package tun2

import (
	"bufio"
	"context"
	"crypto/tls"
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"math/rand"
	"net"
	"net/http"
	"strings"
	"sync"
	"time"

	"git.xeserv.us/xena/route/database"
	"github.com/Xe/ln"
	failure "github.com/dgryski/go-failure"
	"github.com/mtneug/pkg/ulid"
	cmap "github.com/streamrail/concurrent-map"
	kcp "github.com/xtaci/kcp-go"
	"github.com/xtaci/smux"
)

type ServerConfig struct {
	TCPAddr   string
	KCPAddr   string
	TLSConfig *tls.Config

	SmuxConf *smux.Config
	Storage  Storage
}

type Storage interface {
	GetRouteForHost(name string) (*database.Route, error)
	//ValidateToken(token string) (username string, ok bool, err error) // XXX RIP implement when users are implemented
}

type Server struct {
	cfg *ServerConfig

	connlock sync.Mutex
	conns    map[net.Conn]*Connection

	domains cmap.ConcurrentMap
}

type Connection struct {
	id            string
	conn          net.Conn
	isKCP         bool
	session       *smux.Session
	controlStream *smux.Stream
	user          string
	domain        string
	cancel        context.CancelFunc
	detector      *failure.Detector
}

func (c *Connection) F() ln.F {
	return map[string]interface{}{
		"id":     c.id,
		"remote": c.conn.RemoteAddr(),
		"local":  c.conn.LocalAddr(),
		"isKCP":  c.isKCP,
		"user":   c.user,
		"domain": c.domain,
	}
}

func NewServer(cfg *ServerConfig) (*Server, error) {
	if cfg == nil {
		return nil, errors.New("tun2: config must be specified")
	}

	if cfg.SmuxConf == nil {
		cfg.SmuxConf = smux.DefaultConfig()
	}

	server := &Server{
		cfg: cfg,

		conns:   map[net.Conn]*Connection{},
		domains: cmap.New(),
	}

	return server, nil
}

func (s *Server) ListenAndServe() error {
	ln.Log(ln.F{
		"action": "listen_and_serve_called",
	})

	if s.cfg.TCPAddr != "" {
		go func() {
			l, err := tls.Listen("tcp", s.cfg.TCPAddr, s.cfg.TLSConfig)
			if err != nil {
				panic(err)
			}

			ln.Log(ln.F{
				"action": "tcp+tls_listening",
				"addr":   l.Addr(),
			})

			for {
				conn, err := l.Accept()
				if err != nil {
					ln.Error(err, ln.F{"kind": "tcp", "addr": l.Addr().String()})
					continue
				}

				ln.Log(ln.F{
					"action": "new_client",
					"kcp":    false,
					"addr":   conn.RemoteAddr(),
				})

				go s.HandleConn(conn, false)
			}
		}()
	}

	if s.cfg.KCPAddr != "" {
		go func() {
			l, err := kcp.Listen(s.cfg.KCPAddr)
			if err != nil {
				panic(err)
			}

			ln.Log(ln.F{
				"action": "kcp+tls_listening",
				"addr":   l.Addr(),
			})

			for {
				conn, err := l.Accept()
				if err != nil {
					ln.Error(err, ln.F{"kind": "kcp", "addr": l.Addr().String()})
				}

				ln.Log(ln.F{
					"action": "new_client",
					"kcp":    true,
					"addr":   conn.RemoteAddr(),
				})

				tc := tls.Server(conn, s.cfg.TLSConfig)

				go s.HandleConn(tc, true)
			}
		}()
	}

	go func() {
		for {
			time.Sleep(5 * time.Second)

			now := time.Now()

			s.connlock.Lock()
			for _, c := range s.conns {
				failureChance := c.detector.Phi(now)

				if failureChance != 0 {
					ln.Log(c.F(), ln.F{
						"action": "phi_failure_detection",
						"value":  failureChance,
					})
				}
			}
			s.connlock.Unlock()
		}
	}()

	return nil
}

// Ping ends a "ping" to the client. If the client doesn't respond or the connection
// dies, then the connection needs to be cleaned up.
func (c *Connection) Ping() error {
	req, err := http.NewRequest("GET", "http://backend/health", nil)
	if err != nil {
		panic(err)
	}

	stream, err := c.OpenStream()
	if err != nil {
		ln.Error(err, c.F())
		defer c.cancel()
		return err
	}
	defer stream.Close()

	stream.SetWriteDeadline(time.Now().Add(time.Second))
	err = req.Write(stream)
	if err != nil {
		ln.Error(err, c.F())
		defer c.cancel()
		return err
	}

	stream.SetReadDeadline(time.Now().Add(5 * time.Second))
	_, err = stream.Read(make([]byte, 30))
	if err != nil {
		ln.Error(err, c.F())
		defer c.cancel()
		return err
	}

	c.detector.Ping(time.Now())

	return nil
}

// OpenStream creates a new stream (connection) to the backend server.
func (c *Connection) OpenStream() (net.Conn, error) {
	err := c.conn.SetDeadline(time.Now().Add(time.Second))
	if err != nil {
		ln.Error(err, c.F())
		return nil, err
	}

	stream, err := c.session.OpenStream()
	if err != nil {
		ln.Error(err, c.F())
		return nil, err
	}

	return stream, c.conn.SetDeadline(time.Time{})
}

// Close destroys resouces specific to the connection.
func (c *Connection) Close() error {
	err := c.controlStream.Close()
	if err != nil {
		return err
	}

	err = c.session.Close()
	if err != nil {
		return err
	}

	err = c.conn.Close()
	if err != nil {
		return err
	}

	return nil
}

func (s *Server) HandleConn(c net.Conn, isKCP bool) {
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	session, err := smux.Server(c, s.cfg.SmuxConf)
	if err != nil {
		ln.Error(err, ln.F{
			"action": "session_failure",
			"local":  c.LocalAddr().String(),
			"remote": c.RemoteAddr().String(),
		})

		c.Close()

		return
	}

	controlStream, err := session.OpenStream()
	if err != nil {
		ln.Error(err, ln.F{
			"action": "control_stream_failure",
			"local":  c.LocalAddr().String(),
			"remote": c.RemoteAddr().String(),
		})

		session.Close()
		c.Close()

		return
	}

	csd := json.NewDecoder(controlStream)
	auth := &Auth{}
	err = csd.Decode(auth)
	if err != nil {
		ln.Error(err, ln.F{
			"action": "control_stream_auth_decoding_failure",
			"local":  c.LocalAddr().String(),
			"remote": c.RemoteAddr().String(),
		})

		controlStream.Close()
		session.Close()
		c.Close()

		return
	}

	route, err := s.cfg.Storage.GetRouteForHost(auth.Domain)
	if err != nil {
		ln.Error(err, ln.F{
			"action": "nosuch_domain",
			"local":  c.LocalAddr().String(),
			"remote": c.RemoteAddr().String(),
		})

		controlStream.Close()
		session.Close()
		c.Close()

		return
	}

	if route.Token != auth.Token {
		ln.Error(err, ln.F{
			"action": "bad_token",
			"local":  c.LocalAddr().String(),
			"remote": c.RemoteAddr().String(),
		})

		fmt.Fprintln(controlStream, "bad token")

		controlStream.Close()
		session.Close()
		c.Close()

		return
	}

	connection := &Connection{
		id:       ulid.New().String(),
		conn:     c,
		isKCP:    isKCP,
		session:  session,
		user:     defaultUser, // XXX RIP replace this with the actual token user once users are implemented
		domain:   auth.Domain,
		cancel:   cancel,
		detector: failure.New(15, 1),
	}

	ln.Log(ln.F{
		"action": "backend_connected",
	}, connection.F())

	s.connlock.Lock()
	s.conns[c] = connection
	s.connlock.Unlock()

	var conns []*Connection

	val, ok := s.domains.Get(auth.Domain)
	if ok {
		conns, ok = val.([]*Connection)
		if !ok {
			conns = nil

			s.domains.Remove(auth.Domain)
		}
	}

	conns = append(conns, connection)

	s.domains.Set(auth.Domain, conns)

	ticker := time.NewTicker(5 * time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			err := connection.Ping()
			if err != nil {
				cancel()
			}
		case <-ctx.Done():
			s.RemoveConn(auth, connection)
			connection.Close()

			return
		}
	}
}

func (s *Server) RemoveConn(auth *Auth, connection *Connection) {
	s.connlock.Lock()
	delete(s.conns, connection.conn)
	s.connlock.Unlock()

	var conns []*Connection

	val, ok := s.domains.Get(auth.Domain)
	if ok {
		conns, ok = val.([]*Connection)
		if !ok {
			ln.Error(errors.New("fundamental assertion is not met"), connection.F(), ln.F{
				"action": "looking_up_for_disconnect_removal",
			})
			return
		}
	}

	for i, cntn := range conns {
		if cntn.id == connection.id {
			conns[i] = conns[len(conns)-1]
			conns = conns[:len(conns)-1]
		}
	}

	if len(conns) != 0 {
		s.domains.Set(auth.Domain, conns)
	} else {
		s.domains.Remove(auth.Domain)
	}

	ln.Log(connection.F(), ln.F{
		"action": "client_disconnecting",
	})
}

func (s *Server) RoundTrip(req *http.Request) (*http.Response, error) {
	var conns []*Connection

	val, ok := s.domains.Get(req.Host)
	if ok {
		conns, ok = val.([]*Connection)
		if !ok {
			ln.Error(errors.New("no backend connected"), ln.F{
				"action": "no_backend_connected",
				"remote": req.RemoteAddr,
				"host":   req.Host,
				"uri":    req.RequestURI,
			})

			resp := &http.Response{
				StatusCode:    http.StatusBadGateway,
				Body:          ioutil.NopCloser(strings.NewReader("no such domain")),
				ContentLength: 14,
				Close:         true,
				Request:       req,
			}

			return resp, errors.New("no backend connected")
		}
	}

	if len(conns) == 0 {
		ln.Error(errors.New("no backend connected"), ln.F{
			"action": "no_backend_connected",
			"remote": req.RemoteAddr,
			"host":   req.Host,
			"uri":    req.RequestURI,
		})

		return nil, errors.New("no backend connected")
	}

	c := conns[rand.Intn(len(conns))]

	c.conn.SetDeadline(time.Now().Add(time.Second))
	stream, err := c.session.OpenStream()
	if err != nil {
		ln.Error(err, ln.F{
			"action":      "opening_session_stream",
			"remote_addr": req.RemoteAddr,
			"host":        req.Host,
			"uri":         req.RequestURI,
		}, c.F())

		c.cancel()

		return s.RoundTrip(req)
	}
	defer stream.Close()
	c.conn.SetDeadline(time.Time{})

	err = req.Write(stream)
	if err != nil {
		ln.Error(err, ln.F{
			"action":      "request_writing",
			"remote_addr": req.RemoteAddr,
			"host":        req.Host,
			"uri":         req.RequestURI,
		}, c.F())

		c.cancel()

		return s.RoundTrip(req)
	}

	buf := bufio.NewReader(stream)

	resp, err := http.ReadResponse(buf, req)
	if err != nil {
		ln.Error(err, ln.F{
			"action":      "response_reading",
			"remote_addr": req.RemoteAddr,
			"host":        req.Host,
			"uri":         req.RequestURI,
		}, c.F())

		c.cancel()

		return nil, err
	}

	ln.Log(c.F(), ln.F{
		"action":      "http_traffic",
		"remote_addr": req.RemoteAddr,
		"host":        req.Host,
		"uri":         req.RequestURI,
	})

	return resp, nil
}

type Auth struct {
	Token  string `json:"token"`
	Domain string `json:"domain"`
}

const defaultUser = "Cadey"