use std::collections::HashMap;
use std::net::SocketAddr;
use std::sync::{Arc, Mutex};

use arc_swap::ArcSwapOption;
use async_trait::async_trait;
use log::*;

use futures::io::{AsyncReadExt, AsyncWriteExt};
use kuska_handshake::async_std::{handshake_server, BoxStream};
use tokio::net::TcpStream;
use tokio::select;
use tokio::sync::{mpsc, watch};
use tokio_util::compat::*;

#[cfg(feature = "telemetry")]
use opentelemetry::{
	trace::{FutureExt, Span, SpanKind, TraceContextExt, TraceId, Tracer},
	Context, KeyValue,
};
#[cfg(feature = "telemetry")]
use opentelemetry_contrib::trace::propagator::binary::*;
#[cfg(feature = "telemetry")]
use rand::{thread_rng, Rng};

use crate::error::*;
use crate::message::*;
use crate::netapp::*;
use crate::recv::*;
use crate::send::*;
use crate::stream::*;
use crate::util::*;

// The client and server connection structs (client.rs and server.rs)
// build upon the chunking mechanism which is exclusively contained
// in proto.rs.
// Here, we just care about sending big messages without size limit.
// The format of these messages is described below.
// Chunking happens independently.

// Request message format (client -> server):
// - u8 priority
// - u8 path length
// - [u8; path length] path
// - [u8; *] data

// Response message format (server -> client):
// - u8 response code
// - [u8; *] response

pub(crate) struct ServerConn {
	pub(crate) remote_addr: SocketAddr,
	pub(crate) peer_id: NodeID,

	netapp: Arc<NetApp>,

	resp_send: ArcSwapOption<mpsc::UnboundedSender<SendItem>>,
	running_handlers: Mutex<HashMap<RequestID, tokio::task::JoinHandle<()>>>,
}

impl ServerConn {
	pub(crate) async fn run(
		netapp: Arc<NetApp>,
		socket: TcpStream,
		must_exit: watch::Receiver<bool>,
	) -> Result<(), Error> {
		let remote_addr = socket.peer_addr()?;
		let mut socket = socket.compat();

		// Do handshake to authenticate client
		let handshake = handshake_server(
			&mut socket,
			netapp.netid.clone(),
			netapp.id,
			netapp.privkey.clone(),
		)
		.await?;
		let peer_id = handshake.peer_pk;

		debug!(
			"Handshake complete (server) with {}@{}",
			hex::encode(&peer_id),
			remote_addr
		);

		// Create BoxStream layer that encodes content
		let (read, write) = socket.split();
		let (read, mut write) =
			BoxStream::from_handshake(read, write, handshake, 0x8000).split_read_write();

		// Before doing anything, send version tag, so that client
		// can check and disconnect if version is wrong
		write.write_all(&netapp.version_tag[..]).await?;
		write.flush().await?;

		// Build and launch stuff that handles requests server-side
		let (resp_send, resp_recv) = mpsc::unbounded_channel();

		let conn = Arc::new(ServerConn {
			netapp: netapp.clone(),
			remote_addr,
			peer_id,
			resp_send: ArcSwapOption::new(Some(Arc::new(resp_send))),
			running_handlers: Mutex::new(HashMap::new()),
		});

		netapp.connected_as_server(peer_id, conn.clone());

		let debug_name = format!("SRV {}", hex::encode(&peer_id[..8]));
		let debug_name_2 = debug_name.clone();

		let conn2 = conn.clone();
		let recv_future = tokio::spawn(async move {
			select! {
				r = conn2.recv_loop(read, debug_name_2) => r,
				_ = await_exit(must_exit) => Ok(())
			}
		});
		let send_future = tokio::spawn(conn.clone().send_loop(resp_recv, write, debug_name));

		recv_future.await.log_err("ServerConn recv_loop");
		conn.resp_send.store(None);
		send_future.await.log_err("ServerConn send_loop");

		netapp.disconnected_as_server(&peer_id, conn);

		Ok(())
	}

	async fn recv_handler_aux(self: &Arc<Self>, req_enc: ReqEnc) -> Result<RespEnc, Error> {
		let path = String::from_utf8(req_enc.path.to_vec())?;

		let handler_opt = {
			let endpoints = self.netapp.endpoints.read().unwrap();
			endpoints.get(&path).map(|e| e.clone_endpoint())
		};

		if let Some(handler) = handler_opt {
			cfg_if::cfg_if! {
				if #[cfg(feature = "telemetry")] {
					let tracer = opentelemetry::global::tracer("netapp");

					let mut span = if !req_enc.telemetry_id.is_empty() {
						let propagator = BinaryPropagator::new();
						let context = propagator.from_bytes(req_enc.telemetry_id.to_vec());
						let context = Context::new().with_remote_span_context(context);
						tracer.span_builder(format!(">> RPC {}", path))
							.with_kind(SpanKind::Server)
							.start_with_context(&tracer, &context)
					} else {
						let mut rng = thread_rng();
						let trace_id = TraceId::from_bytes(rng.gen());
						tracer
							.span_builder(format!(">> RPC {}", path))
							.with_kind(SpanKind::Server)
							.with_trace_id(trace_id)
							.start(&tracer)
					};
					span.set_attribute(KeyValue::new("path", path.to_string()));
					span.set_attribute(KeyValue::new("len_query_msg", req_enc.msg.len() as i64));

					handler.handle(req_enc, self.peer_id)
						.with_context(Context::current_with_span(span))
						.await
				} else {
					handler.handle(req_enc, self.peer_id).await
				}
			}
		} else {
			Err(Error::NoHandler)
		}
	}
}

impl SendLoop for ServerConn {}

#[async_trait]
impl RecvLoop for ServerConn {
	fn recv_handler(self: &Arc<Self>, id: RequestID, stream: ByteStream) {
		let resp_send = match self.resp_send.load_full() {
			Some(c) => c,
			None => return,
		};

		let mut rh = self.running_handlers.lock().unwrap();

		let self2 = self.clone();
		let jh = tokio::spawn(async move {
			debug!("server: recv_handler got {}", id);

			let (prio, resp_enc_result) = match ReqEnc::decode(stream).await {
				Ok(req_enc) => (req_enc.prio, self2.recv_handler_aux(req_enc).await),
				Err(e) => (PRIO_HIGH, Err(e)),
			};

			debug!("server: sending response to {}", id);

			let (resp_stream, resp_order) = RespEnc::encode(resp_enc_result);
			resp_send
				.send(SendItem::Stream(id, prio, resp_order, resp_stream))
				.log_err("ServerConn recv_handler send resp bytes");

			self2.running_handlers.lock().unwrap().remove(&id);
		});

		rh.insert(id, jh);
	}

	fn cancel_handler(self: &Arc<Self>, id: RequestID) {
		trace!("received cancel for request {}", id);

		// If the handler is still running, abort it now
		if let Some(jh) = self.running_handlers.lock().unwrap().remove(&id) {
			jh.abort();
		}

		// Inform the response sender that we don't need to send the response
		if let Some(resp_send) = self.resp_send.load_full() {
			let _ = resp_send.send(SendItem::Cancel(id));
		}
	}
}