package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"net/http"
	"os"
	"time"

	log "github.com/sirupsen/logrus"
	"nhooyr.io/websocket"
)

var (
	Listen  = flag.String("listen", "0.0.0.0:8080", "listen interface:port")
	Peers   = flag.String("peers", "peers.json", "peer definition file")
	Verbose = flag.Bool("verbose", false, "verbose logging")
)

type Pair struct {
	P string `json:"p"`
	U string `json:"u"`
}

type Intro struct {
	Location int
	Conn     *websocket.Conn
	Addr     string
}

type Msg struct {
	Location int
	Bytes    []byte
	Type     websocket.MessageType
}

type Handler struct {
	pairs     []Pair
	locations map[string]int
	conns     []*websocket.Conn
	addrs     []string
	closeReqs chan int
	intros    chan Intro
	messages  chan Msg
}

func NewHandler() *Handler {
	h := &Handler{}
	h.init()
	return h
}

func (h *Handler) init() {
	h.closeReqs = make(chan int)
	h.intros = make(chan Intro)
	h.messages = make(chan Msg)
	go h.monitorChannels()
}

func (h *Handler) peer(location int) int {
	if location%2 == 0 {
		return location + 1
	} else {
		return location - 1
	}
}

func (h *Handler) monitorChannels() {
	for {
		select {
		case intro := <-h.intros:
			old := h.conns[intro.Location]
			if old != nil {
				log.WithField("old", h.addrs[intro.Location]).
					WithField("new", intro.Addr).
					WithField("uuid", h.uuidOf(intro.Location)).Info("duplicate user")
				intro.Conn.Close(websocket.StatusNormalClosure, "duplicate user")
				break
			}
			h.conns[intro.Location] = intro.Conn
			h.addrs[intro.Location] = intro.Addr
			log.WithField("client", intro.Addr).
				WithField("uuid", h.uuidOf(intro.Location)).
				Debug("drained")
			go h.relay(intro.Conn, intro.Location)
		case msg := <-h.messages:
			peerLocation := h.peer(msg.Location)
			peer := h.conns[peerLocation]
			log.WithField("client", h.addrs[msg.Location]).
				WithField("uuid", h.uuidOf(msg.Location)).
				WithField("message", string(msg.Bytes)).Debug("received")
			if peer != nil {
				log.WithField("client", h.addrs[peerLocation]).
					WithField("uuid", h.uuidOf(peerLocation)).
					Debug("sent")
				err := peer.Write(context.Background(),
					msg.Type, msg.Bytes)
				if err != nil {
					err := peer.Close(websocket.StatusNormalClosure, "write error")
					if err != nil {
						log.Warning(err)
					}
					h.conns[peerLocation] = nil
					h.addrs[peerLocation] = ""
				}
			}
		case closeLoc := <-h.closeReqs:
			err := h.conns[closeLoc].
				Close(websocket.StatusNormalClosure, "")
			if err != nil {
				log.Warning(err)
			}

			h.conns[closeLoc] = nil
			h.addrs[closeLoc] = ""
			log.Trace(h.conns)
		}
	}
}

func (h *Handler) uuidOf(location int) string {
	if location%2 == 0 {
		return h.pairs[location/2].P
	} else {
		return h.pairs[location/2].U
	}
}

func (h *Handler) relay(from *websocket.Conn, location int) {
	for {
		msgType, msgBytes, err := from.Read(context.Background())
		if err != nil {
			log.Debug("sending close message ", location)
			h.closeReqs <- location
			log.Debug("returning from Relay")
			return
		}
		h.messages <- Msg{
			Location: location,
			Type:     msgType,
			Bytes:    msgBytes,
		}
	}
}

func (h *Handler) LoadPeers(filename string) error {
	file, err := os.Open(filename)
	if err != nil {
		return err
	}
	decoder := json.NewDecoder(file)
	err = decoder.Decode(&h.pairs)
	if err != nil {
		return err
	}
	h.locations = map[string]int{}
	for i, pair := range h.pairs {
		if _, ok := h.locations[pair.P]; ok {
			return fmt.Errorf("duplicate uuid %v", pair.P)
		}
		if _, ok := h.locations[pair.U]; ok {
			return fmt.Errorf("duplicate uuid %v", pair.U)
		}
		h.locations[pair.P] = i * 2
		h.locations[pair.U] = i*2 + 1
	}
	h.conns = make([]*websocket.Conn, len(h.pairs)*2)
	h.addrs = make([]string, len(h.pairs)*2)
	return nil
}

func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	wsConn, err := websocket.Accept(w, r, nil)
	if err != nil {
		log.WithField("client", r.RemoteAddr).Error(err)
		return
	}
	wsConn.SetReadLimit(-1)
	go h.ServeWebSocket(wsConn, r.RemoteAddr)
}

func (h *Handler) ServeWebSocket(wsConn *websocket.Conn, rAddr string) {
	authLog := log.WithField("client", rAddr)
	authLog.Trace("waiting for auth")
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()
	_, msgBytes, err := wsConn.Read(ctx)
	if err != nil {
		authLog.Error(err)
		wsConn.Close(websocket.StatusNormalClosure, "")
		return
	}
	uuid := string(msgBytes)
	loc, ok := h.locations[uuid]
	if !ok {
		authLog.WithField("uuid", uuid).Error("unknown user")
		wsConn.CloseNow()
		return
	} else {
		authLog.WithField("uuid", uuid).Info("logged in")
	}
	h.intros <- Intro{loc, wsConn, rAddr}
}

func main() {
	flag.Parse()
	if *Verbose {
		log.SetLevel(log.TraceLevel)
		log.Trace("verbose logging")
	}
	h := NewHandler()
	log.Info("Parsing peers from ", *Peers)
	err := h.LoadPeers(*Peers)
	if err != nil {
		log.Fatal(err)
	}
	log.Info("Starting relay on ", *Listen)
	log.Fatal(http.ListenAndServe(*Listen, h))
}