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    use std::{io, cmp};
    use futures::{Future, Poll, Async};
    use tokio_io::{AsyncRead, AsyncWrite};
    use message::{Message, MessageResult, Error};
    use message::types::{Version, Verack};
    use network::Magic;
    use io::{write_message, WriteMessage, ReadMessage, read_message};

    pub fn handshake<A>(a: A, magic: Magic, version: Version, min_version: u32) -> Handshake<A> where A: AsyncWrite + AsyncRead {
    	Handshake {
    		version: version.version(),
    		nonce: version.nonce(),
    		state: HandshakeState::SendVersion(write_message(a, version_message(magic, version))),
    		magic: magic,
    		min_version: min_version,
    	}
    }

    pub fn accept_handshake<A>(a: A, magic: Magic, version: Version, min_version: u32) -> AcceptHandshake<A> where A: AsyncWrite + AsyncRead {
    	AcceptHandshake {
    		version: version.version(),
    		nonce: version.nonce(),
    		state: AcceptHandshakeState::ReceiveVersion {
    			local_version: Some(version),
    			future: read_message(a, magic, 0),
    		},
    		magic: magic,
    		min_version: min_version,
    	}
    }

    pub fn negotiate_version(local: u32, other: u32) -> u32 {
    	cmp::min(local, other)
    }

    #[derive(Debug, PartialEq)]
    pub struct HandshakeResult {
    	pub version: Version,
    	pub negotiated_version: u32,
    }

    fn version_message(magic: Magic, version: Version) -> Message<Version> {
    	Message::new(magic, version.version(), &version).expect("version message should always be serialized correctly")
    }

    fn verack_message(magic: Magic) -> Message<Verack> {
    	Message::new(magic, 0, &Verack).expect("verack message should always be serialized correctly")
    }

    enum HandshakeState<A> {
    	SendVersion(WriteMessage<Version, A>),
    	ReceiveVersion(ReadMessage<Version, A>),
    	SendVerack {
    		version: Option<Version>,
    		future: WriteMessage<Verack, A>,
    	},
    	ReceiveVerack {
    		version: Option<Version>,
    		future: ReadMessage<Verack, A>,
    	},
    }

    enum AcceptHandshakeState<A> {
    	ReceiveVersion {
    		local_version: Option<Version>,
    		future: ReadMessage<Version, A>
    	},
    	SendVersion {
    		version: Option<Version>,
    		future: WriteMessage<Version, A>,
    	},
    	SendVerack {
    		version: Option<Version>,
    		future: WriteMessage<Verack, A>,
    	},
    }

    pub struct Handshake<A> {
    	state: HandshakeState<A>,
    	magic: Magic,
    	version: u32,
    	nonce: Option<u64>,
    	min_version: u32,
    }

    pub struct AcceptHandshake<A> {
    	state: AcceptHandshakeState<A>,
    	magic: Magic,
    	version: u32,
    	nonce: Option<u64>,
    	min_version: u32,
    }

    impl<A> Future for Handshake<A> where A: AsyncRead + AsyncWrite {
    	type Item = (A, MessageResult<HandshakeResult>);
    	type Error = io::Error;

    	fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
    		loop {
    			let next_state = match self.state {
    				HandshakeState::SendVersion(ref mut future) => {
    					let (stream, _) = try_ready!(future.poll());
    					HandshakeState::ReceiveVersion(read_message(stream, self.magic, 0))
    				},
    				HandshakeState::ReceiveVersion(ref mut future) => {
    					let (stream, version) = try_ready!(future.poll());
    					let version = match version {
    						Ok(version) => version,
    						Err(err) => return Ok((stream, Err(err.into())).into()),
    					};

    					if version.version() < self.min_version {
    						return Ok((stream, Err(Error::InvalidVersion)).into());
    					}
    					if let (Some(self_nonce), Some(nonce)) = (self.nonce, version.nonce()) {
    						if self_nonce == nonce {
    							return Ok((stream, Err(Error::InvalidVersion)).into());
    						}
    					}

    					HandshakeState::SendVerack {
    						version: Some(version),
    						future: write_message(stream, verack_message(self.magic)),
    					}
    				},
    				HandshakeState::SendVerack { ref mut version, ref mut future } => {
    					let (stream, _) = try_ready!(future.poll());

    					let version = version.take().expect("verack must be preceded by version");

    					HandshakeState::ReceiveVerack {
    						version: Some(version),
    						future: read_message(stream, self.magic, 0),
    					}
    				},
    				HandshakeState::ReceiveVerack { ref mut version, ref mut future } => {
    					let (stream, _verack) = try_ready!(future.poll());
    					let version = version.take().expect("verack must be preceded by version");

    					let result = HandshakeResult {
    						negotiated_version: negotiate_version(self.version, version.version()),
    						version: version,
    					};

    					return Ok(Async::Ready((stream, Ok(result))));
    				},
    			};
    			self.state = next_state;
    		}
    	}
    }

    impl<A> Future for AcceptHandshake<A> where A: AsyncRead + AsyncWrite {
    	type Item = (A, MessageResult<HandshakeResult>);
    	type Error = io::Error;

    	fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
    		loop {
    			let next_state = match self.state {
    				AcceptHandshakeState::ReceiveVersion { ref mut local_version, ref mut future } => {
    					let (stream, version) = try_ready!(future.poll());
    					let version = match version {
    						Ok(version) => version,
    						Err(err) => return Ok((stream, Err(err.into())).into()),
    					};

    					if version.version() < self.min_version {
    						return Ok((stream, Err(Error::InvalidVersion)).into());
    					}
    					if let (Some(self_nonce), Some(nonce)) = (self.nonce, version.nonce()) {
    						if self_nonce == nonce {
    							return Ok((stream, Err(Error::InvalidVersion)).into());
    						}
    					}

    					let local_version = local_version.take().expect("local version must be set");
    					AcceptHandshakeState::SendVersion {
    						version: Some(version),
    						future: write_message(stream, version_message(self.magic, local_version)),
    					}
    				},
    				AcceptHandshakeState::SendVersion { ref mut version, ref mut future } => {
    					let (stream, _) = try_ready!(future.poll());
    					AcceptHandshakeState::SendVerack {
    						version: version.take(),
    						future: write_message(stream, verack_message(self.magic)),
    					}
    				},
    				AcceptHandshakeState::SendVerack { ref mut version, ref mut future } => {
    					let (stream, _) = try_ready!(future.poll());

    					let version = version.take().expect("verack must be preceded by version");

    					let result = HandshakeResult {
    						negotiated_version: negotiate_version(self.version, version.version()),
    						version: version,
    					};

    					return Ok(Async::Ready((stream, Ok(result))));
    				},
    			};
    			self.state = next_state;
    		}
    	}
    }

    #[cfg(test)]
    mod tests {
    	use std::io;
    	use futures::{Future, Poll};
    	use tokio_io::{AsyncRead, AsyncWrite};
    	use bytes::Bytes;
    	use ser::Stream;
    	use network::{Network, ConsensusFork, BitcoinCashConsensusParams};
    	use message::{Message, Error};
    	use message::types::Verack;
    	use message::types::version::{Version, V0, V106, V70001};
    	use super::{handshake, accept_handshake, HandshakeResult};

    	pub struct TestIo {
    		read: io::Cursor<Bytes>,
    		write: Bytes,
    	}

    	impl io::Read for TestIo {
    		fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
    			io::Read::read(&mut self.read, buf)
    		}
    	}

    	impl AsyncRead for TestIo {}

    	impl io::Write for TestIo {
    		fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
    			io::Write::write(&mut self.write, buf)
    		}

    		fn flush(&mut self) -> io::Result<()> {
    			io::Write::flush(&mut self.write)
    		}
    	}

    	impl AsyncWrite for TestIo {
    		fn shutdown(&mut self) -> Poll<(), io::Error> {
    			Ok(().into())
    		}
    	}

    	fn local_version() -> Version {
    		Version::V70001(V0 {
    			version: 70001,
    			services: 1u64.into(),
    			timestamp: 0x4d1015e6,
    			// address and port of remote
    			// services set to 0, cause we know nothing about the node
    			receiver: "00000000000000000000000000000000000000002f5a0808208d".into(),
    		}, V106 {
    			// our local address (not sure if it is valid, or if it is checked at all
    			// services set to 0, because we support nothing
    			from: "00000000000000000000000000000000000000007f000001208d".into(),
    			nonce: 0x3c76a409eb48a227,
    			user_agent: "pbtc".into(),
    			start_height: 0,
    		}, V70001 {
    			relay: true,
    		})
    	}

    	fn remote_version() -> Version {
    		Version::V70001(V0 {
    			version: 70012,
    			services: 1u64.into(),
    			timestamp: 0x4d1015e6,
    			// services set to 1, house receiver supports at least the network
    			receiver: "010000000000000000000000000000000000ffffc2b5936adde9".into(),
    		}, V106 {
    			// remote address, port
    			// and supported protocols
    			from: "050000000000000000000000000000000000ffff2f5a0808208d".into(),
    			nonce: 0x3c76a409eb48a228,
    			user_agent: "/Satoshi:0.12.1/".into(),
    			start_height: 0,
    		}, V70001 {
    			relay: true,
    		})
    	}

    	#[test]
    	fn test_handshake() {
    		let magic = Network::Mainnet.magic(&ConsensusFork::BitcoinCore);
    		let version = 70012;
    		let local_version = local_version();
    		let remote_version = remote_version();

    		let mut remote_stream = Stream::new();
    		remote_stream.append_slice(Message::new(magic, version, &remote_version).unwrap().as_ref());
    		remote_stream.append_slice(Message::new(magic, version, &Verack).unwrap().as_ref());

    		let expected = HandshakeResult {
    			version: remote_version,
    			negotiated_version: 70001,
    		};

    		let mut expected_stream = Stream::new();
    		expected_stream.append_slice(Message::new(magic, version, &local_version).unwrap().as_ref());
    		expected_stream.append_slice(Message::new(magic, version, &Verack).unwrap().as_ref());

    		let test_io = TestIo {
    			read: io::Cursor::new(remote_stream.out()),
    			write: Bytes::default(),
    		};

    		let hs = handshake(test_io, magic, local_version, 0).wait().unwrap();
    		assert_eq!(hs.0.write, expected_stream.out());
    		assert_eq!(hs.1.unwrap(), expected);
    	}

    	#[test]
    	fn test_accept_handshake() {
    		let magic = Network::Mainnet.magic(&ConsensusFork::BitcoinCore);
    		let version = 70012;
    		let local_version = local_version();
    		let remote_version = remote_version();

    		let mut remote_stream = Stream::new();
    		remote_stream.append_slice(Message::new(magic, version, &remote_version).unwrap().as_ref());

    		let test_io = TestIo {
    			read: io::Cursor::new(remote_stream.out()),
    			write: Bytes::default(),
    		};

    		let expected = HandshakeResult {
    			version: remote_version,
    			negotiated_version: 70001,
    		};

    		let mut expected_stream = Stream::new();
    		expected_stream.append_slice(Message::new(magic, version, &local_version).unwrap().as_ref());
    		expected_stream.append_slice(Message::new(magic, version, &Verack).unwrap().as_ref());

    		let hs = accept_handshake(test_io, magic, local_version, 0).wait().unwrap();
    		assert_eq!(hs.0.write, expected_stream.out());
    		assert_eq!(hs.1.unwrap(), expected);
    	}

    	#[test]
    	fn test_self_handshake() {
    		let magic = Network::Mainnet.magic(&ConsensusFork::BitcoinCore);
    		let version = 70012;
    		let remote_version = local_version();
    		let local_version = local_version();

    		let mut remote_stream = Stream::new();
    		remote_stream.append_slice(Message::new(magic, version, &remote_version).unwrap().as_ref());

    		let test_io = TestIo {
    			read: io::Cursor::new(remote_stream.out()),
    			write: Bytes::default(),
    		};

    		let expected = Error::InvalidVersion;

    		let hs = handshake(test_io, magic, local_version, 0).wait().unwrap();
    		assert_eq!(hs.1.unwrap_err(), expected);
    	}

    	#[test]
    	fn test_accept_self_handshake() {
    		let magic = Network::Mainnet.magic(&ConsensusFork::BitcoinCore);
    		let version = 70012;
    		let remote_version = local_version();
    		let local_version = local_version();

    		let mut remote_stream = Stream::new();
    		remote_stream.append_slice(Message::new(magic, version, &remote_version).unwrap().as_ref());

    		let test_io = TestIo {
    			read: io::Cursor::new(remote_stream.out()),
    			write: Bytes::default(),
    		};

    		let expected = Error::InvalidVersion;

    		let hs = accept_handshake(test_io, magic, local_version, 0).wait().unwrap();
    		assert_eq!(hs.1.unwrap_err(), expected);
    	}

    	#[test]
    	fn test_fails_to_accept_other_fork_node() {
    		let magic1 = Network::Mainnet.magic(&ConsensusFork::BitcoinCore);
    		let magic2 = Network::Mainnet.magic(&ConsensusFork::BitcoinCash(BitcoinCashConsensusParams::new(Network::Mainnet)));
    		let version = 70012;
    		let local_version = local_version();
    		let remote_version = remote_version();

    		let mut remote_stream = Stream::new();
    		remote_stream.append_slice(Message::new(magic2, version, &remote_version).unwrap().as_ref());

    		let test_io = TestIo {
    			read: io::Cursor::new(remote_stream.out()),
    			write: Bytes::default(),
    		};

    		let expected = Error::InvalidMagic;

    		let hs = accept_handshake(test_io, magic1, local_version, 0).wait().unwrap();
    		assert_eq!(hs.1.unwrap_err(), expected);
    	}
    }

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