package v4

import (
	"bufio"
	"bytes"
	"context"
	"crypto/tls"
	"errors"
	"net"
	"time"

	"github.com/go-gost/core/handler"
	"github.com/go-gost/core/limiter"
	"github.com/go-gost/core/limiter/traffic"
	"github.com/go-gost/core/logger"
	md "github.com/go-gost/core/metadata"
	"github.com/go-gost/core/observer"
	"github.com/go-gost/core/observer/stats"
	"github.com/go-gost/core/recorder"
	"github.com/go-gost/gosocks4"
	ctxvalue "github.com/go-gost/x/ctx"
	xnet "github.com/go-gost/x/internal/net"
	"github.com/go-gost/x/internal/util/sniffing"
	stats_util "github.com/go-gost/x/internal/util/stats"
	tls_util "github.com/go-gost/x/internal/util/tls"
	rate_limiter "github.com/go-gost/x/limiter/rate"
	cache_limiter "github.com/go-gost/x/limiter/traffic/cache"
	traffic_wrapper "github.com/go-gost/x/limiter/traffic/wrapper"
	xstats "github.com/go-gost/x/observer/stats"
	stats_wrapper "github.com/go-gost/x/observer/stats/wrapper"
	xrecorder "github.com/go-gost/x/recorder"
	"github.com/go-gost/x/registry"
)

var (
	ErrUnknownCmd    = errors.New("socks4: unknown command")
	ErrUnimplemented = errors.New("socks4: unimplemented")
)

func init() {
	registry.HandlerRegistry().Register("socks4", NewHandler)
	registry.HandlerRegistry().Register("socks4a", NewHandler)
}

type socks4Handler struct {
	md       metadata
	options  handler.Options
	stats    *stats_util.HandlerStats
	limiter  traffic.TrafficLimiter
	cancel   context.CancelFunc
	recorder recorder.RecorderObject
	certPool tls_util.CertPool
}

func NewHandler(opts ...handler.Option) handler.Handler {
	options := handler.Options{}
	for _, opt := range opts {
		opt(&options)
	}

	return &socks4Handler{
		options: options,
	}
}

func (h *socks4Handler) Init(md md.Metadata) (err error) {
	if err := h.parseMetadata(md); err != nil {
		return err
	}

	ctx, cancel := context.WithCancel(context.Background())
	h.cancel = cancel

	if h.options.Observer != nil {
		h.stats = stats_util.NewHandlerStats(h.options.Service, h.md.observerResetTraffic)
		go h.observeStats(ctx)
	}

	if h.options.Limiter != nil {
		h.limiter = cache_limiter.NewCachedTrafficLimiter(h.options.Limiter,
			cache_limiter.RefreshIntervalOption(h.md.limiterRefreshInterval),
			cache_limiter.CleanupIntervalOption(h.md.limiterCleanupInterval),
			cache_limiter.ScopeOption(limiter.ScopeClient),
		)
	}

	for _, ro := range h.options.Recorders {
		if ro.Record == xrecorder.RecorderServiceHandler {
			h.recorder = ro
			break
		}
	}

	if h.md.certificate != nil && h.md.privateKey != nil {
		h.certPool = tls_util.NewMemoryCertPool()
	}

	return nil
}

func (h *socks4Handler) Handle(ctx context.Context, conn net.Conn, opts ...handler.HandleOption) (err error) {
	defer conn.Close()

	start := time.Now()

	ro := &xrecorder.HandlerRecorderObject{
		Service:    h.options.Service,
		Network:    "tcp",
		RemoteAddr: conn.RemoteAddr().String(),
		LocalAddr:  conn.LocalAddr().String(),
		Time:       start,
		SID:        string(ctxvalue.SidFromContext(ctx)),
	}

	ro.ClientIP = conn.RemoteAddr().String()
	if clientAddr := ctxvalue.ClientAddrFromContext(ctx); clientAddr != "" {
		ro.ClientIP = string(clientAddr)
	}
	if h, _, _ := net.SplitHostPort(ro.ClientIP); h != "" {
		ro.ClientIP = h
	}

	log := h.options.Logger.WithFields(map[string]any{
		"remote": conn.RemoteAddr().String(),
		"local":  conn.LocalAddr().String(),
		"sid":    ctxvalue.SidFromContext(ctx),
		"client": ro.ClientIP,
	})
	log.Infof("%s <> %s", conn.RemoteAddr(), conn.LocalAddr())

	pStats := xstats.Stats{}
	conn = stats_wrapper.WrapConn(conn, &pStats)

	defer func() {
		if err != nil {
			ro.Err = err.Error()
		}
		ro.InputBytes = pStats.Get(stats.KindInputBytes)
		ro.OutputBytes = pStats.Get(stats.KindOutputBytes)
		ro.Duration = time.Since(start)
		if err := ro.Record(ctx, h.recorder.Recorder); err != nil {
			log.Errorf("record: %v", err)
		}

		log.WithFields(map[string]any{
			"duration":    time.Since(start),
			"inputBytes":  ro.InputBytes,
			"outputBytes": ro.OutputBytes,
		}).Infof("%s >< %s", conn.RemoteAddr(), conn.LocalAddr())
	}()

	if !h.checkRateLimit(conn.RemoteAddr()) {
		return rate_limiter.ErrRateLimit
	}

	if h.md.readTimeout > 0 {
		conn.SetReadDeadline(time.Now().Add(h.md.readTimeout))
	}

	req, err := gosocks4.ReadRequest(conn)
	if err != nil {
		log.Error(err)
		return err
	}

	ro.Host = req.Addr.String()
	log.Trace(req)

	conn.SetReadDeadline(time.Time{})

	if h.options.Auther != nil {
		clientID, ok := h.options.Auther.Authenticate(ctx, string(req.Userid), "")
		if !ok {
			resp := gosocks4.NewReply(gosocks4.RejectedUserid, nil)
			log.Trace(resp)
			return resp.Write(conn)
		}
		ctx = ctxvalue.ContextWithClientID(ctx, ctxvalue.ClientID(clientID))
		ro.ClientID = clientID
	}

	switch req.Cmd {
	case gosocks4.CmdConnect:
		return h.handleConnect(ctx, conn, req, ro, log)
	case gosocks4.CmdBind:
		return h.handleBind(ctx, conn, req)
	default:
		err = ErrUnknownCmd
		log.Error(err)
		return err
	}
}

func (h *socks4Handler) Close() error {
	if h.cancel != nil {
		h.cancel()
	}
	return nil
}

func (h *socks4Handler) handleConnect(ctx context.Context, conn net.Conn, req *gosocks4.Request, ro *xrecorder.HandlerRecorderObject, log logger.Logger) error {
	addr := req.Addr.String()

	log = log.WithFields(map[string]any{
		"dst":  addr,
		"host": addr,
	})
	log.Debugf("%s >> %s", conn.RemoteAddr(), addr)

	{
		clientID := ctxvalue.ClientIDFromContext(ctx)
		rw := traffic_wrapper.WrapReadWriter(
			h.limiter,
			conn,
			string(clientID),
			limiter.ScopeOption(limiter.ScopeClient),
			limiter.ServiceOption(h.options.Service),
			limiter.NetworkOption("tcp"),
			limiter.AddrOption(addr),
			limiter.ClientOption(string(clientID)),
			limiter.SrcOption(conn.RemoteAddr().String()),
		)
		if h.options.Observer != nil {
			pstats := h.stats.Stats(string(clientID))
			pstats.Add(stats.KindTotalConns, 1)
			pstats.Add(stats.KindCurrentConns, 1)
			defer pstats.Add(stats.KindCurrentConns, -1)
			rw = stats_wrapper.WrapReadWriter(rw, pstats)
		}

		conn = xnet.NewReadWriteConn(rw, rw, conn)
	}

	if h.options.Bypass != nil && h.options.Bypass.Contains(ctx, "tcp", addr) {
		resp := gosocks4.NewReply(gosocks4.Rejected, nil)
		log.Trace(resp)
		log.Debug("bypass: ", addr)
		return resp.Write(conn)
	}

	switch h.md.hash {
	case "host":
		ctx = ctxvalue.ContextWithHash(ctx, &ctxvalue.Hash{Source: addr})
	}

	var buf bytes.Buffer
	cc, err := h.options.Router.Dial(ctxvalue.ContextWithBuffer(ctx, &buf), "tcp", addr)
	ro.Route = buf.String()
	if err != nil {
		resp := gosocks4.NewReply(gosocks4.Failed, nil)
		log.Trace(resp)
		resp.Write(conn)
		return err
	}
	defer cc.Close()

	resp := gosocks4.NewReply(gosocks4.Granted, nil)
	log.Trace(resp)
	if err := resp.Write(conn); err != nil {
		log.Error(err)
		return err
	}

	if h.md.sniffing {
		if h.md.sniffingTimeout > 0 {
			conn.SetReadDeadline(time.Now().Add(h.md.sniffingTimeout))
		}

		br := bufio.NewReader(conn)
		proto, _ := sniffing.Sniff(ctx, br)
		ro.Proto = proto

		if h.md.sniffingTimeout > 0 {
			conn.SetReadDeadline(time.Time{})
		}

		dial := func(ctx context.Context, network, address string) (net.Conn, error) {
			return cc, nil
		}
		dialTLS := func(ctx context.Context, network, address string, cfg *tls.Config) (net.Conn, error) {
			return cc, nil
		}
		sniffer := &sniffing.Sniffer{
			Websocket:           h.md.sniffingWebsocket,
			WebsocketSampleRate: h.md.sniffingWebsocketSampleRate,
			Recorder:            h.recorder.Recorder,
			RecorderOptions:     h.recorder.Options,
			Certificate:         h.md.certificate,
			PrivateKey:          h.md.privateKey,
			NegotiatedProtocol:  h.md.alpn,
			CertPool:            h.certPool,
			MitmBypass:          h.md.mitmBypass,
			ReadTimeout:         h.md.readTimeout,
		}

		conn = xnet.NewReadWriteConn(br, conn, conn)
		switch proto {
		case sniffing.ProtoHTTP:
			return sniffer.HandleHTTP(ctx, conn,
				sniffing.WithDial(dial),
				sniffing.WithDialTLS(dialTLS),
				sniffing.WithRecorderObject(ro),
				sniffing.WithLog(log),
			)
		case sniffing.ProtoTLS:
			return sniffer.HandleTLS(ctx, conn,
				sniffing.WithDial(dial),
				sniffing.WithDialTLS(dialTLS),
				sniffing.WithRecorderObject(ro),
				sniffing.WithLog(log),
			)
		}
	}

	t := time.Now()
	log.Infof("%s <-> %s", conn.RemoteAddr(), ro.Host)
	xnet.Transport(conn, cc)
	log.WithFields(map[string]any{
		"duration": time.Since(t),
	}).Infof("%s >-< %s", conn.RemoteAddr(), ro.Host)

	return nil
}

func (h *socks4Handler) handleBind(ctx context.Context, conn net.Conn, req *gosocks4.Request) error {
	// TODO: bind
	return ErrUnimplemented
}

func (h *socks4Handler) checkRateLimit(addr net.Addr) bool {
	if h.options.RateLimiter == nil {
		return true
	}
	host, _, _ := net.SplitHostPort(addr.String())
	if limiter := h.options.RateLimiter.Limiter(host); limiter != nil {
		return limiter.Allow(1)
	}

	return true
}

func (h *socks4Handler) observeStats(ctx context.Context) {
	if h.options.Observer == nil {
		return
	}

	var events []observer.Event

	ticker := time.NewTicker(h.md.observerPeriod)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			if len(events) > 0 {
				if err := h.options.Observer.Observe(ctx, events); err == nil {
					events = nil
				}
				break
			}

			evs := h.stats.Events()
			if err := h.options.Observer.Observe(ctx, evs); err != nil {
				events = evs
			}

		case <-ctx.Done():
			return
		}
	}
}
