package session

import (
	"encoding/base64"
	"fmt"
	"io"
	"log"
	"math/rand"
	"time"

	"badat.dev/maeqtt/v2/mqtt/packets"
	"badat.dev/maeqtt/v2/subscription"
)

func init() {
	rand.Seed(time.Now().UnixNano())
}

func Auth(username string, password []byte) bool {
	return true
}

type Session struct {
	ClientID *string

	// Nullable
	Connection          *Connection
	SubscriptionChannel chan packets.PublishPacket
	ConnecionChannel    chan ConnectionRequest

	ExpiryInterval time.Duration // TODO
	expireTimer    time.Timer    // TODO

	freePacketID uint16
}

type ConnectionRequest struct {
	Connection    *Connection
	ConnectPakcet packets.ConnectPacket
}

func NewSession(req ConnectionRequest) Session {
	sess := Session{}
	sess.SubscriptionChannel = make(chan packets.PublishPacket)

	sess.Connect(req)
	return sess
}

func (s *Session) Connect(req ConnectionRequest) {
	if s.Connection != nil {
		s.Disconnect(packets.DisconnectReasonCodeSessionTakenOver)
	}
	connAck := packets.ConnackPacket{}

	s.updateExpireTimer(req.ConnectPakcet.Properties.SessionExpiryInterval.Value)

	if req.ConnectPakcet.ClientId != nil {
		if s.ClientID == nil {
			s.ClientID = genClientID()
		}
		connAck.Properties.AssignedClientIdentifier.Value = s.ClientID
	}

	true := byte(1)
	false := byte(0)
	connAck.Properties.WildcardSubscriptionAvailable.Value = &true

	connAck.Properties.RetainAvailable.Value = &false
	connAck.Properties.SharedSubscriptionAvailable.Value = &false

	s.Connection = req.Connection
	err := s.Connection.sendPacket(connAck)
	if err != nil {
		// TODO
		panic(err)
	}
}

// Starts a loop the recieves and responds to packets
func (s *Session) HandlerLoop() {
	go s.Connection.PacketReadLoop()
	for s.Connection != nil {
		select {
		case packet := <-s.Connection.PacketChannel:
			packet.Visit(s)
		case _ = <-s.Connection.ClientDisconnectedChan:
			s.onDisconnect()
		case c := <-s.ConnecionChannel:
			s.Connect(c)
		case subMessage := <-s.SubscriptionChannel:
			subMessage.QOSLevel = 0
			subMessage.Dup = false
			s.Connection.sendPacket(subMessage)
		}
	}
	c := <-s.ConnecionChannel
	s.Connect(c)
	s.HandlerLoop()
}

func (s *Session) Disconnect(code packets.DisconnectReasonCode) error {
	s.Connection.sendPacket(packets.DisconnectPacket{
		ReasonCode: code,
	})

	err := s.Connection.close()
	if err != nil {
		return err
	}
	s.onDisconnect()
	return nil
}

func (s *Session) onDisconnect() {
	s.Connection = nil
	s.resetExpireTimer()
	log.Printf("Client disconnected, id: %s", *s.ClientID)
}

func (s *Session) expireSession() {
	subscription.Subscriptions.RemoveSubsForChannel(s.SubscriptionChannel)
}

// newTime is nullable
func (s *Session) updateExpireTimer(newTime *uint32) {
	var expiry = uint32(0)
	if newTime != nil {
		expiry = *newTime
	} else {
		expiry = uint32(0)
	}
	s.ExpiryInterval = time.Duration(expiry) * time.Second

	if s.Connection == nil {
		s.resetExpireTimer()
	}
}
func (s *Session) resetExpireTimer() {
	//s.expireTimer.Reset(s.ExpiryInterval)
}

func genClientID() *string {
	buf := make([]byte, 32)
	_, err := rand.Read(buf)
	if err != nil {
		// I don't think this can actually happen but just in case panic
		panic(fmt.Errorf("Failed to generate a client id, %e", err))
	}
	id := "Client_rand_" + base64.URLEncoding.WithPadding(base64.NoPadding).EncodeToString(buf)
	return &id
}

func (s *Session) VisitConnect(_ packets.ConnectPacket) {
	// Disconnect, we handle the connect packet in Connect,
	// this means that we have an estabilished connection already
	log.Println("WARN: Got a connect packet on an already estabilished connection")
	s.Disconnect(packets.DisconnectReasonCodeProtocolError)
}

func (s *Session) VisitPublish(p packets.PublishPacket) {
	subNodes := subscription.Subscriptions.GetSubscriptions(p.TopicName)
	for _, subNode := range subNodes {
		subNode.NodeLock.RLock()
		defer subNode.NodeLock.RUnlock()
		if p.QOSLevel == 0 {
			if p.PacketId != nil {
				log.Printf("Client: %v, Got publish with qos 0 and a packet id, ignoring\n", s.ClientID)
				return
			}
		} else if p.QOSLevel == 1 {
			var reason packets.PubackReasonCode = packets.PubackReasonCodeSuccess
			ack := packets.PubackPacket{
				PacketID: *p.PacketId,
				Reason:   reason,
			}
			s.Connection.sendPacket(ack)
		} else if p.QOSLevel == 2 {
			panic("UNIMPLEMENTED QOS level 2")
		}

		for _, sub := range subNode.Subscriptions {
			if !(sub.NoLocal && sub.SubscriptionChannel == s.SubscriptionChannel) {
				go func(sub subscription.Subscription) { sub.SubscriptionChannel <- p }(sub)
			}
		}
	}
}

func (s *Session) VisitDisconnect(p packets.DisconnectPacket) {
	err := s.Connection.close()
	if err != nil && err != io.ErrClosedPipe {
		log.Println("Error closing connection", err)
	}
	s.onDisconnect()
}

func (s *Session) VisitSubscribe(p packets.SubscribePacket) {
	for _, filter := range p.TopicFilters {
		subscription.Subscriptions.Subscribe(filter, s.SubscriptionChannel)
	}
	s.Connection.sendPacket(packets.SubAckPacket{
		PacketID: p.PacketId,
		Reason:   packets.SubackReasonGrantedQoSTwo,
	})
}

func (s *Session) VisitUnsubscribe(p packets.UnsubscribePacket) {
	for _, topic := range p.Topics {
		subscription.Subscriptions.Unsubscribe(topic, s.SubscriptionChannel)
	}
	s.Connection.sendPacket(packets.UnsubAckPacket{
		PacketID: p.PacketID,
		Reason:   packets.UnsubackReasonSuccess,
	})
}

func (s *Session) VisitPing(p packets.PingreqPacket) {
	s.Connection.sendPacket(packets.PingrespPacket{})
}

func (s *Session) VisitPubackPacket(_ packets.PubackPacket) {
	panic("not implemented") // TODO: Implement
}

func (s *Session) VisitPubrecPacket(_ packets.PubrecPacket) {
	panic("not implemented") // TODO: Implement
}

func (s *Session) VisitPubrelPacket(_ packets.PubrelPacket) {
	panic("not implemented") // TODO: Implement
}

func (s *Session) VisitPubcompPacket(_ packets.PubcompPacket) {
	panic("not implemented") // TODO: Implement
}

func (s *Session) getFreePacketId() uint16 {
	s.freePacketID += 1
	return s.freePacketID
}