package floodsub

import (
	"context"
	"time"

	pb "github.com/libp2p/go-floodsub/pb"

	host "github.com/libp2p/go-libp2p-host"
	peer "github.com/libp2p/go-libp2p-peer"
	protocol "github.com/libp2p/go-libp2p-protocol"
)

const (
	GossipSubID = protocol.ID("/meshsub/1.0.0")

	// overlay parameters
	GossipSubD   = 6
	GossipSubDlo = 4
	GossipSubDhi = 12
)

func NewGossipSub(ctx context.Context, h host.Host, opts ...Option) (*PubSub, error) {
	rt := &GossipSubRouter{
		peers:  make(map[peer.ID]protocol.ID),
		mesh:   make(map[string]map[peer.ID]struct{}),
		fanout: make(map[string]map[peer.ID]struct{}),
		mcache: NewMessageCache(5),
	}
	return NewPubSub(ctx, h, rt, opts...)
}

type GossipSubRouter struct {
	p      *PubSub
	peers  map[peer.ID]protocol.ID         // peer protocols
	mesh   map[string]map[peer.ID]struct{} // topic meshes
	fanout map[string]map[peer.ID]struct{} // topic fanout
	mcache *MessageCache
}

func (gs *GossipSubRouter) Protocols() []protocol.ID {
	return []protocol.ID{GossipSubID, FloodSubID}
}

func (gs *GossipSubRouter) Attach(p *PubSub) {
	gs.p = p
	go gs.heartbeatTimer()
}

func (gs *GossipSubRouter) AddPeer(p peer.ID, proto protocol.ID) {
	gs.peers[p] = proto
}

func (gs *GossipSubRouter) RemovePeer(p peer.ID) {
	delete(gs.peers, p)
	for _, peers := range gs.mesh {
		delete(peers, p)
	}
	for _, peers := range gs.fanout {
		delete(peers, p)
	}
}

func (gs *GossipSubRouter) HandleRPC(rpc *RPC) {
	ctl := rpc.GetControl()
	if ctl == nil {
		return
	}

	iwant := gs.handleIHave(ctl)
	msgs := gs.handleIWant(ctl)
	prune := gs.handleGraft(rpc.from, ctl)
	gs.handlePrune(rpc.from, ctl)

	if len(iwant) == 0 && len(msgs) == 0 && len(prune) == 0 {
		return
	}

	// TODO piggyback gossip IHAVE
	out := rpcWithControl(msgs, nil, iwant, nil, prune)

	mch, ok := gs.p.peers[rpc.from]
	if !ok {
		return
	}

	select {
	case mch <- out:
	default:
		// TODO PRUNE messages should be reliable; schedule for piggybacking or retry
		log.Infof("dropping message to peer %s: queue full", rpc.from)
	}
}

func (gs *GossipSubRouter) handleIHave(ctl *pb.ControlMessage) []*pb.ControlIWant {
	iwant := make(map[string]struct{})

	for _, ihave := range ctl.GetIhave() {
		topic := ihave.GetTopicID()
		_, ok := gs.mesh[topic]
		if !ok {
			continue
		}

		for _, mid := range ihave.GetMessageIDs() {
			if gs.p.seenMessage(mid) {
				continue
			}
			iwant[mid] = struct{}{}
		}
	}

	if len(iwant) == 0 {
		return nil
	}

	iwantlst := make([]string, 0, len(iwant))
	for mid := range iwant {
		iwantlst = append(iwantlst, mid)
	}

	return []*pb.ControlIWant{&pb.ControlIWant{MessageIDs: iwantlst}}
}

func (gs *GossipSubRouter) handleIWant(ctl *pb.ControlMessage) []*pb.Message {
	ihave := make(map[string]*pb.Message)
	for _, iwant := range ctl.GetIwant() {
		for _, mid := range iwant.GetMessageIDs() {
			msg, ok := gs.mcache.Get(mid)
			if ok {
				ihave[mid] = msg
			}
		}
	}

	if len(ihave) == 0 {
		return nil
	}

	msgs := make([]*pb.Message, 0, len(ihave))
	for _, msg := range ihave {
		msgs = append(msgs, msg)
	}

	return msgs
}

func (gs *GossipSubRouter) handleGraft(p peer.ID, ctl *pb.ControlMessage) []*pb.ControlPrune {
	var prune []string
	for _, graft := range ctl.GetGraft() {
		topic := graft.GetTopicID()
		peers, ok := gs.mesh[topic]
		if !ok {
			prune = append(prune, topic)
		} else {
			peers[p] = struct{}{}
		}
	}

	if len(prune) == 0 {
		return nil
	}

	cprune := make([]*pb.ControlPrune, 0, len(prune))
	for _, topic := range prune {
		cprune = append(cprune, &pb.ControlPrune{TopicID: &topic})
	}

	return cprune
}

func (gs *GossipSubRouter) handlePrune(p peer.ID, ctl *pb.ControlMessage) {
	for _, prune := range ctl.GetPrune() {
		topic := prune.GetTopicID()
		peers, ok := gs.mesh[topic]
		if ok {
			delete(peers, p)
		}
	}
}

func (gs *GossipSubRouter) Publish(from peer.ID, msg *pb.Message) {
	gs.mcache.Add(msg)

	tosend := make(map[peer.ID]struct{})
	for _, topic := range msg.GetTopicIDs() {
		// any peers in the topic?
		tmap, ok := gs.p.topics[topic]
		if !ok {
			continue
		}

		// floodsub peers
		for p := range tmap {
			if gs.peers[p] == FloodSubID {
				tosend[p] = struct{}{}
			}
		}

		// gossipsub peers
		gmap, ok := gs.mesh[topic]
		if ok {
			// direct peers in the mesh for topic
			for p := range gmap {
				tosend[p] = struct{}{}
			}
		} else {
			// fanout peers, we are not in the mesh for topic
			gmap, ok = gs.fanout[topic]
			if !ok {
				// we don't have any yet, pick some
				var peers []peer.ID
				for p := range tmap {
					if gs.peers[p] == GossipSubID {
						peers = append(peers, p)
					}
				}

				if len(peers) > 0 {
					gmap = make(map[peer.ID]struct{})

					shufflePeers(peers)
					for _, p := range peers[:GossipSubD] {
						gmap[p] = struct{}{}
					}

					gs.fanout[topic] = gmap
				}
			}
		}

		for p := range gmap {
			tosend[p] = struct{}{}
		}
	}

	out := rpcWithMessages(msg)
	for pid := range tosend {
		if pid == from || pid == peer.ID(msg.GetFrom()) {
			continue
		}

		mch, ok := gs.p.peers[pid]
		if !ok {
			continue
		}

		select {
		case mch <- out:
		default:
			log.Infof("dropping message to peer %s: queue full", pid)
			// Drop it. The peer is too slow.
		}
	}
}

func (gs *GossipSubRouter) Join(topic string) {
	// TODO
}

func (gs *GossipSubRouter) Leave(topic string) {
	// TODO
}

func (gs *GossipSubRouter) heartbeatTimer() {
	ticker := time.NewTicker(1 * time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			select {
			case gs.p.eval <- gs.heartbeat:
			case <-gs.p.ctx.Done():
				return
			}
		case <-gs.p.ctx.Done():
			return
		}
	}
}

func (gs *GossipSubRouter) heartbeat() {
	// TODO
}

func shufflePeers(peers []peer.ID) {
	// TODO
}