// Copyright 2021 COMIT Network.
//
// 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.

use crate::codec::Message::*;
use crate::codec::{Cookie, ErrorCode, Message, Namespace, NewRegistration, Registration, Ttl};
use futures::future::BoxFuture;
use futures::future::FutureExt;
use futures::stream::FuturesUnordered;
use futures::stream::StreamExt;
use libp2p_core::{Endpoint, Multiaddr, PeerRecord};
use libp2p_identity::{Keypair, PeerId, SigningError};
use libp2p_request_response::{OutboundRequestId, ProtocolSupport};
use libp2p_swarm::{
    ConnectionDenied, ConnectionId, ExternalAddresses, FromSwarm, NetworkBehaviour, THandler,
    THandlerInEvent, THandlerOutEvent, ToSwarm,
};
use std::collections::HashMap;
use std::iter;
use std::task::{Context, Poll};
use std::time::Duration;

pub struct Behaviour {
    inner: libp2p_request_response::Behaviour<crate::codec::Codec>,

    keypair: Keypair,

    waiting_for_register: HashMap<OutboundRequestId, (PeerId, Namespace)>,
    waiting_for_discovery: HashMap<OutboundRequestId, (PeerId, Option<Namespace>)>,

    /// Hold addresses of all peers that we have discovered so far.
    ///
    /// Storing these internally allows us to assist the [`libp2p_swarm::Swarm`] in dialing by returning addresses from [`NetworkBehaviour::handle_pending_outbound_connection`].
    discovered_peers: HashMap<(PeerId, Namespace), Vec<Multiaddr>>,

    registered_namespaces: HashMap<(PeerId, Namespace), Ttl>,

    /// Tracks the expiry of registrations that we have discovered and stored in `discovered_peers` otherwise we have a memory leak.
    expiring_registrations: FuturesUnordered<BoxFuture<'static, (PeerId, Namespace)>>,

    external_addresses: ExternalAddresses,
}

impl Behaviour {
    /// Create a new instance of the rendezvous [`NetworkBehaviour`].
    pub fn new(keypair: Keypair) -> Self {
        Self {
            inner: libp2p_request_response::Behaviour::with_codec(
                crate::codec::Codec::default(),
                iter::once((crate::PROTOCOL_IDENT, ProtocolSupport::Outbound)),
                libp2p_request_response::Config::default(),
            ),
            keypair,
            waiting_for_register: Default::default(),
            waiting_for_discovery: Default::default(),
            discovered_peers: Default::default(),
            registered_namespaces: Default::default(),
            expiring_registrations: FuturesUnordered::from_iter(vec![
                futures::future::pending().boxed()
            ]),
            external_addresses: Default::default(),
        }
    }

    /// Register our external addresses in the given namespace with the given rendezvous peer.
    ///
    /// External addresses are either manually added via [`libp2p_swarm::Swarm::add_external_address`] or reported
    /// by other [`NetworkBehaviour`]s via [`ToSwarm::ExternalAddrConfirmed`].
    pub fn register(
        &mut self,
        namespace: Namespace,
        rendezvous_node: PeerId,
        ttl: Option<Ttl>,
    ) -> Result<(), RegisterError> {
        let external_addresses = self.external_addresses.iter().cloned().collect::<Vec<_>>();
        if external_addresses.is_empty() {
            return Err(RegisterError::NoExternalAddresses);
        }

        let peer_record = PeerRecord::new(&self.keypair, external_addresses)?;
        let req_id = self.inner.send_request(
            &rendezvous_node,
            Register(NewRegistration::new(namespace.clone(), peer_record, ttl)),
        );
        self.waiting_for_register
            .insert(req_id, (rendezvous_node, namespace));

        Ok(())
    }

    /// Unregister ourselves from the given namespace with the given rendezvous peer.
    pub fn unregister(&mut self, namespace: Namespace, rendezvous_node: PeerId) {
        self.registered_namespaces
            .retain(|(rz_node, ns), _| rz_node.ne(&rendezvous_node) && ns.ne(&namespace));

        self.inner
            .send_request(&rendezvous_node, Unregister(namespace));
    }

    /// Discover other peers at a given rendezvous peer.
    ///
    /// If desired, the registrations can be filtered by a namespace.
    /// If no namespace is given, peers from all namespaces will be returned.
    /// A successfully discovery returns a cookie within [`Event::Discovered`].
    /// Such a cookie can be used to only fetch the _delta_ of registrations since
    /// the cookie was acquired.
    pub fn discover(
        &mut self,
        namespace: Option<Namespace>,
        cookie: Option<Cookie>,
        limit: Option<u64>,
        rendezvous_node: PeerId,
    ) {
        let req_id = self.inner.send_request(
            &rendezvous_node,
            Discover {
                namespace: namespace.clone(),
                cookie,
                limit,
            },
        );

        self.waiting_for_discovery
            .insert(req_id, (rendezvous_node, namespace));
    }
}

#[derive(Debug, thiserror::Error)]
pub enum RegisterError {
    #[error("We don't know about any externally reachable addresses of ours")]
    NoExternalAddresses,
    #[error("Failed to make a new PeerRecord")]
    FailedToMakeRecord(#[from] SigningError),
}

#[derive(Debug)]
#[allow(clippy::large_enum_variant)]
pub enum Event {
    /// We successfully discovered other nodes with using the contained rendezvous node.
    Discovered {
        rendezvous_node: PeerId,
        registrations: Vec<Registration>,
        cookie: Cookie,
    },
    /// We failed to discover other nodes on the contained rendezvous node.
    DiscoverFailed {
        rendezvous_node: PeerId,
        namespace: Option<Namespace>,
        error: ErrorCode,
    },
    /// We successfully registered with the contained rendezvous node.
    Registered {
        rendezvous_node: PeerId,
        ttl: Ttl,
        namespace: Namespace,
    },
    /// We failed to register with the contained rendezvous node.
    RegisterFailed {
        rendezvous_node: PeerId,
        namespace: Namespace,
        error: ErrorCode,
    },
    /// The connection details we learned from this node expired.
    Expired { peer: PeerId },
}

impl NetworkBehaviour for Behaviour {
    type ConnectionHandler = <libp2p_request_response::Behaviour<
        crate::codec::Codec,
    > as NetworkBehaviour>::ConnectionHandler;

    type ToSwarm = Event;

    fn handle_established_inbound_connection(
        &mut self,
        connection_id: ConnectionId,
        peer: PeerId,
        local_addr: &Multiaddr,
        remote_addr: &Multiaddr,
    ) -> Result<THandler<Self>, ConnectionDenied> {
        self.inner.handle_established_inbound_connection(
            connection_id,
            peer,
            local_addr,
            remote_addr,
        )
    }

    fn handle_established_outbound_connection(
        &mut self,
        connection_id: ConnectionId,
        peer: PeerId,
        addr: &Multiaddr,
        role_override: Endpoint,
    ) -> Result<THandler<Self>, ConnectionDenied> {
        self.inner
            .handle_established_outbound_connection(connection_id, peer, addr, role_override)
    }

    fn on_connection_handler_event(
        &mut self,
        peer_id: PeerId,
        connection_id: ConnectionId,
        event: THandlerOutEvent<Self>,
    ) {
        self.inner
            .on_connection_handler_event(peer_id, connection_id, event);
    }

    fn on_swarm_event(&mut self, event: FromSwarm) {
        let changed = self.external_addresses.on_swarm_event(&event);

        self.inner.on_swarm_event(event);

        if changed && self.external_addresses.iter().count() > 0 {
            let registered = self.registered_namespaces.clone();
            for ((rz_node, ns), ttl) in registered {
                if let Err(e) = self.register(ns, rz_node, Some(ttl)) {
                    tracing::warn!("refreshing registration failed: {e}")
                }
            }
        }
    }

    fn poll(
        &mut self,
        cx: &mut Context<'_>,
    ) -> Poll<ToSwarm<Self::ToSwarm, THandlerInEvent<Self>>> {
        use libp2p_request_response as req_res;

        loop {
            match self.inner.poll(cx) {
                Poll::Ready(ToSwarm::GenerateEvent(req_res::Event::Message {
                    message:
                        req_res::Message::Response {
                            request_id,
                            response,
                        },
                    ..
                })) => {
                    if let Some(event) = self.handle_response(&request_id, response) {
                        return Poll::Ready(ToSwarm::GenerateEvent(event));
                    }

                    continue; // not a request we care about
                }
                Poll::Ready(ToSwarm::GenerateEvent(req_res::Event::OutboundFailure {
                    request_id,
                    ..
                })) => {
                    if let Some(event) = self.event_for_outbound_failure(&request_id) {
                        return Poll::Ready(ToSwarm::GenerateEvent(event));
                    }

                    continue; // not a request we care about
                }
                Poll::Ready(ToSwarm::GenerateEvent(
                    req_res::Event::InboundFailure { .. }
                    | req_res::Event::ResponseSent { .. }
                    | req_res::Event::Message {
                        message: req_res::Message::Request { .. },
                        ..
                    },
                )) => {
                    unreachable!("rendezvous clients never receive requests")
                }
                Poll::Ready(other) => {
                    let new_to_swarm =
                        other.map_out(|_| unreachable!("we manually map `GenerateEvent` variants"));

                    return Poll::Ready(new_to_swarm);
                }
                Poll::Pending => {}
            }

            if let Poll::Ready(Some(expired_registration)) =
                self.expiring_registrations.poll_next_unpin(cx)
            {
                self.discovered_peers.remove(&expired_registration);
                return Poll::Ready(ToSwarm::GenerateEvent(Event::Expired {
                    peer: expired_registration.0,
                }));
            }

            return Poll::Pending;
        }
    }

    fn handle_pending_outbound_connection(
        &mut self,
        _connection_id: ConnectionId,
        maybe_peer: Option<PeerId>,
        _addresses: &[Multiaddr],
        _effective_role: Endpoint,
    ) -> Result<Vec<Multiaddr>, ConnectionDenied> {
        let peer = match maybe_peer {
            None => return Ok(vec![]),
            Some(peer) => peer,
        };

        let addresses = self
            .discovered_peers
            .iter()
            .filter_map(|((candidate, _), addresses)| (candidate == &peer).then_some(addresses))
            .flatten()
            .cloned()
            .collect();

        Ok(addresses)
    }
}

impl Behaviour {
    fn event_for_outbound_failure(&mut self, req_id: &OutboundRequestId) -> Option<Event> {
        if let Some((rendezvous_node, namespace)) = self.waiting_for_register.remove(req_id) {
            return Some(Event::RegisterFailed {
                rendezvous_node,
                namespace,
                error: ErrorCode::Unavailable,
            });
        };

        if let Some((rendezvous_node, namespace)) = self.waiting_for_discovery.remove(req_id) {
            return Some(Event::DiscoverFailed {
                rendezvous_node,
                namespace,
                error: ErrorCode::Unavailable,
            });
        };

        None
    }

    fn handle_response(
        &mut self,
        request_id: &OutboundRequestId,
        response: Message,
    ) -> Option<Event> {
        match response {
            RegisterResponse(Ok(ttl)) => {
                if let Some((rendezvous_node, namespace)) =
                    self.waiting_for_register.remove(request_id)
                {
                    self.registered_namespaces
                        .insert((rendezvous_node, namespace.clone()), ttl);

                    return Some(Event::Registered {
                        rendezvous_node,
                        ttl,
                        namespace,
                    });
                }

                None
            }
            RegisterResponse(Err(error_code)) => {
                if let Some((rendezvous_node, namespace)) =
                    self.waiting_for_register.remove(request_id)
                {
                    return Some(Event::RegisterFailed {
                        rendezvous_node,
                        namespace,
                        error: error_code,
                    });
                }

                None
            }
            DiscoverResponse(Ok((registrations, cookie))) => {
                if let Some((rendezvous_node, _ns)) = self.waiting_for_discovery.remove(request_id)
                {
                    self.discovered_peers
                        .extend(registrations.iter().map(|registration| {
                            let peer_id = registration.record.peer_id();
                            let namespace = registration.namespace.clone();

                            let addresses = registration.record.addresses().to_vec();

                            ((peer_id, namespace), addresses)
                        }));

                    self.expiring_registrations
                        .extend(registrations.iter().cloned().map(|registration| {
                            async move {
                                // if the timer errors we consider it expired
                                futures_timer::Delay::new(Duration::from_secs(registration.ttl))
                                    .await;

                                (registration.record.peer_id(), registration.namespace)
                            }
                            .boxed()
                        }));

                    return Some(Event::Discovered {
                        rendezvous_node,
                        registrations,
                        cookie,
                    });
                }

                None
            }
            DiscoverResponse(Err(error_code)) => {
                if let Some((rendezvous_node, ns)) = self.waiting_for_discovery.remove(request_id) {
                    return Some(Event::DiscoverFailed {
                        rendezvous_node,
                        namespace: ns,
                        error: error_code,
                    });
                }

                None
            }
            _ => unreachable!("rendezvous clients never receive requests"),
        }
    }
}