package main

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/base64"
	"encoding/json"
	"encoding/pem"
	"flag"
	"fmt"
	"io"
	"log"
	"math/big"
	"net"
	"net/http"
	"os"
	"strings"
	"sync"
	"time"

	"github.com/pquerna/otp/totp"
	"golang.org/x/crypto/acme/autocert"
)

var (
	store    *UserStore
	sessions = struct {
		sync.RWMutex
		m map[string]*Session
	}{m: make(map[string]*Session)}
	logger *Logger
)

type Session struct {
	UserID    string
	ExpiresAt time.Time
}

func main() {
	// --- FLAGS ---
	addUser := flag.String("add-user", "", "Add a new user (provide user ID)")
	port := flag.String("port", os.Getenv("MANAGER_PORT"), "Port to run the server on (use 443 for Let's Encrypt)")
	domain := flag.String("domain", os.Getenv("DYFI_DOMAIN"), "Your dy.fi domain (e.g. example.dy.fi)")
	dyfiUser := flag.String("dyfi-user", os.Getenv("DYFI_USER"), "dy.fi username (email)")
	dyfiPass := flag.String("dyfi-pass", os.Getenv("DYFI_PASS"), "dy.fi password")
	email := flag.String("email", os.Getenv("ACME_EMAIL"), "Email for Let's Encrypt notifications")

	flag.Parse()

	logger = NewLogger()

	// --- ENCRYPTION INITIALIZATION ---
	serverKey := os.Getenv("SERVER_KEY")
	if serverKey == "" {
		logger.Warn("SERVER_KEY not set, generating new key")
		var err error
		serverKey, err = GenerateServerKey()
		if err != nil {
			logger.Error("Failed to generate server key: %v", err)
			log.Fatal(err)
		}
		fmt.Printf("\n⚠️  IMPORTANT: Save this SERVER_KEY to your environment:\n")
		fmt.Printf("export SERVER_KEY=%s\n\n", serverKey)
	}

	crypto, err := NewCrypto(serverKey)
	if err != nil {
		logger.Error("Failed to initialize crypto: %v", err)
		log.Fatal(err)
	}

	store = NewUserStore("users_data", crypto)

	// --- BACKGROUND TASKS ---
	// Reload user store from disk periodically
	go func() {
		ticker := time.NewTicker(1 * time.Minute)
		for range ticker.C {
			if err := store.Reload(); err != nil {
				logger.Error("Failed to reload user store: %v", err)
			}
		}
	}()

	// Cleanup expired sessions
	go func() {
		ticker := time.NewTicker(5 * time.Minute)
		for range ticker.C {
			cleanupSessions()
		}
	}()

	// dy.fi Dynamic DNS Updater
	if *domain != "" && *dyfiUser != "" {
		startDyfiUpdater(*domain, *dyfiUser, *dyfiPass)
	}

	// --- CLI COMMANDS ---
	if *addUser != "" {
		handleNewUser(*addUser)
		return
	}

	// --- TEMPLATE LOADING ---
	tmpl, err := LoadTemplate()
	if err != nil {
		log.Fatal(err)
	}
	appTmpl, err := LoadAppTemplate()
	if err != nil {
		log.Fatal(err)
	}

	// --- ROUTES ---
	// Routes must be defined BEFORE the server starts

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if session := getValidSession(r, crypto); session != nil {
			http.Redirect(w, r, "/app", http.StatusSeeOther)
			return
		}
		tmpl.Execute(w, map[string]interface{}{"Step2": false})
	})

	http.HandleFunc("/app", func(w http.ResponseWriter, r *http.Request) {
		session := getValidSession(r, crypto)
		if session == nil {
			http.Redirect(w, r, "/", http.StatusSeeOther)
			return
		}
		appTmpl.Execute(w, map[string]interface{}{"UserID": session.UserID})
	})

	http.HandleFunc("/logout", func(w http.ResponseWriter, r *http.Request) {
		cookie, err := r.Cookie("auth_session")
		if err == nil {
			sessions.Lock()
			delete(sessions.m, cookie.Value)
			sessions.Unlock()
		}
		http.SetCookie(w, &http.Cookie{
			Name:   "auth_session",
			Value:  "",
			Path:   "/",
			MaxAge: -1,
		})
		http.Redirect(w, r, "/", http.StatusSeeOther)
	})

	http.HandleFunc("/api/request", func(w http.ResponseWriter, r *http.Request) {
		session := getValidSession(r, crypto)
		if session == nil {
			w.WriteHeader(http.StatusUnauthorized)
			json.NewEncoder(w).Encode(map[string]string{"error": "Unauthorized"})
			return
		}

		var req struct {
			Method  string            `json:"method"`
			URL     string            `json:"url"`
			Headers map[string]string `json:"headers"`
			Body    string            `json:"body"`
		}

		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			w.WriteHeader(http.StatusBadRequest)
			return
		}

		result := makeHTTPRequest(req.Method, req.URL, req.Headers, req.Body)
		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(result)
	})

	http.HandleFunc("/verify-user", func(w http.ResponseWriter, r *http.Request) {
		userID := strings.TrimSpace(r.FormValue("userid"))
		user, err := store.GetUser(userID)
		if err != nil || user == nil {
			tmpl.Execute(w, map[string]interface{}{"Step2": false, "Error": "User not found"})
			return
		}

		sessionID := fmt.Sprintf("%d", time.Now().UnixNano())
		sessions.Lock()
		sessions.m[sessionID] = &Session{
			UserID:    userID,
			ExpiresAt: time.Now().Add(5 * time.Minute),
		}
		sessions.Unlock()

		http.SetCookie(w, &http.Cookie{
			Name:     "temp_session",
			Value:    sessionID,
			Path:     "/",
			HttpOnly: true,
			Secure:   true,
			SameSite: http.SameSiteStrictMode,
		})
		tmpl.Execute(w, map[string]interface{}{"Step2": true})
	})

	http.HandleFunc("/verify-totp", func(w http.ResponseWriter, r *http.Request) {
		cookie, err := r.Cookie("temp_session")
		if err != nil {
			http.Redirect(w, r, "/", http.StatusSeeOther)
			return
		}

		sessions.RLock()
		session, ok := sessions.m[cookie.Value]
		sessions.RUnlock()

		if !ok || time.Now().After(session.ExpiresAt) {
			http.Redirect(w, r, "/", http.StatusSeeOther)
			return
		}

		user, _ := store.GetUser(session.UserID)
		totpCode := strings.TrimSpace(r.FormValue("totp"))

		if !totp.Validate(totpCode, user.TOTPSecret) {
			tmpl.Execute(w, map[string]interface{}{"Step2": true, "Error": "Invalid TOTP code"})
			return
		}

		sessions.Lock()
		delete(sessions.m, cookie.Value)

		authSessionID := fmt.Sprintf("%d", time.Now().UnixNano())
		sessions.m[authSessionID] = &Session{
			UserID:    session.UserID,
			ExpiresAt: time.Now().Add(1 * time.Hour),
		}
		sessions.Unlock()

		encryptedSession, _ := crypto.EncryptWithServerKey([]byte(authSessionID))

		http.SetCookie(w, &http.Cookie{
			Name:     "auth_session",
			Value:    base64.StdEncoding.EncodeToString(encryptedSession),
			Path:     "/",
			HttpOnly: true,
			Secure:   true,
			SameSite: http.SameSiteStrictMode,
			MaxAge:   3600,
		})

		http.Redirect(w, r, "/app", http.StatusSeeOther)
	})

	// --- SERVER STARTUP ---

	if *domain != "" {
		// Let's Encrypt / ACME Setup
		certManager := autocert.Manager{
			Prompt:     autocert.AcceptTOS,
			HostPolicy: autocert.HostWhitelist(*domain),
			Cache:      autocert.DirCache("certs_cache"),
			Email:      *email,
		}

		// Let's Encrypt requires port 80 for the HTTP-01 challenge
		go func() {
			logger.Info("Starting HTTP-01 challenge listener on port 80")
			// This handler automatically redirects HTTP to HTTPS while solving challenges
			log.Fatal(http.ListenAndServe(":80", certManager.HTTPHandler(nil)))
		}()

		server := &http.Server{
			Addr: ":" + *port,
			TLSConfig: certManager.TLSConfig(),
		}

		logger.Info("Secure Server starting with Let's Encrypt on https://%s", *domain)
		log.Fatal(server.ListenAndServeTLS("", "")) // Certs provided by autocert
	} else {
		// Fallback to Self-Signed Certs
		certFile, keyFile, err := setupCerts()
		if err != nil {
			logger.Error("TLS Setup Error: %v", err)
			log.Fatal(err)
		}

		server := &http.Server{
			Addr: ":" + *port,
			TLSConfig: &tls.Config{
				MinVersion: tls.VersionTLS12,
			},
		}

		logger.Info("Secure Server starting with self-signed certs on https://localhost:%s", *port)
		log.Fatal(server.ListenAndServeTLS(certFile, keyFile))
	}
}

// setupCerts creates self-signed certs if they don't exist
func setupCerts() (string, string, error) {
	certFile, keyFile := "cert.pem", "key.pem"
	if _, err := os.Stat(certFile); err == nil {
		return certFile, keyFile, nil
	}

	logger.Info("Generating self-signed certificates for HTTPS...")
	priv, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)

	serialNumber, _ := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject:      pkix.Name{Organization: []string{"TwoStepAuth Dev"}},
		NotBefore:    time.Now(),
		NotAfter:     time.Now().Add(365 * 24 * time.Hour),
		KeyUsage:     x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		DNSNames:     []string{"localhost"},
		IPAddresses:  []net.IP{net.ParseIP("127.0.0.1")},
	}

	derBytes, _ := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)

	certOut, _ := os.Create(certFile)
	pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
	certOut.Close()

	keyOut, _ := os.OpenFile(keyFile, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	privBytes, _ := x509.MarshalECPrivateKey(priv)
	pem.Encode(keyOut, &pem.Block{Type: "EC PRIVATE KEY", Bytes: privBytes})
	keyOut.Close()

	return certFile, keyFile, nil
}

func handleNewUser(userID string) {
	secret, _ := generateSecret()
	store.AddUser(userID, secret)
	otpauthURL := fmt.Sprintf("otpauth://totp/TwoStepAuth:%s?secret=%s&issuer=TwoStepAuth", userID, secret)
	fmt.Printf("\nUser: %s\nSecret: %s\n", userID, secret)
	PrintQRCode(otpauthURL)
}

func getValidSession(r *http.Request, crypto *Crypto) *Session {
	cookie, err := r.Cookie("auth_session")
	if err != nil {
		return nil
	}
	enc, _ := base64.StdEncoding.DecodeString(cookie.Value)
	sid, err := crypto.DecryptWithServerKey(enc)
	if err != nil {
		return nil
	}
	sessions.RLock()
	session, ok := sessions.m[string(sid)]
	sessions.RUnlock()
	if !ok || time.Now().After(session.ExpiresAt) {
		return nil
	}
	return session
}

func cleanupSessions() {
	sessions.Lock()
	defer sessions.Unlock()
	now := time.Now()
	for id, s := range sessions.m {
		if now.After(s.ExpiresAt) {
			delete(sessions.m, id)
		}
	}
}

func makeHTTPRequest(method, url string, headers map[string]string, body string) map[string]interface{} {
	client := &http.Client{Timeout: 30 * time.Second}

	var reqBody io.Reader
	if body != "" {
		reqBody = strings.NewReader(body)
	}

	req, err := http.NewRequest(method, url, reqBody)
	if err != nil {
		return map[string]interface{}{
			"error": err.Error(),
		}
	}

	for key, value := range headers {
		req.Header.Set(key, value)
	}

	start := time.Now()
	resp, err := client.Do(req)
	duration := time.Since(start).Milliseconds()

	if err != nil {
		return map[string]interface{}{
			"error":    err.Error(),
			"duration": duration,
		}
	}
	defer resp.Body.Close()

	bodyBytes, err := io.ReadAll(resp.Body)
	if err != nil {
		return map[string]interface{}{
			"error":    err.Error(),
			"duration": duration,
		}
	}

	respHeaders := make(map[string]string)
	for key, values := range resp.Header {
		respHeaders[key] = strings.Join(values, ", ")
	}

	return map[string]interface{}{
		"status":   resp.StatusCode,
		"headers":  respHeaders,
		"body":     string(bodyBytes),
		"duration": duration,
	}
}