package internet

import (
	"context"
	core "github.com/v2fly/v2ray-core/v4"
	"github.com/v2fly/v2ray-core/v4/features/routing"

	"github.com/v2fly/v2ray-core/v4/common/net"
	"github.com/v2fly/v2ray-core/v4/common/session"
)

// Dialer is the interface for dialing outbound connections.
type Dialer interface {
	// Dial dials a system connection to the given destination.
	Dial(ctx context.Context, destination net.Destination) (Connection, error)

	// Address returns the address used by this Dialer. Maybe nil if not known.
	Address() net.Address
}

// dialFunc is an interface to dial network connection to a specific destination.
type dialFunc func(ctx context.Context, dest net.Destination, streamSettings *MemoryStreamConfig) (Connection, error)

var (
	transportDialerCache = make(map[string]dialFunc)
)

// RegisterTransportDialer registers a Dialer with given name.
func RegisterTransportDialer(protocol string, dialer dialFunc) error {
	if _, found := transportDialerCache[protocol]; found {
		return newError(protocol, " dialer already registered").AtError()
	}
	transportDialerCache[protocol] = dialer
	return nil
}

// Dial dials a internet connection towards the given destination.
func Dial(ctx context.Context, dest net.Destination, streamSettings *MemoryStreamConfig) (Connection, error) {
	if dest.Network == net.Network_TCP {
		if streamSettings == nil {
			s, err := ToMemoryStreamConfig(nil)
			if err != nil {
				return nil, newError("failed to create default stream settings").Base(err)
			}
			streamSettings = s
		}

		protocol := streamSettings.ProtocolName
		dialer := transportDialerCache[protocol]
		if dialer == nil {
			return nil, newError(protocol, " dialer not registered").AtError()
		}
		return dialer(ctx, dest, streamSettings)
	}

	if dest.Network == net.Network_UDP {
		udpDialer := transportDialerCache["udp"]
		if udpDialer == nil {
			return nil, newError("UDP dialer not registered").AtError()
		}
		return udpDialer(ctx, dest, streamSettings)
	}

	return nil, newError("unknown network ", dest.Network)
}

// DialSystem calls system dialer to create a network connection.
func DialSystem(ctx context.Context, dest net.Destination, sockopt *SocketConfig) (net.Conn, error) {
	var src net.Address
	if outbound := session.OutboundFromContext(ctx); outbound != nil {
		src = outbound.Gateway
	}

	if transportLayerOutgoingTag := session.GetTransportLayerProxyTagFromContext(ctx); transportLayerOutgoingTag != "" {
		return DialTaggedOutbound(ctx, dest, transportLayerOutgoingTag)
	}

	return effectiveSystemDialer.Dial(ctx, src, dest, sockopt)
}

func DialTaggedOutbound(ctx context.Context, dest net.Destination, tag string) (net.Conn, error) {
	var dispatcher routing.Dispatcher
	if err := core.RequireFeatures(ctx, func(dispatcherInstance routing.Dispatcher) {
		dispatcher = dispatcherInstance
	}); err != nil {
		return nil, newError("Required Feature dispatcher not resolved").Base(err)
	}

	content := new(session.Content)
	content.SkipDNSResolve = true
	session.SetForcedOutboundTagToContext(ctx, tag)

	ctx = session.ContextWithContent(ctx, content)

	r, err := dispatcher.Dispatch(ctx, dest)
	if err != nil {
		return nil, err
	}
	var readerOpt net.ConnectionOption
	if dest.Network == net.Network_TCP {
		readerOpt = net.ConnectionOutputMulti(r.Reader)
	} else {
		readerOpt = net.ConnectionOutputMultiUDP(r.Reader)
	}
	return net.NewConnection(net.ConnectionInputMulti(r.Writer), readerOpt), nil
}