// backend\auth_passkey.go

package main

import (
	"crypto/rand"
	"encoding/base64"
	"encoding/json"
	"errors"
	"net"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

	"github.com/go-webauthn/webauthn/protocol"
	"github.com/go-webauthn/webauthn/webauthn"
)

const passkeyChallengeCookieName = "pk_challenge"

type recorderWebAuthnUser struct {
	id          []byte
	name        string
	displayName string
	credentials []webauthn.Credential
}

func (u recorderWebAuthnUser) WebAuthnID() []byte {
	return u.id
}

func (u recorderWebAuthnUser) WebAuthnName() string {
	return u.name
}

func (u recorderWebAuthnUser) WebAuthnDisplayName() string {
	return u.displayName
}

func (u recorderWebAuthnUser) WebAuthnIcon() string {
	return ""
}

func (u recorderWebAuthnUser) WebAuthnCredentials() []webauthn.Credential {
	return u.credentials
}

func randomBase64URL(n int) (string, error) {
	b := make([]byte, n)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return base64.RawURLEncoding.EncodeToString(b), nil
}

func (am *AuthManager) ensurePasskeyUserID() error {
	am.confMu.Lock()
	needsID := strings.TrimSpace(am.conf.PasskeyUserID) == ""
	if needsID {
		id, err := randomBase64URL(32)
		if err != nil {
			am.confMu.Unlock()
			return err
		}
		am.conf.PasskeyUserID = id
	}
	am.confMu.Unlock()

	if needsID {
		am.persistConfBestEffort()
	}

	return nil
}

func (am *AuthManager) initWebAuthn() error {
	origins := authAllowedRPOrigins()
	if len(origins) == 0 {
		return errors.New("no WebAuthn RP origins configured")
	}

	appLogln("🔐 WebAuthn allowed origins:", strings.Join(origins, ", "))
	appLogln("🔐 AUTH_RP_ID:", strings.TrimSpace(os.Getenv("AUTH_RP_ID")))

	rpID, err := rpIDForOrigin(origins[0])
	if err != nil {
		return err
	}

	wa, err := webauthn.New(&webauthn.Config{
		RPDisplayName: "Recorder",
		RPID:          rpID,
		RPOrigins:     origins,
	})
	if err != nil {
		return err
	}

	am.webAuthn = wa
	return nil
}

func authAllowedRPOrigins() []string {
	raw := strings.TrimSpace(os.Getenv("AUTH_RP_ORIGINS"))

	// Backward compatible: alter Einzelwert funktioniert weiter.
	if raw == "" {
		raw = strings.TrimSpace(os.Getenv("AUTH_RP_ORIGIN"))
	}

	if raw == "" {
		raw = strings.Join([]string{
			"https://l14pbbk95100006.tegdssd.de:9999",
			"https://localhost:9999",
			"https://127.0.0.1:9999",
			"https://10.0.1.25:9999",
			"http://localhost:9999",
			"http://127.0.0.1:9999",
			"http://10.0.1.25:9999",
			"http://l14pbbk95100006.tegdssd.de:5173",
			"http://localhost:5173",
			"http://127.0.0.1:5173",
			"http://10.0.1.25:5173",
		}, ",")
	}

	parts := strings.Split(raw, ",")
	out := make([]string, 0, len(parts))
	seen := map[string]bool{}

	for _, p := range parts {
		origin := strings.TrimSpace(p)
		origin = strings.TrimRight(origin, "/")
		if origin == "" {
			continue
		}

		if seen[origin] {
			continue
		}

		seen[origin] = true
		out = append(out, origin)
	}

	return out
}

func originFromRequest(r *http.Request) string {
	origin := strings.TrimSpace(r.Header.Get("Origin"))
	if origin != "" {
		return strings.TrimRight(origin, "/")
	}

	proto := "http"
	if isSecureRequest(r) {
		proto = "https"
	}

	host := strings.TrimSpace(r.Host)
	if host == "" {
		return ""
	}

	return proto + "://" + host
}

func rpIDFromOrigin(origin string) (string, error) {
	u, err := url.Parse(strings.TrimSpace(origin))
	if err != nil {
		return "", err
	}

	host := strings.ToLower(strings.TrimSpace(u.Hostname()))
	if host == "" {
		return "", errors.New("origin has no hostname")
	}

	if net.ParseIP(host) != nil {
		return "", errors.New(
			"Passkeys/WebAuthn funktionieren nicht mit einer IP-Adresse als RP-ID. " +
				"Öffne die App über einen Hostnamen, z. B. https://recorder.home.arpa:9999",
		)
	}

	return host, nil
}

func rpIDIsValidForOrigin(rpID string, origin string) bool {
	rpID = strings.ToLower(strings.TrimSpace(rpID))
	if rpID == "" {
		return false
	}

	u, err := url.Parse(strings.TrimSpace(origin))
	if err != nil {
		return false
	}

	host := strings.ToLower(strings.TrimSpace(u.Hostname()))
	if host == "" {
		return false
	}

	// IP-Adressen dürfen bei WebAuthn nur exakt als RP-ID verwendet werden.
	if net.ParseIP(host) != nil {
		return rpID == host
	}

	// localhost darf ebenfalls nur exakt localhost sein.
	if host == "localhost" {
		return rpID == "localhost"
	}

	// Normale Domains: RP-ID darf Host selbst oder Parent-Domain sein.
	return host == rpID || strings.HasSuffix(host, "."+rpID)
}

func rpIDForOrigin(origin string) (string, error) {
	configured := strings.TrimSpace(os.Getenv("AUTH_RP_ID"))

	if configured != "" {
		if rpIDIsValidForOrigin(configured, origin) {
			return configured, nil
		}

		appLogln(
			"⚠️ AUTH_RP_ID passt nicht zur aktuellen Origin, nutze Origin-Host:",
			"AUTH_RP_ID=", configured,
			"origin=", origin,
		)
	}

	return rpIDFromOrigin(origin)
}

func originIsAllowed(origin string, allowed []string) bool {
	origin = strings.TrimRight(strings.TrimSpace(origin), "/")

	for _, a := range allowed {
		if origin == strings.TrimRight(strings.TrimSpace(a), "/") {
			return true
		}
	}

	return false
}

func (am *AuthManager) webAuthnForRequest(r *http.Request) (*webauthn.WebAuthn, error) {
	origin := originFromRequest(r)
	if origin == "" {
		return nil, errors.New("request origin missing")
	}

	allowedOrigins := authAllowedRPOrigins()
	if !originIsAllowed(origin, allowedOrigins) {
		return nil, errors.New("origin not allowed for WebAuthn: " + origin)
	}

	rpID, err := rpIDForOrigin(origin)
	if err != nil {
		return nil, err
	}

	appLogln("🔐 WebAuthn Request:", "origin=", origin, "rpID=", rpID)

	return webauthn.New(&webauthn.Config{
		RPDisplayName: "Recorder",
		RPID:          rpID,
		RPOrigins:     []string{origin},
	})
}

func (am *AuthManager) webAuthnUser() (recorderWebAuthnUser, error) {
	am.confMu.Lock()
	defer am.confMu.Unlock()

	idRaw := strings.TrimSpace(am.conf.PasskeyUserID)
	id, err := base64.RawURLEncoding.DecodeString(idRaw)
	if err != nil {
		return recorderWebAuthnUser{}, err
	}

	username := strings.TrimSpace(am.conf.Username)
	if username == "" {
		username = "admin"
	}

	return recorderWebAuthnUser{
		id:          id,
		name:        username,
		displayName: username,
		credentials: append([]webauthn.Credential(nil), am.conf.Passkeys...),
	}, nil
}

func setPasskeyChallengeCookie(w http.ResponseWriter, id string, secure bool) {
	http.SetCookie(w, &http.Cookie{
		Name:     passkeyChallengeCookieName,
		Value:    id,
		Path:     "/",
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		Secure:   secure,
		Expires:  time.Now().Add(5 * time.Minute),
	})
}

func clearPasskeyChallengeCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{
		Name:     passkeyChallengeCookieName,
		Value:    "",
		Path:     "/",
		HttpOnly: true,
		Expires:  time.Unix(0, 0),
		MaxAge:   -1,
		SameSite: http.SameSiteLaxMode,
	})
}

func (am *AuthManager) savePasskeySession(key string, data *webauthn.SessionData) {
	am.passkeyMu.Lock()
	defer am.passkeyMu.Unlock()
	am.passkeySessions[key] = data
}

func (am *AuthManager) takePasskeySession(key string) *webauthn.SessionData {
	am.passkeyMu.Lock()
	defer am.passkeyMu.Unlock()

	data := am.passkeySessions[key]
	delete(am.passkeySessions, key)
	return data
}

func authPasskeyRegisterOptionsHandler(am *AuthManager) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "POST required", http.StatusMethodNotAllowed)
			return
		}

		s, sid := am.getSession(r)
		if s == nil || !s.Authed || sid == "" {
			http.Error(w, "unauthorized", http.StatusUnauthorized)
			return
		}

		user, err := am.webAuthnUser()
		if err != nil {
			http.Error(w, "passkey user error", http.StatusInternalServerError)
			return
		}

		wa, err := am.webAuthnForRequest(r)
		if err != nil {
			appLogln("passkey registration options config failed:", err)
			http.Error(w, "passkey registration options config failed: "+err.Error(), http.StatusBadRequest)
			return
		}

		options, sessionData, err := wa.BeginRegistration(
			user,
			webauthn.WithResidentKeyRequirement(protocol.ResidentKeyRequirementPreferred),
			webauthn.WithExclusions(webauthn.Credentials(user.WebAuthnCredentials()).CredentialDescriptors()),
			webauthn.WithExtensions(map[string]any{"credProps": true}),
		)
		if err != nil {
			http.Error(w, "passkey registration options failed", http.StatusInternalServerError)
			return
		}

		am.savePasskeySession("register:"+sid, sessionData)

		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-store")
		_ = json.NewEncoder(w).Encode(options)
	}
}

func authPasskeyRegisterVerifyHandler(am *AuthManager) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "POST required", http.StatusMethodNotAllowed)
			return
		}

		s, sid := am.getSession(r)
		if s == nil || !s.Authed || sid == "" {
			http.Error(w, "unauthorized", http.StatusUnauthorized)
			return
		}

		sessionData := am.takePasskeySession("register:" + sid)
		if sessionData == nil {
			http.Error(w, "passkey challenge expired", http.StatusBadRequest)
			return
		}

		user, err := am.webAuthnUser()
		if err != nil {
			http.Error(w, "passkey user error", http.StatusInternalServerError)
			return
		}

		wa, err := am.webAuthnForRequest(r)
		if err != nil {
			appLogln("passkey registration verify config failed:", err)
			http.Error(w, "passkey registration verify config failed: "+err.Error(), http.StatusBadRequest)
			return
		}

		credential, err := wa.FinishRegistration(user, *sessionData, r)
		if err != nil {
			appLogln("passkey registration verify failed:", err)
			http.Error(w, "passkey registration verify failed: "+err.Error(), http.StatusUnauthorized)
			return
		}

		now := time.Now().Format(time.RFC3339)
		credentialID := credentialIDString(credential.ID)

		am.confMu.Lock()
		am.conf.Passkeys = append(am.conf.Passkeys, *credential)
		am.conf.PasskeyInfos = upsertPasskeyInfo(am.conf.PasskeyInfos, passkeyInfo{
			CredentialID: credentialID,
			Label:        "Passkey " + shortCredentialID(credentialID),
			CreatedAt:    now,
		})
		am.confMu.Unlock()

		go am.persistConfBestEffort()

		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-store")
		_ = json.NewEncoder(w).Encode(map[string]any{"ok": true})
	}
}

func authPasskeyLoginOptionsHandler(am *AuthManager) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "POST required", http.StatusMethodNotAllowed)
			return
		}

		user, err := am.webAuthnUser()
		if err != nil {
			http.Error(w, "passkey user error", http.StatusInternalServerError)
			return
		}

		if len(user.credentials) == 0 {
			http.Error(w, "no passkey configured", http.StatusBadRequest)
			return
		}

		wa, err := am.webAuthnForRequest(r)
		if err != nil {
			appLogln("passkey login options config failed:", err)
			http.Error(w, "passkey login options config failed: "+err.Error(), http.StatusBadRequest)
			return
		}

		options, sessionData, err := wa.BeginLogin(
			user,
			webauthn.WithUserVerification(protocol.VerificationPreferred),
		)
		if err != nil {
			http.Error(w, "passkey login options failed", http.StatusInternalServerError)
			return
		}

		challengeID, err := randomBase64URL(24)
		if err != nil {
			http.Error(w, "challenge error", http.StatusInternalServerError)
			return
		}

		am.savePasskeySession("login:"+challengeID, sessionData)
		setPasskeyChallengeCookie(w, challengeID, isSecureRequest(r))

		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-store")
		_ = json.NewEncoder(w).Encode(options)
	}
}

func authPasskeyLoginVerifyHandler(am *AuthManager) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "POST required", http.StatusMethodNotAllowed)
			return
		}

		c, err := r.Cookie(passkeyChallengeCookieName)
		if err != nil || strings.TrimSpace(c.Value) == "" {
			http.Error(w, "passkey challenge missing", http.StatusBadRequest)
			return
		}

		challengeID := strings.TrimSpace(c.Value)
		clearPasskeyChallengeCookie(w)

		sessionData := am.takePasskeySession("login:" + challengeID)
		if sessionData == nil {
			http.Error(w, "passkey challenge expired", http.StatusBadRequest)
			return
		}

		user, err := am.webAuthnUser()
		if err != nil {
			http.Error(w, "passkey user error", http.StatusInternalServerError)
			return
		}

		wa, err := am.webAuthnForRequest(r)
		if err != nil {
			appLogln("passkey login verify config failed:", err)
			http.Error(w, "passkey login verify config failed: "+err.Error(), http.StatusBadRequest)
			return
		}

		credential, err := wa.FinishLogin(user, *sessionData, r)
		if err != nil {
			appLogln("passkey login verify failed:", err)
			http.Error(w, "passkey login verify failed: "+err.Error(), http.StatusUnauthorized)
			return
		}

		credentialID := credentialIDString(credential.ID)
		nowISO := time.Now().Format(time.RFC3339)

		am.confMu.Lock()
		for i := range am.conf.Passkeys {
			if string(am.conf.Passkeys[i].ID) == string(credential.ID) {
				am.conf.Passkeys[i].Authenticator.SignCount = credential.Authenticator.SignCount
				break
			}
		}
		am.conf.PasskeyInfos = upsertPasskeyInfo(am.conf.PasskeyInfos, passkeyInfo{
			CredentialID: credentialID,
			LastUsedAt:   nowISO,
		})
		username := am.conf.Username
		am.confMu.Unlock()

		go am.persistConfBestEffort()

		sid, err := newSessionID()
		if err != nil {
			http.Error(w, "session error", http.StatusInternalServerError)
			return
		}

		now := time.Now()
		s := &session{
			User:       username,
			Authed:     true,
			Pending2FA: false,
			CreatedAt:  now,
			LastSeenAt: now,
			ExpiresAt:  now.Add(sessionTTL),
		}

		am.sessMu.Lock()
		am.sess[sid] = s
		am.sessMu.Unlock()

		setSessionCookie(w, sid, isSecureRequest(r))

		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-store")
		_ = json.NewEncoder(w).Encode(map[string]any{"ok": true})
	}
}