use tokio::{
	net::TcpListener,
	sync::watch,
	task::JoinHandle,
};

use crate::prelude::*;

pub struct ForwardingInstance {
	task: JoinHandle <anyhow::Result <()>>,
	shutdown_flag: watch::Sender <bool>,
	local_port: u16,
}

impl ForwardingInstance {
	pub async fn new (
		connection_p2_p3: quinn::Connection,
		params: ForwardingParams,
	) -> anyhow::Result <Self>
	{
		let (shutdown_flag, shutdown_flag_rx) = tokio::sync::watch::channel (true);
		
		let listener = TcpListener::bind (("127.0.0.1", params.client_tcp_port)).await?;
		let local_port = listener.local_addr ()?.port ();
		trace! ("Accepting local TCP connections from P1 on {}", local_port);
		
		let task = tokio::spawn (forward_port (
			listener,
			connection_p2_p3,
			params,
			shutdown_flag_rx
		));
		
		Ok (Self {
			task,
			shutdown_flag,
			local_port,
		})
	}
	
	pub async fn close (self) -> anyhow::Result <()> {
		if self.shutdown_flag.send (false).is_err () {
			warn! ("Trying to gracefully shutdown forwarding task but it appears to already be shut down");
		}
		self.task.await
		.context ("awaiting ForwardingInstance task")?
		.context ("inside ForwardingInstance task")?;
		Ok (())
	}
	
	pub fn local_port (&self) -> u16 {
		self.local_port
	}
}

pub struct ForwardingParams {
	pub client_tcp_port: u16,
	pub server_id: String,
	pub server_tcp_port: u16,
}

/// Starts a TCP listener that can forward any number of TCP streams to
/// the same client:server port combination

pub async fn forward_port (
	listener: TcpListener,
	connection_p2_p3: quinn::Connection,
	params: ForwardingParams,
	mut shutdown_flag_rx: tokio::sync::watch::Receiver <bool>,
) -> anyhow::Result <()>
{
	let ForwardingParams {
		server_id,
		server_tcp_port,
		..
	} = params;
	
	while *shutdown_flag_rx.borrow () {
		tokio::select! {
			x = listener.accept () => {
				let (tcp_socket, _) = x?;
				let connection = connection_p2_p3.clone ();
				let server_id = server_id.clone ();
				let shutdown_flag_rx = shutdown_flag_rx.clone ();
				
				tokio::spawn (handle_p1 (connection, server_id, server_tcp_port, tcp_socket, shutdown_flag_rx));
			},
			_ = shutdown_flag_rx.changed () => (),
		};
	}

	Ok::<_, anyhow::Error> (())
}

async fn handle_p1 (
	connection: quinn::Connection,
	server_id: String,
	server_tcp_port: u16,
	tcp_socket: tokio::net::TcpStream,
	shutdown_flag_rx: tokio::sync::watch::Receiver <bool>,
) -> anyhow::Result <()>
{
	let (mut local_recv, mut local_send) = tcp_socket.into_split ();
	
	debug! ("Starting PTTH connection");
	
	let (mut relay_send, mut relay_recv) = protocol::p2_connect_to_p5 (&connection, &server_id, server_tcp_port).await?;
	
	trace! ("Relaying bytes...");
	
	let task_blue = {
		let mut shutdown_flag_rx = shutdown_flag_rx.clone ();
		
		tokio::spawn (async move {
			let mut buf = vec! [0u8; 65_536];
			while *shutdown_flag_rx.borrow () {
				trace! ("Blue reading from QUIC...");
				tokio::select! {
					x = relay_recv.read (&mut buf) => {
						let bytes_read = match x? {
							None => break,
							Some (0) => break,
							Some (x) => x,
						};
						let buf_slice = &buf [0..bytes_read];
						trace! ("Uplink relaying {} bytes", bytes_read);
						local_send.write_all (buf_slice).await?;
					},
					_ = shutdown_flag_rx.changed () => (),
				};
			}
			
			debug! ("Blue QUIC --> TCP closed");
			
			Ok::<_, anyhow::Error> (())
		})
	};
	
	let task_green = {
		let mut shutdown_flag_rx = shutdown_flag_rx.clone ();
		
		tokio::spawn (async move {
			let mut buf = vec! [0u8; 65_536];
			while *shutdown_flag_rx.borrow () {
				trace! ("Green reading from TCP...");
				tokio::select! {
					x = local_recv.read (&mut buf) => {
						let bytes_read = match x? {
							0 => break,
							x => x,
						};
						let buf_slice = &buf [0..bytes_read];
						trace! ("Downlink relaying {} bytes", bytes_read);
						relay_send.write_all (buf_slice).await?;
					},
					_ = shutdown_flag_rx.changed () => (),
				};
			}
			
			debug! ("Green TCP --> QUIC closed");
			
			Ok::<_, anyhow::Error> (())
		})
	};
	
	task_blue.await??;
	task_green.await??;
	
	debug! ("Ended PTTH connection");
	
	Ok (())
}