bytes(&self) -> Vec<u8> {
        self.public_key.serialize().to_vec()
    }

    fn secret_key_bytes(&self) -> Vec<u8> {
        self.secret_key
            .as_ref()
            .map_or(vec![], |x| x.serialize().to_vec())
    }

    fn to_bytes(&self) -> Vec<u8> {
        let mut bytes: [u8; KEYPAIR_LENGTH] = [0u8; KEYPAIR_LENGTH];
        bytes[..SECRET_KEY_LENGTH].copy_from_slice(&self.secret_key_bytes());
        bytes[SECRET_KEY_LENGTH..].copy_from_slice(&self.public_key_bytes());
        bytes.to_vec()
    }
}

impl DSA for Secp256k1KeyPair {
    fn sign(&self, payload: Payload) -> Result<Vec<u8>, Error> {
        match payload {
            Payload::Buffer(payload) => {
                let signature = match &self.secret_key {
                    Some(sig) => {
                        let message = Message::parse(&get_hash(&payload));
                        libsecp256k1::sign(&message, sig).0
                    }
                    None => panic!("secret key not found"),
                };
                let signature = signature.serialize();
                Ok(signature.as_ref().to_vec())
            }
            _ => Err(Error::SignError(
                "Payload type not supported for this key".into(),
            )),
        }
    }

    fn verify(&self, payload: Payload, signature: &[u8]) -> Result<(), Error> {
        let verified = match payload {
            Payload::Buffer(payload) => {
                let message = Message::parse(&get_hash(&payload));
                let signature =
                    Signature::parse_standard_slice(signature).expect("Couldn't parse signature");

                libsecp256k1::verify(&message, &signature, &self.public_key)
            }
            _ => unimplemented!("payload type not supported for this key"),
        };

        if verified {
            Ok(())
        } else {
            Err(Error::SignError("Signature verify failed".into()))
        }
    }
}

impl DHKE for Secp256k1KeyPair {
    fn key_exchange(&self, _: &Self) -> Result<Vec<u8>, Error> {
        unimplemented!("ECDH is not supported for this key type")
    }
}

/// Serde compatible Serialize
impl Serialize for Secp256k1KeyPair {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_str(&self.to_str())
    }
}

/// Serde compatible Deserialize
impl<'de> Deserialize<'de> for Secp256k1KeyPair {
    fn deserialize<D>(deserializer: D) -> Result<Secp256k1KeyPair, D::Error>
    where
        D: Deserializer<'de>,
    {
        let s = String::deserialize(deserializer)?;
        let bytes = decode_config(&s, base64::URL_SAFE).map_err(serde::de::Error::custom)?;

        Ok(Secp256k1KeyPair::from_secret_key(
            &bytes[..SECRET_KEY_LENGTH],
        ))
    }
}

fn get_hash(payload: &[u8]) -> [u8; 32] {
    let hash = Sha256::digest(&payload);
    let mut output = [0u8; 32];
    output.copy_from_slice(&hash[..32]);
    output
}

impl From<Secp256k1KeyPair> for KeyPair {
    fn from(key_pair: Secp256k1KeyPair) -> Self {
        KeyPair::Secp256k1(key_pair)
    }
}

#[cfg(test)]
mod tests {

    use super::Secp256k1KeyPair;
    use crate::commons::crypto::{KeyGenerator, Payload, DSA};

    #[test]
    fn test_ser_des() {
        let msg = b"message";
        let kp = Secp256k1KeyPair::new();
        let signature = kp.sign(Payload::Buffer(msg.to_vec())).unwrap();
        let kp_str = serde_json::to_string_pretty(&kp).unwrap();
        let new_kp: Result<Secp256k1KeyPair, serde_json::Error> = serde_json::from_str(&kp_str);
        assert!(new_kp.is_ok());
        let result = new_kp
            .unwrap()
            .verify(Payload::Buffer(msg.to_vec()), &signature);
        assert!(result.is_ok());
    }
}