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    use std::{io, net, error, time};
    use std::sync::Arc;
    use std::net::SocketAddr;
    use parking_lot::RwLock;
    use futures::{Future, finished, failed};
    use futures::stream::Stream;
    use futures_cpupool::CpuPool;
    use tokio_io::IoFuture;
    use tokio_core::net::{TcpListener, TcpStream};
    use tokio_core::reactor::{Handle, Remote, Timeout, Interval};
    use abstract_ns::Resolver;
    use ns_dns_tokio::DnsResolver;
    use message::{Payload, MessageResult, Message};
    use message::common::Services;
    use message::types::addr::AddressEntry;
    use net::{connect, Connections, Channel, Config as NetConfig, accept_connection, ConnectionCounter};
    use util::{NodeTable, Node, NodeTableError, Direction};
    use session::{SessionFactory, SeednodeSessionFactory, NormalSessionFactory};
    use {Config, PeerId};
    use protocol::{LocalSyncNodeRef, InboundSyncConnectionRef, OutboundSyncConnectionRef};
    use io::DeadlineStatus;

    pub type BoxedEmptyFuture = Box<Future<Item=(), Error=()> + Send>;

    /// Network context.
    pub struct Context {
    	/// Connections.
    	connections: Connections,
    	/// Connection counter.
    	connection_counter: ConnectionCounter,
    	/// Node Table.
    	node_table: RwLock<NodeTable>,
    	/// Thread pool handle.
    	pool: CpuPool,
    	/// Remote event loop handle.
    	remote: Remote,
    	/// Local synchronization node.
    	local_sync_node: LocalSyncNodeRef,
    	/// Node table path.
    	config: Config,
    }

    impl Context {
    	/// Creates new context with reference to local sync node, thread pool and event loop.
    	pub fn new(local_sync_node: LocalSyncNodeRef, pool_handle: CpuPool, remote: Remote, config: Config) -> Result<Self, Box<error::Error>> {
    		let context = Context {
    			connections: Default::default(),
    			connection_counter: ConnectionCounter::new(config.inbound_connections, config.outbound_connections),
    			node_table: RwLock::new(try!(NodeTable::from_file(config.preferable_services, &config.node_table_path))),
    			pool: pool_handle,
    			remote: remote,
    			local_sync_node: local_sync_node,
    			config: config,
    		};

    		Ok(context)
    	}

    	/// Spawns a future using thread pool and schedules execution of it with event loop handle.
    	pub fn spawn<F>(&self, f: F) where F: Future + Send + 'static, F::Item: Send + 'static, F::Error: Send + 'static {
    		let pool_work = self.pool.spawn(f);
    		self.remote.spawn(move |_handle| {
    			pool_work.then(|_| finished(()))
    		})
    	}

    	/// Schedules execution of function in future.
    	/// Use wisely, it keeps used objects in memory until after it is resolved.
    	pub fn execute_after<F>(&self, duration: time::Duration, f: F) where F: FnOnce() + 'static + Send {
    		let pool = self.pool.clone();
    		self.remote.spawn(move |handle| {
    			let timeout = Timeout::new(duration, handle)
    				.expect("Expected to schedule timeout")
    				.then(move |_| {
    					f();
    					finished(())
    				});
    			pool.spawn(timeout)
    		});
    	}

    	/// Returns addresses of recently active nodes. Sorted and limited to 1000.
    	pub fn node_table_entries(&self) -> Vec<Node> {
    		self.node_table.read().recently_active_nodes(self.config.internet_protocol)
    	}

    	/// Updates node table.
    	pub fn update_node_table(&self, nodes: Vec<AddressEntry>) {
    		trace!("Updating node table with {} entries", nodes.len());
    		self.node_table.write().insert_many(nodes);
    	}

    	/// Penalize node.
    	pub fn penalize_node(&self, addr: &SocketAddr) {
    		trace!("Penalizing node {}", addr);
    		self.node_table.write().note_failure(addr);
    	}

    	/// Adds node to table.
    	pub fn add_node(&self, addr: SocketAddr) -> Result<(), NodeTableError> {
    		trace!("Adding node {} to node table", &addr);
    		self.node_table.write().add(addr, self.config.connection.services)
    	}

    	/// Removes node from table.
    	pub fn remove_node(&self, addr: SocketAddr) -> Result<(), NodeTableError> {
    		trace!("Removing node {} from node table", &addr);
    		self.node_table.write().remove(&addr)
    	}

    	/// Every 10 seconds check if we have reached maximum number of outbound connections.
    	/// If not, connect to best peers.
    	pub fn autoconnect(context: Arc<Context>, handle: &Handle) {
    		let c = context.clone();
    		// every 10 seconds connect to new peers (if needed)
    		let interval: BoxedEmptyFuture = Box::new(Interval::new_at(time::Instant::now(), time::Duration::new(10, 0), handle).expect("Failed to create interval")
    			.and_then(move |_| {
    				// print traces
    				let ic = context.connection_counter.inbound_connections();
    				let oc = context.connection_counter.outbound_connections();
    				info!("Inbound connections: ({}/{})", ic.0, ic.1);
    				info!("Outbound connections: ({}/{})", oc.0, oc.1);

    				for channel in context.connections.channels().values() {
    					channel.session().maintain();
    				}

    				let needed = context.connection_counter.outbound_connections_needed() as usize;
    				if needed != 0 {
    					// TODO: pass Services::with_bitcoin_cash(true) after HF block
    					let used_addresses = context.connections.addresses();
    					let peers = context.node_table.read().nodes_with_services(&Services::default(), context.config.internet_protocol, &used_addresses, needed);
    					let addresses = peers.into_iter()
    						.map(|peer| peer.address())
    						.collect::<Vec<_>>();

    					trace!("Creating {} more outbound connections", addresses.len());
    					for address in addresses {
    						Context::connect::<NormalSessionFactory>(context.clone(), address);
    					}
    				}

    				if let Err(_err) = context.node_table.read().save_to_file(&context.config.node_table_path) {
    					error!("Saving node table to disk failed");
    				}

    				Ok(())
    			})
    			.for_each(|_| Ok(()))
    			.then(|_| finished(())));
    		c.spawn(interval);
    	}

    	/// Connect to socket using given context and handle.
    	fn connect_future<T>(context: Arc<Context>, socket: net::SocketAddr, handle: &Handle, config: &NetConfig) -> BoxedEmptyFuture where T: SessionFactory {
    		trace!("Trying to connect to: {}", socket);
    		let connection = connect(&socket, handle, config);
    		Box::new(connection.then(move |result| {
    			match result {
    				Ok(DeadlineStatus::Meet(Ok(connection))) => {
    					// successfull hanshake
    					trace!("Connected to {}", connection.address);
    					context.node_table.write().insert(connection.address, connection.services);
    					let channel = context.connections.store::<T>(context.clone(), connection, Direction::Outbound);

    					// initialize session and then start reading messages
    					channel.session().initialize();
    					Context::on_message(context, channel)
    				},
    				Ok(DeadlineStatus::Meet(Err(_))) => {
    					// protocol error
    					trace!("Handshake with {} failed", socket);
    					// TODO: close socket
    					context.node_table.write().note_failure(&socket);
    					context.connection_counter.note_close_outbound_connection();
    					Box::new(finished(Ok(())))
    				},
    				Ok(DeadlineStatus::Timeout) => {
    					// connection time out
    					trace!("Handshake with {} timed out", socket);
    					// TODO: close socket
    					context.node_table.write().note_failure(&socket);
    					context.connection_counter.note_close_outbound_connection();
    					Box::new(finished(Ok(())))
    				},
    				Err(_) => {
    					// network error
    					trace!("Unable to connect to {}", socket);
    					context.node_table.write().note_failure(&socket);
    					context.connection_counter.note_close_outbound_connection();
    					Box::new(finished(Ok(())))
    				}
    			}
    		})
    		.then(|_| finished(())))
    	}

    	/// Connect to socket using given context.
    	pub fn connect<T>(context: Arc<Context>, socket: net::SocketAddr) where T: SessionFactory {
    		context.connection_counter.note_new_outbound_connection();
    		context.remote.clone().spawn(move |handle| {
    			let config = context.config.clone();
    			context.pool.clone().spawn(Context::connect_future::<T>(context, socket, handle, &config.connection))
    		})
    	}

    	pub fn connect_normal(context: Arc<Context>, socket: net::SocketAddr) {
    		Self::connect::<NormalSessionFactory>(context, socket)
    	}

    	pub fn accept_connection_future(context: Arc<Context>, stream: TcpStream, socket: net::SocketAddr, handle: &Handle, config: NetConfig) -> BoxedEmptyFuture {
    		Box::new(accept_connection(stream, handle, &config, socket).then(move |result| {
    			match result {
    				Ok(DeadlineStatus::Meet(Ok(connection))) => {
    					// successfull hanshake
    					trace!("Accepted connection from {}", connection.address);
    					context.node_table.write().insert(connection.address, connection.services);
    					let channel = context.connections.store::<NormalSessionFactory>(context.clone(), connection, Direction::Inbound);

    					// initialize session and then start reading messages
    					channel.session().initialize();
    					Context::on_message(context.clone(), channel)
    				},
    				Ok(DeadlineStatus::Meet(Err(err))) => {
    					// protocol error
    					trace!("Accepting handshake from {} failed with error: {}", socket, err);
    					// TODO: close socket
    					context.node_table.write().note_failure(&socket);
    					context.connection_counter.note_close_inbound_connection();
    					Box::new(finished(Ok(())))
    				},
    				Ok(DeadlineStatus::Timeout) => {
    					// connection time out
    					trace!("Accepting handshake from {} timed out", socket);
    					// TODO: close socket
    					context.node_table.write().note_failure(&socket);
    					context.connection_counter.note_close_inbound_connection();
    					Box::new(finished(Ok(())))
    				},
    				Err(_) => {
    					// network error
    					trace!("Accepting handshake from {} failed with network error", socket);
    					context.node_table.write().note_failure(&socket);
    					context.connection_counter.note_close_inbound_connection();
    					Box::new(finished(Ok(())))
    				}
    			}
    		})
    		.then(|_| finished(())))
    	}

    	pub fn accept_connection(context: Arc<Context>, stream: TcpStream, socket: net::SocketAddr, config: NetConfig) {
    		context.connection_counter.note_new_inbound_connection();
    		context.remote.clone().spawn(move |handle| {
    			context.pool.clone().spawn(Context::accept_connection_future(context, stream, socket, handle, config))
    		})
    	}

    	/// Starts tcp server and listens for incomming connections.
    	pub fn listen(context: Arc<Context>, handle: &Handle, config: NetConfig) -> Result<BoxedEmptyFuture, io::Error> {
    		trace!("Starting tcp server");
    		let server = try!(TcpListener::bind(&config.local_address, handle));
    		let server = Box::new(server.incoming()
    			.and_then(move |(stream, socket)| {
    				// because we acquire atomic value twice,
    				// it may happen that accept slightly more connections than we need
    				// we don't mind
    				if context.connection_counter.inbound_connections_needed() > 0 {
    					Context::accept_connection(context.clone(), stream, socket, config.clone());
    				} else {
    					// ignore result
    					let _ = stream.shutdown(net::Shutdown::Both);
    				}
    				Ok(())
    			})
    			.for_each(|_| Ok(()))
    			.then(|_| finished(())));
    		Ok(server)
    	}

    	/// Called on incomming mesage.
    	pub fn on_message(context: Arc<Context>, channel: Arc<Channel>) -> IoFuture<MessageResult<()>> {
    		Box::new(channel.read_message().then(move |result| {
    			match result {
    				Ok(Ok((command, payload))) => {
    					// successful read
    					trace!("Received {} message from {}", command, channel.peer_info().address);
    					// handle message and read the next one
    					match channel.session().on_message(command, payload) {
    						Ok(_) => {
    							context.node_table.write().note_used(&channel.peer_info().address);
    							let on_message = Context::on_message(context.clone(), channel);
    							context.spawn(on_message);
    							Box::new(finished(Ok(())))
    						},
    						Err(err) => {
    							// protocol error
    							context.close_channel_with_error(channel.peer_info().id, &err);
    							Box::new(finished(Err(err)))
    						}
    					}
    				},
    				Ok(Err(err)) => {
    					// protocol error
    					context.close_channel_with_error(channel.peer_info().id, &err);
    					Box::new(finished(Err(err)))
    				},
    				Err(err) => {
    					// network error
    					// TODO: remote node was just turned off. should we mark it as not reliable?
    					context.close_channel_with_error(channel.peer_info().id, &err);
    					Box::new(failed(err))
    				}
    			}
    		}))
    	}

    	/// Send message to a channel with given peer id.
    	pub fn send_to_peer<T>(context: Arc<Context>, peer: PeerId, payload: &T, serialization_flags: u32) -> IoFuture<()> where T: Payload {
    		match context.connections.channel(peer) {
    			Some(channel) => {
    				let info = channel.peer_info();
    				let message = Message::with_flags(info.magic, info.version, payload, serialization_flags).expect("failed to create outgoing message");
    				channel.session().stats().lock().report_send(T::command().into(), message.len());
    				Context::send(context, channel, message)
    			},
    			None => {
    				// peer no longer exists.
    				// TODO: should we return error here?
    				Box::new(finished(()))
    			}
    		}
    	}

    	pub fn send_message_to_peer<T>(context: Arc<Context>, peer: PeerId, message: T) -> IoFuture<()> where T: AsRef<[u8]> + Send + 'static {
    		match context.connections.channel(peer) {
    			Some(channel) => Context::send(context, channel, message),
    			None => {
    				// peer no longer exists.
    				// TODO: should we return error here?
    				Box::new(finished(()))
    			}
    		}
    	}

    	/// Send message using given channel.
    	pub fn send<T>(_context: Arc<Context>, channel: Arc<Channel>, message: T) -> IoFuture<()> where T: AsRef<[u8]> + Send + 'static {
    		//trace!("Sending {} message to {}", T::command(), channel.peer_info().address);
    		Box::new(channel.write_message(message).then(move |result| {
    			match result {
    				Ok(_) => {
    					// successful send
    					//trace!("Sent {} message to {}", T::command(), channel.peer_info().address);
    					Box::new(finished(()))
    				},
    				Err(err) => {
    					// network error
    					// closing connection is handled in on_message`
    					Box::new(failed(err))
    				},
    			}
    		}))
    	}

    	/// Close channel with given peer info.
    	pub fn close_channel(&self, id: PeerId) {
    		if let Some(channel) = self.connections.remove(id) {
    			let info = channel.peer_info();
    			channel.session().on_close();
    			trace!("Disconnecting from {}", info.address);
    			channel.shutdown();
    			match info.direction {
    				Direction::Inbound => self.connection_counter.note_close_inbound_connection(),
    				Direction::Outbound => self.connection_counter.note_close_outbound_connection(),
    			}
    		}
    	}

    	/// Close channel with given peer info.
    	pub fn close_channel_with_error(&self, id: PeerId, error: &error::Error) {
    		if let Some(channel) = self.connections.remove(id) {
    			let info = channel.peer_info();
    			channel.session().on_close();
    			trace!("Disconnecting from {} caused by {}", info.address, error.description());
    			channel.shutdown();
    			self.node_table.write().note_failure(&info.address);
    			match info.direction {
    				Direction::Inbound => self.connection_counter.note_close_inbound_connection(),
    				Direction::Outbound => self.connection_counter.note_close_outbound_connection(),
    			}
    		}
    	}

    	pub fn create_sync_session(&self, start_height: i32, services: Services, outbound_connection: OutboundSyncConnectionRef) -> InboundSyncConnectionRef {
    		self.local_sync_node.create_sync_session(start_height, services, outbound_connection)
    	}

    	pub fn connections(&self) -> &Connections {
    		&self.connections
    	}

    	pub fn nodes(&self) -> Vec<Node> {
    		self.node_table.read().nodes()
    	}
    }

    pub struct P2P {
    	/// Global event loop handle.
    	event_loop_handle: Handle,
    	/// Worker thread pool.
    	pool: CpuPool,
    	/// P2P config.
    	config: Config,
    	/// Network context.
    	context: Arc<Context>,
    }

    impl Drop for P2P {
    	fn drop(&mut self) {
    		// there are retain cycles
    		// context->connections->channel->session->protocol->context
    		// context->connections->channel->on_message closure->context
    		// first let's get rid of session retain cycle
    		for channel in &self.context.connections.remove_all() {
    			// done, now let's finish on_message
    			channel.shutdown();
    		}
    	}
    }

    impl P2P {
    	pub fn new(config: Config, local_sync_node: LocalSyncNodeRef, handle: Handle) -> Result<Self, Box<error::Error>> {
    		let pool = CpuPool::new(config.threads);

    		let context = try!(Context::new(local_sync_node, pool.clone(), handle.remote().clone(), config.clone()));

    		let p2p = P2P {
    			event_loop_handle: handle.clone(),
    			pool: pool,
    			context: Arc::new(context),
    			config: config,
    		};

    		Ok(p2p)
    	}

    	pub fn run(&self) -> Result<(), Box<error::Error>> {
    		for peer in &self.config.peers {
    			self.connect::<NormalSessionFactory>(*peer);
    		}

    		let resolver = try!(DnsResolver::system_config(&self.event_loop_handle));
    		for seed in &self.config.seeds {
    			self.connect_to_seednode(&resolver, seed);
    		}

    		Context::autoconnect(self.context.clone(), &self.event_loop_handle);
    		try!(self.listen());
    		Ok(())
    	}

    	/// Attempts to connect to the specified node
    	pub fn connect<T>(&self, addr: net::SocketAddr) where T: SessionFactory {
    		Context::connect::<T>(self.context.clone(), addr);
    	}

    	pub fn connect_to_seednode(&self, resolver: &Resolver, seednode: &str) {
    		let owned_seednode = seednode.to_owned();
    		let context = self.context.clone();
    		let dns_lookup = resolver.resolve(seednode).then(move |result| {
    			match result {
    				Ok(address) => match address.pick_one() {
    					Some(socket) => {
    						trace!("Dns lookup of seednode {} finished. Connecting to {}", owned_seednode, socket);
    						Context::connect::<SeednodeSessionFactory>(context, socket);
    					},
    					None => {
    						trace!("Dns lookup of seednode {} resolved with no results", owned_seednode);
    					}
    				},
    				Err(_err) => {
    					trace!("Dns lookup of seednode {} failed", owned_seednode);
    				}
    			}
    			finished(())
    		});
    		let pool_work = self.pool.spawn(dns_lookup);
    		self.event_loop_handle.spawn(pool_work);
    	}

    	fn listen(&self) -> Result<(), Box<error::Error>> {
    		let server = try!(Context::listen(self.context.clone(), &self.event_loop_handle, self.config.connection.clone()));
    		self.event_loop_handle.spawn(server);
    		Ok(())
    	}

    	pub fn context(&self) -> &Arc<Context> {
    		&self.context
    	}
    }

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