package api

import (
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"time"

	"github.com/cynfo/rmm-backend/db"
	"github.com/cynfo/rmm-backend/models"
	"github.com/golang-jwt/jwt/v5"
	"github.com/pquerna/otp/totp"
	"golang.org/x/crypto/bcrypt"
)

type AuthHandler struct {
	db     *db.Database
	secret []byte
}

type JWTClaims struct {
	UserID      int    `json:"user_id"`
	Username    string `json:"username"`
	Role        string `json:"role"`
	TOTPPending bool   `json:"totp_pending,omitempty"` // temp token während 2FA-Schritt
	jwt.RegisteredClaims
}

func NewAuthHandler(database *db.Database, jwtSecret string) *AuthHandler {
	secret := jwtSecret
	if secret == "" {
		b := make([]byte, 32)
		rand.Read(b)
		secret = hex.EncodeToString(b)
		log.Println("JWT Secret automatisch generiert (nicht persistent)")
	}
	return &AuthHandler{db: database, secret: []byte(secret)}
}

func (a *AuthHandler) EnsureDefaultAdmin() {
	count, err := a.db.UserCount()
	if err != nil {
		log.Printf("User-Count Fehler: %v", err)
		return
	}
	if count == 0 {
		_, err := a.db.CreateUser("admin", "admin", "Administrator", "admin")
		if err != nil {
			log.Printf("Default-Admin anlegen fehlgeschlagen: %v", err)
		} else {
			log.Println("Default-Admin angelegt (admin/admin) - bitte Passwort aendern!")
		}
	}
}

func (a *AuthHandler) GenerateToken(user *models.User) (string, time.Time, error) {
	expiresAt := time.Now().Add(8 * time.Hour)
	claims := JWTClaims{
		UserID:   user.ID,
		Username: user.Username,
		Role:     user.Role,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(expiresAt),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
		},
	}
	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	signed, err := token.SignedString(a.secret)
	return signed, expiresAt, err
}

// Kurzlebiger Token nur für den TOTP-Schritt (5 Minuten, kein echter API-Zugriff)
func (a *AuthHandler) generateTOTPPendingToken(user *models.User) (string, error) {
	claims := JWTClaims{
		UserID:      user.ID,
		Username:    user.Username,
		Role:        user.Role,
		TOTPPending: true,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(time.Now().Add(5 * time.Minute)),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
		},
	}
	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString(a.secret)
}

func (a *AuthHandler) ValidateToken(tokenStr string) (*JWTClaims, error) {
	token, err := jwt.ParseWithClaims(tokenStr, &JWTClaims{}, func(t *jwt.Token) (interface{}, error) {
		if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, fmt.Errorf("unexpected signing method: %v", t.Header["alg"])
		}
		return a.secret, nil
	})
	if err != nil {
		return nil, err
	}
	claims, ok := token.Claims.(*JWTClaims)
	if !ok || !token.Valid {
		return nil, fmt.Errorf("invalid token")
	}
	// Echte API-Calls mit Pending-Token ablehnen
	if claims.TOTPPending {
		return nil, fmt.Errorf("totp pending token not valid for api access")
	}
	return claims, nil
}

// POST /api/v1/auth/login
func (a *AuthHandler) Login(w http.ResponseWriter, r *http.Request) {
	var req models.LoginRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "Ungueltige Anfrage")
		return
	}

	user, err := a.db.GetUserByUsername(req.Username)
	if err != nil || user == nil {
		writeError(w, http.StatusUnauthorized, "Ungueltige Anmeldedaten")
		return
	}

	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(req.Password)); err != nil {
		writeError(w, http.StatusUnauthorized, "Ungueltige Anmeldedaten")
		return
	}

	// 2FA aktiv → Pending-Token zurückgeben
	if user.TOTPEnabled {
		pendingToken, err := a.generateTOTPPendingToken(user)
		if err != nil {
			writeError(w, http.StatusInternalServerError, "Token-Generierung fehlgeschlagen")
			return
		}
		go a.db.AddAuditLog(user.Username, "login_2fa_pending", "user", "", user.Username, "", r.RemoteAddr)
		writeJSON(w, http.StatusOK, models.LoginResponse{
			TOTPRequired: true,
			TOTPToken:    pendingToken,
		})
		return
	}

	// Kein 2FA → direkt JWT
	token, expiresAt, err := a.GenerateToken(user)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Token-Generierung fehlgeschlagen")
		return
	}

	a.db.UpdateUserLastLogin(user.ID)
	go a.db.AddAuditLog(user.Username, "login", "user", "", user.Username, "", r.RemoteAddr)

	writeJSON(w, http.StatusOK, models.LoginResponse{
		Token:     token,
		ExpiresAt: expiresAt.Format(time.RFC3339),
		User:      user,
	})
}

// POST /api/v1/auth/2fa/validate — zweiter Schritt beim Login
func (a *AuthHandler) TOTPValidate(w http.ResponseWriter, r *http.Request) {
	var req models.TOTPValidateRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "Ungueltige Anfrage")
		return
	}

	// Pending-Token parsen (ohne ValidateToken, der lehnt Pending-Tokens ab)
	jwtToken, err := jwt.ParseWithClaims(req.TOTPToken, &JWTClaims{}, func(t *jwt.Token) (interface{}, error) {
		if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, fmt.Errorf("unexpected signing method")
		}
		return a.secret, nil
	})
	if err != nil {
		writeError(w, http.StatusUnauthorized, "Ungueltige Session")
		return
	}
	claims, ok := jwtToken.Claims.(*JWTClaims)
	if !ok || !jwtToken.Valid || !claims.TOTPPending {
		writeError(w, http.StatusUnauthorized, "Ungueltige Session")
		return
	}

	user, err := a.db.GetUserByID(claims.UserID)
	if err != nil || user == nil || !user.TOTPEnabled {
		writeError(w, http.StatusUnauthorized, "Ungueltige Session")
		return
	}

	if !totp.Validate(req.Code, user.TOTPSecret) {
		writeError(w, http.StatusUnauthorized, "Ungültiger 2FA-Code")
		return
	}

	token, expiresAt, err := a.GenerateToken(user)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Token-Generierung fehlgeschlagen")
		return
	}

	a.db.UpdateUserLastLogin(user.ID)
	go a.db.AddAuditLog(user.Username, "login_2fa_success", "user", "", user.Username, "", r.RemoteAddr)

	writeJSON(w, http.StatusOK, models.LoginResponse{
		Token:     token,
		ExpiresAt: expiresAt.Format(time.RFC3339),
		User:      user,
	})
}

// POST /api/v1/auth/2fa/setup — Secret generieren, QR-URI zurückgeben
func (a *AuthHandler) TOTPSetup(w http.ResponseWriter, r *http.Request) {
	claims, ok := r.Context().Value(UserContextKey).(*JWTClaims)
	if !ok {
		writeError(w, http.StatusUnauthorized, "Nicht authentifiziert")
		return
	}

	user, err := a.db.GetUserByID(claims.UserID)
	if err != nil || user == nil {
		writeError(w, http.StatusNotFound, "User nicht gefunden")
		return
	}

	key, err := totp.Generate(totp.GenerateOpts{
		Issuer:      "cynfo RMM",
		AccountName: user.Username,
		Period:      30,
		Digits:      6,
	})
	if err != nil {
		writeError(w, http.StatusInternalServerError, "TOTP-Generierung fehlgeschlagen")
		return
	}

	if err := a.db.SetTOTPSecret(user.ID, key.Secret()); err != nil {
		writeError(w, http.StatusInternalServerError, "Speichern fehlgeschlagen")
		return
	}

	writeJSON(w, http.StatusOK, models.TOTPSetupResponse{
		Secret: key.Secret(),
		URI:    key.URL(),
	})
}

// POST /api/v1/auth/2fa/confirm — ersten Code prüfen und 2FA aktivieren
func (a *AuthHandler) TOTPConfirm(w http.ResponseWriter, r *http.Request) {
	claims, ok := r.Context().Value(UserContextKey).(*JWTClaims)
	if !ok {
		writeError(w, http.StatusUnauthorized, "Nicht authentifiziert")
		return
	}

	var req models.TOTPConfirmRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "Ungueltige Anfrage")
		return
	}

	user, err := a.db.GetUserByID(claims.UserID)
	if err != nil || user == nil || user.TOTPSecret == "" {
		writeError(w, http.StatusBadRequest, "Kein Setup gefunden — bitte zuerst /2fa/setup aufrufen")
		return
	}

	if !totp.Validate(req.Code, user.TOTPSecret) {
		writeError(w, http.StatusUnauthorized, "Ungültiger Code")
		return
	}

	if err := a.db.EnableTOTP(user.ID); err != nil {
		writeError(w, http.StatusInternalServerError, "Aktivierung fehlgeschlagen")
		return
	}

	go a.db.AddAuditLog(claims.Username, "2fa_enabled", "user", "", claims.Username, "", r.RemoteAddr)
	writeJSON(w, http.StatusOK, map[string]any{"ok": true})
}

// POST /api/v1/auth/2fa/disable — 2FA deaktivieren (Passwort + aktueller Code nötig)
func (a *AuthHandler) TOTPDisable(w http.ResponseWriter, r *http.Request) {
	claims, ok := r.Context().Value(UserContextKey).(*JWTClaims)
	if !ok {
		writeError(w, http.StatusUnauthorized, "Nicht authentifiziert")
		return
	}

	var req models.TOTPDisableRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "Ungueltige Anfrage")
		return
	}

	user, err := a.db.GetUserByID(claims.UserID)
	if err != nil || user == nil {
		writeError(w, http.StatusNotFound, "User nicht gefunden")
		return
	}

	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(req.Password)); err != nil {
		writeError(w, http.StatusUnauthorized, "Falsches Passwort")
		return
	}

	if user.TOTPEnabled {
		if !totp.Validate(req.Code, user.TOTPSecret) {
			writeError(w, http.StatusUnauthorized, "Ungültiger 2FA-Code")
			return
		}
	}

	if err := a.db.DisableTOTP(user.ID); err != nil {
		writeError(w, http.StatusInternalServerError, "Deaktivierung fehlgeschlagen")
		return
	}

	go a.db.AddAuditLog(claims.Username, "2fa_disabled", "user", "", claims.Username, "", r.RemoteAddr)
	writeJSON(w, http.StatusOK, map[string]any{"ok": true})
}

// GET /api/v1/auth/me
func (a *AuthHandler) Me(w http.ResponseWriter, r *http.Request) {
	claims, ok := r.Context().Value(UserContextKey).(*JWTClaims)
	if !ok {
		writeError(w, http.StatusUnauthorized, "Nicht authentifiziert")
		return
	}

	user, err := a.db.GetUserByUsername(claims.Username)
	if err != nil || user == nil {
		writeError(w, http.StatusNotFound, "User nicht gefunden")
		return
	}

	writeJSON(w, http.StatusOK, user)
}

// SetupAuthRoutes registriert Auth-Routes (ohne Auth-Middleware)
func (a *AuthHandler) SetupAuthRoutes(mux *http.ServeMux) {
	mux.HandleFunc("POST /api/v1/auth/login", a.Login)
	mux.HandleFunc("POST /api/v1/auth/2fa/validate", a.TOTPValidate)
}