cashu 0.16.0

use core::fmt;
use core::ops::Deref;
use core::str::FromStr;

use bitcoin::hashes::sha256::Hash as Sha256Hash;
use bitcoin::hashes::Hash;
use bitcoin::secp256k1;
use bitcoin::secp256k1::rand::rngs::OsRng;
use bitcoin::secp256k1::schnorr::Signature;
use bitcoin::secp256k1::{Keypair, Message, Scalar};
use serde::de::Visitor;
use serde::{Deserialize, Deserializer, Serialize};

use super::{Error, PublicKey};
use crate::SECP256K1;

/// SecretKey
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "swagger", derive(utoipa::ToSchema))]
pub struct SecretKey {
    #[cfg_attr(feature = "swagger", schema(value_type = String))]
    inner: secp256k1::SecretKey,
}

impl Deref for SecretKey {
    type Target = secp256k1::SecretKey;

    fn deref(&self) -> &Self::Target {
        &self.inner
    }
}

impl From<secp256k1::SecretKey> for SecretKey {
    fn from(inner: secp256k1::SecretKey) -> Self {
        Self { inner }
    }
}

impl fmt::Display for SecretKey {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.to_secret_hex())
    }
}

impl SecretKey {
    /// Parse from `bytes`
    pub fn from_slice(slice: &[u8]) -> Result<Self, Error> {
        Ok(Self {
            inner: secp256k1::SecretKey::from_slice(slice)?,
        })
    }

    /// Parse from `hex` string
    pub fn from_hex<S>(hex: S) -> Result<Self, Error>
    where
        S: AsRef<str>,
    {
        Ok(Self {
            inner: secp256k1::SecretKey::from_str(hex.as_ref())?,
        })
    }

    /// Generate random secret key
    pub fn generate() -> Self {
        let (secret_key, _) = SECP256K1.generate_keypair(&mut OsRng);
        Self { inner: secret_key }
    }

    /// Get secret key as `hex` string
    pub fn to_secret_hex(&self) -> String {
        self.inner.display_secret().to_string()
    }

    /// Get secret key as `bytes`
    pub fn as_secret_bytes(&self) -> &[u8] {
        self.inner.as_ref()
    }

    /// Get secret key as `bytes`
    pub fn to_secret_bytes(&self) -> [u8; 32] {
        self.inner.secret_bytes()
    }

    /// Schnorr Signature on Message
    pub fn sign(&self, msg: &[u8]) -> Result<Signature, Error> {
        let hash: Sha256Hash = Sha256Hash::hash(msg);
        let msg = Message::from_digest_slice(hash.as_ref())?;
        Ok(SECP256K1.sign_schnorr(&msg, &Keypair::from_secret_key(&SECP256K1, &self.inner)))
    }

    /// Get public key
    pub fn public_key(&self) -> PublicKey {
        self.inner.public_key(&SECP256K1).into()
    }

    /// [`SecretKey`] to [`Scalar`]
    #[inline]
    pub fn to_scalar(self) -> Scalar {
        Scalar::from(self.inner)
    }

    /// [`SecretKey`] as [`Scalar`]
    #[inline]
    pub fn as_scalar(&self) -> Scalar {
        Scalar::from(self.inner)
    }
}

impl FromStr for SecretKey {
    type Err = Error;

    /// Try to parse [SecretKey] from `hex` or `bech32`
    fn from_str(secret_key: &str) -> Result<Self, Self::Err> {
        Self::from_hex(secret_key)
    }
}

impl Serialize for SecretKey {
    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        match serializer.is_human_readable() {
            // For human-readable formats like JSON, serialize as hex string
            true => serializer.serialize_str(&self.to_secret_hex()),
            // For binary formats like CBOR, use the bytes serialization
            false => serializer.serialize_bytes(self.as_secret_bytes()),
        }
    }
}

impl<'de> Deserialize<'de> for SecretKey {
    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        match deserializer.is_human_readable() {
            // For human-readable formats like JSON, deserialize from hex string
            true => {
                let secret_key: String = String::deserialize(deserializer)?;
                SecretKey::from_hex(secret_key).map_err(serde::de::Error::custom)
            }
            // For binary formats like CBOR, use the bytes deserialization
            false => {
                struct SecretKeyVisitor;

                impl Visitor<'_> for SecretKeyVisitor {
                    type Value = SecretKey;

                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
                        formatter.write_str("a byte array")
                    }

                    fn visit_bytes<E>(self, value: &[u8]) -> Result<Self::Value, E>
                    where
                        E: serde::de::Error,
                    {
                        SecretKey::from_slice(value).map_err(serde::de::Error::custom)
                    }
                }

                deserializer.deserialize_bytes(SecretKeyVisitor)
            }
        }
    }
}

impl Drop for SecretKey {
    fn drop(&mut self) {
        self.inner.non_secure_erase();
        tracing::trace!("Secret Key dropped.");
    }
}