package main

import (
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"crypto/subtle"
	"embed"
	"encoding/base64"
	"encoding/binary"
	"encoding/hex"
	"flag"
	"fmt"
	"html/template"
	"io"
	"log"
	"net/http"
	"os"
	"strings"
	"sync"
	"time"

	"roseh.moe/pkg/roseh.moe/internal/ini"
	"roseh.moe/pkg/roseh.moe/internal/pwhash"
	"roseh.moe/pkg/wordlist"
)

var (
	port        = flag.Int("port", 42069, "port to listen on")
	selfURL     = flag.String("self-url", "http://localhost:42069", "base URL of the server")
	secretsFile = flag.String("secrets", "secrets.ini", "secrets file")
	configFile  = flag.String("config", "config.ini", "configuration file (no spec or examples, sorry)")

	serverStartTime = time.Now()
)

var notepadPassword, secretKey []byte

func loadSecrets() error {
	f, err := os.Open(*secretsFile)
	if err != nil {
		return err
	}
	defer f.Close()
	p := new(ini.Parser)
	for keyVal, err := range p.Parse(f) {
		if err != nil {
			return fmt.Errorf("%s:%d %s", *secretsFile, p.LineNumber, err)
		}
		switch keyVal.Key {
		case "notepad-password":
			notepadPassword, err = hex.AppendDecode(nil, []byte(keyVal.Val))
			if err != nil {
				return fmt.Errorf("%s:%d %s", *secretsFile, p.LineNumber, err)
			}
		case "secret-key":
			secretKey, err = hex.AppendDecode(nil, []byte(keyVal.Val))
			if err != nil {
				return fmt.Errorf("%s:%d %s", *secretsFile, p.LineNumber, err)
			}
		default:
			return fmt.Errorf("%s:%d unknown key", *secretsFile, p.LineNumber)
		}
	}
	if len(notepadPassword) == 0 {
		return fmt.Errorf("%s: missing notepad-password", *secretsFile)
	}
	if len(secretKey) == 0 {
		return fmt.Errorf("%s: missing secret-key", *secretsFile)
	}
	return nil
}

type serviceConfiguration struct {
	packageRedirects map[string]string
	commandRedirects map[string]string
}

var (
	serviceConfigMu           sync.Mutex
	serviceConfig             *serviceConfiguration
	serviceConfigLastModified time.Time
)

func loadConfig() (*serviceConfiguration, error) {
	stat, err := os.Stat(*configFile)
	if err != nil {
		return nil, err
	}
	serviceConfigMu.Lock()
	oldConfig := serviceConfig
	configLastModified := serviceConfigLastModified
	serviceConfigMu.Unlock()
	newModTime := stat.ModTime()
	if !newModTime.After(configLastModified) {
		return oldConfig, nil
	}
	log.Printf("Reloading config file...")
	f, err := os.Open(*configFile)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	config := &serviceConfiguration{
		packageRedirects: make(map[string]string),
		commandRedirects: make(map[string]string),
	}
	p := new(ini.Parser)
	for keyVal, err := range p.Parse(f) {
		if err != nil {
			log.Printf("Warning: %s:%d %s", *configFile, p.LineNumber, err)
			continue
		}
		switch p.Section {
		case "package-redirects":
			config.packageRedirects[keyVal.Key] = keyVal.Val
		case "command-redirects":
			config.commandRedirects[keyVal.Key] = keyVal.Val
		default:
			log.Printf("Warning: %s:%d unknown section", *configFile, p.LineNumber)
		}
	}
	serviceConfigMu.Lock()
	serviceConfig = config
	serviceConfigLastModified = newModTime
	serviceConfigMu.Unlock()
	return config, nil
}

var (
	//go:embed templates/404.html.template
	notFoundString   string
	notFoundTemplate = template.Must(template.New("notFound").Parse(notFoundString))
)

func notFound(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusNotFound)
	type args struct {
		Path string
	}
	if err := notFoundTemplate.Execute(w, args{Path: r.URL.Path}); err != nil {
		log.Printf("Warning: notFound: %s", err)
	}
}

var (
	//go:embed templates/outline.html.template
	outlineString   string
	outlineTemplate = template.Must(template.New("outline").Parse(outlineString))

	//go:embed templates/index.html.template
	indexString   string
	indexTemplate = template.Must(template.Must(outlineTemplate.Clone()).New("body").Parse(indexString)).Lookup("outline")
)

func index(w http.ResponseWriter, _ *http.Request) {
	if err := indexTemplate.Execute(w, nil); err != nil {
		log.Printf("Warning: index: %s", err)
	}
}

var (
	//go:embed templates/pong.html.template
	pongString   string
	pongTemplate = template.Must(template.New("pong").Parse(pongString))
)

func pong(w http.ResponseWriter, _ *http.Request) {
	if err := pongTemplate.Execute(w, nil); err != nil {
		log.Printf("Warning: pong: %s", err)
	}
}

//go:embed static
var staticFiles embed.FS

func serveStaticFile(w http.ResponseWriter, r *http.Request, path string) {
	f, err := staticFiles.Open(path)
	if err != nil {
		notFound(w, r)
		return
	}
	defer f.Close()
	http.ServeContent(w, r, path, serverStartTime, f.(io.ReadSeeker))
}

func static(w http.ResponseWriter, r *http.Request) {
	serveStaticFile(w, r, strings.TrimPrefix(r.URL.Path, "/"))
}

func favicon(w http.ResponseWriter, r *http.Request) {
	serveStaticFile(w, r, "static/favicon.ico")
}

var (
	//go:embed templates/wormhole.html.template
	wormholeTemplateString string
	wormholeTemplate       = template.Must(template.Must(outlineTemplate.Clone()).New("body").Parse(wormholeTemplateString)).Lookup("outline")
)

type wormholeTemplateArgs struct {
	Self string
	Hole string
}

func makeHole() string {
	const nWords = 10
	buf := make([]byte, 2*nWords)
	rand.Read(buf)
	words := make([]string, nWords)
	for i := range words {
		words[i] = wordlist.Words[binary.NativeEndian.Uint16(buf[2*i:])&0x1fff]
	}
	return strings.Join(words, "-")
}

func wormhole(w http.ResponseWriter, r *http.Request) {
	if err := wormholeTemplate.Execute(w, wormholeTemplateArgs{Self: *selfURL, Hole: makeHole()}); err != nil {
		log.Printf("Warning: wormhole: %s", err)
	}
}

type wormholeConn struct {
	done chan struct{}
	w    http.ResponseWriter
}

var wormholeConnsMu sync.Mutex
var wormholeConns = make(map[string]*wormholeConn)

var wormholeNotifyMu sync.Mutex
var wormholeNotify = make(map[string]chan struct{})

func wormholeSend(w http.ResponseWriter, r *http.Request) {
	reader, err := r.MultipartReader()
	if err != nil {
		http.Error(w, fmt.Sprintf("Not a multipart/form-data request: %s", err), http.StatusBadRequest)
		return
	}
	for {
		part, err := reader.NextPart()
		if err != nil {
			break
		}
		if part.FormName() != "file" {
			continue
		}
		hole := r.PathValue("hole")
		wormholeConnsMu.Lock()
		conn := wormholeConns[hole]
		delete(wormholeConns, hole)
		wormholeConnsMu.Unlock()
		if conn == nil {
			http.Error(w, "no such connection", http.StatusBadRequest)
			return
		}
		defer close(conn.done)
		conn.w.Header().Set("Content-Disposition", "attachment; filename*=UTF-8''"+part.FileName())
		if _, err := io.Copy(conn.w, part); err != nil {
			http.Error(w, fmt.Sprintf("Error during copy: %s", err), http.StatusServiceUnavailable)
			return
		}
		fmt.Fprintf(w, "uploaded!")
		return
	}
	http.Error(w, "file not found", http.StatusBadRequest)
}

func wormholeRecv(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	hole := r.PathValue("hole")
	conn := &wormholeConn{
		done: make(chan struct{}),
		w:    w,
	}
	wormholeConnsMu.Lock()
	wormholeConns[hole] = conn
	wormholeConnsMu.Unlock()
	defer func() {
		wormholeConnsMu.Lock()
		delete(wormholeConns, hole)
		wormholeConnsMu.Unlock()
	}()
	wormholeNotifyMu.Lock()
	notify := wormholeNotify[hole]
	wormholeNotifyMu.Unlock()
	if notify == nil {
		http.Error(w, "no such connection", http.StatusBadRequest)
		return
	}
	select {
	case notify <- struct{}{}:
	default:
		http.Error(w, "connection not ready", http.StatusBadRequest)
		return
	}
	select {
	case <-ctx.Done():
	case <-conn.done:
	}
}

func wormholeReady(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	hole := r.PathValue("hole")
	notify := make(chan struct{})
	wormholeNotifyMu.Lock()
	wormholeNotify[hole] = notify
	wormholeNotifyMu.Unlock()
	defer func() {
		wormholeNotifyMu.Lock()
		delete(wormholeNotify, hole)
		wormholeNotifyMu.Unlock()
	}()
	w.Header().Set("Content-Type", "text/event-stream")
	select {
	case <-ctx.Done():
		return
	case <-notify:
	}
	fmt.Fprintf(w, "event: ready\ndata:\n\n")
}

func mac(msg []byte) []byte {
	mac := hmac.New(sha256.New, secretKey)
	mac.Write(msg)
	return mac.Sum(nil)
}

func sign(msg []byte) []byte {
	return append(msg, mac(msg)...)
}

func verify(msg []byte) ([]byte, bool) {
	if len(msg) < sha256.Size {
		return nil, false
	}
	msg, messageMAC := msg[:len(msg)-sha256.Size], msg[len(msg)-sha256.Size:]
	expectedMAC := mac(msg)
	if !hmac.Equal(messageMAC, expectedMAC) {
		return nil, false
	}
	return msg, true
}

func makeToken() (string, error) {
	b, err := time.Now().MarshalBinary()
	if err != nil {
		return "", err
	}
	return base64.RawURLEncoding.EncodeToString(sign(b)), nil
}

const cookieExpiration = 180 * 24 * time.Hour

func attachCookie(w http.ResponseWriter) error {
	token, err := makeToken()
	if err != nil {
		return err
	}
	http.SetCookie(w, &http.Cookie{
		Name:        "auth",
		Value:       token,
		Path:        "/",
		Expires:     time.Now().Add(cookieExpiration),
		Secure:      true,
		HttpOnly:    true,
		SameSite:    http.SameSiteStrictMode,
		Partitioned: true,
	})
	return nil
}

func cookieAuth(w http.ResponseWriter, r *http.Request) bool {
	cookie, err := r.Cookie("auth")
	if err != nil {
		return false
	}
	authCookie, err := base64.RawURLEncoding.DecodeString(cookie.Value)
	if err != nil {
		return false
	}
	msg, ok := verify(authCookie)
	if !ok {
		return false
	}
	var t time.Time
	if err := t.UnmarshalBinary(msg); err != nil {
		return false
	}
	cookieAge := time.Since(t)
	if cookieAge > cookieExpiration {
		return false
	}
	if cookieAge > 24*time.Hour {
		attachCookie(w)
	}
	return true
}

func checkPassword(password string) bool {
	expectedHash, salt := notepadPassword[:len(notepadPassword)-pwhash.SaltSize], notepadPassword[len(notepadPassword)-pwhash.SaltSize:]
	hash, err := pwhash.Hash(password, salt)
	return err == nil && subtle.ConstantTimeCompare(hash, expectedHash) != 0
}

var (
	//go:embed templates/login.html.template
	loginTemplateString string
	loginTemplate       = template.Must(template.Must(outlineTemplate.Clone()).New("body").Parse(loginTemplateString)).Lookup("outline")
)

type loginTemplateArgs struct {
	Error bool
}

func executeLoginTemplate(w io.Writer) {
	if err := loginTemplate.Execute(w, loginTemplateArgs{}); err != nil {
		log.Printf("Warning: login: %s", err)
	}
}

func login(w http.ResponseWriter, r *http.Request) {
	if !checkPassword(r.FormValue("password")) {
		if err := loginTemplate.Execute(w, loginTemplateArgs{Error: true}); err != nil {
			log.Printf("Warning: login: %s", err)
		}
		return
	}
	attachCookie(w)
	http.Redirect(w, r, "/notepad", http.StatusSeeOther)
}

var (
	//go:embed templates/note.html.template
	notepadString   string
	notepadTemplate = template.Must(template.Must(outlineTemplate.Clone()).New("body").Parse(notepadString)).Lookup("outline")

	notepadContentsMu sync.Mutex
	notepadContents   string
)

type notepadTemplateArgs struct {
	Content string
}

func notepad(w http.ResponseWriter, r *http.Request) {
	if !cookieAuth(w, r) {
		executeLoginTemplate(w)
		return
	}
	notepadContentsMu.Lock()
	currentContent := notepadContents
	notepadContentsMu.Unlock()
	if err := notepadTemplate.Execute(w, notepadTemplateArgs{Content: currentContent}); err != nil {
		log.Printf("Warning: notepad: %s", err)
	}
}

func saveNote(w http.ResponseWriter, r *http.Request) error {
	if !cookieAuth(w, r) {
		return fmt.Errorf("not logged in")
	}
	newContent := r.FormValue("content")
	notepadContentsMu.Lock()
	notepadContents = newContent
	notepadContentsMu.Unlock()
	return nil
}

func autosave(w http.ResponseWriter, r *http.Request) {
	msg := "Saved ✓"
	if err := saveNote(w, r); err != nil {
		msg = fmt.Sprintf("Failed to save: %s", err)
	}
	if err := notepadTemplate.ExecuteTemplate(w, "saveIndicator", msg); err != nil {
		log.Printf("Warning: autosave: %s", err)
	}
}

func cmd(w http.ResponseWriter, r *http.Request) {
	serviceConfig, err := loadConfig()
	if err != nil {
		http.Error(w, fmt.Sprintf("load config: %s", err), http.StatusInternalServerError)
		return
	}
	source, ok := serviceConfig.commandRedirects[r.PathValue("cmd")]
	if !ok {
		notFound(w, r)
		return
	}
	if r.FormValue("go-get") == "1" {
		fmt.Fprintf(w, `<meta name="go-import" content="roseh.moe/cmd/%s %s">`, r.PathValue("cmd"), source)
	} else {
		http.Redirect(w, r, "https://pkg.go.dev/roseh.moe/cmd/"+r.PathValue("cmd"), http.StatusFound)
	}
}

func pkg(w http.ResponseWriter, r *http.Request) {
	serviceConfig, err := loadConfig()
	if err != nil {
		http.Error(w, fmt.Sprintf("load config: %s", err), http.StatusInternalServerError)
		return
	}
	source, ok := serviceConfig.packageRedirects[r.PathValue("pkg")]
	if !ok {
		notFound(w, r)
		return
	}
	if r.FormValue("go-get") == "1" {
		fmt.Fprintf(w, `<meta name="go-import" content="roseh.moe/pkg/%s %s">`, r.PathValue("pkg"), source)
	} else {
		http.Redirect(w, r, "https://pkg.go.dev/roseh.moe/pkg/"+r.PathValue("pkg"), http.StatusFound)
	}
}

func main() {
	flag.Parse()

	if err := loadSecrets(); err != nil {
		log.Fatal(err)
	}

	mux := http.NewServeMux()
	mux.HandleFunc("GET /pong", pong)
	mux.HandleFunc("GET /wormhole", wormhole)
	mux.HandleFunc("POST /wormhole/{hole}", wormholeSend)
	mux.HandleFunc("GET /wormhole/{hole}", wormholeRecv)
	mux.HandleFunc("GET /wormhole/{hole}/ready", wormholeReady)
	mux.HandleFunc("POST /login", login)
	mux.HandleFunc("GET /notepad", notepad)
	mux.HandleFunc("POST /notepad", autosave)
	mux.HandleFunc("GET /cmd/{cmd}", cmd)
	mux.HandleFunc("GET /pkg/{pkg}", pkg)
	mux.HandleFunc("GET /static/", static)
	mux.HandleFunc("GET /favicon.ico", favicon)
	mux.HandleFunc("GET /{$}", index)
	mux.HandleFunc("GET /", notFound)

	addr := fmt.Sprintf(":%d", *port)
	log.Printf("Listening on %q", addr)
	log.Fatal(http.ListenAndServe(addr, http.NewCrossOriginProtection().Handler(mux)))
}