// Copyright 2015-2017 Parity Technologies (UK) Ltd.
// This file is part of Parity.

// Parity 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 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.  If not, see <http://www.gnu.org/licenses/>.

use std::fmt;
use std::ops::Deref;
use std::str::FromStr;
use secp256k1::key;
use bigint::hash::H256;
use {Error, SECP256K1};

#[derive(Clone, PartialEq, Eq)]
pub struct Secret {
	inner: H256,
}

impl fmt::Debug for Secret {
	fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
		write!(fmt, "Secret: 0x{:x}{:x}..{:x}{:x}", self.inner[0], self.inner[1], self.inner[30], self.inner[31])
	}
}

impl Secret {
	fn from_slice_unchecked(key: &[u8]) -> Self {
		assert_eq!(32, key.len(), "Caller should provide 32-byte length slice");

		let mut h = H256::default();
		h.copy_from_slice(&key[0..32]);
		Secret { inner: h }
	}

	pub fn from_slice(key: &[u8]) -> Result<Self, Error> {
		let secret = key::SecretKey::from_slice(&super::SECP256K1, key)?;
		Ok(secret.into())
	}

	/// Inplace add one secret key to another (scalar + scalar)
	pub fn add(&mut self, other: &Secret) -> Result<(), Error> {
		let mut key_secret = self.to_secp256k1_secret()?;
		let other_secret = other.to_secp256k1_secret()?;
		key_secret.add_assign(&SECP256K1, &other_secret)?;

		*self = key_secret.into();
		Ok(())
	}

	/// Inplace subtract one secret key from another (scalar - scalar)
	pub fn sub(&mut self, other: &Secret) -> Result<(), Error> {
		let mut key_secret = self.to_secp256k1_secret()?;
		let mut other_secret = other.to_secp256k1_secret()?;
		other_secret.mul_assign(&SECP256K1, &key::MINUS_ONE_KEY)?;
		key_secret.add_assign(&SECP256K1, &other_secret)?;

		*self = key_secret.into();
		Ok(())
	}

	/// Inplace multiply one secret key to another (scalar * scalar)
	pub fn mul(&mut self, other: &Secret) -> Result<(), Error> {
		let mut key_secret = self.to_secp256k1_secret()?;
		let other_secret = other.to_secp256k1_secret()?;
		key_secret.mul_assign(&SECP256K1, &other_secret)?;

		*self = key_secret.into();
		Ok(())
	}

	/// Inplace inverse secret key (1 / scalar)
	pub fn inv(&mut self) -> Result<(), Error> {
		let mut key_secret = self.to_secp256k1_secret()?;
		key_secret.inv_assign(&SECP256K1)?;

		*self = key_secret.into();
		Ok(())
	}

	/// Compute power of secret key inplace (secret ^ pow).
	/// This function is not intended to be used with large powers.
	pub fn pow(&mut self, pow: usize) -> Result<(), Error> {
		match pow {
			0 => *self = key::ONE_KEY.into(),
			1 => (),
			_ => {
				let c = self.clone();
				for _ in 1..pow {
					self.mul(&c)?;
				}
			},
		}

		Ok(())
	}

	/// Create `secp256k1::key::SecretKey` based on this secret
	pub fn to_secp256k1_secret(&self) -> Result<key::SecretKey, Error> {
		Ok(key::SecretKey::from_slice(&SECP256K1, &self[..])?)
	}
}

impl FromStr for Secret {
	type Err = Error;
	fn from_str(s: &str) -> Result<Self, Self::Err> {
		let hash = H256::from_str(s).map_err(|e| Error::Custom(format!("{:?}", e)))?;
		Self::from_slice(&hash)
	}
}

impl From<key::SecretKey> for Secret {
	fn from(key: key::SecretKey) -> Self {
		Self::from_slice_unchecked(&key[0..32])
	}
}

impl Deref for Secret {
	type Target = H256;

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

#[cfg(test)]
mod tests {
	use std::str::FromStr;
	use super::super::{Random, Generator};
	use super::Secret;

	#[test]
	fn multiplicating_secret_inversion_with_secret_gives_one() {
		let secret = Random.generate().unwrap().secret().clone();
		let mut inversion = secret.clone();
		inversion.inv().unwrap();
		inversion.mul(&secret).unwrap();
		assert_eq!(inversion, Secret::from_str("0000000000000000000000000000000000000000000000000000000000000001").unwrap());
	}

	#[test]
	fn secret_inversion_is_reversible_with_inversion() {
		let secret = Random.generate().unwrap().secret().clone();
		let mut inversion = secret.clone();
		inversion.inv().unwrap();
		inversion.inv().unwrap();
		assert_eq!(inversion, secret);
	}

	#[test]
	fn secret_pow() {
		let secret = Random.generate().unwrap().secret().clone();

		let mut pow0 = secret.clone();
		pow0.pow(0).unwrap();
		assert_eq!(pow0, Secret::from_str("0000000000000000000000000000000000000000000000000000000000000001").unwrap());

		let mut pow1 = secret.clone();
		pow1.pow(1).unwrap();
		assert_eq!(pow1, secret);

		let mut pow2 = secret.clone();
		pow2.pow(2).unwrap();
		let mut pow2_expected = secret.clone();
		pow2_expected.mul(&secret).unwrap();
		assert_eq!(pow2, pow2_expected);

		let mut pow3 = secret.clone();
		pow3.pow(3).unwrap();
		let mut pow3_expected = secret.clone();
		pow3_expected.mul(&secret).unwrap();
		pow3_expected.mul(&secret).unwrap();
		assert_eq!(pow3, pow3_expected);
	}
}