package protocol

import (
	"context"
	"errors"
	"github.com/bolkedebruin/rdpgw/cmd/rdpgw/common"
	"github.com/bolkedebruin/rdpgw/cmd/rdpgw/transport"
	"github.com/google/uuid"
	"github.com/gorilla/websocket"
	"github.com/patrickmn/go-cache"
	"log"
	"net"
	"net/http"
	"reflect"
	"syscall"
	"time"
)

const (
	rdgConnectionIdKey = "Rdg-Connection-Id"
	MethodRDGIN        = "RDG_IN_DATA"
	MethodRDGOUT       = "RDG_OUT_DATA"
)

type CheckPAACookieFunc func(context.Context, string) (bool, error)
type CheckClientNameFunc func(context.Context, string) (bool, error)
type CheckHostFunc func(context.Context, string) (bool, error)

type Gateway struct {
	// CheckPAACookie verifies if the PAA cookie sent by the client is valid
	CheckPAACookie CheckPAACookieFunc

	// CheckClientName verifies if the client name is allowed to connect
	CheckClientName CheckClientNameFunc

	// CheckHost verifies if the client is allowed to connect to the remote host
	CheckHost CheckHostFunc

	// RedirectFlags sets what devices the client is allowed to redirect to the remote host
	RedirectFlags RedirectFlags

	// IdleTimeOut is used to determine when to disconnect clients that have been idle
	IdleTimeout int

	// SmartCardAuth sets whether to use smart card based authentication
	SmartCardAuth bool

	// TokenAuth sets whether to use token/cookie based authentication
	TokenAuth bool

	ReceiveBuf int
	SendBuf    int
}

var upgrader = websocket.Upgrader{}
var c = cache.New(5*time.Minute, 10*time.Minute)

func (g *Gateway) HandleGatewayProtocol(w http.ResponseWriter, r *http.Request) {
	connectionCache.Set(float64(c.ItemCount()))

	var t *Tunnel

	ctx := context.WithValue(r.Context(), common.TunnelCtx, t)

	connId := r.Header.Get(rdgConnectionIdKey)
	x, found := c.Get(connId)
	if !found {
		t = &Tunnel{
			RDGId:      connId,
			RemoteAddr: ctx.Value(common.ClientIPCtx).(string),
			UserName:   ctx.Value(common.UsernameCtx).(string),
		}
	} else {
		t = x.(*Tunnel)
	}

	if r.Method == MethodRDGOUT {
		if r.Header.Get("Connection") != "upgrade" && r.Header.Get("Upgrade") != "websocket" {
			g.handleLegacyProtocol(w, r.WithContext(ctx), t)
			return
		}
		r.Method = "GET" // force
		conn, err := upgrader.Upgrade(w, r, nil)
		if err != nil {
			log.Printf("Cannot upgrade falling back to old protocol: %t", err)
			return
		}
		defer conn.Close()

		err = g.setSendReceiveBuffers(conn.UnderlyingConn())
		if err != nil {
			log.Printf("Cannot set send/receive buffers: %t", err)
		}

		g.handleWebsocketProtocol(ctx, conn, t)
	} else if r.Method == MethodRDGIN {
		g.handleLegacyProtocol(w, r.WithContext(ctx), t)
	}
}

func (g *Gateway) setSendReceiveBuffers(conn net.Conn) error {
	if g.SendBuf < 1 && g.ReceiveBuf < 1 {
		return nil
	}

	// conn == tls.Tunnel
	ptr := reflect.ValueOf(conn)
	val := reflect.Indirect(ptr)

	if val.Kind() != reflect.Struct {
		return errors.New("didn't get a struct from conn")
	}

	// this gets net.Tunnel -> *net.TCPConn -> net.TCPConn
	ptrConn := val.FieldByName("conn")
	valConn := reflect.Indirect(ptrConn)
	if !valConn.IsValid() {
		return errors.New("cannot find conn field")
	}
	valConn = valConn.Elem().Elem()

	// net.FD
	ptrNetFd := valConn.FieldByName("fd")
	valNetFd := reflect.Indirect(ptrNetFd)
	if !valNetFd.IsValid() {
		return errors.New("cannot find fd field")
	}

	// pfd member
	ptrPfd := valNetFd.FieldByName("pfd")
	valPfd := reflect.Indirect(ptrPfd)
	if !valPfd.IsValid() {
		return errors.New("cannot find pfd field")
	}

	// finally the exported Sysfd
	ptrSysFd := valPfd.FieldByName("Sysfd")
	if !ptrSysFd.IsValid() {
		return errors.New("cannot find Sysfd field")
	}
	fd := int(ptrSysFd.Int())

	if g.ReceiveBuf > 0 {
		err := syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_RCVBUF, g.ReceiveBuf)
		if err != nil {
			return wrapSyscallError("setsockopt", err)
		}
	}

	if g.SendBuf > 0 {
		err := syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_SNDBUF, g.SendBuf)
		if err != nil {
			return wrapSyscallError("setsockopt", err)
		}
	}

	return nil
}

func (g *Gateway) handleWebsocketProtocol(ctx context.Context, c *websocket.Conn, t *Tunnel) {
	websocketConnections.Inc()
	defer websocketConnections.Dec()

	inout, _ := transport.NewWS(c)
	defer inout.Close()

	t.Id = uuid.New().String()
	t.transportOut = inout
	t.transportIn = inout
	t.ConnectedOn = time.Now()

	handler := NewProcessor(g, t)
	RegisterTunnel(t, handler)
	defer RemoveTunnel(t)
	handler.Process(ctx)
}

// The legacy protocol (no websockets) uses an RDG_IN_DATA for client -> server
// and RDG_OUT_DATA for server -> client data. The handshakeRequest procedure is a bit different
// to ensure the connections do not get cached or terminated by a proxy prematurely.
func (g *Gateway) handleLegacyProtocol(w http.ResponseWriter, r *http.Request, t *Tunnel) {
	log.Printf("Session %s, %t, %t", t.RDGId, t.transportOut != nil, t.transportIn != nil)

	if r.Method == MethodRDGOUT {
		out, err := transport.NewLegacy(w)
		if err != nil {
			log.Printf("cannot hijack connection to support RDG OUT data channel: %s", err)
			return
		}
		log.Printf("Opening RDGOUT for client %s", common.GetClientIp(r.Context()))

		t.transportOut = out
		out.SendAccept(true)

		c.Set(t.RDGId, t, cache.DefaultExpiration)
	} else if r.Method == MethodRDGIN {
		legacyConnections.Inc()
		defer legacyConnections.Dec()

		in, err := transport.NewLegacy(w)
		if err != nil {
			log.Printf("cannot hijack connection to support RDG IN data channel: %s", err)
			return
		}
		defer in.Close()

		if t.transportIn == nil {
			t.Id = uuid.New().String()
			t.transportIn = in
			c.Set(t.RDGId, t, cache.DefaultExpiration)

			log.Printf("Opening RDGIN for client %s", common.GetClientIp(r.Context()))
			in.SendAccept(false)

			// read some initial data
			in.Drain()

			log.Printf("Legacy handshakeRequest done for client %s", common.GetClientIp(r.Context()))
			handler := NewProcessor(g, t)
			RegisterTunnel(t, handler)
			defer RemoveTunnel(t)
			handler.Process(r.Context())
		}
	}
}