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    // 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::ops::{Deref, DerefMut};
    use std::cmp::PartialEq;
    use std::fmt;
    use std::str::FromStr;
    use std::hash::{Hash, Hasher};
    use secp256k1::{Message as SecpMessage, RecoverableSignature, RecoveryId, Error as SecpError};
    use secp256k1::key::{SecretKey, PublicKey};
    use rustc_serialize::hex::{ToHex, FromHex};
    use bigint::hash::{H520, H256, FixedHash};
    use {Secret, Public, SECP256K1, Error, Message, public_to_address, Address};

    #[repr(C)]
    pub struct Signature([u8; 65]);

    impl Signature {
    	/// Get a slice into the 'r' portion of the data.
    	pub fn r(&self) -> &[u8] {
    		&self.0[0..32]
    	}

    	/// Get a slice into the 's' portion of the data.
    	pub fn s(&self) -> &[u8] {
    		&self.0[32..64]
    	}

    	/// Get the recovery byte.
    	pub fn v(&self) -> u8 {
    		self.0[64]
    	}

    	/// Create a signature object from the sig.
    	pub fn from_rsv(r: &H256, s: &H256, v: u8) -> Signature {
    		let mut sig = [0u8; 65];
    		sig[0..32].copy_from_slice(&r);
    		sig[32..64].copy_from_slice(&s);
    		sig[64] = v;
    		Signature(sig)
    	}

    	/// Check if this is a "low" signature.
    	pub fn is_low_s(&self) -> bool {
    		H256::from_slice(self.s()) <= "7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0".into()
    	}

    	/// Check if each component of the signature is in range.
    	pub fn is_valid(&self) -> bool {
    		self.v() <= 1 &&
    			H256::from_slice(self.r()) < "fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141".into() &&
    			H256::from_slice(self.r()) >= 1.into() &&
    			H256::from_slice(self.s()) < "fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141".into() &&
    			H256::from_slice(self.s()) >= 1.into()
    	}
    }

    // manual implementation large arrays don't have trait impls by default.
    // remove when integer generics exist
    impl PartialEq for Signature {
    	fn eq(&self, other: &Self) -> bool {
    		&self.0[..] == &other.0[..]
    	}
    }

    // manual implementation required in Rust 1.13+, see `std::cmp::AssertParamIsEq`.
    impl Eq for Signature { }

    // also manual for the same reason, but the pretty printing might be useful.
    impl fmt::Debug for Signature {
    	fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
    		f.debug_struct("Signature")
    			.field("r", &self.0[0..32].to_hex())
    			.field("s", &self.0[32..64].to_hex())
    			.field("v", &self.0[64..65].to_hex())
    		.finish()
    	}
    }

    impl fmt::Display for Signature {
    	fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
    		write!(f, "{}", self.to_hex())
    	}
    }

    impl FromStr for Signature {
    	type Err = Error;

    	fn from_str(s: &str) -> Result<Self, Self::Err> {
    		match s.from_hex() {
    			Ok(ref hex) if hex.len() == 65 => {
    				let mut data = [0; 65];
    				data.copy_from_slice(&hex[0..65]);
    				Ok(Signature(data))
    			},
    			_ => Err(Error::InvalidSignature)
    		}
    	}
    }

    impl Default for Signature {
    	fn default() -> Self {
    		Signature([0; 65])
    	}
    }

    impl Hash for Signature {
        fn hash<H: Hasher>(&self, state: &mut H) {
        	H520::from(self.0).hash(state);
        }
    }

    impl Clone for Signature {
        fn clone(&self) -> Self {
    		Signature(self.0)
        }
    }

    impl From<[u8; 65]> for Signature {
    	fn from(s: [u8; 65]) -> Self {
    		Signature(s)
    	}
    }

    impl Into<[u8; 65]> for Signature {
    	fn into(self) -> [u8; 65] {
    		self.0
    	}
    }

    impl From<Signature> for H520 {
    	fn from(s: Signature) -> Self {
    		H520::from(s.0)
    	}
    }

    impl From<H520> for Signature {
    	fn from(bytes: H520) -> Self {
    		Signature(bytes.into())
    	}
    }

    impl Deref for Signature {
    	type Target = [u8; 65];

    	fn deref(&self) -> &Self::Target {
    		&self.0
    	}
    }

    impl DerefMut for Signature {
    	fn deref_mut(&mut self) -> &mut Self::Target {
    		&mut self.0
    	}
    }

    pub fn sign(secret: &Secret, message: &Message) -> Result<Signature, Error> {
    	let context = &SECP256K1;
    	let sec = SecretKey::from_slice(context, &secret)?;
    	let s = context.sign_recoverable(&SecpMessage::from_slice(&message[..])?, &sec)?;
    	let (rec_id, data) = s.serialize_compact(context);
    	let mut data_arr = [0; 65];

    	// no need to check if s is low, it always is
    	data_arr[0..64].copy_from_slice(&data[0..64]);
    	data_arr[64] = rec_id.to_i32() as u8;
    	Ok(Signature(data_arr))
    }

    pub fn verify_public(public: &Public, signature: &Signature, message: &Message) -> Result<bool, Error> {
    	let context = &SECP256K1;
    	let rsig = RecoverableSignature::from_compact(context, &signature[0..64], RecoveryId::from_i32(signature[64] as i32)?)?;
    	let sig = rsig.to_standard(context);

    	let pdata: [u8; 65] = {
    		let mut temp = [4u8; 65];
    		temp[1..65].copy_from_slice(&**public);
    		temp
    	};

    	let publ = PublicKey::from_slice(context, &pdata)?;
    	match context.verify(&SecpMessage::from_slice(&message[..])?, &sig, &publ) {
    		Ok(_) => Ok(true),
    		Err(SecpError::IncorrectSignature) => Ok(false),
    		Err(x) => Err(Error::from(x))
    	}
    }

    pub fn verify_address(address: &Address, signature: &Signature, message: &Message) -> Result<bool, Error> {
    	let public = recover(signature, message)?;
    	let recovered_address = public_to_address(&public);
    	Ok(address == &recovered_address)
    }

    pub fn recover(signature: &Signature, message: &Message) -> Result<Public, Error> {
    	let context = &SECP256K1;
    	let rsig = RecoverableSignature::from_compact(context, &signature[0..64], RecoveryId::from_i32(signature[64] as i32)?)?;
    	let pubkey = context.recover(&SecpMessage::from_slice(&message[..])?, &rsig)?;
    	let serialized = pubkey.serialize_vec(context, false);

    	let mut public = Public::default();
    	public.copy_from_slice(&serialized[1..65]);
    	Ok(public)
    }

    #[cfg(test)]
    mod tests {
    	use std::str::FromStr;
    	use {Generator, Random, Message};
    	use super::{sign, verify_public, verify_address, recover, Signature};

    	#[test]
    	fn signature_to_and_from_str() {
    		let keypair = Random.generate().unwrap();
    		let message = Message::default();
    		let signature = sign(keypair.secret(), &message).unwrap();
    		let string = format!("{}", signature);
    		let deserialized = Signature::from_str(&string).unwrap();
    		assert_eq!(signature, deserialized);
    	}

    	#[test]
    	fn sign_and_recover_public() {
    		let keypair = Random.generate().unwrap();
    		let message = Message::default();
    		let signature = sign(keypair.secret(), &message).unwrap();
    		assert_eq!(keypair.public(), &recover(&signature, &message).unwrap());
    	}

    	#[test]
    	fn sign_and_verify_public() {
    		let keypair = Random.generate().unwrap();
    		let message = Message::default();
    		let signature = sign(keypair.secret(), &message).unwrap();
    		assert!(verify_public(keypair.public(), &signature, &message).unwrap());
    	}

    	#[test]
    	fn sign_and_verify_address() {
    		let keypair = Random.generate().unwrap();
    		let message = Message::default();
    		let signature = sign(keypair.secret(), &message).unwrap();
    		assert!(verify_address(&keypair.address(), &signature, &message).unwrap());
    	}
    }

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