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use std::{future::Future, io, time::Duration};

use tokio::{
    io::{split, AsyncRead, AsyncWrite},
    net::TcpStream,
    sync::{mpsc, oneshot},
    time::timeout,
};
use tracing::*;

use crate::{
    node::NodeTask,
    protocols::{ProtocolHandler, ReturnableConnection},
    Connection, Pea2Pea,
};

/// Can be used to specify and enable network handshakes. Upon establishing a connection, both sides will
/// need to adhere to the specified handshake rules in order to finalize the connection and be able to send
/// or receive any messages.
pub trait Handshake: Pea2Pea
where
    Self: Clone + Send + Sync + 'static,
{
    /// The maximum time allowed for a connection to perform a handshake before it is rejected.
    ///
    /// The default value is 3000ms.
    const TIMEOUT_MS: u64 = 3_000;

    /// Prepares the node to perform specified network handshakes.
    fn enable_handshake(&self) -> impl Future<Output = ()> + Send {
        async {
            let (from_node_sender, mut from_node_receiver) =
                mpsc::unbounded_channel::<ReturnableConnection>();

            // use a channel to know when the handshake task is ready
            let (tx, rx) = oneshot::channel();

            // spawn a background task dedicated to handling the handshakes
            let self_clone = self.clone();
            let handshake_task = tokio::spawn(async move {
                trace!(parent: self_clone.node().span(), "spawned the Handshake handler task");
                if tx.send(()).is_err() {
                    error!(parent: self_clone.node().span(), "Handshake handler creation interrupted! shutting down the node");
                    self_clone.node().shut_down().await;
                    return;
                }

                while let Some((conn, result_sender)) = from_node_receiver.recv().await {
                    let addr = conn.addr();

                    let node = self_clone.clone();
                    tokio::spawn(async move {
                        debug!(parent: node.node().span(), "shaking hands with {} as the {:?}", addr, !conn.side());
                        let result = timeout(
                            Duration::from_millis(Self::TIMEOUT_MS),
                            node.perform_handshake(conn),
                        )
                        .await;

                        let ret = match result {
                            Ok(Ok(conn)) => {
                                debug!(parent: node.node().span(), "successfully handshaken with {}", addr);
                                Ok(conn)
                            }
                            Ok(Err(e)) => {
                                error!(parent: node.node().span(), "handshake with {} failed: {}", addr, e);
                                Err(e)
                            }
                            Err(_) => {
                                error!(parent: node.node().span(), "handshake with {} timed out", addr);
                                Err(io::ErrorKind::TimedOut.into())
                            }
                        };

                        // return the Connection to the Node, resuming Node::adapt_stream
                        if result_sender.send(ret).is_err() {
                            error!(parent: node.node().span(), "couldn't return a Connection with {} from the Handshake handler", addr);
                        }
                    });
                }
            });
            let _ = rx.await;
            self.node()
                .tasks
                .lock()
                .insert(NodeTask::Handshake, handshake_task);

            // register the Handshake handler with the Node
            let hdl = ProtocolHandler(from_node_sender);
            assert!(
                self.node().protocols.handshake.set(hdl).is_ok(),
                "the Handshake protocol was enabled more than once!"
            );
        }
    }

    /// Performs the handshake; temporarily assumes control of the [`Connection`] and returns it if the handshake is
    /// successful.
    fn perform_handshake(
        &self,
        conn: Connection,
    ) -> impl Future<Output = io::Result<Connection>> + Send;

    /// Borrows the full connection stream to be used in the implementation of [`Handshake::perform_handshake`].
    fn borrow_stream<'a>(&self, conn: &'a mut Connection) -> &'a mut TcpStream {
        conn.stream.as_mut().unwrap()
    }

    /// Assumes full control of a connection's stream in the implementation of [`Handshake::perform_handshake`], by
    /// the end of which it *must* be followed by [`Handshake::return_stream`].
    fn take_stream(&self, conn: &mut Connection) -> TcpStream {
        conn.stream.take().unwrap()
    }

    /// This method only needs to be called if [`Handshake::take_stream`] had been called before; it is used to
    /// return a (potentially modified) stream back to the applicable connection.
    fn return_stream<T: AsyncRead + AsyncWrite + Send + Sync + 'static>(
        &self,
        conn: &mut Connection,
        stream: T,
    ) {
        let (reader, writer) = split(stream);
        conn.reader = Some(Box::new(reader));
        conn.writer = Some(Box::new(writer));
    }
}