package wireproxy

import (
	"context"
	"crypto/subtle"
	"errors"
	"io"
	"log"
	"math/rand"
	"net"
	"os"
	"strconv"

	"github.com/sourcegraph/conc"
	"github.com/things-go/go-socks5"
	"github.com/things-go/go-socks5/bufferpool"

	"net/netip"

	"golang.zx2c4.com/wireguard/tun/netstack"
)

// errorLogger is the logger to print error message
var errorLogger = log.New(os.Stderr, "ERROR: ", log.LstdFlags)

// CredentialValidator stores the authentication data of a socks5 proxy
type CredentialValidator struct {
	username string
	password string
}

// VirtualTun stores a reference to netstack network and DNS configuration
type VirtualTun struct {
	Tnet      *netstack.Net
	SystemDNS bool
}

// RoutineSpawner spawns a routine (e.g. socks5, tcp static routes) after the configuration is parsed
type RoutineSpawner interface {
	SpawnRoutine(vt *VirtualTun)
}

type addressPort struct {
	address string
	port    uint16
}

// LookupAddr lookups a hostname.
// DNS traffic may or may not be routed depending on VirtualTun's setting
func (d VirtualTun) LookupAddr(ctx context.Context, name string) ([]string, error) {
	if d.SystemDNS {
		return net.DefaultResolver.LookupHost(ctx, name)
	}
	return d.Tnet.LookupContextHost(ctx, name)
}

// ResolveAddrWithContext resolves a hostname and returns an AddrPort.
// DNS traffic may or may not be routed depending on VirtualTun's setting
func (d VirtualTun) ResolveAddrWithContext(ctx context.Context, name string) (*netip.Addr, error) {
	addrs, err := d.LookupAddr(ctx, name)
	if err != nil {
		return nil, err
	}

	size := len(addrs)
	if size == 0 {
		return nil, errors.New("no address found for: " + name)
	}

	rand.Shuffle(size, func(i, j int) {
		addrs[i], addrs[j] = addrs[j], addrs[i]
	})

	var addr netip.Addr
	for _, saddr := range addrs {
		addr, err = netip.ParseAddr(saddr)
		if err == nil {
			break
		}
	}

	if err != nil {
		return nil, err
	}

	return &addr, nil
}

// Resolve resolves a hostname and returns an IP.
// DNS traffic may or may not be routed depending on VirtualTun's setting
func (d VirtualTun) Resolve(ctx context.Context, name string) (context.Context, net.IP, error) {
	addr, err := d.ResolveAddrWithContext(ctx, name)
	if err != nil {
		return nil, nil, err
	}

	return ctx, addr.AsSlice(), nil
}

func parseAddressPort(endpoint string) (*addressPort, error) {
	name, sport, err := net.SplitHostPort(endpoint)
	if err != nil {
		return nil, err
	}

	port, err := strconv.Atoi(sport)
	if err != nil || port < 0 || port > 65535 {
		return nil, &net.OpError{Op: "dial", Err: errors.New("port must be numeric")}
	}

	return &addressPort{address: name, port: uint16(port)}, nil
}

func (d VirtualTun) resolveToAddrPort(endpoint *addressPort) (*netip.AddrPort, error) {
	addr, err := d.ResolveAddrWithContext(context.Background(), endpoint.address)
	if err != nil {
		return nil, err
	}

	addrPort := netip.AddrPortFrom(*addr, endpoint.port)
	return &addrPort, nil
}

// SpawnRoutine spawns a socks5 server.
func (config *Socks5Config) SpawnRoutine(vt *VirtualTun) {
	var authMethods []socks5.Authenticator
	if username := config.Username; username != "" {
		authMethods = append(authMethods, socks5.UserPassAuthenticator{
			Credentials: socks5.StaticCredentials{username: config.Password},
		})
	} else {
		authMethods = append(authMethods, socks5.NoAuthAuthenticator{})
	}

	options := []socks5.Option{
		socks5.WithDial(vt.Tnet.DialContext),
		socks5.WithResolver(vt),
		socks5.WithAuthMethods(authMethods),
		socks5.WithBufferPool(bufferpool.NewPool(256 * 1024)),
	}

	server := socks5.NewServer(options...)

	if err := server.ListenAndServe("tcp", config.BindAddress); err != nil {
		log.Fatal(err)
	}
}

// SpawnRoutine spawns a http server.
func (config *HTTPConfig) SpawnRoutine(vt *VirtualTun) {
	http := &HTTPServer{
		config: config,
		dial:   vt.Tnet.Dial,
		auth:   CredentialValidator{config.Username, config.Password},
	}
	if config.Username != "" || config.Password != "" {
		http.authRequired = true
	}

	if err := http.ListenAndServe("tcp", config.BindAddress); err != nil {
		log.Fatal(err)
	}
}

// Valid checks the authentication data in CredentialValidator and compare them
// to username and password in constant time.
func (c CredentialValidator) Valid(username, password string) bool {
	u := subtle.ConstantTimeCompare([]byte(c.username), []byte(username))
	p := subtle.ConstantTimeCompare([]byte(c.password), []byte(password))
	return u&p == 1
}

// connForward copy data from `from` to `to`
func connForward(from io.ReadWriteCloser, to io.ReadWriteCloser) {
	_, err := io.Copy(to, from)
	if err != nil {
		errorLogger.Printf("Cannot forward traffic: %s\n", err.Error())
	}
}

// tcpClientForward starts a new connection via wireguard and forward traffic from `conn`
func tcpClientForward(vt *VirtualTun, raddr *addressPort, conn net.Conn) {
	target, err := vt.resolveToAddrPort(raddr)
	if err != nil {
		errorLogger.Printf("TCP Server Tunnel to %s: %s\n", target, err.Error())
		return
	}

	tcpAddr := TCPAddrFromAddrPort(*target)

	sconn, err := vt.Tnet.DialTCP(tcpAddr)
	if err != nil {
		errorLogger.Printf("TCP Client Tunnel to %s: %s\n", target, err.Error())
		return
	}

	go func() {
		wg := conc.NewWaitGroup()
		wg.Go(func() {
			connForward(sconn, conn)
		})
		wg.Go(func() {
			connForward(conn, sconn)
		})
		wg.Wait()
		_ = sconn.Close()
		_ = conn.Close()
		sconn = nil
		conn = nil
	}()
}

// STDIOTcpForward starts a new connection via wireguard and forward traffic from `conn`
func STDIOTcpForward(vt *VirtualTun, raddr *addressPort) {
	target, err := vt.resolveToAddrPort(raddr)
	if err != nil {
		errorLogger.Printf("Name resolution error for %s: %s\n", raddr.address, err.Error())
		return
	}

	// os.Stdout has previously been remapped to stderr, se we can't use it
	stdout, err := os.OpenFile("/dev/stdout", os.O_WRONLY, 0)
	if err != nil {
		errorLogger.Printf("Failed to open /dev/stdout: %s\n", err.Error())
		return
	}

	tcpAddr := TCPAddrFromAddrPort(*target)
	sconn, err := vt.Tnet.DialTCP(tcpAddr)
	if err != nil {
		errorLogger.Printf("TCP Client Tunnel to %s (%s): %s\n", target, tcpAddr, err.Error())
		return
	}

	go func() {
		wg := conc.NewWaitGroup()
		wg.Go(func() {
			connForward(os.Stdin, sconn)
		})
		wg.Go(func() {
			connForward(sconn, stdout)
		})
		wg.Wait()
		_ = sconn.Close()
		sconn = nil
	}()
}

// SpawnRoutine spawns a local TCP server which acts as a proxy to the specified target
func (conf *TCPClientTunnelConfig) SpawnRoutine(vt *VirtualTun) {
	raddr, err := parseAddressPort(conf.Target)
	if err != nil {
		log.Fatal(err)
	}

	server, err := net.ListenTCP("tcp", conf.BindAddress)
	if err != nil {
		log.Fatal(err)
	}

	for {
		conn, err := server.Accept()
		if err != nil {
			log.Fatal(err)
		}
		go tcpClientForward(vt, raddr, conn)
	}
}

// SpawnRoutine connects to the specified target and plumbs it to STDIN / STDOUT
func (conf *STDIOTunnelConfig) SpawnRoutine(vt *VirtualTun) {
	raddr, err := parseAddressPort(conf.Target)
	if err != nil {
		log.Fatal(err)
	}

	go STDIOTcpForward(vt, raddr)
}

// tcpServerForward starts a new connection locally and forward traffic from `conn`
func tcpServerForward(vt *VirtualTun, raddr *addressPort, conn net.Conn) {
	target, err := vt.resolveToAddrPort(raddr)
	if err != nil {
		errorLogger.Printf("TCP Server Tunnel to %s: %s\n", target, err.Error())
		return
	}

	tcpAddr := TCPAddrFromAddrPort(*target)

	sconn, err := net.DialTCP("tcp", nil, tcpAddr)
	if err != nil {
		errorLogger.Printf("TCP Server Tunnel to %s: %s\n", target, err.Error())
		return
	}

	go func() {
		gr := conc.NewWaitGroup()
		gr.Go(func() {
			connForward(sconn, conn)
		})
		gr.Go(func() {
			connForward(conn, sconn)
		})
		gr.Wait()
		_ = sconn.Close()
		_ = conn.Close()
		sconn = nil
		conn = nil
	}()
}

// SpawnRoutine spawns a TCP server on wireguard which acts as a proxy to the specified target
func (conf *TCPServerTunnelConfig) SpawnRoutine(vt *VirtualTun) {
	raddr, err := parseAddressPort(conf.Target)
	if err != nil {
		log.Fatal(err)
	}

	addr := &net.TCPAddr{Port: conf.ListenPort}
	server, err := vt.Tnet.ListenTCP(addr)
	if err != nil {
		log.Fatal(err)
	}

	for {
		conn, err := server.Accept()
		if err != nil {
			log.Fatal(err)
		}
		go tcpServerForward(vt, raddr, conn)
	}
}