use std::io;

use quiche::h3::webtransport;

use super::app;
use super::connection;

const MAX_DATAGRAM_SIZE: usize = 1350;

pub struct Server<T: app::App> {
	// IO stuff
	socket: mio::net::UdpSocket,
	poll: mio::Poll,
	events: mio::Events,

	// QUIC stuff
	quic: quiche::Config,
	seed: ring::hmac::Key, // connection ID seed

	conns: connection::Map<T>,
}

pub struct Config {
	pub addr: String,
	pub cert: String,
	pub key: String,
}

impl<T: app::App> Server<T> {
	pub fn new(config: Config) -> io::Result<Self> {
		// Listen on the provided socket address
		let addr = config.addr.parse().unwrap();
		let mut socket = mio::net::UdpSocket::bind(addr).unwrap();

		// Setup the event loop.
		let poll = mio::Poll::new().unwrap();
		let events = mio::Events::with_capacity(1024);

		poll.registry()
			.register(&mut socket, mio::Token(0), mio::Interest::READABLE)
			.unwrap();

		// Generate random values for connection IDs.
		let rng = ring::rand::SystemRandom::new();
		let seed = ring::hmac::Key::generate(ring::hmac::HMAC_SHA256, &rng).unwrap();

		// Create the configuration for the QUIC conns.
		let mut quic = quiche::Config::new(quiche::PROTOCOL_VERSION).unwrap();
		quic.load_cert_chain_from_pem_file(&config.cert).unwrap();
		quic.load_priv_key_from_pem_file(&config.key).unwrap();
		quic.set_application_protos(quiche::h3::APPLICATION_PROTOCOL).unwrap();
		quic.set_max_idle_timeout(5000);
		quic.set_max_recv_udp_payload_size(MAX_DATAGRAM_SIZE);
		quic.set_max_send_udp_payload_size(MAX_DATAGRAM_SIZE);
		quic.set_initial_max_data(10_000_000);
		quic.set_initial_max_stream_data_bidi_local(1_000_000);
		quic.set_initial_max_stream_data_bidi_remote(1_000_000);
		quic.set_initial_max_stream_data_uni(1_000_000);
		quic.set_initial_max_streams_bidi(100);
		quic.set_initial_max_streams_uni(100);
		quic.set_disable_active_migration(true);
		quic.enable_early_data();
		quic.enable_dgram(true, 65536, 65536);

		let conns = Default::default();

		Ok(Server {
			socket,
			poll,
			events,

			quic,
			seed,

			conns,
		})
	}

	pub fn run(&mut self) -> anyhow::Result<()> {
		log::info!("listening on {}", self.socket.local_addr()?);

		loop {
			self.wait()?;
			self.receive()?;
			self.app()?;
			self.send()?;
			self.cleanup();
		}
	}

	pub fn wait(&mut self) -> anyhow::Result<()> {
		// Find the shorter timeout from all the active connections.
		//
		// TODO: use event loop that properly supports timers
		let timeout = self
			.conns
			.values()
			.filter_map(|c| {
				let timeout = c.quiche.timeout();
				let expires = c.app.timeout();

				match (timeout, expires) {
					(Some(a), Some(b)) => Some(a.min(b)),
					(Some(a), None) => Some(a),
					(None, Some(b)) => Some(b),
					(None, None) => None,
				}
			})
			.min();

		self.poll.poll(&mut self.events, timeout).unwrap();

		// If the event loop reported no events, it means that the timeout
		// has expired, so handle it without attempting to read packets. We
		// will then proceed with the send loop.
		if self.events.is_empty() {
			for conn in self.conns.values_mut() {
				conn.quiche.on_timeout();
			}
		}

		Ok(())
	}

	// Reads packets from the socket, updating any internal connection state.
	fn receive(&mut self) -> anyhow::Result<()> {
		let mut src = [0; MAX_DATAGRAM_SIZE];

		// Try reading any data currently available on the socket.
		loop {
			let (len, from) = match self.socket.recv_from(&mut src) {
				Ok(v) => v,
				Err(e) if e.kind() == std::io::ErrorKind::WouldBlock => return Ok(()),
				Err(e) => return Err(e.into()),
			};

			let src = &mut src[..len];

			let info = quiche::RecvInfo {
				to: self.socket.local_addr().unwrap(),
				from,
			};

			// Parse the QUIC packet's header.
			let hdr = quiche::Header::from_slice(src, quiche::MAX_CONN_ID_LEN).unwrap();

			let conn_id = ring::hmac::sign(&self.seed, &hdr.dcid);
			let conn_id = &conn_id.as_ref()[..quiche::MAX_CONN_ID_LEN];
			let conn_id = conn_id.to_vec().into();

			// Check if it's an existing connection.
			if let Some(conn) = self.conns.get_mut(&hdr.dcid) {
				conn.quiche.recv(src, info)?;

				if conn.session.is_none() && conn.quiche.is_established() {
					conn.session = Some(webtransport::ServerSession::with_transport(&mut conn.quiche)?)
				}

				continue;
			} else if let Some(conn) = self.conns.get_mut(&conn_id) {
				conn.quiche.recv(src, info)?;

				// TODO is this needed here?
				if conn.session.is_none() && conn.quiche.is_established() {
					conn.session = Some(webtransport::ServerSession::with_transport(&mut conn.quiche)?)
				}

				continue;
			}

			if hdr.ty != quiche::Type::Initial {
				log::warn!("unknown connection ID");
				continue;
			}

			let mut dst = [0; MAX_DATAGRAM_SIZE];

			if !quiche::version_is_supported(hdr.version) {
				let len = quiche::negotiate_version(&hdr.scid, &hdr.dcid, &mut dst).unwrap();
				let dst = &dst[..len];

				self.socket.send_to(dst, from).unwrap();
				continue;
			}

			let mut scid = [0; quiche::MAX_CONN_ID_LEN];
			scid.copy_from_slice(&conn_id);

			let scid = quiche::ConnectionId::from_ref(&scid);

			// Token is always present in Initial packets.
			let token = hdr.token.as_ref().unwrap();

			// Do stateless retry if the client didn't send a token.
			if token.is_empty() {
				let new_token = mint_token(&hdr, &from);

				let len = quiche::retry(&hdr.scid, &hdr.dcid, &scid, &new_token, hdr.version, &mut dst).unwrap();

				let dst = &dst[..len];

				self.socket.send_to(dst, from).unwrap();
				continue;
			}

			let odcid = validate_token(&from, token);

			// The token was not valid, meaning the retry failed, so
			// drop the packet.
			if odcid.is_none() {
				log::warn!("invalid token");
				continue;
			}

			if scid.len() != hdr.dcid.len() {
				log::warn!("invalid connection ID");
				continue;
			}

			// Reuse the source connection ID we sent in the Retry packet,
			// instead of changing it again.
			let conn_id = hdr.dcid.clone();
			let local_addr = self.socket.local_addr().unwrap();

			log::debug!("new connection: dcid={:?} scid={:?}", hdr.dcid, scid);

			let mut conn = quiche::accept(&conn_id, odcid.as_ref(), local_addr, from, &mut self.quic)?;

			// Log each session with QLOG if the ENV var is set.
			if let Some(dir) = std::env::var_os("QLOGDIR") {
				let id = format!("{:?}", &scid);

				let mut path = std::path::PathBuf::from(dir);
				let filename = format!("server-{id}.sqlog");
				path.push(filename);

				let writer = match std::fs::File::create(&path) {
					Ok(f) => std::io::BufWriter::new(f),

					Err(e) => panic!("Error creating qlog file attempted path was {:?}: {}", path, e),
				};

				conn.set_qlog(
					std::boxed::Box::new(writer),
					"warp-server qlog".to_string(),
					format!("{} id={}", "warp-server qlog", id),
				);
			}

			// Process potentially coalesced packets.
			conn.recv(src, info)?;

			let user = connection::Connection {
				quiche: conn,
				session: None,
				app: T::default(),
			};

			self.conns.insert(conn_id, user);
		}
	}

	pub fn app(&mut self) -> anyhow::Result<()> {
		for conn in self.conns.values_mut() {
			if conn.quiche.is_closed() {
				continue;
			}

			if let Some(session) = &mut conn.session {
				if let Err(e) = conn.app.poll(&mut conn.quiche, session) {
					log::debug!("app error: {:?}", e);

					// Close the connection on any application error
					let reason = format!("app error: {:?}", e);
					conn.quiche.close(true, 0xff, reason.as_bytes()).ok();
				}
			}
		}

		Ok(())
	}

	// Generate outgoing QUIC packets for all active connections and send
	// them on the UDP socket, until quiche reports that there are no more
	// packets to be sent.
	pub fn send(&mut self) -> anyhow::Result<()> {
		for conn in self.conns.values_mut() {
			let conn = &mut conn.quiche;

			if let Err(e) = send_conn(&self.socket, conn) {
				log::error!("{} send failed: {:?}", conn.trace_id(), e);
				conn.close(false, 0x1, b"fail").ok();
			}
		}

		Ok(())
	}

	pub fn cleanup(&mut self) {
		// Garbage collect closed connections.
		self.conns.retain(|_, ref mut c| !c.quiche.is_closed());
	}
}

// Send any pending packets for the connection over the socket.
fn send_conn(socket: &mio::net::UdpSocket, conn: &mut quiche::Connection) -> anyhow::Result<()> {
	let mut pkt = [0; MAX_DATAGRAM_SIZE];

	loop {
		let (size, info) = match conn.send(&mut pkt) {
			Ok(v) => v,
			Err(quiche::Error::Done) => return Ok(()),
			Err(e) => return Err(e.into()),
		};

		let pkt = &pkt[..size];

		match socket.send_to(pkt, info.to) {
			Err(e) if e.kind() == io::ErrorKind::WouldBlock => return Ok(()),
			Err(e) => return Err(e.into()),
			Ok(_) => (),
		}
	}
}

/// Generate a stateless retry token.
///
/// The token includes the static string `"quiche"` followed by the IP address
/// of the client and by the original destination connection ID generated by the
/// client.
///
/// Note that this function is only an example and doesn't do any cryptographic
/// authenticate of the token. *It should not be used in production system*.
fn mint_token(hdr: &quiche::Header, src: &std::net::SocketAddr) -> Vec<u8> {
	let mut token = Vec::new();

	token.extend_from_slice(b"quiche");

	let addr = match src.ip() {
		std::net::IpAddr::V4(a) => a.octets().to_vec(),
		std::net::IpAddr::V6(a) => a.octets().to_vec(),
	};

	token.extend_from_slice(&addr);
	token.extend_from_slice(&hdr.dcid);

	token
}

/// Validates a stateless retry token.
///
/// This checks that the ticket includes the `"quiche"` static string, and that
/// the client IP address matches the address stored in the ticket.
///
/// Note that this function is only an example and doesn't do any cryptographic
/// authenticate of the token. *It should not be used in production system*.
fn validate_token<'a>(src: &std::net::SocketAddr, token: &'a [u8]) -> Option<quiche::ConnectionId<'a>> {
	if token.len() < 6 {
		return None;
	}

	if &token[..6] != b"quiche" {
		return None;
	}

	let token = &token[6..];

	let addr = match src.ip() {
		std::net::IpAddr::V4(a) => a.octets().to_vec(),
		std::net::IpAddr::V6(a) => a.octets().to_vec(),
	};

	if token.len() < addr.len() || &token[..addr.len()] != addr.as_slice() {
		return None;
	}

	Some(quiche::ConnectionId::from_ref(&token[addr.len()..]))
}