package net

import (
	"bytes"
	"errors"
	"lux/crypto"
	"lux/proto"
	"net"
	"sync"
)

type LuxRoute struct {
	Key         crypto.LuxKey
	Destination *net.UDPAddr
	Associated  *LuxChannel
}

type LuxRouter struct {
	thisKey  crypto.LuxKey
	keyStore crypto.LuxKeyStore

	routes []LuxRoute

	channelLock sync.RWMutex
	outbound    []LuxChannel
	inbound     []LuxChannel

	dgramChan chan LuxDatagram
}

func NewLuxRouter(key crypto.LuxKey, ks crypto.LuxKeyStore) LuxRouter {
	return LuxRouter{
		thisKey:   key,
		keyStore:  ks,
		routes:    make([]LuxRoute, 0),
		outbound:  make([]LuxChannel, 0),
		inbound:   make([]LuxChannel, 0),
		dgramChan: make(chan LuxDatagram),
	}
}

func (r *LuxRouter) addOutboundChannel(ch LuxChannel) *LuxChannel {
	r.channelLock.Lock()

	r.outbound = append(r.outbound, ch)
	channel := &r.outbound[len(r.outbound)-1]

	r.channelLock.Unlock()
	return channel
}

func (r *LuxRouter) addInboundChannel(ch LuxChannel) *LuxChannel {
	r.channelLock.Lock()

	r.inbound = append(r.inbound, ch)
	channel := &r.inbound[len(r.inbound)-1]

	r.channelLock.Unlock()
	return channel
}

func (r *LuxRouter) CreateOutboundRoute(id proto.LuxID, chType LuxChannelType, udpAddr string) error {
	// we gonna look up key by id from key store
	key, ok := r.keyStore.Get(id)
	if !ok {
		return errors.New("key not found")
	}

	// create outbound channel
	channel, err := NewLuxOutboundChannel(udpAddr, chType)
	if err != nil {
		return err
	}

	r.routes = append(r.routes, LuxRoute{
		Key:         key,
		Destination: channel.Address,
		Associated:  r.addOutboundChannel(channel),
	})
	return nil
}

func (r *LuxRouter) CreateInboundChannel(chType LuxChannelType, udpAddr string) error {
	channel, err := NewLuxInboundChannel(udpAddr, chType)
	if err != nil {
		return err
	}

	r.routes = append(r.routes, LuxRoute{
		Key:         r.thisKey,
		Destination: channel.Address,
		Associated:  r.addInboundChannel(channel),
	})
	return nil
}

// close channel when error happened
func (r *LuxRouter) CloseChannel(channel *LuxChannel, closeInbound bool) {
	r.channelLock.Lock()
	for i, ch := range r.outbound {
		if &ch == channel {
			r.outbound = append(r.outbound[:i], r.outbound[i+1:]...)
		}
	}

	if closeInbound {
		for i, ch := range r.inbound {
			if &ch == channel {
				r.inbound = append(r.inbound[:i], r.inbound[:i+1]...)
			}
		}
	}
	r.channelLock.Unlock()
}

func (r *LuxRouter) GetDgramChannel() chan<- LuxDatagram {
	return r.dgramChan
}

// goroutine to receive datagrams and send them to router over channel
func channelReceiver(r *LuxRouter, channel *LuxChannel) {
	dgramChan := r.GetDgramChannel()

	var dgram LuxDatagram
	var err error

	for err == nil {
		dgram, err = channel.Recv()
		dgramChan <- dgram
	}

	r.CloseChannel(channel, true)
}

func (r *LuxRouter) Start() {
	r.channelLock.RLock()
	for _, inbound := range r.inbound {
		go channelReceiver(r, &inbound)
	}
	r.channelLock.RUnlock()
}

func (r *LuxRouter) RecvDgram() LuxDatagram {
	return <-r.dgramChan
}

func udpAddrEqual(addr *net.UDPAddr, other *net.UDPAddr) bool {
	return addr.IP.Equal(other.IP) && addr.Port == other.Port
}

func (r *LuxRouter) getRouteIndex(udpAddr *net.UDPAddr) (LuxRoute, int) {
	for idx, route := range r.routes {
		if udpAddrEqual(route.Destination, udpAddr) {
			return route, idx
		}
	}
	return LuxRoute{}, -1
}

func (r *LuxRouter) GetRoute(udpAddr *net.UDPAddr) (LuxRoute, bool) {
	route, idx := r.getRouteIndex(udpAddr)
	return route, idx != -1
}

func (r *LuxRouter) DeleteRoute(route *LuxRoute) {
	_, idx := r.getRouteIndex(route.Destination)
	if idx == -1 {
		return
	}

	r.CloseChannel(route.Associated, false)
	r.routes = append(r.routes[idx:], r.routes[:idx+1]...)
}

func (r *LuxRouter) Recv() (LuxPacket, error) {
	dgram := r.RecvDgram()

	var err error
	var packet LuxPacket

	// first we look key from routes
	if route, ok := r.GetRoute(dgram.Target); ok {
		packet, err = DecryptLuxPacket(dgram, route.Key)
		if err != nil {
			return packet, err
		}

		// check if LuxID matches
		if !bytes.Equal(packet.Target.UUID[:], route.Key.Id.UUID[:]) {
			// not matches.. we discard route and throw away packet
			r.DeleteRoute(&route)
			return packet, errors.New("bogus packet from established route")
			/* NOTE:
			*	there may be rare situation where multiple clients behind NAT/CGNAT
			*	reusing same IP:Port of established route, confusing routing table.
			*	This is not critical, since hosts and nodes are expected to send
			*	data again after interval of time, and packet loss is expected and
			*	tolerated at protocol design level.
			 */
		}

		// packet arrived to right route and successfully decrypted
		return packet, nil
	} else {
		// first time seeing peer - bruteforce keys from keystore
		for _, key := range r.keyStore.Keys() {
			packet, err = DecryptLuxPacket(dgram, key)
			if err != nil {
				continue
			}

			if bytes.Equal(packet.Target.UUID[:], key.Id.UUID[:]) {
				// key UUID and decrypted UUID matching - create new route and return packet
				// TODO: inject lux channel into dgram
			}
		}
	}

	return packet, nil
}