// Copyright 2018 Parity Technologies (UK) Ltd.
//
// 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::handler::{self, Handler, InEvent};
use crate::protocol::{Info, UpgradeError};
use libp2p_core::{multiaddr, ConnectedPoint, Endpoint, Multiaddr};
use libp2p_identity::PeerId;
use libp2p_identity::PublicKey;
use libp2p_swarm::behaviour::{ConnectionClosed, ConnectionEstablished, DialFailure, FromSwarm};
use libp2p_swarm::{
    ConnectionDenied, DialError, ExternalAddresses, ListenAddresses, NetworkBehaviour,
    NotifyHandler, StreamUpgradeError, THandlerInEvent, ToSwarm,
};
use libp2p_swarm::{ConnectionId, THandler, THandlerOutEvent};
use lru::LruCache;
use std::collections::hash_map::Entry;
use std::num::NonZeroUsize;
use std::{
    collections::{HashMap, HashSet, VecDeque},
    iter::FromIterator,
    task::Context,
    task::Poll,
    time::Duration,
};

/// Network behaviour that automatically identifies nodes periodically, returns information
/// about them, and answers identify queries from other nodes.
///
/// All external addresses of the local node supposedly observed by remotes
/// are reported via [`ToSwarm::NewExternalAddrCandidate`].
pub struct Behaviour {
    config: Config,
    /// For each peer we're connected to, the observed address to send back to it.
    connected: HashMap<PeerId, HashMap<ConnectionId, Multiaddr>>,

    /// The address a remote observed for us.
    our_observed_addresses: HashMap<ConnectionId, Multiaddr>,

    /// Pending events to be emitted when polled.
    events: VecDeque<ToSwarm<Event, InEvent>>,
    /// The addresses of all peers that we have discovered.
    discovered_peers: PeerCache,

    listen_addresses: ListenAddresses,
    external_addresses: ExternalAddresses,
}

/// Configuration for the [`identify::Behaviour`](Behaviour).
#[non_exhaustive]
#[derive(Debug, Clone)]
pub struct Config {
    /// Application-specific version of the protocol family used by the peer,
    /// e.g. `ipfs/1.0.0` or `polkadot/1.0.0`.
    pub protocol_version: String,
    /// The public key of the local node. To report on the wire.
    pub local_public_key: PublicKey,
    /// Name and version of the local peer implementation, similar to the
    /// `User-Agent` header in the HTTP protocol.
    ///
    /// Defaults to `rust-libp2p/<libp2p-identify-version>`.
    pub agent_version: String,
    /// The interval at which identification requests are sent to
    /// the remote on established connections after the first request,
    /// i.e. the delay between identification requests.
    ///
    /// Defaults to 5 minutes.
    pub interval: Duration,

    /// Whether new or expired listen addresses of the local node should
    /// trigger an active push of an identify message to all connected peers.
    ///
    /// Enabling this option can result in connected peers being informed
    /// earlier about new or expired listen addresses of the local node,
    /// i.e. before the next periodic identify request with each peer.
    ///
    /// Disabled by default.
    pub push_listen_addr_updates: bool,

    /// How many entries of discovered peers to keep before we discard
    /// the least-recently used one.
    ///
    /// Disabled by default.
    pub cache_size: usize,
}

impl Config {
    /// Creates a new configuration for the identify [`Behaviour`] that
    /// advertises the given protocol version and public key.
    pub fn new(protocol_version: String, local_public_key: PublicKey) -> Self {
        Self {
            protocol_version,
            agent_version: format!("rust-libp2p/{}", env!("CARGO_PKG_VERSION")),
            local_public_key,
            interval: Duration::from_secs(5 * 60),
            push_listen_addr_updates: false,
            cache_size: 100,
        }
    }

    /// Configures the agent version sent to peers.
    pub fn with_agent_version(mut self, v: String) -> Self {
        self.agent_version = v;
        self
    }

    /// Configures the interval at which identification requests are
    /// sent to peers after the initial request.
    pub fn with_interval(mut self, d: Duration) -> Self {
        self.interval = d;
        self
    }

    /// Configures whether new or expired listen addresses of the local
    /// node should trigger an active push of an identify message to all
    /// connected peers.
    pub fn with_push_listen_addr_updates(mut self, b: bool) -> Self {
        self.push_listen_addr_updates = b;
        self
    }

    /// Configures the size of the LRU cache, caching addresses of discovered peers.
    pub fn with_cache_size(mut self, cache_size: usize) -> Self {
        self.cache_size = cache_size;
        self
    }
}

impl Behaviour {
    /// Creates a new identify [`Behaviour`].
    pub fn new(config: Config) -> Self {
        let discovered_peers = match NonZeroUsize::new(config.cache_size) {
            None => PeerCache::disabled(),
            Some(size) => PeerCache::enabled(size),
        };

        Self {
            config,
            connected: HashMap::new(),
            our_observed_addresses: Default::default(),
            events: VecDeque::new(),
            discovered_peers,
            listen_addresses: Default::default(),
            external_addresses: Default::default(),
        }
    }

    /// Initiates an active push of the local peer information to the given peers.
    pub fn push<I>(&mut self, peers: I)
    where
        I: IntoIterator<Item = PeerId>,
    {
        for p in peers {
            if !self.connected.contains_key(&p) {
                tracing::debug!(peer=%p, "Not pushing to peer because we are not connected");
                continue;
            }

            self.events.push_back(ToSwarm::NotifyHandler {
                peer_id: p,
                handler: NotifyHandler::Any,
                event: InEvent::Push,
            });
        }
    }

    fn on_connection_established(
        &mut self,
        ConnectionEstablished {
            peer_id,
            connection_id: conn,
            endpoint,
            failed_addresses,
            ..
        }: ConnectionEstablished,
    ) {
        let addr = match endpoint {
            ConnectedPoint::Dialer { address, .. } => address.clone(),
            ConnectedPoint::Listener { send_back_addr, .. } => send_back_addr.clone(),
        };

        self.connected
            .entry(peer_id)
            .or_default()
            .insert(conn, addr);

        if let Some(entry) = self.discovered_peers.get_mut(&peer_id) {
            for addr in failed_addresses {
                entry.remove(addr);
            }
        }
    }

    fn all_addresses(&self) -> HashSet<Multiaddr> {
        self.listen_addresses
            .iter()
            .chain(self.external_addresses.iter())
            .cloned()
            .collect()
    }
}

impl NetworkBehaviour for Behaviour {
    type ConnectionHandler = Handler;
    type ToSwarm = Event;

    fn handle_established_inbound_connection(
        &mut self,
        _: ConnectionId,
        peer: PeerId,
        _: &Multiaddr,
        remote_addr: &Multiaddr,
    ) -> Result<THandler<Self>, ConnectionDenied> {
        Ok(Handler::new(
            self.config.interval,
            peer,
            self.config.local_public_key.clone(),
            self.config.protocol_version.clone(),
            self.config.agent_version.clone(),
            remote_addr.clone(),
            self.all_addresses(),
        ))
    }

    fn handle_established_outbound_connection(
        &mut self,
        _: ConnectionId,
        peer: PeerId,
        addr: &Multiaddr,
        _: Endpoint,
    ) -> Result<THandler<Self>, ConnectionDenied> {
        Ok(Handler::new(
            self.config.interval,
            peer,
            self.config.local_public_key.clone(),
            self.config.protocol_version.clone(),
            self.config.agent_version.clone(),
            addr.clone(), // TODO: This is weird? That is the public address we dialed, shouldn't need to tell the other party?
            self.all_addresses(),
        ))
    }

    fn on_connection_handler_event(
        &mut self,
        peer_id: PeerId,
        id: ConnectionId,
        event: THandlerOutEvent<Self>,
    ) {
        match event {
            handler::Event::Identified(mut info) => {
                // Remove invalid multiaddrs.
                info.listen_addrs
                    .retain(|addr| multiaddr_matches_peer_id(addr, &peer_id));

                // Replace existing addresses to prevent other peer from filling up our memory.
                self.discovered_peers
                    .put(peer_id, info.listen_addrs.iter().cloned());

                let observed = info.observed_addr.clone();
                self.events
                    .push_back(ToSwarm::GenerateEvent(Event::Received { peer_id, info }));

                match self.our_observed_addresses.entry(id) {
                    Entry::Vacant(not_yet_observed) => {
                        not_yet_observed.insert(observed.clone());
                        self.events
                            .push_back(ToSwarm::NewExternalAddrCandidate(observed));
                    }
                    Entry::Occupied(already_observed) if already_observed.get() == &observed => {
                        // No-op, we already observed this address.
                    }
                    Entry::Occupied(mut already_observed) => {
                        tracing::info!(
                            old_address=%already_observed.get(),
                            new_address=%observed,
                            "Our observed address on connection {id} changed",
                        );

                        *already_observed.get_mut() = observed.clone();
                        self.events
                            .push_back(ToSwarm::NewExternalAddrCandidate(observed));
                    }
                }
            }
            handler::Event::Identification => {
                self.events
                    .push_back(ToSwarm::GenerateEvent(Event::Sent { peer_id }));
            }
            handler::Event::IdentificationPushed(info) => {
                self.events
                    .push_back(ToSwarm::GenerateEvent(Event::Pushed { peer_id, info }));
            }
            handler::Event::IdentificationError(error) => {
                self.events
                    .push_back(ToSwarm::GenerateEvent(Event::Error { peer_id, error }));
            }
        }
    }

    #[tracing::instrument(level = "trace", name = "NetworkBehaviour::poll", skip(self))]
    fn poll(&mut self, _: &mut Context<'_>) -> Poll<ToSwarm<Self::ToSwarm, THandlerInEvent<Self>>> {
        if let Some(event) = self.events.pop_front() {
            return Poll::Ready(event);
        }

        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,
        };

        Ok(self.discovered_peers.get(&peer))
    }

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

        if listen_addr_changed || external_addr_changed {
            // notify all connected handlers about our changed addresses
            let change_events = self
                .connected
                .iter()
                .flat_map(|(peer, map)| map.keys().map(|id| (*peer, id)))
                .map(|(peer_id, connection_id)| ToSwarm::NotifyHandler {
                    peer_id,
                    handler: NotifyHandler::One(*connection_id),
                    event: InEvent::AddressesChanged(self.all_addresses()),
                })
                .collect::<Vec<_>>();

            self.events.extend(change_events)
        }

        if listen_addr_changed && self.config.push_listen_addr_updates {
            // trigger an identify push for all connected peers
            let push_events = self.connected.keys().map(|peer| ToSwarm::NotifyHandler {
                peer_id: *peer,
                handler: NotifyHandler::Any,
                event: InEvent::Push,
            });

            self.events.extend(push_events);
        }

        match event {
            FromSwarm::ConnectionEstablished(connection_established) => {
                self.on_connection_established(connection_established)
            }
            FromSwarm::ConnectionClosed(ConnectionClosed {
                peer_id,
                connection_id,
                remaining_established,
                ..
            }) => {
                if remaining_established == 0 {
                    self.connected.remove(&peer_id);
                } else if let Some(addrs) = self.connected.get_mut(&peer_id) {
                    addrs.remove(&connection_id);
                }

                self.our_observed_addresses.remove(&connection_id);
            }
            FromSwarm::DialFailure(DialFailure { peer_id, error, .. }) => {
                if let Some(entry) = peer_id.and_then(|id| self.discovered_peers.get_mut(&id)) {
                    if let DialError::Transport(errors) = error {
                        for (addr, _error) in errors {
                            entry.remove(addr);
                        }
                    }
                }
            }
            _ => {}
        }
    }
}

/// Event emitted  by the `Identify` behaviour.
#[allow(clippy::large_enum_variant)]
#[derive(Debug)]
pub enum Event {
    /// Identification information has been received from a peer.
    Received {
        /// The peer that has been identified.
        peer_id: PeerId,
        /// The information provided by the peer.
        info: Info,
    },
    /// Identification information of the local node has been sent to a peer in
    /// response to an identification request.
    Sent {
        /// The peer that the information has been sent to.
        peer_id: PeerId,
    },
    /// Identification information of the local node has been actively pushed to
    /// a peer.
    Pushed {
        /// The peer that the information has been sent to.
        peer_id: PeerId,
        /// The full Info struct we pushed to the remote peer. Clients must
        /// do some diff'ing to know what has changed since the last push.
        info: Info,
    },
    /// Error while attempting to identify the remote.
    Error {
        /// The peer with whom the error originated.
        peer_id: PeerId,
        /// The error that occurred.
        error: StreamUpgradeError<UpgradeError>,
    },
}

/// If there is a given peer_id in the multiaddr, make sure it is the same as
/// the given peer_id. If there is no peer_id for the peer in the mutiaddr, this returns true.
fn multiaddr_matches_peer_id(addr: &Multiaddr, peer_id: &PeerId) -> bool {
    let last_component = addr.iter().last();
    if let Some(multiaddr::Protocol::P2p(multi_addr_peer_id)) = last_component {
        return multi_addr_peer_id == *peer_id;
    }
    true
}

struct PeerCache(Option<LruCache<PeerId, HashSet<Multiaddr>>>);

impl PeerCache {
    fn disabled() -> Self {
        Self(None)
    }

    fn enabled(size: NonZeroUsize) -> Self {
        Self(Some(LruCache::new(size)))
    }

    fn get_mut(&mut self, peer: &PeerId) -> Option<&mut HashSet<Multiaddr>> {
        self.0.as_mut()?.get_mut(peer)
    }

    fn put(&mut self, peer: PeerId, addresses: impl Iterator<Item = Multiaddr>) {
        let cache = match self.0.as_mut() {
            None => return,
            Some(cache) => cache,
        };

        let addresses = addresses.filter_map(|a| a.with_p2p(peer).ok());
        cache.put(peer, HashSet::from_iter(addresses));
    }

    fn get(&mut self, peer: &PeerId) -> Vec<Multiaddr> {
        let cache = match self.0.as_mut() {
            None => return Vec::new(),
            Some(cache) => cache,
        };

        cache
            .get(peer)
            .cloned()
            .map(Vec::from_iter)
            .unwrap_or_default()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn check_multiaddr_matches_peer_id() {
        let peer_id = PeerId::random();
        let other_peer_id = PeerId::random();
        let mut addr: Multiaddr = "/ip4/147.75.69.143/tcp/4001"
            .parse()
            .expect("failed to parse multiaddr");

        let addr_without_peer_id: Multiaddr = addr.clone();
        let mut addr_with_other_peer_id = addr.clone();

        addr.push(multiaddr::Protocol::P2p(peer_id));
        addr_with_other_peer_id.push(multiaddr::Protocol::P2p(other_peer_id));

        assert!(multiaddr_matches_peer_id(&addr, &peer_id));
        assert!(!multiaddr_matches_peer_id(
            &addr_with_other_peer_id,
            &peer_id
        ));
        assert!(multiaddr_matches_peer_id(&addr_without_peer_id, &peer_id));
    }
}