use crate::discovery::Discovery;
use crate::rpc::{RPCEvent, RPCMessage, RPC};
use crate::{error, NetworkConfig};
use crate::{Topic, TopicHash};
use futures::prelude::*;
use libp2p::{
    core::{
        identity::Keypair,
        swarm::{NetworkBehaviourAction, NetworkBehaviourEventProcess},
    },
    discv5::Discv5Event,
    gossipsub::{Gossipsub, GossipsubEvent},
    ping::{Ping, PingConfig, PingEvent},
    tokio_io::{AsyncRead, AsyncWrite},
    NetworkBehaviour, PeerId,
};
use slog::{o, trace, warn};
use ssz::{ssz_encode, Decode, DecodeError, Encode};
use std::num::NonZeroU32;
use std::time::Duration;
use types::{Attestation, BeaconBlock, EthSpec};

/// Builds the network behaviour that manages the core protocols of eth2.
/// This core behaviour is managed by `Behaviour` which adds peer management to all core
/// behaviours.
#[derive(NetworkBehaviour)]
#[behaviour(out_event = "BehaviourEvent<E>", poll_method = "poll")]
pub struct Behaviour<TSubstream: AsyncRead + AsyncWrite, E: EthSpec> {
    /// The routing pub-sub mechanism for eth2.
    gossipsub: Gossipsub<TSubstream>,
    /// The serenity RPC specified in the wire-0 protocol.
    serenity_rpc: RPC<TSubstream, E>,
    /// Keep regular connection to peers and disconnect if absent.
    ping: Ping<TSubstream>,
    /// Kademlia for peer discovery.
    discovery: Discovery<TSubstream>,
    #[behaviour(ignore)]
    /// The events generated by this behaviour to be consumed in the swarm poll.
    events: Vec<BehaviourEvent<E>>,
    /// Logger for behaviour actions.
    #[behaviour(ignore)]
    log: slog::Logger,
}

impl<TSubstream: AsyncRead + AsyncWrite, E: EthSpec> Behaviour<TSubstream, E> {
    pub fn new(
        local_key: &Keypair,
        net_conf: &NetworkConfig,
        log: &slog::Logger,
    ) -> error::Result<Self> {
        let local_peer_id = local_key.public().clone().into_peer_id();
        let behaviour_log = log.new(o!());
        let ping_config = PingConfig::new()
            .with_timeout(Duration::from_secs(30))
            .with_interval(Duration::from_secs(20))
            .with_max_failures(NonZeroU32::new(2).expect("2 != 0"))
            .with_keep_alive(false);

        Ok(Behaviour {
            serenity_rpc: RPC::new(log),
            gossipsub: Gossipsub::new(local_peer_id.clone(), net_conf.gs_config.clone()),
            discovery: Discovery::new(local_key, net_conf, log)?,
            ping: Ping::new(ping_config),
            events: Vec::new(),
            log: behaviour_log,
        })
    }
}

// Implement the NetworkBehaviourEventProcess trait so that we can derive NetworkBehaviour for Behaviour
impl<TSubstream: AsyncRead + AsyncWrite, E: EthSpec> NetworkBehaviourEventProcess<GossipsubEvent>
    for Behaviour<TSubstream, E>
{
    fn inject_event(&mut self, event: GossipsubEvent) {
        match event {
            GossipsubEvent::Message(gs_msg) => {
                trace!(self.log, "Received GossipEvent"; "msg" => format!("{:?}", gs_msg));

                let pubsub_message = match PubsubMessage::from_ssz_bytes(&gs_msg.data) {
                    //TODO: Punish peer on error
                    Err(e) => {
                        warn!(
                            self.log,
                            "Received undecodable message from Peer {:?} error", gs_msg.source;
                            "error" => format!("{:?}", e)
                        );
                        return;
                    }
                    Ok(msg) => msg,
                };

                self.events.push(BehaviourEvent::GossipMessage {
                    source: gs_msg.source,
                    topics: gs_msg.topics,
                    message: Box::new(pubsub_message),
                });
            }
            GossipsubEvent::Subscribed { .. } => {}
            GossipsubEvent::Unsubscribed { .. } => {}
        }
    }
}

impl<TSubstream: AsyncRead + AsyncWrite, E: EthSpec> NetworkBehaviourEventProcess<RPCMessage>
    for Behaviour<TSubstream, E>
{
    fn inject_event(&mut self, event: RPCMessage) {
        match event {
            RPCMessage::PeerDialed(peer_id) => {
                self.events.push(BehaviourEvent::PeerDialed(peer_id))
            }
            RPCMessage::PeerDisconnected(peer_id) => {
                self.events.push(BehaviourEvent::PeerDisconnected(peer_id))
            }
            RPCMessage::RPC(peer_id, rpc_event) => {
                self.events.push(BehaviourEvent::RPC(peer_id, rpc_event))
            }
        }
    }
}

impl<TSubstream: AsyncRead + AsyncWrite, E: EthSpec> NetworkBehaviourEventProcess<PingEvent>
    for Behaviour<TSubstream, E>
{
    fn inject_event(&mut self, _event: PingEvent) {
        // not interested in ping responses at the moment.
    }
}

impl<TSubstream: AsyncRead + AsyncWrite, E: EthSpec> Behaviour<TSubstream, E> {
    /// Consumes the events list when polled.
    fn poll<TBehaviourIn>(
        &mut self,
    ) -> Async<NetworkBehaviourAction<TBehaviourIn, BehaviourEvent<E>>> {
        if !self.events.is_empty() {
            return Async::Ready(NetworkBehaviourAction::GenerateEvent(self.events.remove(0)));
        }

        Async::NotReady
    }
}

impl<TSubstream: AsyncRead + AsyncWrite, E: EthSpec> NetworkBehaviourEventProcess<Discv5Event>
    for Behaviour<TSubstream, E>
{
    fn inject_event(&mut self, _event: Discv5Event) {
        // discv5 has no events to inject
    }
}

/// Implements the combined behaviour for the libp2p service.
impl<TSubstream: AsyncRead + AsyncWrite, E: EthSpec> Behaviour<TSubstream, E> {
    /* Pubsub behaviour functions */

    /// Subscribes to a gossipsub topic.
    pub fn subscribe(&mut self, topic: Topic) -> bool {
        self.gossipsub.subscribe(topic)
    }

    /// Publishes a message on the pubsub (gossipsub) behaviour.
    pub fn publish(&mut self, topics: Vec<Topic>, message: PubsubMessage<E>) {
        let message_bytes = ssz_encode(&message);
        for topic in topics {
            self.gossipsub.publish(topic, message_bytes.clone());
        }
    }

    /* Eth2 RPC behaviour functions */

    /// Sends an RPC Request/Response via the RPC protocol.
    pub fn send_rpc(&mut self, peer_id: PeerId, rpc_event: RPCEvent) {
        self.serenity_rpc.send_rpc(peer_id, rpc_event);
    }

    /* Discovery / Peer management functions */
    pub fn connected_peers(&self) -> usize {
        self.discovery.connected_peers()
    }
}

/// The types of events than can be obtained from polling the behaviour.
pub enum BehaviourEvent<E: EthSpec> {
    RPC(PeerId, RPCEvent),
    PeerDialed(PeerId),
    PeerDisconnected(PeerId),
    GossipMessage {
        source: PeerId,
        topics: Vec<TopicHash>,
        message: Box<PubsubMessage<E>>,
    },
}

/// Messages that are passed to and from the pubsub (Gossipsub) behaviour.
#[derive(Debug, Clone, PartialEq)]
pub enum PubsubMessage<E: EthSpec> {
    /// Gossipsub message providing notification of a new block.
    Block(BeaconBlock<E>),
    /// Gossipsub message providing notification of a new attestation.
    Attestation(Attestation<E>),
}

//TODO: Correctly encode/decode enums. Prefixing with integer for now.
impl<E: EthSpec> Encode for PubsubMessage<E> {
    fn is_ssz_fixed_len() -> bool {
        false
    }

    fn ssz_append(&self, buf: &mut Vec<u8>) {
        let offset = <u32 as Encode>::ssz_fixed_len() + <Vec<u8> as Encode>::ssz_fixed_len();

        let mut encoder = ssz::SszEncoder::container(buf, offset);

        match self {
            PubsubMessage::Block(block_gossip) => {
                encoder.append(&0_u32);

                // Encode the gossip as a Vec<u8>;
                encoder.append(&block_gossip.as_ssz_bytes());
            }
            PubsubMessage::Attestation(attestation_gossip) => {
                encoder.append(&1_u32);

                // Encode the gossip as a Vec<u8>;
                encoder.append(&attestation_gossip.as_ssz_bytes());
            }
        }

        encoder.finalize();
    }
}

impl<E: EthSpec> Decode for PubsubMessage<E> {
    fn is_ssz_fixed_len() -> bool {
        false
    }

    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, ssz::DecodeError> {
        let mut builder = ssz::SszDecoderBuilder::new(&bytes);

        builder.register_type::<u32>()?;
        builder.register_type::<Vec<u8>>()?;

        let mut decoder = builder.build()?;

        let id: u32 = decoder.decode_next()?;
        let body: Vec<u8> = decoder.decode_next()?;

        match id {
            0 => Ok(PubsubMessage::Block(BeaconBlock::from_ssz_bytes(&body)?)),
            1 => Ok(PubsubMessage::Attestation(Attestation::from_ssz_bytes(
                &body,
            )?)),
            _ => Err(DecodeError::BytesInvalid(
                "Invalid PubsubMessage id".to_string(),
            )),
        }
    }
}

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

    #[test]
    fn ssz_encoding() {
        let original = PubsubMessage::Block(BeaconBlock::<MainnetEthSpec>::empty(
            &MainnetEthSpec::default_spec(),
        ));

        let encoded = ssz_encode(&original);

        let decoded = PubsubMessage::from_ssz_bytes(&encoded).unwrap();

        assert_eq!(original, decoded);
    }
}