package main

import (
	"context"
	"fmt"
	"io"
	"net"
	"net/netip"
	"net/url"
	"os"

	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"

	gen "golang.zx2c4.com/wireguard/android/gen"
	"golang.zx2c4.com/wireguard/device"
)

const (
	IPPROTO_TCP = 6
)

type UidRequest struct {
	Data AddrPortPair
	RetCh chan string
}

type LibwgServiceImpl struct {
	gen.UnimplementedLibwgServer
	logger *device.Logger
	httpProxy *HttpProxy
	uidRequest chan UidRequest
	stopReverse chan bool
}

var service *LibwgServiceImpl
var server *grpc.Server

func NewLibwgService(logger *device.Logger) gen.LibwgServer {
	return &LibwgServiceImpl{
		logger: logger,
		uidRequest: make(chan UidRequest),
		stopReverse: make(chan bool),
	}
}

func StartGrpc(sock_path string, logger *device.Logger) (int, string) {
	if server != nil {
		return -1, "Already started"
	}

	if _, err := os.Stat(sock_path); err == nil {
		if err := os.RemoveAll(sock_path); err != nil {
			return -1, fmt.Sprintf("Cleanup failed: %v %v", sock_path, err)
		}
	}

	listener, err := net.Listen("unix", sock_path)
	if err != nil {
		return -1, fmt.Sprintf("Listen failed: %v %v", sock_path, err)
	}

	server = grpc.NewServer()
	service = NewLibwgService(logger).(*LibwgServiceImpl)

	gen.RegisterLibwgServer(server, service)

	go func() {
		server.Serve(listener)
	}()

	logger.Verbosef("gRPC started")

	return 0, ""
}

func (e *LibwgServiceImpl) Version(ctx context.Context, req *gen.VersionRequest) (*gen.VersionResponse, error) {

	r := &gen.VersionResponse{
		Version: Version(),
	}

	return r, nil
}

func (e *LibwgServiceImpl) StopGrpc(ctx context.Context, req *gen.StopGrpcRequest) (*gen.StopGrpcResponse, error) {
	if server != nil {
		server.Stop()
		server = nil
		service = nil
	}

	r := &gen.StopGrpcResponse{
	}

	return r, nil
}

func buildStartHttpProxyError(message string) (*gen.StartHttpProxyResponse, error) {
	r := &gen.StartHttpProxyResponse{
		Error: &gen.Error{
			Message: message,
		},
	}
	return r, nil
}

func (e *LibwgServiceImpl) StartHttpProxy(ctx context.Context, req *gen.StartHttpProxyRequest) (*gen.StartHttpProxyResponse, error) {
	var listenPort uint16
	if e.httpProxy == nil {
		e.httpProxy = NewHttpProxy(e.uidRequest, e.logger)
		var err error
		listenPort, err = e.httpProxy.Start()

		if err != nil {
			e.httpProxy = nil
			return buildStartHttpProxyError(fmt.Sprintf("Http proxy start failed: %v", err))
		}
	} else {
		listenPort = e.httpProxy.GetAddrPort().Port()
	}

	content := req.GetPacFileContent()
	if content != "" {
		err := e.httpProxy.SetPacFileContent(content)
		if err != nil {
			return buildStartHttpProxyError(fmt.Sprintf("Bad pacFileContent: %v (%s)", content))
		}
	} else {
		pacFileUrl, err := url.Parse(req.GetPacFileUrl())
		if err != nil {
			return buildStartHttpProxyError(fmt.Sprintf("Bad pacFileUrl: %v (%s)", err, req.GetPacFileUrl()))
		}
		err = e.httpProxy.SetPacFileUrl(pacFileUrl)
		if err != nil {
			return buildStartHttpProxyError(fmt.Sprintf("Bad pacFileUrl: %v (%s)", err, pacFileUrl))
		}
	}

	r := &gen.StartHttpProxyResponse{
		ListenPort: uint32(listenPort),
	}
	return r, nil
}

func (e *LibwgServiceImpl) StopHttpProxy(ctx context.Context, req *gen.StopHttpProxyRequest) (*gen.StopHttpProxyResponse, error) {
	if e.httpProxy == nil {
		r := &gen.StopHttpProxyResponse{
			Error: &gen.Error{
				Message: fmt.Sprintf("Http proxy not running"),
			},
		}
		return r, nil
	}

	e.httpProxy.Stop()
	e.httpProxy = nil
	e.stopReverse <- true
	r := &gen.StopHttpProxyResponse{}
	return r, nil
}

func (e *LibwgServiceImpl) Reverse(stream gen.Libwg_ReverseServer) error {
	e.logger.Verbosef("Reverse enter loop")
	for e.httpProxy != nil {
		var err error

		//		err := contextError(stream.Context())
		err = stream.Context().Err()
		if err != nil {
			e.logger.Verbosef("Reverse: context: %v", err)
			return err
		}

		select {
		case <-e.stopReverse:
			e.logger.Verbosef("Reverse: stop")
			break
		case uidReq := <-e.uidRequest:
			addrPortPair := uidReq.Data
			local := addrPortPair.local
			remote := addrPortPair.remote
			r := &gen.ReverseResponse{
				Request: &gen.ReverseResponse_Uid{
					Uid: &gen.GetConnectionOwnerUidRequest{
						Protocol: IPPROTO_TCP,
						Local: &gen.InetSocketAddress{
							Address: &gen.InetAddress{
								Address: local.Addr().AsSlice(),
							},
							Port: uint32(local.Port()),
						},
						Remote: &gen.InetSocketAddress{
							Address: &gen.InetAddress{
								Address: remote.Addr().AsSlice(),
							},
							Port: uint32(remote.Port()),
						},
					},
				},
			}

			stream.Send(r)

			req, err := stream.Recv()
			if err == io.EOF {
				e.logger.Verbosef("no more data")
				uidReq.RetCh <- ""
				break
			}
			if err != nil {
				err = status.Errorf(codes.Unknown, "cannot receive stream request: %v", err)
				e.logger.Verbosef("Reverse: %v", err)
				uidReq.RetCh <- ""
				return err
			}

			e.logger.Verbosef("Reverse: received, wait: %v", req)
			uidReq.RetCh <- req.GetUid().GetPackage()
		}
	}


	e.logger.Verbosef("Reverse returns")
	return nil
}

func (e *LibwgServiceImpl) Dhcp(ctx context.Context, req *gen.DhcpRequest) (*gen.DhcpResponse, error) {
	var relayAddr netip.Addr
	var sourceAddr netip.Addr

	source := req.GetSource()
	if source != nil {
		sourceAddr, _ = netip.AddrFromSlice(source.GetAddress())
	}

	if !sourceAddr.IsValid() || !sourceAddr.Is6() {
		r := &gen.DhcpResponse{
			Error: &gen.Error{
				Message: fmt.Sprintf("DHCPv6 source address missing"),
			},
		}
		return r, nil
	}

	relay := req.GetRelay()
	if relay != nil {
		relayAddr, _ = netip.AddrFromSlice(relay.GetAddress())
	} else {
		// Construct relay address from source prefix
		relayRaw := source.GetAddress()[:8]
		relayRaw = append(relayRaw, 0)
		relayRaw = append(relayRaw, 0)
		relayRaw = append(relayRaw, 0)
		relayRaw = append(relayRaw, 0)
		relayRaw = append(relayRaw, 0)
		relayRaw = append(relayRaw, 0)
		relayRaw = append(relayRaw, 0)
		relayRaw = append(relayRaw, 1)
		relayAddr, _ = netip.AddrFromSlice(relayRaw)
	}

	if !relayAddr.IsValid() || !relayAddr.Is6() {
		r := &gen.DhcpResponse{
			Error: &gen.Error{
				Message: fmt.Sprintf("DHCPv6 relay address calculation failed"),
			},
		}
		return r, nil
	}

	e.logger.Verbosef("RunDhcp %v %v", sourceAddr, relayAddr)

	leases, err := RunDhcp(ctx, sourceAddr, relayAddr)
	if err != nil {
		r := &gen.DhcpResponse{
			Error: &gen.Error{
				Message: fmt.Sprintf("RunDhcp failed: %v", err),
			},
		}
		return r, nil
	}

	r := &gen.DhcpResponse{
		Leases: leases,
	}
	return r, nil
}