package inbound

import (
	"bytes"
	"context"
	gotls "crypto/tls"
	"io"
	"reflect"
	"strconv"
	"strings"
	"time"
	"unsafe"

	"github.com/xtls/xray-core/common"
	"github.com/xtls/xray-core/common/buf"
	"github.com/xtls/xray-core/common/errors"
	"github.com/xtls/xray-core/common/log"
	"github.com/xtls/xray-core/common/net"
	"github.com/xtls/xray-core/common/protocol"
	"github.com/xtls/xray-core/common/retry"
	"github.com/xtls/xray-core/common/session"
	"github.com/xtls/xray-core/common/signal"
	"github.com/xtls/xray-core/common/task"
	"github.com/xtls/xray-core/core"
	"github.com/xtls/xray-core/features/dns"
	feature_inbound "github.com/xtls/xray-core/features/inbound"
	"github.com/xtls/xray-core/features/policy"
	"github.com/xtls/xray-core/features/routing"
	"github.com/xtls/xray-core/proxy"
	"github.com/xtls/xray-core/proxy/vless"
	"github.com/xtls/xray-core/proxy/vless/encoding"
	"github.com/xtls/xray-core/transport/internet/reality"
	"github.com/xtls/xray-core/transport/internet/stat"
	"github.com/xtls/xray-core/transport/internet/tls"
)

func init() {
	common.Must(common.RegisterConfig((*Config)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
		var dc dns.Client
		if err := core.RequireFeatures(ctx, func(d dns.Client) error {
			dc = d
			return nil
		}); err != nil {
			return nil, err
		}

		c := config.(*Config)

		validator := new(vless.MemoryValidator)
		for _, user := range c.Clients {
			u, err := user.ToMemoryUser()
			if err != nil {
				return nil, errors.New("failed to get VLESS user").Base(err).AtError()
			}
			if err := validator.Add(u); err != nil {
				return nil, errors.New("failed to initiate user").Base(err).AtError()
			}
		}

		return New(ctx, c, dc, validator)
	}))
}

// Handler is an inbound connection handler that handles messages in VLess protocol.
type Handler struct {
	inboundHandlerManager feature_inbound.Manager
	policyManager         policy.Manager
	validator             vless.Validator
	dns                   dns.Client
	fallbacks             map[string]map[string]map[string]*Fallback // or nil
	// regexps               map[string]*regexp.Regexp       // or nil
}

// New creates a new VLess inbound handler.
func New(ctx context.Context, config *Config, dc dns.Client, validator vless.Validator) (*Handler, error) {
	v := core.MustFromContext(ctx)
	handler := &Handler{
		inboundHandlerManager: v.GetFeature(feature_inbound.ManagerType()).(feature_inbound.Manager),
		policyManager:         v.GetFeature(policy.ManagerType()).(policy.Manager),
		dns:                   dc,
		validator:             validator,
	}

	if config.Fallbacks != nil {
		handler.fallbacks = make(map[string]map[string]map[string]*Fallback)
		// handler.regexps = make(map[string]*regexp.Regexp)
		for _, fb := range config.Fallbacks {
			if handler.fallbacks[fb.Name] == nil {
				handler.fallbacks[fb.Name] = make(map[string]map[string]*Fallback)
			}
			if handler.fallbacks[fb.Name][fb.Alpn] == nil {
				handler.fallbacks[fb.Name][fb.Alpn] = make(map[string]*Fallback)
			}
			handler.fallbacks[fb.Name][fb.Alpn][fb.Path] = fb
			/*
				if fb.Path != "" {
					if r, err := regexp.Compile(fb.Path); err != nil {
						return nil, errors.New("invalid path regexp").Base(err).AtError()
					} else {
						handler.regexps[fb.Path] = r
					}
				}
			*/
		}
		if handler.fallbacks[""] != nil {
			for name, apfb := range handler.fallbacks {
				if name != "" {
					for alpn := range handler.fallbacks[""] {
						if apfb[alpn] == nil {
							apfb[alpn] = make(map[string]*Fallback)
						}
					}
				}
			}
		}
		for _, apfb := range handler.fallbacks {
			if apfb[""] != nil {
				for alpn, pfb := range apfb {
					if alpn != "" { // && alpn != "h2" {
						for path, fb := range apfb[""] {
							if pfb[path] == nil {
								pfb[path] = fb
							}
						}
					}
				}
			}
		}
		if handler.fallbacks[""] != nil {
			for name, apfb := range handler.fallbacks {
				if name != "" {
					for alpn, pfb := range handler.fallbacks[""] {
						for path, fb := range pfb {
							if apfb[alpn][path] == nil {
								apfb[alpn][path] = fb
							}
						}
					}
				}
			}
		}
	}

	return handler, nil
}

func isMuxAndNotXUDP(request *protocol.RequestHeader, first *buf.Buffer) bool {
	if request.Command != protocol.RequestCommandMux {
		return false
	}
	if first.Len() < 7 {
		return true
	}
	firstBytes := first.Bytes()
	return !(firstBytes[2] == 0 && // ID high
		firstBytes[3] == 0 && // ID low
		firstBytes[6] == 2) // Network type: UDP
}

// Close implements common.Closable.Close().
func (h *Handler) Close() error {
	return errors.Combine(common.Close(h.validator))
}

// AddUser implements proxy.UserManager.AddUser().
func (h *Handler) AddUser(ctx context.Context, u *protocol.MemoryUser) error {
	return h.validator.Add(u)
}

// RemoveUser implements proxy.UserManager.RemoveUser().
func (h *Handler) RemoveUser(ctx context.Context, e string) error {
	return h.validator.Del(e)
}

// GetUser implements proxy.UserManager.GetUser().
func (h *Handler) GetUser(ctx context.Context, email string) *protocol.MemoryUser {
	return h.validator.GetByEmail(email)
}

// GetUsers implements proxy.UserManager.GetUsers().
func (h *Handler) GetUsers(ctx context.Context) []*protocol.MemoryUser {
	return h.validator.GetAll()
}

// GetUsersCount implements proxy.UserManager.GetUsersCount().
func (h *Handler) GetUsersCount(context.Context) int64 {
	return h.validator.GetCount()
}

// Network implements proxy.Inbound.Network().
func (*Handler) Network() []net.Network {
	return []net.Network{net.Network_TCP, net.Network_UNIX}
}

// Process implements proxy.Inbound.Process().
func (h *Handler) Process(ctx context.Context, network net.Network, connection stat.Connection, dispatcher routing.Dispatcher) error {
	iConn := connection
	if statConn, ok := iConn.(*stat.CounterConnection); ok {
		iConn = statConn.Connection
	}

	sessionPolicy := h.policyManager.ForLevel(0)
	if err := connection.SetReadDeadline(time.Now().Add(sessionPolicy.Timeouts.Handshake)); err != nil {
		return errors.New("unable to set read deadline").Base(err).AtWarning()
	}

	first := buf.FromBytes(make([]byte, buf.Size))
	first.Clear()
	firstLen, _ := first.ReadFrom(connection)
	errors.LogInfo(ctx, "firstLen = ", firstLen)

	reader := &buf.BufferedReader{
		Reader: buf.NewReader(connection),
		Buffer: buf.MultiBuffer{first},
	}

	var request *protocol.RequestHeader
	var requestAddons *encoding.Addons
	var err error

	napfb := h.fallbacks
	isfb := napfb != nil

	if isfb && firstLen < 18 {
		err = errors.New("fallback directly")
	} else {
		request, requestAddons, isfb, err = encoding.DecodeRequestHeader(isfb, first, reader, h.validator)
	}

	if err != nil {
		if isfb {
			if err := connection.SetReadDeadline(time.Time{}); err != nil {
				errors.LogWarningInner(ctx, err, "unable to set back read deadline")
			}
			errors.LogInfoInner(ctx, err, "fallback starts")

			name := ""
			alpn := ""
			if tlsConn, ok := iConn.(*tls.Conn); ok {
				cs := tlsConn.ConnectionState()
				name = cs.ServerName
				alpn = cs.NegotiatedProtocol
				errors.LogInfo(ctx, "realName = "+name)
				errors.LogInfo(ctx, "realAlpn = "+alpn)
			} else if realityConn, ok := iConn.(*reality.Conn); ok {
				cs := realityConn.ConnectionState()
				name = cs.ServerName
				alpn = cs.NegotiatedProtocol
				errors.LogInfo(ctx, "realName = "+name)
				errors.LogInfo(ctx, "realAlpn = "+alpn)
			}
			name = strings.ToLower(name)
			alpn = strings.ToLower(alpn)

			if len(napfb) > 1 || napfb[""] == nil {
				if name != "" && napfb[name] == nil {
					match := ""
					for n := range napfb {
						if n != "" && strings.Contains(name, n) && len(n) > len(match) {
							match = n
						}
					}
					name = match
				}
			}

			if napfb[name] == nil {
				name = ""
			}
			apfb := napfb[name]
			if apfb == nil {
				return errors.New(`failed to find the default "name" config`).AtWarning()
			}

			if apfb[alpn] == nil {
				alpn = ""
			}
			pfb := apfb[alpn]
			if pfb == nil {
				return errors.New(`failed to find the default "alpn" config`).AtWarning()
			}

			path := ""
			if len(pfb) > 1 || pfb[""] == nil {
				/*
					if lines := bytes.Split(firstBytes, []byte{'\r', '\n'}); len(lines) > 1 {
						if s := bytes.Split(lines[0], []byte{' '}); len(s) == 3 {
							if len(s[0]) < 8 && len(s[1]) > 0 && len(s[2]) == 8 {
								errors.New("realPath = " + string(s[1])).AtInfo().WriteToLog(sid)
								for _, fb := range pfb {
									if fb.Path != "" && h.regexps[fb.Path].Match(s[1]) {
										path = fb.Path
										break
									}
								}
							}
						}
					}
				*/
				if firstLen >= 18 && first.Byte(4) != '*' { // not h2c
					firstBytes := first.Bytes()
					for i := 4; i <= 8; i++ { // 5 -> 9
						if firstBytes[i] == '/' && firstBytes[i-1] == ' ' {
							search := len(firstBytes)
							if search > 64 {
								search = 64 // up to about 60
							}
							for j := i + 1; j < search; j++ {
								k := firstBytes[j]
								if k == '\r' || k == '\n' { // avoid logging \r or \n
									break
								}
								if k == '?' || k == ' ' {
									path = string(firstBytes[i:j])
									errors.LogInfo(ctx, "realPath = "+path)
									if pfb[path] == nil {
										path = ""
									}
									break
								}
							}
							break
						}
					}
				}
			}
			fb := pfb[path]
			if fb == nil {
				return errors.New(`failed to find the default "path" config`).AtWarning()
			}

			ctx, cancel := context.WithCancel(ctx)
			timer := signal.CancelAfterInactivity(ctx, cancel, sessionPolicy.Timeouts.ConnectionIdle)
			ctx = policy.ContextWithBufferPolicy(ctx, sessionPolicy.Buffer)

			var conn net.Conn
			if err := retry.ExponentialBackoff(5, 100).On(func() error {
				var dialer net.Dialer
				conn, err = dialer.DialContext(ctx, fb.Type, fb.Dest)
				if err != nil {
					return err
				}
				return nil
			}); err != nil {
				return errors.New("failed to dial to " + fb.Dest).Base(err).AtWarning()
			}
			defer conn.Close()

			serverReader := buf.NewReader(conn)
			serverWriter := buf.NewWriter(conn)

			postRequest := func() error {
				defer timer.SetTimeout(sessionPolicy.Timeouts.DownlinkOnly)
				if fb.Xver != 0 {
					ipType := 4
					remoteAddr, remotePort, err := net.SplitHostPort(connection.RemoteAddr().String())
					if err != nil {
						ipType = 0
					}
					localAddr, localPort, err := net.SplitHostPort(connection.LocalAddr().String())
					if err != nil {
						ipType = 0
					}
					if ipType == 4 {
						for i := 0; i < len(remoteAddr); i++ {
							if remoteAddr[i] == ':' {
								ipType = 6
								break
							}
						}
					}
					pro := buf.New()
					defer pro.Release()
					switch fb.Xver {
					case 1:
						if ipType == 0 {
							pro.Write([]byte("PROXY UNKNOWN\r\n"))
							break
						}
						if ipType == 4 {
							pro.Write([]byte("PROXY TCP4 " + remoteAddr + " " + localAddr + " " + remotePort + " " + localPort + "\r\n"))
						} else {
							pro.Write([]byte("PROXY TCP6 " + remoteAddr + " " + localAddr + " " + remotePort + " " + localPort + "\r\n"))
						}
					case 2:
						pro.Write([]byte("\x0D\x0A\x0D\x0A\x00\x0D\x0A\x51\x55\x49\x54\x0A")) // signature
						if ipType == 0 {
							pro.Write([]byte("\x20\x00\x00\x00")) // v2 + LOCAL + UNSPEC + UNSPEC + 0 bytes
							break
						}
						if ipType == 4 {
							pro.Write([]byte("\x21\x11\x00\x0C")) // v2 + PROXY + AF_INET + STREAM + 12 bytes
							pro.Write(net.ParseIP(remoteAddr).To4())
							pro.Write(net.ParseIP(localAddr).To4())
						} else {
							pro.Write([]byte("\x21\x21\x00\x24")) // v2 + PROXY + AF_INET6 + STREAM + 36 bytes
							pro.Write(net.ParseIP(remoteAddr).To16())
							pro.Write(net.ParseIP(localAddr).To16())
						}
						p1, _ := strconv.ParseUint(remotePort, 10, 16)
						p2, _ := strconv.ParseUint(localPort, 10, 16)
						pro.Write([]byte{byte(p1 >> 8), byte(p1), byte(p2 >> 8), byte(p2)})
					}
					if err := serverWriter.WriteMultiBuffer(buf.MultiBuffer{pro}); err != nil {
						return errors.New("failed to set PROXY protocol v", fb.Xver).Base(err).AtWarning()
					}
				}
				if err := buf.Copy(reader, serverWriter, buf.UpdateActivity(timer)); err != nil {
					return errors.New("failed to fallback request payload").Base(err).AtInfo()
				}
				return nil
			}

			writer := buf.NewWriter(connection)

			getResponse := func() error {
				defer timer.SetTimeout(sessionPolicy.Timeouts.UplinkOnly)
				if err := buf.Copy(serverReader, writer, buf.UpdateActivity(timer)); err != nil {
					return errors.New("failed to deliver response payload").Base(err).AtInfo()
				}
				return nil
			}

			if err := task.Run(ctx, task.OnSuccess(postRequest, task.Close(serverWriter)), task.OnSuccess(getResponse, task.Close(writer))); err != nil {
				common.Interrupt(serverReader)
				common.Interrupt(serverWriter)
				return errors.New("fallback ends").Base(err).AtInfo()
			}
			return nil
		}

		if errors.Cause(err) != io.EOF {
			log.Record(&log.AccessMessage{
				From:   connection.RemoteAddr(),
				To:     "",
				Status: log.AccessRejected,
				Reason: err,
			})
			err = errors.New("invalid request from ", connection.RemoteAddr()).Base(err).AtInfo()
		}
		return err
	}

	if err := connection.SetReadDeadline(time.Time{}); err != nil {
		errors.LogWarningInner(ctx, err, "unable to set back read deadline")
	}
	errors.LogInfo(ctx, "received request for ", request.Destination())

	inbound := session.InboundFromContext(ctx)
	if inbound == nil {
		panic("no inbound metadata")
	}
	inbound.Name = "vless"
	inbound.User = request.User

	account := request.User.Account.(*vless.MemoryAccount)

	responseAddons := &encoding.Addons{
		// Flow: requestAddons.Flow,
	}
	encoding.PopulateSeed(account.Seed, responseAddons)
	if check := encoding.CheckSeed(requestAddons, responseAddons); check != nil {
		return errors.New("Seed configuration mis-match").Base(check).AtWarning()
	}

	var input *bytes.Reader
	var rawInput *bytes.Buffer
	switch requestAddons.Flow {
	case vless.XRV:
		if account.Flow == requestAddons.Flow {
			inbound.CanSpliceCopy = 2
			switch request.Command {
			case protocol.RequestCommandUDP:
				return errors.New(requestAddons.Flow + " doesn't support UDP").AtWarning()
			case protocol.RequestCommandMux:
				fallthrough // we will break Mux connections that contain TCP requests
			case protocol.RequestCommandTCP:
				var t reflect.Type
				var p uintptr
				if tlsConn, ok := iConn.(*tls.Conn); ok {
					if tlsConn.ConnectionState().Version != gotls.VersionTLS13 {
						return errors.New(`failed to use `+requestAddons.Flow+`, found outer tls version `, tlsConn.ConnectionState().Version).AtWarning()
					}
					t = reflect.TypeOf(tlsConn.Conn).Elem()
					p = uintptr(unsafe.Pointer(tlsConn.Conn))
				} else if realityConn, ok := iConn.(*reality.Conn); ok {
					t = reflect.TypeOf(realityConn.Conn).Elem()
					p = uintptr(unsafe.Pointer(realityConn.Conn))
				} else {
					return errors.New("XTLS only supports TLS and REALITY directly for now.").AtWarning()
				}
				i, _ := t.FieldByName("input")
				r, _ := t.FieldByName("rawInput")
				input = (*bytes.Reader)(unsafe.Pointer(p + i.Offset))
				rawInput = (*bytes.Buffer)(unsafe.Pointer(p + r.Offset))
			}
		} else {
			return errors.New("account " + account.ID.String() + " is not able to use the flow " + requestAddons.Flow).AtWarning()
		}
	case "":
		inbound.CanSpliceCopy = 3
		if account.Flow == vless.XRV && (request.Command == protocol.RequestCommandTCP || isMuxAndNotXUDP(request, first)) {
			return errors.New("account " + account.ID.String() + " is rejected since the client flow is empty. Note that the pure TLS proxy has certain TLS in TLS characters.").AtWarning()
		}
	default:
		return errors.New("unknown request flow " + requestAddons.Flow).AtWarning()
	}

	if request.Command != protocol.RequestCommandMux {
		ctx = log.ContextWithAccessMessage(ctx, &log.AccessMessage{
			From:   connection.RemoteAddr(),
			To:     request.Destination(),
			Status: log.AccessAccepted,
			Reason: "",
			Email:  request.User.Email,
		})
	} else if account.Flow == vless.XRV {
		ctx = session.ContextWithAllowedNetwork(ctx, net.Network_UDP)
	}

	sessionPolicy = h.policyManager.ForLevel(request.User.Level)
	ctx, cancel := context.WithCancel(ctx)
	timer := signal.CancelAfterInactivity(ctx, cancel, sessionPolicy.Timeouts.ConnectionIdle)
	inbound.Timer = timer
	ctx = policy.ContextWithBufferPolicy(ctx, sessionPolicy.Buffer)

	link, err := dispatcher.Dispatch(ctx, request.Destination())
	if err != nil {
		return errors.New("failed to dispatch request to ", request.Destination()).Base(err).AtWarning()
	}

	serverReader := link.Reader // .(*pipe.Reader)
	serverWriter := link.Writer // .(*pipe.Writer)
	trafficState := proxy.NewTrafficState(account.ID.Bytes(), account.Flow)
	postRequest := func() error {
		defer timer.SetTimeout(sessionPolicy.Timeouts.DownlinkOnly)

		// default: clientReader := reader
		clientReader := encoding.DecodeBodyAddons(reader, request, requestAddons, trafficState, ctx)

		var err error

		if requestAddons.Flow == vless.XRV {
			ctx1 := session.ContextWithInbound(ctx, nil) // TODO enable splice
			err = encoding.XtlsRead(clientReader, serverWriter, timer, connection, input, rawInput, trafficState, nil, ctx1)
		} else {
			// from clientReader.ReadMultiBuffer to serverWriter.WriteMultiBuffer
			err = buf.Copy(clientReader, serverWriter, buf.UpdateActivity(timer))
		}

		if err != nil {
			return errors.New("failed to transfer request payload").Base(err).AtInfo()
		}

		return nil
	}

	getResponse := func() error {
		defer timer.SetTimeout(sessionPolicy.Timeouts.UplinkOnly)

		bufferWriter := buf.NewBufferedWriter(buf.NewWriter(connection))
		if err := encoding.EncodeResponseHeader(bufferWriter, request, responseAddons); err != nil {
			return errors.New("failed to encode response header").Base(err).AtWarning()
		}

		// default: clientWriter := bufferWriter
		clientWriter := encoding.EncodeBodyAddons(bufferWriter, request, requestAddons, trafficState, ctx)
		multiBuffer, err1 := serverReader.ReadMultiBuffer()
		if err1 != nil {
			return err1 // ...
		}
		if err := clientWriter.WriteMultiBuffer(multiBuffer); err != nil {
			return err // ...
		}
		// Flush; bufferWriter.WriteMultiBuffer now is bufferWriter.writer.WriteMultiBuffer
		if err := bufferWriter.SetBuffered(false); err != nil {
			return errors.New("failed to write A response payload").Base(err).AtWarning()
		}

		var err error
		if requestAddons.Flow == vless.XRV {
			err = encoding.XtlsWrite(serverReader, clientWriter, timer, connection, trafficState, nil, ctx)
		} else {
			// from serverReader.ReadMultiBuffer to clientWriter.WriteMultiBuffer
			err = buf.Copy(serverReader, clientWriter, buf.UpdateActivity(timer))
		}
		if err != nil {
			return errors.New("failed to transfer response payload").Base(err).AtInfo()
		}
		// Indicates the end of response payload.
		switch responseAddons.Flow {
		default:
		}

		return nil
	}

	if err := task.Run(ctx, task.OnSuccess(postRequest, task.Close(serverWriter)), getResponse); err != nil {
		common.Interrupt(serverReader)
		common.Interrupt(serverWriter)
		return errors.New("connection ends").Base(err).AtInfo()
	}

	return nil
}