// Copyright 2021 Protocol Labs.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

//! [`NetworkBehaviour`] to act as a circuit relay v2 **client**.

mod handler;
pub mod transport;

use crate::v2::protocol::{self, inbound_stop, outbound_hop};
use bytes::Bytes;
use either::Either;
use futures::channel::mpsc::Receiver;
use futures::channel::oneshot;
use futures::future::{BoxFuture, FutureExt};
use futures::io::{AsyncRead, AsyncWrite};
use futures::ready;
use futures::stream::StreamExt;
use libp2p_core::connection::{ConnectedPoint, ConnectionId};
use libp2p_core::{Multiaddr, PeerId};
use libp2p_swarm::dial_opts::DialOpts;
use libp2p_swarm::handler::DummyConnectionHandler;
use libp2p_swarm::{
    ConnectionHandlerUpgrErr, NegotiatedSubstream, NetworkBehaviour, NetworkBehaviourAction,
    NotifyHandler, PollParameters,
};
use std::collections::{hash_map, HashMap, VecDeque};
use std::io::{Error, IoSlice};
use std::ops::DerefMut;
use std::pin::Pin;
use std::task::{Context, Poll};

/// The events produced by the [`Client`] behaviour.
#[derive(Debug)]
pub enum Event {
    /// An outbound reservation has been accepted.
    ReservationReqAccepted {
        relay_peer_id: PeerId,
        /// Indicates whether the request replaces an existing reservation.
        renewal: bool,
        limit: Option<protocol::Limit>,
    },
    ReservationReqFailed {
        relay_peer_id: PeerId,
        /// Indicates whether the request replaces an existing reservation.
        renewal: bool,
        error: ConnectionHandlerUpgrErr<outbound_hop::ReservationFailedReason>,
    },
    OutboundCircuitEstablished {
        relay_peer_id: PeerId,
        limit: Option<protocol::Limit>,
    },
    OutboundCircuitReqFailed {
        relay_peer_id: PeerId,
        error: ConnectionHandlerUpgrErr<outbound_hop::CircuitFailedReason>,
    },
    /// An inbound circuit has been established.
    InboundCircuitEstablished {
        src_peer_id: PeerId,
        limit: Option<protocol::Limit>,
    },
    InboundCircuitReqFailed {
        relay_peer_id: PeerId,
        error: ConnectionHandlerUpgrErr<void::Void>,
    },
    /// An inbound circuit request has been denied.
    InboundCircuitReqDenied { src_peer_id: PeerId },
    /// Denying an inbound circuit request failed.
    InboundCircuitReqDenyFailed {
        src_peer_id: PeerId,
        error: std::io::Error,
    },
}

pub struct Client {
    local_peer_id: PeerId,

    from_transport: Receiver<transport::TransportToBehaviourMsg>,
    /// Set of directly connected peers, i.e. not connected via a relayed
    /// connection.
    directly_connected_peers: HashMap<PeerId, Vec<ConnectionId>>,

    /// Queue of actions to return when polled.
    queued_actions: VecDeque<Event>,
}

impl Client {
    pub fn new_transport_and_behaviour(
        local_peer_id: PeerId,
    ) -> (transport::ClientTransport, Self) {
        let (transport, from_transport) = transport::ClientTransport::new();
        let behaviour = Client {
            local_peer_id,
            from_transport,
            directly_connected_peers: Default::default(),
            queued_actions: Default::default(),
        };
        (transport, behaviour)
    }
}

impl NetworkBehaviour for Client {
    type ConnectionHandler = handler::Prototype;
    type OutEvent = Event;

    fn new_handler(&mut self) -> Self::ConnectionHandler {
        handler::Prototype::new(self.local_peer_id, None)
    }

    fn inject_connection_established(
        &mut self,
        peer_id: &PeerId,
        connection_id: &ConnectionId,
        endpoint: &ConnectedPoint,
        _failed_addresses: Option<&Vec<Multiaddr>>,
        _other_established: usize,
    ) {
        if !endpoint.is_relayed() {
            self.directly_connected_peers
                .entry(*peer_id)
                .or_default()
                .push(*connection_id);
        }
    }

    fn inject_connection_closed(
        &mut self,
        peer_id: &PeerId,
        connection_id: &ConnectionId,
        endpoint: &ConnectedPoint,
        _handler: Either<handler::Handler, DummyConnectionHandler>,
        _remaining_established: usize,
    ) {
        if !endpoint.is_relayed() {
            match self.directly_connected_peers.entry(*peer_id) {
                hash_map::Entry::Occupied(mut connections) => {
                    let position = connections
                        .get()
                        .iter()
                        .position(|c| c == connection_id)
                        .expect("Connection to be known.");
                    connections.get_mut().remove(position);

                    if connections.get().is_empty() {
                        connections.remove();
                    }
                }
                hash_map::Entry::Vacant(_) => {
                    unreachable!("`inject_connection_closed` for unconnected peer.")
                }
            };
        }
    }

    fn inject_event(
        &mut self,
        event_source: PeerId,
        _connection: ConnectionId,
        handler_event: Either<handler::Event, void::Void>,
    ) {
        let handler_event = match handler_event {
            Either::Left(e) => e,
            Either::Right(v) => void::unreachable(v),
        };

        match handler_event {
            handler::Event::ReservationReqAccepted { renewal, limit } => self
                .queued_actions
                .push_back(Event::ReservationReqAccepted {
                    relay_peer_id: event_source,
                    renewal,
                    limit,
                }),
            handler::Event::ReservationReqFailed { renewal, error } => {
                self.queued_actions.push_back(Event::ReservationReqFailed {
                    relay_peer_id: event_source,
                    renewal,
                    error,
                })
            }
            handler::Event::OutboundCircuitEstablished { limit } => {
                self.queued_actions
                    .push_back(Event::OutboundCircuitEstablished {
                        relay_peer_id: event_source,
                        limit,
                    })
            }
            handler::Event::OutboundCircuitReqFailed { error } => {
                self.queued_actions
                    .push_back(Event::OutboundCircuitReqFailed {
                        relay_peer_id: event_source,
                        error,
                    })
            }
            handler::Event::InboundCircuitEstablished { src_peer_id, limit } => self
                .queued_actions
                .push_back(Event::InboundCircuitEstablished { src_peer_id, limit }),
            handler::Event::InboundCircuitReqFailed { error } => {
                self.queued_actions
                    .push_back(Event::InboundCircuitReqFailed {
                        relay_peer_id: event_source,
                        error,
                    })
            }
            handler::Event::InboundCircuitReqDenied { src_peer_id } => self
                .queued_actions
                .push_back(Event::InboundCircuitReqDenied { src_peer_id }),
            handler::Event::InboundCircuitReqDenyFailed { src_peer_id, error } => self
                .queued_actions
                .push_back(Event::InboundCircuitReqDenyFailed { src_peer_id, error }),
        }
    }

    fn poll(
        &mut self,
        cx: &mut Context<'_>,
        _poll_parameters: &mut impl PollParameters,
    ) -> Poll<NetworkBehaviourAction<Self::OutEvent, Self::ConnectionHandler>> {
        if let Some(event) = self.queued_actions.pop_front() {
            return Poll::Ready(NetworkBehaviourAction::GenerateEvent(event));
        }

        let action = match ready!(self.from_transport.poll_next_unpin(cx)) {
            Some(transport::TransportToBehaviourMsg::ListenReq {
                relay_peer_id,
                relay_addr,
                to_listener,
            }) => {
                match self
                    .directly_connected_peers
                    .get(&relay_peer_id)
                    .and_then(|cs| cs.get(0))
                {
                    Some(connection_id) => NetworkBehaviourAction::NotifyHandler {
                        peer_id: relay_peer_id,
                        handler: NotifyHandler::One(*connection_id),
                        event: Either::Left(handler::In::Reserve { to_listener }),
                    },
                    None => {
                        let handler = handler::Prototype::new(
                            self.local_peer_id,
                            Some(handler::In::Reserve { to_listener }),
                        );
                        NetworkBehaviourAction::Dial {
                            opts: DialOpts::peer_id(relay_peer_id)
                                .addresses(vec![relay_addr])
                                .extend_addresses_through_behaviour()
                                .build(),
                            handler,
                        }
                    }
                }
            }
            Some(transport::TransportToBehaviourMsg::DialReq {
                relay_addr,
                relay_peer_id,
                dst_peer_id,
                send_back,
                ..
            }) => {
                match self
                    .directly_connected_peers
                    .get(&relay_peer_id)
                    .and_then(|cs| cs.get(0))
                {
                    Some(connection_id) => NetworkBehaviourAction::NotifyHandler {
                        peer_id: relay_peer_id,
                        handler: NotifyHandler::One(*connection_id),
                        event: Either::Left(handler::In::EstablishCircuit {
                            send_back,
                            dst_peer_id,
                        }),
                    },
                    None => {
                        let handler = handler::Prototype::new(
                            self.local_peer_id,
                            Some(handler::In::EstablishCircuit {
                                send_back,
                                dst_peer_id,
                            }),
                        );
                        NetworkBehaviourAction::Dial {
                            opts: DialOpts::peer_id(relay_peer_id)
                                .addresses(vec![relay_addr])
                                .extend_addresses_through_behaviour()
                                .build(),
                            handler,
                        }
                    }
                }
            }
            None => unreachable!(
                "`Relay` `NetworkBehaviour` polled after channel from \
                     `RelayTransport` has been closed. Unreachable under \
                     the assumption that the `Client` is never polled after \
                     `ClientTransport` is dropped.",
            ),
        };

        return Poll::Ready(action);
    }
}

/// A [`NegotiatedSubstream`] acting as a [`RelayedConnection`].
pub enum RelayedConnection {
    InboundAccepting {
        accept: BoxFuture<'static, Result<RelayedConnection, std::io::Error>>,
    },
    Operational {
        read_buffer: Bytes,
        substream: NegotiatedSubstream,
        drop_notifier: oneshot::Sender<void::Void>,
    },
}

impl Unpin for RelayedConnection {}

impl RelayedConnection {
    pub(crate) fn new_inbound(
        circuit: inbound_stop::Circuit,
        drop_notifier: oneshot::Sender<void::Void>,
    ) -> Self {
        RelayedConnection::InboundAccepting {
            accept: async {
                let (substream, read_buffer) = circuit.accept().await?;
                Ok(RelayedConnection::Operational {
                    read_buffer,
                    substream,
                    drop_notifier,
                })
            }
            .boxed(),
        }
    }

    pub(crate) fn new_outbound(
        substream: NegotiatedSubstream,
        read_buffer: Bytes,
        drop_notifier: oneshot::Sender<void::Void>,
    ) -> Self {
        RelayedConnection::Operational {
            substream,
            read_buffer,
            drop_notifier,
        }
    }
}

impl AsyncWrite for RelayedConnection {
    fn poll_write(
        mut self: Pin<&mut Self>,
        cx: &mut Context,
        buf: &[u8],
    ) -> Poll<Result<usize, Error>> {
        loop {
            match self.deref_mut() {
                RelayedConnection::InboundAccepting { accept } => {
                    *self = ready!(accept.poll_unpin(cx))?;
                }
                RelayedConnection::Operational { substream, .. } => {
                    return Pin::new(substream).poll_write(cx, buf);
                }
            }
        }
    }
    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Error>> {
        loop {
            match self.deref_mut() {
                RelayedConnection::InboundAccepting { accept } => {
                    *self = ready!(accept.poll_unpin(cx))?;
                }
                RelayedConnection::Operational { substream, .. } => {
                    return Pin::new(substream).poll_flush(cx);
                }
            }
        }
    }
    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Error>> {
        loop {
            match self.deref_mut() {
                RelayedConnection::InboundAccepting { accept } => {
                    *self = ready!(accept.poll_unpin(cx))?;
                }
                RelayedConnection::Operational { substream, .. } => {
                    return Pin::new(substream).poll_close(cx);
                }
            }
        }
    }

    fn poll_write_vectored(
        mut self: Pin<&mut Self>,
        cx: &mut Context,
        bufs: &[IoSlice],
    ) -> Poll<Result<usize, Error>> {
        loop {
            match self.deref_mut() {
                RelayedConnection::InboundAccepting { accept } => {
                    *self = ready!(accept.poll_unpin(cx))?;
                }
                RelayedConnection::Operational { substream, .. } => {
                    return Pin::new(substream).poll_write_vectored(cx, bufs);
                }
            }
        }
    }
}

impl AsyncRead for RelayedConnection {
    fn poll_read(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut [u8],
    ) -> Poll<Result<usize, Error>> {
        loop {
            match self.deref_mut() {
                RelayedConnection::InboundAccepting { accept } => {
                    *self = ready!(accept.poll_unpin(cx))?;
                }
                RelayedConnection::Operational {
                    read_buffer,
                    substream,
                    ..
                } => {
                    if !read_buffer.is_empty() {
                        let n = std::cmp::min(read_buffer.len(), buf.len());
                        let data = read_buffer.split_to(n);
                        buf[0..n].copy_from_slice(&data[..]);
                        return Poll::Ready(Ok(n));
                    }

                    return Pin::new(substream).poll_read(cx, buf);
                }
            }
        }
    }
}