package main

import (
	"bytes"
	"context"
	"crypto/ed25519"
	"crypto/rand"
	"embed"
	"encoding/hex"
	"errors"
	"flag"
	"fmt"
	"io/fs"
	"log"
	"log/slog"
	"net"
	"net/http"
	"net/http/httputil"
	"net/url"
	"os"
	"os/signal"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/TecharoHQ/anubis"
	"github.com/TecharoHQ/anubis/data"
	"github.com/TecharoHQ/anubis/internal"
	libanubis "github.com/TecharoHQ/anubis/lib"
	botPolicy "github.com/TecharoHQ/anubis/lib/policy"
	"github.com/TecharoHQ/anubis/lib/policy/config"
	"github.com/TecharoHQ/anubis/web"
	"github.com/facebookgo/flagenv"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

var (
	basePrefix               = flag.String("base-prefix", "", "base prefix (root URL) the application is served under e.g. /myapp")
	bind                     = flag.String("bind", ":8923", "network address to bind HTTP to")
	bindNetwork              = flag.String("bind-network", "tcp", "network family to bind HTTP to, e.g. unix, tcp")
	challengeDifficulty      = flag.Int("difficulty", anubis.DefaultDifficulty, "difficulty of the challenge")
	cookieDomain             = flag.String("cookie-domain", "", "if set, the top-level domain that the Anubis cookie will be valid for")
	cookiePartitioned        = flag.Bool("cookie-partitioned", false, "if true, sets the partitioned flag on Anubis cookies, enabling CHIPS support")
	ed25519PrivateKeyHex     = flag.String("ed25519-private-key-hex", "", "private key used to sign JWTs, if not set a random one will be assigned")
	ed25519PrivateKeyHexFile = flag.String("ed25519-private-key-hex-file", "", "file name containing value for ed25519-private-key-hex")
	metricsBind              = flag.String("metrics-bind", ":9090", "network address to bind metrics to")
	metricsBindNetwork       = flag.String("metrics-bind-network", "tcp", "network family for the metrics server to bind to")
	socketMode               = flag.String("socket-mode", "0770", "socket mode (permissions) for unix domain sockets.")
	robotsTxt                = flag.Bool("serve-robots-txt", false, "serve a robots.txt file that disallows all robots")
	policyFname              = flag.String("policy-fname", "", "full path to anubis policy document (defaults to a sensible built-in policy)")
	redirectDomains          = flag.String("redirect-domains", "", "list of domains separated by commas which anubis is allowed to redirect to. Leaving this unset allows any domain.")
	slogLevel                = flag.String("slog-level", "INFO", "logging level (see https://pkg.go.dev/log/slog#hdr-Levels)")
	target                   = flag.String("target", "http://localhost:3923", "target to reverse proxy to, set to an empty string to disable proxying when only using auth request")
	healthcheck              = flag.Bool("healthcheck", false, "run a health check against Anubis")
	useRemoteAddress         = flag.Bool("use-remote-address", false, "read the client's IP address from the network request, useful for debugging and running Anubis on bare metal")
	debugBenchmarkJS         = flag.Bool("debug-benchmark-js", false, "respond to every request with a challenge for benchmarking hashrate")
	ogPassthrough            = flag.Bool("og-passthrough", false, "enable Open Graph tag passthrough")
	ogTimeToLive             = flag.Duration("og-expiry-time", 24*time.Hour, "Open Graph tag cache expiration time")
	extractResources         = flag.String("extract-resources", "", "if set, extract the static resources to the specified folder")
	webmasterEmail           = flag.String("webmaster-email", "", "if set, displays webmaster's email on the reject page for appeals")
)

func keyFromHex(value string) (ed25519.PrivateKey, error) {
	keyBytes, err := hex.DecodeString(value)
	if err != nil {
		return nil, fmt.Errorf("supplied key is not hex-encoded: %w", err)
	}

	if len(keyBytes) != ed25519.SeedSize {
		return nil, fmt.Errorf("supplied key is not %d bytes long, got %d bytes", ed25519.SeedSize, len(keyBytes))
	}

	return ed25519.NewKeyFromSeed(keyBytes), nil
}

func doHealthCheck() error {
	resp, err := http.Get("http://localhost" + *metricsBind + anubis.BasePrefix + "/metrics")
	if err != nil {
		return fmt.Errorf("failed to fetch metrics: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("unexpected status code: %d", resp.StatusCode)
	}

	return nil
}

func setupListener(network string, address string) (net.Listener, string) {
	formattedAddress := ""
	switch network {
	case "unix":
		formattedAddress = "unix:" + address
	case "tcp":
		if strings.HasPrefix(address, ":") { // assume it's just a port e.g. :4259
			formattedAddress = "http://localhost" + address
		} else {
			formattedAddress = "http://" + address
		}
	default:
		formattedAddress = fmt.Sprintf(`(%s) %s`, network, address)
	}

	listener, err := net.Listen(network, address)
	if err != nil {
		log.Fatal(fmt.Errorf("failed to bind to %s: %w", formattedAddress, err))
	}

	// additional permission handling for unix sockets
	if network == "unix" {
		mode, err := strconv.ParseUint(*socketMode, 8, 0)
		if err != nil {
			listener.Close()
			log.Fatal(fmt.Errorf("could not parse socket mode %s: %w", *socketMode, err))
		}

		err = os.Chmod(address, os.FileMode(mode))
		if err != nil {
			err := listener.Close()
			if err != nil {
				log.Printf("failed to close listener: %v", err)
			}
			log.Fatal(fmt.Errorf("could not change socket mode: %w", err))
		}
	}

	return listener, formattedAddress
}

func makeReverseProxy(target string) (http.Handler, error) {
	targetUri, err := url.Parse(target)
	if err != nil {
		return nil, fmt.Errorf("failed to parse target URL: %w", err)
	}

	transport := http.DefaultTransport.(*http.Transport).Clone()

	// https://github.com/oauth2-proxy/oauth2-proxy/blob/4e2100a2879ef06aea1411790327019c1a09217c/pkg/upstream/http.go#L124
	if targetUri.Scheme == "unix" {
		// clean path up so we don't use the socket path in proxied requests
		addr := targetUri.Path
		targetUri.Path = ""
		// tell transport how to dial unix sockets
		transport.DialContext = func(ctx context.Context, _, _ string) (net.Conn, error) {
			dialer := net.Dialer{}
			return dialer.DialContext(ctx, "unix", addr)
		}
		// tell transport how to handle the unix url scheme
		transport.RegisterProtocol("unix", libanubis.UnixRoundTripper{Transport: transport})
	}

	rp := httputil.NewSingleHostReverseProxy(targetUri)
	rp.Transport = transport

	return rp, nil
}

func startDecayMapCleanup(ctx context.Context, s *libanubis.Server) {
	ticker := time.NewTicker(1 * time.Hour)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			s.CleanupDecayMap()
		case <-ctx.Done():
			return
		}
	}
}

func main() {
	flagenv.Parse()
	flag.Parse()

	internal.InitSlog(*slogLevel)

	if *extractResources != "" {
		if err := extractEmbedFS(data.BotPolicies, ".", *extractResources); err != nil {
			log.Fatal(err)
		}
		if err := extractEmbedFS(web.Static, "static", *extractResources); err != nil {
			log.Fatal(err)
		}
		fmt.Printf("Extracted embedded static files to %s\n", *extractResources)
		return
	}

	var rp http.Handler
	// when using anubis via Systemd and environment variables, then it is not possible to set targe to an empty string but only to space
	if strings.TrimSpace(*target) != "" {
		var err error
		rp, err = makeReverseProxy(*target)
		if err != nil {
			log.Fatalf("can't make reverse proxy: %v", err)
		}
	}

	policy, err := libanubis.LoadPoliciesOrDefault(*policyFname, *challengeDifficulty)
	if err != nil {
		log.Fatalf("can't parse policy file: %v", err)
	}

	fmt.Println("Rule error IDs:")
	for _, rule := range policy.Bots {
		if rule.Action != config.RuleDeny {
			continue
		}

		hash := rule.Hash()
		fmt.Printf("* %s: %s\n", rule.Name, hash)
	}
	fmt.Println()

	// replace the bot policy rules with a single rule that always benchmarks
	if *debugBenchmarkJS {
		policy.Bots = []botPolicy.Bot{{
			Name:   "",
			Rules:  botPolicy.NewHeaderExistsChecker("User-Agent"),
			Action: config.RuleBenchmark,
		}}
	}
	if *basePrefix != "" && !strings.HasPrefix(*basePrefix, "/") {
		log.Fatalf("[misconfiguration] base-prefix must start with a slash, eg: /%s", *basePrefix)
	} else if strings.HasSuffix(*basePrefix, "/") {
		log.Fatalf("[misconfiguration] base-prefix must not end with a slash")
	}

	var priv ed25519.PrivateKey
	if *ed25519PrivateKeyHex != "" && *ed25519PrivateKeyHexFile != "" {
		log.Fatal("do not specify both ED25519_PRIVATE_KEY_HEX and ED25519_PRIVATE_KEY_HEX_FILE")
	} else if *ed25519PrivateKeyHex != "" {
		priv, err = keyFromHex(*ed25519PrivateKeyHex)
		if err != nil {
			log.Fatalf("failed to parse and validate ED25519_PRIVATE_KEY_HEX: %v", err)
		}
	} else if *ed25519PrivateKeyHexFile != "" {
		hexFile, err := os.ReadFile(*ed25519PrivateKeyHexFile)
		if err != nil {
			log.Fatalf("failed to read ED25519_PRIVATE_KEY_HEX_FILE %s: %v", *ed25519PrivateKeyHexFile, err)
		}

		priv, err = keyFromHex(string(bytes.TrimSpace(hexFile)))
		if err != nil {
			log.Fatalf("failed to parse and validate content of ED25519_PRIVATE_KEY_HEX_FILE: %v", err)
		}
	} else {
		_, priv, err = ed25519.GenerateKey(rand.Reader)
		if err != nil {
			log.Fatalf("failed to generate ed25519 key: %v", err)
		}

		slog.Warn("generating random key, Anubis will have strange behavior when multiple instances are behind the same load balancer target, for more information: see https://anubis.techaro.lol/docs/admin/installation#key-generation")
	}

	var redirectDomainsList []string
	if *redirectDomains != "" {
		domains := strings.Split(*redirectDomains, ",")
		for _, domain := range domains {
			_, err = url.Parse(domain)
			if err != nil {
				log.Fatalf("cannot parse redirect-domain %q: %s", domain, err.Error())
			}
			redirectDomainsList = append(redirectDomainsList, strings.TrimSpace(domain))
		}
	} else {
		slog.Warn("REDIRECT_DOMAINS is not set, Anubis will only redirect to the same domain a request is coming from, see https://anubis.techaro.lol/docs/admin/configuration/redirect-domains")
	}

	s, err := libanubis.New(libanubis.Options{
		BasePrefix:        *basePrefix,
		Next:              rp,
		Policy:            policy,
		ServeRobotsTXT:    *robotsTxt,
		PrivateKey:        priv,
		CookieDomain:      *cookieDomain,
		CookiePartitioned: *cookiePartitioned,
		OGPassthrough:     *ogPassthrough,
		OGTimeToLive:      *ogTimeToLive,
		RedirectDomains:   redirectDomainsList,
		Target:            *target,
		WebmasterEmail:    *webmasterEmail,
	})
	if err != nil {
		log.Fatalf("can't construct libanubis.Server: %v", err)
	}

	wg := new(sync.WaitGroup)
	// install signal handler
	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()

	if *metricsBind != "" {
		wg.Add(1)
		go metricsServer(ctx, wg.Done)
	}
	go startDecayMapCleanup(ctx, s)

	var h http.Handler
	h = s
	h = internal.RemoteXRealIP(*useRemoteAddress, *bindNetwork, h)
	h = internal.XForwardedForToXRealIP(h)
	h = internal.XForwardedForUpdate(h)

	srv := http.Server{Handler: h}
	listener, listenerUrl := setupListener(*bindNetwork, *bind)
	slog.Info(
		"listening",
		"url", listenerUrl,
		"difficulty", *challengeDifficulty,
		"serveRobotsTXT", *robotsTxt,
		"target", *target,
		"version", anubis.Version,
		"use-remote-address", *useRemoteAddress,
		"debug-benchmark-js", *debugBenchmarkJS,
		"og-passthrough", *ogPassthrough,
		"og-expiry-time", *ogTimeToLive,
		"base-prefix", *basePrefix,
	)

	go func() {
		<-ctx.Done()
		c, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		if err := srv.Shutdown(c); err != nil {
			log.Printf("cannot shut down: %v", err)
		}
	}()

	if err := srv.Serve(listener); !errors.Is(err, http.ErrServerClosed) {
		log.Fatal(err)
	}
	wg.Wait()
}

func metricsServer(ctx context.Context, done func()) {
	defer done()

	mux := http.NewServeMux()
	mux.Handle(anubis.BasePrefix+"/metrics", promhttp.Handler())

	srv := http.Server{Handler: mux}
	listener, metricsUrl := setupListener(*metricsBindNetwork, *metricsBind)
	slog.Debug("listening for metrics", "url", metricsUrl)

	if *healthcheck {
		log.Println("running healthcheck")
		if err := doHealthCheck(); err != nil {
			log.Fatal(err)
		}
		return
	}

	go func() {
		<-ctx.Done()
		c, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		if err := srv.Shutdown(c); err != nil {
			log.Printf("cannot shut down: %v", err)
		}
	}()

	if err := srv.Serve(listener); !errors.Is(err, http.ErrServerClosed) {
		log.Fatal(err)
	}
}

func extractEmbedFS(fsys embed.FS, root string, destDir string) error {
	return fs.WalkDir(fsys, root, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}

		relPath, err := filepath.Rel(root, path)
		if err != nil {
			return err
		}

		destPath := filepath.Join(destDir, root, relPath)

		if d.IsDir() {
			return os.MkdirAll(destPath, 0o700)
		}

		data, err := fs.ReadFile(fsys, path)
		if err != nil {
			return err
		}

		return os.WriteFile(destPath, data, 0o644)
	})
}