use std::any::Any;
use std::collections::HashMap;
use std::net::SocketAddr;
use std::pin::Pin;
use std::sync::{Arc, RwLock};

use std::future::Future;

use log::{debug, info};

use arc_swap::{ArcSwap, ArcSwapOption};
use bytes::Bytes;

use sodiumoxide::crypto::auth;
use sodiumoxide::crypto::sign::ed25519;
use tokio::net::{TcpListener, TcpStream};

use crate::conn::*;
use crate::error::*;
use crate::message::*;
use crate::proto::*;
use crate::util::*;

type DynMsg = Box<dyn Any + Send + Sync + 'static>;

pub(crate) struct Handler {
	pub(crate) local_handler:
		Box<dyn Fn(DynMsg) -> Pin<Box<dyn Future<Output = DynMsg> + Sync + Send>> + Sync + Send>,
	pub(crate) net_handler: Box<
		dyn Fn(ed25519::PublicKey, Bytes) -> Pin<Box<dyn Future<Output = Vec<u8>> + Sync + Send>>
			+ Sync
			+ Send,
	>,
}

/// NetApp is the main class that handles incoming and outgoing connections.
///
/// The `request()` method can be used to send a message to any peer to which we have
/// an outgoing connection, or to ourself. On the server side, these messages are
/// processed by the handlers that have been defined using `add_msg_handler()`.
///
///	NetApp can be used in a stand-alone fashion or together with a peering strategy.
///	If using it alone, you will want to set `on_connect` and `on_disconnect` events
///	in order to manage information about the current peer list.
///
/// It is generally not necessary to use NetApp stand-alone, as the provided full mesh
/// and RPS peering strategies take care of the most common use cases.
pub struct NetApp {
	pub listen_addr: SocketAddr,
	pub netid: auth::Key,
	pub pubkey: ed25519::PublicKey,
	pub privkey: ed25519::SecretKey,

	server_conns: RwLock<HashMap<ed25519::PublicKey, Arc<ServerConn>>>,
	client_conns: RwLock<HashMap<ed25519::PublicKey, Arc<ClientConn>>>,
	
	pub(crate) msg_handlers: ArcSwap<HashMap<MessageKind, Arc<Handler>>>,
	on_connected_handler:
		ArcSwapOption<Box<dyn Fn(ed25519::PublicKey, SocketAddr, bool) + Send + Sync>>,
	on_disconnected_handler: ArcSwapOption<Box<dyn Fn(ed25519::PublicKey, bool) + Send + Sync>>,
}

async fn net_handler_aux<M, F, R>(
	handler: Arc<F>,
	remote: ed25519::PublicKey,
	bytes: Bytes,
) -> Vec<u8>
where
	M: Message + 'static,
	F: Fn(ed25519::PublicKey, M) -> R + Send + Sync + 'static,
	R: Future<Output = <M as Message>::Response> + Send + Sync,
{
	debug!(
		"Handling message of kind {:08x} from {}",
		M::KIND,
		hex::encode(remote)
	);
	let res = match rmp_serde::decode::from_read_ref::<_, M>(&bytes[..]) {
		Ok(msg) => Ok(handler(remote, msg).await),
		Err(e) => Err(e.to_string()),
	};
	rmp_to_vec_all_named(&res).unwrap_or(vec![])
}

async fn local_handler_aux<M, F, R>(
	handler: Arc<F>,
	remote: ed25519::PublicKey,
	msg: DynMsg,
) -> DynMsg
where
	M: Message + 'static,
	F: Fn(ed25519::PublicKey, M) -> R + Send + Sync + 'static,
	R: Future<Output = <M as Message>::Response> + Send + Sync,
{
	debug!("Handling message of kind {:08x} from ourself", M::KIND);
	let msg = (msg as Box<dyn Any + 'static>).downcast::<M>().unwrap();
	let res = handler(remote, *msg).await;
	Box::new(res)
}

impl NetApp {
	/// Creates a new instance of NetApp. No background process is
	pub fn new(
		listen_addr: SocketAddr,
		netid: auth::Key,
		privkey: ed25519::SecretKey,
	) -> Arc<Self> {
		let pubkey = privkey.public_key();
		let netapp = Arc::new(Self {
			listen_addr,
			netid,
			pubkey,
			privkey,
			server_conns: RwLock::new(HashMap::new()),
			client_conns: RwLock::new(HashMap::new()),
			msg_handlers: ArcSwap::new(Arc::new(HashMap::new())),
			on_connected_handler: ArcSwapOption::new(None),
			on_disconnected_handler: ArcSwapOption::new(None),
		});

		let netapp2 = netapp.clone();
		netapp.add_msg_handler::<HelloMessage, _, _>(
			move |from: ed25519::PublicKey, msg: HelloMessage| {
				netapp2.handle_hello_message(from, msg);
				async { () }
			},
		);

		netapp
	}

	/// Set the handler to be called when a new connection (incoming or outgoing) has
	/// been successfully established. Do not set this if using a peering strategy,
	/// as the peering strategy will need to set this itself.
	pub fn on_connected<F>(&self, handler: F)
		where F: Fn(ed25519::PublicKey, SocketAddr, bool) + Sized + Send + Sync + 'static
		{
		self.on_connected_handler.store(Some(Arc::new(Box::new(handler))));
	}

	/// Set the handler to be called when an existing connection (incoming or outgoing) has
	/// been closed by either party. Do not set this if using a peering strategy,
	/// as the peering strategy will need to set this itself.
	pub fn on_disconnected<F>(&self, handler: F)
		where F: Fn(ed25519::PublicKey, bool) + Sized + Send + Sync + 'static
		{
		self.on_disconnected_handler.store(Some(Arc::new(Box::new(handler))));
	}

	/// Add a handler for a certain message type. Note that only one handler
	/// can be specified for each message type.
	pub fn add_msg_handler<M, F, R>(&self, handler: F)
	where
		M: Message + 'static,
		F: Fn(ed25519::PublicKey, M) -> R + Send + Sync + 'static,
		R: Future<Output = <M as Message>::Response> + Send + Sync + 'static,
	{
		let handler = Arc::new(handler);

		let handler2 = handler.clone();
		let net_handler = Box::new(move |remote: ed25519::PublicKey, bytes: Bytes| {
			let fun: Pin<Box<dyn Future<Output = Vec<u8>> + Sync + Send>> =
				Box::pin(net_handler_aux(handler2.clone(), remote, bytes));
			fun
		});

		let self_id = self.pubkey.clone();
		let local_handler = Box::new(move |msg: DynMsg| {
			let fun: Pin<Box<dyn Future<Output = DynMsg> + Sync + Send>> =
				Box::pin(local_handler_aux(handler.clone(), self_id, msg));
			fun
		});

		let funs = Arc::new(Handler {
			net_handler,
			local_handler,
		});

		let mut handlers = self.msg_handlers.load().as_ref().clone();
		handlers.insert(M::KIND, funs);
		self.msg_handlers.store(Arc::new(handlers));
	}

	/// Main listening process for our app. This future runs during the whole
	/// run time of our application.
	pub async fn listen(self: Arc<Self>) {
		let mut listener = TcpListener::bind(self.listen_addr).await.unwrap();
		info!("Listening on {}", self.listen_addr);

		loop {
			// The second item contains the IP and port of the new connection.
			let (socket, _) = listener.accept().await.unwrap();
			info!(
				"Incoming connection from {}, negotiating handshake...",
				socket.peer_addr().unwrap()
			);
			let self2 = self.clone();
			tokio::spawn(async move {
				ServerConn::run(self2, socket)
					.await
					.log_err("ServerConn::run");
			});
		}
	}

	/// Attempt to connect to a peer, given by its ip:port and its public key.
	/// The public key will be checked during the secret handshake process.
	/// This function returns once the connection has been established and a
	/// successfull handshake was made. At this point we can send messages to
	/// the other node with `Netapp::request`
	pub async fn try_connect(
		self: Arc<Self>,
		ip: SocketAddr,
		pk: ed25519::PublicKey,
	) -> Result<(), Error> {
		// Don't connect to ourself, we don't care
		// but pretend we did
		if pk == self.pubkey {
			tokio::spawn(async move {
				if let Some(h) = self.on_connected_handler.load().as_ref() {
					h(pk, ip, false);
				}
			});
			return Ok(());
		}

		// Don't connect if already connected
		if self.client_conns.read().unwrap().contains_key(&pk) {
			return Ok(());
		}

		let socket = TcpStream::connect(ip).await?;
		info!("Connected to {}, negotiating handshake...", ip);
		ClientConn::init(self, socket, pk.clone()).await?;
		Ok(())
	}

	/// Close the outgoing connection we have to a node specified by its public key,
	/// if such a connection is currently open.
	pub fn disconnect(self: &Arc<Self>, pk: &ed25519::PublicKey) {
		// If pk is ourself, we're not supposed to have a connection open
		if *pk != self.pubkey {
			let conn = self.client_conns.read().unwrap().remove(pk);
			if let Some(c) = conn {
				debug!("Closing connection to {} ({})",
					   hex::encode(c.peer_pk),
					   c.remote_addr);
				c.close();
			} else {
				return;
			}
		}

		// call on_disconnected_handler immediately, since the connection
		// was removed
		// (if pk == self.pubkey, we pretend we disconnected)
		let pk = *pk;
		let self2 = self.clone();
		tokio::spawn(async move {
			if let Some(h) = self2.on_disconnected_handler.load().as_ref() {
				h(pk, false);
			}
		});
	}

	/// Close the incoming connection from a certain client to us,
	/// if such a connection is currently open.
	pub fn server_disconnect(self: &Arc<Self>, pk: &ed25519::PublicKey) {
		let conn = self.server_conns.read().unwrap().get(pk).cloned();
		if let Some(c) = conn {
			debug!("Closing incoming connection from {} ({})",
				   hex::encode(c.peer_pk),
				   c.remote_addr);
			c.close();
		}
	}

	// Called from conn.rs when an incoming connection is successfully established
	// Registers the connection in our list of connections
	// Do not yet call the on_connected handler, because we don't know if the remote
	// has an actual IP address and port we can call them back on.
	// We will know this when they send a Hello message, which is handled below.
	pub(crate) fn connected_as_server(&self, id: ed25519::PublicKey, conn: Arc<ServerConn>) {
		info!("Accepted connection from {}", hex::encode(id));

		let mut conn_list = self.server_conns.write().unwrap();
		conn_list.insert(id.clone(), conn);
	}

	// Handle hello message from a client. This message is used for them to tell us
	// that they are listening on a certain port number on which we can call them back.
	// At this point we know they are a full network member, and not just a client,
	// and we call the on_connected handler so that the peering strategy knows
	// we have a new potential peer
	fn handle_hello_message(&self, id: ed25519::PublicKey, msg: HelloMessage) {
		if let Some(h) = self.on_connected_handler.load().as_ref() {
			if let Some(c) = self.server_conns.read().unwrap().get(&id) {
				let remote_addr = SocketAddr::new(c.remote_addr.ip(), msg.server_port);
				h(id, remote_addr, true);
			}
		}
	}

	// Called from conn.rs when an incoming connection is closed.
	// We deregister the connection from server_conns and call the
	// handler registered by on_disconnected
	pub(crate) fn disconnected_as_server(&self, id: &ed25519::PublicKey, conn: Arc<ServerConn>) {
		info!("Connection from {} closed", hex::encode(id));

		let mut conn_list = self.server_conns.write().unwrap();
		if let Some(c) = conn_list.get(id) {
			if Arc::ptr_eq(c, &conn) {
				conn_list.remove(id);
			}

			if let Some(h) = self.on_disconnected_handler.load().as_ref() {
				h(conn.peer_pk, true);
			}
		}
	}

	// Called from conn.rs when an outgoinc connection is successfully established.
	// The connection is registered in self.client_conns, and the
	// on_connected handler is called.
	//
	// Since we are ourself listening, we send them a Hello message so that
	// they know on which port to call us back. (TODO: don't do this if we are
	// just a simple client and not a full p2p node)
	pub(crate) fn connected_as_client(&self, id: ed25519::PublicKey, conn: Arc<ClientConn>) {
		info!("Connection established to {}", hex::encode(id));

		{
			let mut conn_list = self.client_conns.write().unwrap();
			if let Some(old_c) = conn_list.insert(id.clone(), conn.clone()) {
				tokio::spawn(async move { old_c.close() });
			}
		}

		if let Some(h) = self.on_connected_handler.load().as_ref() {
			h(conn.peer_pk, conn.remote_addr, false);
		}

		let server_port = self.listen_addr.port();
		tokio::spawn(async move {
			conn.request(HelloMessage { server_port }, PRIO_NORMAL)
				.await
				.log_err("Sending hello message");
		});
	}

	// Called from conn.rs when an outgoinc connection is closed.
	// The connection is removed from conn_list, and the on_disconnected handler
	// is called.
	pub(crate) fn disconnected_as_client(&self, id: &ed25519::PublicKey, conn: Arc<ClientConn>) {
		info!("Connection to {} closed", hex::encode(id));
		let mut conn_list = self.client_conns.write().unwrap();
		if let Some(c) = conn_list.get(id) {
			if Arc::ptr_eq(c, &conn) {
				conn_list.remove(id);

				if let Some(h) = self.on_disconnected_handler.load().as_ref() {
					h(conn.peer_pk, false);
				}
			}
		}
		// else case: happens if connection was removed in .disconnect()
		// in which case on_disconnected_handler was already called
	}

	/// Send a message to a remote host to which a client connection is already
	/// established, and await their response. The target is the id of the peer we
	/// want to send the message to.
	/// The priority is an `u8`, with lower numbers meaning highest priority.
	pub async fn request<T>(
		&self,
		target: &ed25519::PublicKey,
		rq: T,
		prio: RequestPriority,
	) -> Result<<T as Message>::Response, Error>
	where
		T: Message + 'static,
	{
		if *target == self.pubkey {
			let handler = self.msg_handlers.load().get(&T::KIND).cloned();
			match handler {
				None => Err(Error::Message(format!(
					"No handler registered for message kind {:08x}",
					T::KIND
				))),
				Some(h) => {
					let local_handler = &h.local_handler;
					let res = local_handler(Box::new(rq)).await;
					let res_t = (res as Box<dyn Any + 'static>)
						.downcast::<<T as Message>::Response>()
						.unwrap();
					Ok(*res_t)
				}
			}
		} else {
			let conn = self.client_conns.read().unwrap().get(target).cloned();
			match conn {
				None => Err(Error::Message(format!(
					"Not connected: {}",
					hex::encode(target)
				))),
				Some(c) => c.request(rq, prio).await,
			}
		}
	}
}