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package main

import (
	"bytes"
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"flag"
	"fmt"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"

	"go.jolheiser.com/tailroute"
	"golang.org/x/oauth2/clientcredentials"
)

func main() {
	fs := flag.NewFlagSet("tailgrok", flag.ExitOnError)
	if err := fs.Parse(os.Args[1:]); err != nil {
		panic(err)
	}

	if fs.NArg() < 1 {
		panic("tailgrok requires a target URL to proxy")
	}

	target, err := url.Parse(fs.Arg(0))
	if err != nil {
		panic(err)
	}

	homeDir, err := os.UserHomeDir()
	if err != nil {
		panic(err)
	}
	cfgPath := filepath.Join(homeDir, ".config", "tailgrok", "config.json")

	b, err := os.ReadFile(cfgPath)
	if err != nil {
		panic(err)
	}
	var cfg Config
	if err := json.Unmarshal(b, &cfg); err != nil {
		panic(err)
	}

	clientSecret, err := cfg.ClientSecret()
	if err != nil {
		panic(err)
	}

	oauthConfig := &clientcredentials.Config{
		ClientID:     cfg.ClientID,
		ClientSecret: clientSecret,
		TokenURL:     "https://api.tailscale.com/api/v2/oauth/token",
	}
	client := oauthConfig.Client(context.Background())

	payload, err := json.Marshal(M{
		"description": "tailgrok",
		"capabilities": M{
			"devices": M{
				"create": M{
					"reusable":      false,
					"ephemeral":     true,
					"preauthorized": true,
					"tags":          []string{"tag:funnel", "tag:tailgrok"},
				},
			},
		},
		"expirySeconds": 5,
	})
	if err != nil {
		panic(err)
	}
	authTokenReq, err := http.NewRequest(http.MethodPost, "https://api.tailscale.com/api/v2/tailnet/-/keys", bytes.NewReader(payload))
	if err != nil {
		panic(err)
	}
	resp, err := client.Do(authTokenReq)
	if err != nil {
		panic(err)
	}
	defer resp.Body.Close()
	tsKey := struct {
		Key string `json:"key"`
	}{}
	if err := json.NewDecoder(resp.Body).Decode(&tsKey); err != nil {
		panic(err)
	}
	os.Setenv("TS_AUTHKEY", tsKey.Key)

	tmp, err := os.MkdirTemp(os.TempDir(), "tailgrok-*")
	if err != nil {
		panic(err)
	}
	defer os.RemoveAll(tmp)

	random := make([]byte, 8)
	if _, err := rand.Read(random); err != nil {
		panic(err)
	}
	id := hex.EncodeToString(random)

	fmt.Printf("https://%s.serval-vibes.ts.net\n", id)
	r := tailroute.Proxy(target, true)
	r.Ephemeral = true
	if err := r.Serve(id, tmp); err != nil {
		panic(err)
	}
}

type M = map[string]any

type Config struct {
	ClientID         string `json:"clientID"`
	ClientSecretFile string `json:"clientSecretFile"`
}

func (c Config) ClientSecret() (string, error) {
	b, err := os.ReadFile(c.ClientSecretFile)
	if err != nil {
		return "", err
	}
	return strings.TrimSpace(string(b)), nil
}