package network

import (
	"context"
	"errors"
	"fmt"
	"io"
	"net"
	"os"
	"sync"
	"sync/atomic"

	// authentication implements, Currently, only token authentication is implemented
	_ "git.hpds.cc/Component/network/auth"
	"git.hpds.cc/Component/network/frame"
	"git.hpds.cc/Component/network/hpds_err"
	"git.hpds.cc/Component/network/log"
	pkgtls "git.hpds.cc/Component/network/tls"
	"github.com/lucas-clemente/quic-go"
)

const (
	// DefaultListenAddr is the default address to listen.
	DefaultListenAddr = "0.0.0.0:9000"
)

// ServerOption is the option for server.
type ServerOption func(*ServerOptions)

// FrameHandler is the handler for frame.
type FrameHandler func(c *Context) error

// Server is the underlining server of Message Queue
type Server struct {
	name               string
	state              string
	connector          Connector
	router             Router
	metadataBuilder    MetadataBuilder
	counterOfDataFrame int64
	downStreams        map[string]*Client
	mu                 sync.Mutex
	opts               ServerOptions
	beforeHandlers     []FrameHandler
	afterHandlers      []FrameHandler
}

// NewServer create a Server instance.
func NewServer(name string, opts ...ServerOption) *Server {
	s := &Server{
		name:        name,
		connector:   newConnector(),
		downStreams: make(map[string]*Client),
	}
	s.Init(opts...)

	return s
}

// Init the options.
func (s *Server) Init(opts ...ServerOption) error {
	for _, o := range opts {
		o(&s.opts)
	}
	// options defaults
	s.initOptions()

	return nil
}

// ListenAndServe starts the server.
func (s *Server) ListenAndServe(ctx context.Context, addr string) error {
	if addr == "" {
		addr = DefaultListenAddr
	}
	udpAddr, err := net.ResolveUDPAddr("udp", addr)
	if err != nil {
		return err
	}
	conn, err := net.ListenUDP("udp", udpAddr)
	if err != nil {
		return err
	}
	return s.Serve(ctx, conn)
}

// Serve the server with a net.PacketConn.
func (s *Server) Serve(ctx context.Context, conn net.PacketConn) error {
	if err := s.validateMetadataBuilder(); err != nil {
		return err
	}

	if err := s.validateRouter(); err != nil {
		return err
	}

	// listen the address
	listener, err := newListener(conn, s.opts.TLSConfig, s.opts.QuicConfig)
	if err != nil {
		log.Errorf("%slistener.Listen: err=%v", ServerLogPrefix, err)
		return err
	}
	defer listener.Close()
	log.Printf("%s [%s][%d] Listening on: %s, MODE: %s, QUIC: %v, AUTH: %s", ServerLogPrefix, s.name, os.Getpid(), listener.Addr(), mode(), listener.Versions(), s.authNames())

	s.state = ConnStateConnected
	for {
		// create a new connection when new hpds-client connected
		sctx, cancel := context.WithCancel(ctx)
		defer cancel()

		connect, e := listener.Accept(sctx)
		if e != nil {
			log.Errorf("%screate connection error: %v", ServerLogPrefix, e)
			return e
		}

		connID := GetConnId(connect)
		log.Infof("%s1/ new connection: %s", ServerLogPrefix, connID)

		go func(ctx context.Context, qconn quic.Connection) {
			for {
				log.Infof("%s2/ waiting for new stream", ServerLogPrefix)
				stream, err := qconn.AcceptStream(ctx)
				if err != nil {
					// if client close the connection, then we should close the connection
					// @CC: when Source close the connection, it won't affect connectors
					name := "--"
					if conn := s.connector.Get(connID); conn != nil {
						conn.Close()
						// connector
						s.connector.Remove(connID)
						route := s.router.Route(conn.Metadata())
						if route != nil {
							route.Remove(connID)
						}
						name = conn.Name()
					}
					log.Printf("%s [%s](%s) close the connection: %v", ServerLogPrefix, name, connID, err)
					break
				}
				defer stream.Close()

				log.Infof("%s3/ [stream:%d] created, connId=%s", ServerLogPrefix, stream.StreamID(), connID)
				// process frames on stream
				// c := newContext(connId, stream)
				c := newContext(connect, stream)
				defer c.Clean()
				s.handleConnection(c)
				log.Infof("%s4/ [stream:%d] handleConnection DONE", ServerLogPrefix, stream.StreamID())
			}
		}(sctx, connect)
	}
}

// Close will shut down the server.
func (s *Server) Close() error {
	if s.router != nil {
		s.router.Clean()
	}
	// connector
	if s.connector != nil {
		s.connector.Clean()
	}
	return nil
}

// handle streams on a connection
func (s *Server) handleConnection(c *Context) {
	fs := NewFrameStream(c.Stream)
	// check update for stream
	for {
		log.Debugf("%shandleConnection waiting read next...", ServerLogPrefix)
		f, err := fs.ReadFrame()
		if err != nil {
			// if client close connection, will get ApplicationError with code = 0x00
			if e, ok := err.(*quic.ApplicationError); ok {
				if hpds_err.Is(e.ErrorCode, hpds_err.ErrorCodeClientAbort) {
					// client abort
					log.Infof("%sclient close the connection", ServerLogPrefix)
					break
				} else {
					ye := hpds_err.New(hpds_err.Parse(e.ErrorCode), err)
					log.Errorf("%s[ERR] %s", ServerLogPrefix, ye)
				}
			} else if err == io.EOF {
				log.Infof("%sthe connection is EOF", ServerLogPrefix)
				break
			}
			if errors.Is(err, net.ErrClosed) {
				// if client close the connection, net.ErrClosed will be raised
				// by quic-go IdleTimeoutError after connection's KeepAlive config.
				log.Warnf("%s[ERR] net.ErrClosed on [handleConnection] %v", ServerLogPrefix, net.ErrClosed)
				c.CloseWithError(hpds_err.ErrorCodeClosed, "net.ErrClosed")
				break
			}
			// any error occurred, we should close the stream
			// after this, conn.AcceptStream() will raise the error
			c.CloseWithError(hpds_err.ErrorCodeUnknown, err.Error())
			log.Warnf("%sconnection.Close()", ServerLogPrefix)
			break
		}

		frameType := f.Type()
		data := f.Encode()
		log.Debugf("%stype=%s, frame[%d]=%# x", ServerLogPrefix, frameType, len(data), frame.Shortly(data))
		// add frame to context
		context := c.WithFrame(f)

		// before frame handlers
		for _, handler := range s.beforeHandlers {
			if e := handler(context); e != nil {
				log.Errorf("%safterFrameHandler e: %s", ServerLogPrefix, e)
				context.CloseWithError(hpds_err.ErrorCodeBeforeHandler, e.Error())
				return
			}
		}
		// main handler
		if e := s.mainFrameHandler(context); e != nil {
			log.Errorf("%smainFrameHandler e: %s", ServerLogPrefix, e)
			context.CloseWithError(hpds_err.ErrorCodeMainHandler, e.Error())
			return
		}
		// after frame handler
		for _, handler := range s.afterHandlers {
			if e := handler(context); e != nil {
				log.Errorf("%safterFrameHandler e: %s", ServerLogPrefix, e)
				context.CloseWithError(hpds_err.ErrorCodeAfterHandler, e.Error())
				return
			}
		}
	}
}

func (s *Server) mainFrameHandler(c *Context) error {
	var err error
	frameType := c.Frame.Type()

	switch frameType {
	case frame.TagOfHandshakeFrame:
		if err = s.handleHandshakeFrame(c); err != nil {
			log.Errorf("%shandleHandshakeFrame err: %s", ServerLogPrefix, err)
			// close connections early to avoid resource consumption
			if c.Stream != nil {
				goawayFrame := frame.NewGoawayFrame(err.Error())
				if _, e := c.Stream.Write(goawayFrame.Encode()); e != nil {
					log.Errorf("%s write to client[%s] GoawayFrame error:%v", ServerLogPrefix, c.ConnId, e)
					return e
				}
			}
		}
	// case frame.TagOfPingFrame:
	// 	s.handlePingFrame(mainStream, connection, f.(*frame.PingFrame))
	case frame.TagOfDataFrame:
		if err = s.handleDataFrame(c); err != nil {
			c.CloseWithError(hpds_err.ErrorCodeData, fmt.Sprintf("handleDataFrame err: %v", err))
		} else {
			conn := s.connector.Get(c.connId)
			if conn != nil && conn.ClientType() == ClientTypeProtocolGateway {
				f := c.Frame.(*frame.DataFrame)
				f.GetMetaFrame().SetMetadata(conn.Metadata().Encode())
				s.dispatchToDownStreams(f)
			}
			// observe data tags back flow
			s.handleBackFlowFrame(c)
		}
	default:
		log.Errorf("%serr=%v, frame=%v", ServerLogPrefix, err, frame.Shortly(c.Frame.Encode()))
	}
	return nil
}

// handle HandShakeFrame
func (s *Server) handleHandshakeFrame(c *Context) error {
	f := c.Frame.(*frame.HandshakeFrame)

	log.Debugf("%sGOT HandshakeFrame : %# x", ServerLogPrefix, f)
	// basic info
	connId := c.ConnId()
	clientId := f.ClientId
	clientType := ClientType(f.ClientType)
	stream := c.Stream
	// credential
	log.Debugf("%sClientType=%# x is %s, ClientId=%s, Credential=%s", ServerLogPrefix, f.ClientType, ClientType(f.ClientType), clientId, authName(f.AuthName()))
	// authenticate
	if !s.authenticate(f) {
		err := fmt.Errorf("handshake authentication fails, client credential name is %s", authName(f.AuthName()))
		// return err
		log.Debugf("%s <%s> [%s](%s) is connected!", ServerLogPrefix, clientType, f.Name, connId)
		rejectedFrame := frame.NewRejectedFrame(err.Error())
		if _, err = stream.Write(rejectedFrame.Encode()); err != nil {
			log.Debugf("%s write to <%s> [%s](%s) RejectedFrame error:%v", ServerLogPrefix, clientType, f.Name, connId, err)
			return err
		}
		return nil
	}

	// client type
	var conn Connection
	switch clientType {
	case ClientTypeProtocolGateway, ClientTypeStreamFunction:
		// metadata
		metadata, err := s.metadataBuilder.Build(f)
		if err != nil {
			return err
		}
		conn = newConnection(f.Name, f.ClientId, clientType, metadata, stream, f.ObserveDataTags)

		if clientType == ClientTypeStreamFunction {
			// route
			route := s.router.Route(metadata)
			if route == nil {
				return errors.New("handleHandshakeFrame route is nil")
			}
			if e1 := route.Add(connId, f.Name, f.ObserveDataTags); e1 != nil {
				// duplicate name
				if e2, ok := e1.(hpds_err.DuplicateNameError); ok {
					existsConnID := e2.ConnId()
					if conn = s.connector.Get(existsConnID); conn != nil {
						log.Debugf("%s%s, write to SFN[%s](%s) GoawayFrame", ServerLogPrefix, e2.Error(), f.Name, existsConnID)
						goawayFrame := frame.NewGoawayFrame(e2.Error())
						if e3 := conn.Write(goawayFrame); e3 != nil {
							log.Errorf("%s write to SFN[%s] GoawayFrame error:%v", ServerLogPrefix, f.Name, e3)
							return e3
						}
					}
				} else {
					return e1
				}
			}
		}
	case ClientTypeMessageQueue:
		conn = newConnection(f.Name, f.ClientId, clientType, nil, stream, f.ObserveDataTags)
	default:
		// unknown client type
		s.connector.Remove(connId)
		err := fmt.Errorf("Illegal ClientType: %#x", f.ClientType)
		c.CloseWithError(hpds_err.ErrorCodeUnknownClient, err.Error())
		return err
	}

	s.connector.Add(connId, conn)
	log.Printf("%s <%s> [%s][%s](%s) is connected!", ServerLogPrefix, clientType, f.Name, clientId, connId)
	return nil
}

// handle handleGoawayFrame
func (s *Server) handleGoawayFrame(c *Context) error {
	f := c.Frame.(*frame.GoawayFrame)

	log.Debugf("%s GOT GoawayFrame code=%d, message==%s", ServerLogPrefix, hpds_err.ErrorCodeGoaway, f.Message())
	// c.CloseWithError(f.Code(), f.Message())
	_, err := c.Stream.Write(f.Encode())
	return err
}

// will reuse quic-go's keep-alive feature
// func (s *Server) handlePingFrame(stream quic.Stream, conn quic.Connection, f *frame.PingFrame) error {
// 	log.Infof("%s------> GOT PingFrame : %# x", ServerLogPrefix, f)
// 	return nil
// }

func (s *Server) handleDataFrame(c *Context) error {
	// counter +1
	atomic.AddInt64(&s.counterOfDataFrame, 1)
	// currentIssuer := f.GetIssuer()
	fromId := c.ConnId()
	from := s.connector.Get(fromId)
	if from == nil {
		log.Warnf("%shandleDataFrame connector cannot find %s", ServerLogPrefix, fromId)
		return fmt.Errorf("handleDataFrame connector cannot find %s", fromId)
	}

	f := c.Frame.(*frame.DataFrame)

	var metadata Metadata
	if from.ClientType() == ClientTypeMessageQueue {
		m, err := s.metadataBuilder.Decode(f.GetMetaFrame().Metadata())
		if err != nil {
			return err
		}
		metadata = m
	} else {
		metadata = from.Metadata()
	}

	// route
	route := s.router.Route(metadata)
	if route == nil {
		log.Warnf("%shandleDataFrame route is nil", ServerLogPrefix)
		return fmt.Errorf("handleDataFrame route is nil")
	}

	// get stream function connection ids from route
	connIds := route.GetForwardRoutes(f.GetDataTag())
	for _, toId := range connIds {
		conn := s.connector.Get(toId)
		if conn == nil {
			log.Errorf("%sconn is nil: (%s)", ServerLogPrefix, toId)
			continue
		}

		to := conn.Name()
		log.Debugf("%shandleDataFrame tag=%#x tid=%s, counter=%d, from=[%s](%s), to=[%s](%s)", ServerLogPrefix, f.Tag(), f.TransactionId(), s.counterOfDataFrame, from.Name(), fromId, to, toId)

		// write data frame to stream
		if err := conn.Write(f); err != nil {
			log.Warnf("%shandleDataFrame conn.Write tag=%#x tid=%s, from=[%s](%s), to=[%s](%s), %v", ServerLogPrefix, f.Tag(), f.TransactionId(), from.Name(), fromId, to, toId, err)
		}
	}

	return nil
}

func (s *Server) handleBackFlowFrame(c *Context) error {
	f := c.Frame.(*frame.DataFrame)
	tag := f.GetDataTag()
	carriage := f.GetCarriage()
	sourceId := f.SourceId()
	// write to Protocol Gateway with BackFlowFrame
	bf := frame.NewBackFlowFrame(tag, carriage)
	sourceConns := s.connector.GetProtocolGatewayConnections(sourceId, tag)
	// conn := s.connector.Get(c.connId)
	// logger.Printf("%s handleBackFlowFrame tag:%#v --> source:%s, result=%s", ServerLogPrefix, tag, sourceId, carriage)
	for _, source := range sourceConns {
		if source != nil {
			log.Debugf("%s handleBackFlowFrame tag:%#v --> Protocol Gateway:%s, result=%# x", ServerLogPrefix, tag, sourceId, frame.Shortly(carriage))
			if err := source.Write(bf); err != nil {
				log.Errorf("%s handleBackFlowFrame tag:%#v --> Protocol Gateway:%s, error=%v", ServerLogPrefix, tag, sourceId, err)
				return err
			}
		}
	}
	return nil
}

// StatsFunctions returns the sfn stats of server.
func (s *Server) StatsFunctions() map[string]string {
	return s.connector.GetSnapshot()
}

// StatsCounter returns how many DataFrames pass through server.
func (s *Server) StatsCounter() int64 {
	return s.counterOfDataFrame
}

// DownStreams return all the downstream servers.
func (s *Server) DownStreams() map[string]*Client {
	return s.downStreams
}

// ConfigRouter is used to set router by Message Queue
func (s *Server) ConfigRouter(router Router) {
	s.mu.Lock()
	s.router = router
	log.Debugf("%sconfig router is %#v", ServerLogPrefix, router)
	s.mu.Unlock()
}

// ConfigMetadataBuilder is used to set metadataBuilder by Message Queue
func (s *Server) ConfigMetadataBuilder(builder MetadataBuilder) {
	s.mu.Lock()
	s.metadataBuilder = builder
	log.Debugf("%sconfig metadataBuilder is %#v", ServerLogPrefix, builder)
	s.mu.Unlock()
}

// AddDownstreamServer add a downstream server to this server. all the DataFrames will be
// dispatch to all the downStreams.
func (s *Server) AddDownstreamServer(addr string, c *Client) {
	s.mu.Lock()
	s.downStreams[addr] = c
	s.mu.Unlock()
}

// dispatch every DataFrames to all downStreams
func (s *Server) dispatchToDownStreams(df *frame.DataFrame) {
	for addr, ds := range s.downStreams {
		log.Debugf("%sdispatching to [%s]: %# x", ServerLogPrefix, addr, df.Tag())
		ds.WriteFrame(df)
	}
}

// GetConnId get quic connection id
func GetConnId(conn quic.Connection) string {
	return conn.RemoteAddr().String()
}

func (s *Server) initOptions() {
	// defaults
}

func (s *Server) validateRouter() error {
	if s.router == nil {
		return errors.New("server's router is nil")
	}
	return nil
}

func (s *Server) validateMetadataBuilder() error {
	if s.metadataBuilder == nil {
		return errors.New("server's metadataBuilder is nil")
	}
	return nil
}

// Options returns the options of server.
func (s *Server) Options() ServerOptions {
	return s.opts
}

// Connector returns the connector of server.
func (s *Server) Connector() Connector {
	return s.connector
}

// SetBeforeHandlers set the before handlers of server.
func (s *Server) SetBeforeHandlers(handlers ...FrameHandler) {
	s.beforeHandlers = append(s.beforeHandlers, handlers...)
}

// SetAfterHandlers set the after handlers of server.
func (s *Server) SetAfterHandlers(handlers ...FrameHandler) {
	s.afterHandlers = append(s.afterHandlers, handlers...)
}

func (s *Server) authNames() []string {
	if len(s.opts.Auths) == 0 {
		return []string{"none"}
	}
	result := make([]string, 0)
	for _, auth := range s.opts.Auths {
		result = append(result, auth.Name())
	}
	return result
}

func (s *Server) authenticate(f *frame.HandshakeFrame) bool {
	if len(s.opts.Auths) > 0 {
		for _, auth := range s.opts.Auths {
			if f.AuthName() == auth.Name() {
				isAuthenticated := auth.Authenticate(f.AuthPayload())
				if isAuthenticated {
					log.Debugf("%sauthenticated==%v", ServerLogPrefix, isAuthenticated)
					return isAuthenticated
				}
			}
		}
		return false
	}
	return true
}

func mode() string {
	if pkgtls.IsDev() {
		return "DEVELOPMENT"
	}
	return "PRODUCTION"
}

func authName(name string) string {
	if name == "" {
		return "empty"
	}

	return name
}