package route

import (
	"context"
	"io"
	"net"
	"net/netip"
	"sync/atomic"

	"github.com/sagernet/sing-box/adapter"
	"github.com/sagernet/sing-box/common/dialer"
	"github.com/sagernet/sing/common"
	"github.com/sagernet/sing/common/bufio"
	E "github.com/sagernet/sing/common/exceptions"
	"github.com/sagernet/sing/common/logger"
	M "github.com/sagernet/sing/common/metadata"
	N "github.com/sagernet/sing/common/network"
)

var _ adapter.ConnectionManager = (*ConnectionManager)(nil)

type ConnectionManager struct {
	logger  logger.ContextLogger
	monitor *ConnectionMonitor
}

func NewConnectionManager(logger logger.ContextLogger) *ConnectionManager {
	return &ConnectionManager{
		logger:  logger,
		monitor: NewConnectionMonitor(),
	}
}

func (m *ConnectionManager) Start() error {
	return m.monitor.Start()
}

func (m *ConnectionManager) Close() error {
	return m.monitor.Close()
}

func (m *ConnectionManager) NewConnection(ctx context.Context, this N.Dialer, conn net.Conn, metadata adapter.InboundContext, onClose N.CloseHandlerFunc) {
	ctx = adapter.WithContext(ctx, &metadata)
	var (
		remoteConn net.Conn
		err        error
	)
	if len(metadata.DestinationAddresses) > 0 {
		remoteConn, err = dialer.DialSerialNetwork(ctx, this, N.NetworkTCP, metadata.Destination, metadata.DestinationAddresses, metadata.NetworkStrategy, metadata.NetworkType, metadata.FallbackNetworkType, metadata.FallbackDelay)
	} else {
		remoteConn, err = this.DialContext(ctx, N.NetworkTCP, metadata.Destination)
	}
	if err != nil {
		N.CloseOnHandshakeFailure(conn, onClose, err)
		m.logger.ErrorContext(ctx, "open outbound connection: ", err)
		return
	}
	err = N.ReportConnHandshakeSuccess(conn, remoteConn)
	if err != nil {
		remoteConn.Close()
		N.CloseOnHandshakeFailure(conn, onClose, err)
		m.logger.ErrorContext(ctx, "report handshake success: ", err)
		return
	}
	var done atomic.Bool
	if ctx.Done() != nil {
		onClose = N.AppendClose(onClose, m.monitor.Add(ctx, conn))
	}
	go m.connectionCopy(ctx, conn, remoteConn, false, &done, onClose)
	go m.connectionCopy(ctx, remoteConn, conn, true, &done, onClose)
}

func (m *ConnectionManager) connectionCopy(ctx context.Context, source io.Reader, destination io.Writer, direction bool, done *atomic.Bool, onClose N.CloseHandlerFunc) {
	originSource := source
	var readCounters, writeCounters []N.CountFunc
	for {
		source, readCounters = N.UnwrapCountReader(source, readCounters)
		destination, writeCounters = N.UnwrapCountWriter(destination, writeCounters)
		if cachedSrc, isCached := source.(N.CachedReader); isCached {
			cachedBuffer := cachedSrc.ReadCached()
			if cachedBuffer != nil {
				if !cachedBuffer.IsEmpty() {
					dataLen := cachedBuffer.Len()
					for _, counter := range readCounters {
						counter(int64(dataLen))
					}
					_, err := destination.Write(cachedBuffer.Bytes())
					if err != nil {
						m.logger.ErrorContext(ctx, "connection upload payload: ", err)
						cachedBuffer.Release()
						if done.Swap(true) {
							if onClose != nil {
								onClose(err)
							}
							common.Close(source, destination)
						}
						return
					}
					for _, counter := range writeCounters {
						counter(int64(dataLen))
					}
				}
				cachedBuffer.Release()
				continue
			}
		}
		break
	}
	var (
		dstDuplex bool
		err       error
	)
	_, err = bufio.CopyWithCounters(destination, source, originSource, readCounters, writeCounters)
	if _, dstDuplex = common.Cast[N.WriteCloser](destination); dstDuplex && err == nil {
		N.CloseWrite(destination)
	} else {
		common.Close(destination)
	}
	if done.Swap(true) {
		if onClose != nil {
			onClose(err)
		}
		common.Close(source, destination)
	}
	if !direction {
		if err == nil {
			m.logger.DebugContext(ctx, "connection upload finished")
		} else if !E.IsClosedOrCanceled(err) {
			m.logger.ErrorContext(ctx, "connection upload closed: ", err)
		} else {
			m.logger.TraceContext(ctx, "connection upload closed")
		}
	} else {
		if err == nil {
			m.logger.DebugContext(ctx, "connection download finished")
		} else if !E.IsClosedOrCanceled(err) {
			m.logger.ErrorContext(ctx, "connection download closed: ", err)
		} else {
			m.logger.TraceContext(ctx, "connection download closed")
		}
	}
}

func (m *ConnectionManager) NewPacketConnection(ctx context.Context, this N.Dialer, conn N.PacketConn, metadata adapter.InboundContext, onClose N.CloseHandlerFunc) {
	ctx = adapter.WithContext(ctx, &metadata)
	var (
		remotePacketConn   net.PacketConn
		remoteConn         net.Conn
		destinationAddress netip.Addr
		err                error
	)
	if metadata.UDPConnect {
		if len(metadata.DestinationAddresses) > 0 {
			if parallelDialer, isParallelDialer := this.(dialer.ParallelInterfaceDialer); isParallelDialer {
				remoteConn, err = dialer.DialSerialNetwork(ctx, parallelDialer, N.NetworkUDP, metadata.Destination, metadata.DestinationAddresses, metadata.NetworkStrategy, metadata.NetworkType, metadata.FallbackNetworkType, metadata.FallbackDelay)
			} else {
				remoteConn, err = N.DialSerial(ctx, this, N.NetworkUDP, metadata.Destination, metadata.DestinationAddresses)
			}
		} else {
			remoteConn, err = this.DialContext(ctx, N.NetworkUDP, metadata.Destination)
		}
		if err != nil {
			N.CloseOnHandshakeFailure(conn, onClose, err)
			m.logger.ErrorContext(ctx, "open outbound packet connection: ", err)
			return
		}
		remotePacketConn = bufio.NewUnbindPacketConn(remoteConn)
		connRemoteAddr := M.AddrFromNet(remoteConn.RemoteAddr())
		if connRemoteAddr != metadata.Destination.Addr {
			destinationAddress = connRemoteAddr
		}
	} else {
		if len(metadata.DestinationAddresses) > 0 {
			remotePacketConn, destinationAddress, err = dialer.ListenSerialNetworkPacket(ctx, this, metadata.Destination, metadata.DestinationAddresses, metadata.NetworkStrategy, metadata.NetworkType, metadata.FallbackNetworkType, metadata.FallbackDelay)
		} else {
			remotePacketConn, err = this.ListenPacket(ctx, metadata.Destination)
		}
		if err != nil {
			N.CloseOnHandshakeFailure(conn, onClose, err)
			m.logger.ErrorContext(ctx, "listen outbound packet connection: ", err)
			return
		}
	}
	err = N.ReportPacketConnHandshakeSuccess(conn, remotePacketConn)
	if err != nil {
		conn.Close()
		remotePacketConn.Close()
		m.logger.ErrorContext(ctx, "report handshake success: ", err)
		return
	}
	if destinationAddress.IsValid() {
		var originDestination M.Socksaddr
		if metadata.RouteOriginalDestination.IsValid() {
			originDestination = metadata.RouteOriginalDestination
		} else {
			originDestination = metadata.Destination
		}
		if metadata.Destination != M.SocksaddrFrom(destinationAddress, metadata.Destination.Port) {
			if metadata.UDPDisableDomainUnmapping {
				remotePacketConn = bufio.NewUnidirectionalNATPacketConn(bufio.NewPacketConn(remotePacketConn), M.SocksaddrFrom(destinationAddress, metadata.Destination.Port), originDestination)
			} else {
				remotePacketConn = bufio.NewNATPacketConn(bufio.NewPacketConn(remotePacketConn), M.SocksaddrFrom(destinationAddress, metadata.Destination.Port), originDestination)
			}
		}
		if natConn, loaded := common.Cast[bufio.NATPacketConn](conn); loaded {
			natConn.UpdateDestination(destinationAddress)
		}
	}
	destination := bufio.NewPacketConn(remotePacketConn)
	if ctx.Done() != nil {
		onClose = N.AppendClose(onClose, m.monitor.Add(ctx, conn))
	}
	var done atomic.Bool
	go m.packetConnectionCopy(ctx, conn, destination, false, &done, onClose)
	go m.packetConnectionCopy(ctx, destination, conn, true, &done, onClose)
}

func (m *ConnectionManager) packetConnectionCopy(ctx context.Context, source N.PacketReader, destination N.PacketWriter, direction bool, done *atomic.Bool, onClose N.CloseHandlerFunc) {
	_, err := bufio.CopyPacket(destination, source)
	/*var readCounters, writeCounters []N.CountFunc
	var cachedPackets []*N.PacketBuffer
	originSource := source
	for {
		source, readCounters = N.UnwrapCountPacketReader(source, readCounters)
		destination, writeCounters = N.UnwrapCountPacketWriter(destination, writeCounters)
		if cachedReader, isCached := source.(N.CachedPacketReader); isCached {
			packet := cachedReader.ReadCachedPacket()
			if packet != nil {
				cachedPackets = append(cachedPackets, packet)
				continue
			}
		}
		break
	}
	var handled bool
	if natConn, isNatConn := source.(udpnat.Conn); isNatConn {
		natConn.SetHandler(&udpHijacker{
			ctx:           ctx,
			logger:        m.logger,
			source:        natConn,
			destination:   destination,
			direction:     direction,
			readCounters:  readCounters,
			writeCounters: writeCounters,
			done:          done,
			onClose:       onClose,
		})
		handled = true
	}
	if cachedPackets != nil {
		_, err := bufio.WritePacketWithPool(originSource, destination, cachedPackets, readCounters, writeCounters)
		if err != nil {
			common.Close(source, destination)
			m.logger.ErrorContext(ctx, "packet upload payload: ", err)
			return
		}
	}
	if handled {
		return
	}
	_, err := bufio.CopyPacketWithCounters(destination, source, originSource, readCounters, writeCounters)*/
	if !direction {
		if E.IsClosedOrCanceled(err) {
			m.logger.TraceContext(ctx, "packet upload closed")
		} else {
			m.logger.DebugContext(ctx, "packet upload closed: ", err)
		}
	} else {
		if E.IsClosedOrCanceled(err) {
			m.logger.TraceContext(ctx, "packet download closed")
		} else {
			m.logger.DebugContext(ctx, "packet download closed: ", err)
		}
	}
	if !done.Swap(true) {
		common.Close(source, destination)
		if onClose != nil {
			onClose(err)
		}
	}
}

/*type udpHijacker struct {
	ctx           context.Context
	logger        logger.ContextLogger
	source        io.Closer
	destination   N.PacketWriter
	direction     bool
	readCounters  []N.CountFunc
	writeCounters []N.CountFunc
	done          *atomic.Bool
	onClose       N.CloseHandlerFunc
}

func (u *udpHijacker) NewPacketEx(buffer *buf.Buffer, source M.Socksaddr) {
	dataLen := buffer.Len()
	for _, counter := range u.readCounters {
		counter(int64(dataLen))
	}
	err := u.destination.WritePacket(buffer, source)
	if err != nil {
		common.Close(u.source, u.destination)
		u.logger.DebugContext(u.ctx, "packet upload closed: ", err)
		return
	}
	for _, counter := range u.writeCounters {
		counter(int64(dataLen))
	}
}

func (u *udpHijacker) Close() error {
	var err error
	if !u.done.Swap(true) {
		err = common.Close(u.source, u.destination)
		if u.onClose != nil {
			u.onClose(net.ErrClosed)
		}
	}
	if u.direction {
		u.logger.TraceContext(u.ctx, "packet  download closed")
	} else {
		u.logger.TraceContext(u.ctx, "packet upload closed")
	}
	return err
}

func (u *udpHijacker) Upstream() any {
	return u.destination
}
*/