package inbound

import (
	"crypto/md5"
	"io"
	"net"
	"sync"

	"github.com/v2ray/v2ray-core/app"
	"github.com/v2ray/v2ray-core/common/alloc"
	v2crypto "github.com/v2ray/v2ray-core/common/crypto"
	"github.com/v2ray/v2ray-core/common/log"
	v2net "github.com/v2ray/v2ray-core/common/net"
	"github.com/v2ray/v2ray-core/common/retry"
	"github.com/v2ray/v2ray-core/common/serial"
	"github.com/v2ray/v2ray-core/proxy"
	"github.com/v2ray/v2ray-core/proxy/internal"
	"github.com/v2ray/v2ray-core/proxy/vmess"
	"github.com/v2ray/v2ray-core/proxy/vmess/protocol"
)

// Inbound connection handler that handles messages in VMess format.
type VMessInboundHandler struct {
	sync.Mutex
	space         app.Space
	clients       protocol.UserSet
	user          *vmess.User
	accepting     bool
	listener      *net.TCPListener
	features      *FeaturesConfig
	listeningPort v2net.Port
}

func (this *VMessInboundHandler) Port() v2net.Port {
	return this.listeningPort
}

func (this *VMessInboundHandler) Close() {
	this.accepting = false
	if this.listener != nil {
		this.listener.Close()
		this.Lock()
		this.listener = nil
		this.Unlock()
	}
}

func (this *VMessInboundHandler) GetUser() *vmess.User {
	return this.user
}

func (this *VMessInboundHandler) Listen(port v2net.Port) error {
	if this.accepting {
		if this.listeningPort == port {
			return nil
		} else {
			return proxy.ErrorAlreadyListening
		}
	}
	this.listeningPort = port

	listener, err := net.ListenTCP("tcp", &net.TCPAddr{
		IP:   []byte{0, 0, 0, 0},
		Port: int(port),
		Zone: "",
	})
	if err != nil {
		log.Error("Unable to listen tcp port ", port, ": ", err)
		return err
	}
	this.accepting = true
	this.Lock()
	this.listener = listener
	this.Unlock()
	go this.AcceptConnections()
	return nil
}

func (this *VMessInboundHandler) AcceptConnections() error {
	for this.accepting {
		retry.Timed(100 /* times */, 100 /* ms */).On(func() error {
			this.Lock()
			defer this.Unlock()
			if !this.accepting {
				return nil
			}
			connection, err := this.listener.AcceptTCP()
			if err != nil {
				log.Error("Failed to accpet connection: ", err)
				return err
			}
			go this.HandleConnection(connection)
			return nil
		})

	}
	return nil
}

func (this *VMessInboundHandler) HandleConnection(connection *net.TCPConn) error {
	defer connection.Close()

	connReader := v2net.NewTimeOutReader(16, connection)
	requestReader := protocol.NewVMessRequestReader(this.clients)

	request, err := requestReader.Read(connReader)
	if err != nil {
		log.Access(connection.RemoteAddr(), serial.StringLiteral(""), log.AccessRejected, serial.StringLiteral(err.Error()))
		log.Warning("VMessIn: Invalid request from ", connection.RemoteAddr(), ": ", err)
		return err
	}
	log.Access(connection.RemoteAddr(), request.Address, log.AccessAccepted, serial.StringLiteral(""))
	log.Debug("VMessIn: Received request for ", request.Address)

	ray := this.space.PacketDispatcher().DispatchToOutbound(v2net.NewPacket(request.Destination(), nil, true))
	input := ray.InboundInput()
	output := ray.InboundOutput()
	var readFinish, writeFinish sync.Mutex
	readFinish.Lock()
	writeFinish.Lock()

	userSettings := vmess.GetUserSettings(request.User.Level)
	connReader.SetTimeOut(userSettings.PayloadReadTimeout)
	go handleInput(request, connReader, input, &readFinish)

	responseKey := md5.Sum(request.RequestKey)
	responseIV := md5.Sum(request.RequestIV)

	aesStream, err := v2crypto.NewAesEncryptionStream(responseKey[:], responseIV[:])
	if err != nil {
		log.Error("VMessIn: Failed to create AES decryption stream: ", err)
		close(input)
		return err
	}

	responseWriter := v2crypto.NewCryptionWriter(aesStream, connection)

	// Optimize for small response packet
	buffer := alloc.NewLargeBuffer().Clear()
	defer buffer.Release()
	buffer.AppendBytes(request.ResponseHeader, byte(0))
	this.generateCommand(buffer)

	if data, open := <-output; open {
		buffer.Append(data.Value)
		data.Release()
		responseWriter.Write(buffer.Value)
		go handleOutput(request, responseWriter, output, &writeFinish)
		writeFinish.Lock()
	}

	connection.CloseWrite()
	readFinish.Lock()

	return nil
}

func handleInput(request *protocol.VMessRequest, reader io.Reader, input chan<- *alloc.Buffer, finish *sync.Mutex) {
	defer close(input)
	defer finish.Unlock()

	aesStream, err := v2crypto.NewAesDecryptionStream(request.RequestKey, request.RequestIV)
	if err != nil {
		log.Error("VMessIn: Failed to create AES decryption stream: ", err)
		return
	}
	requestReader := v2crypto.NewCryptionReader(aesStream, reader)
	v2net.ReaderToChan(input, requestReader)
}

func handleOutput(request *protocol.VMessRequest, writer io.Writer, output <-chan *alloc.Buffer, finish *sync.Mutex) {
	v2net.ChanToWriter(writer, output)
	finish.Unlock()
}

func init() {
	internal.MustRegisterInboundConnectionHandlerCreator("vmess",
		func(space app.Space, rawConfig interface{}) (proxy.InboundConnectionHandler, error) {
			config := rawConfig.(*Config)

			allowedClients := protocol.NewTimedUserSet()
			for _, user := range config.AllowedUsers {
				allowedClients.AddUser(user)
			}

			return &VMessInboundHandler{
				space:    space,
				clients:  allowedClients,
				features: config.Features,
				user:     config.AllowedUsers[0],
			}, nil
		})
}