package services

import (
	"context"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"regexp"
	"strings"
	"time"

	"github.com/noteapp/backend/internal/application/dto"
	"github.com/noteapp/backend/internal/domain/entities"
	"github.com/noteapp/backend/internal/domain/repositories"
	"github.com/noteapp/backend/internal/infrastructure/auth"
	"github.com/noteapp/backend/internal/infrastructure/security"
	"go.mongodb.org/mongo-driver/v2/bson"
	"golang.org/x/oauth2"
)

// AuthService handles authentication operations
type AuthService struct {
	userRepo          repositories.UserRepository
	groupRepo         repositories.GroupRepository
	providerRepo      repositories.AuthProviderRepository
	linkRepo          repositories.UserProviderLinkRepository
	recoveryRepo      repositories.AccountRecoveryRepository
	featureFlagRepo   repositories.FeatureFlagRepository
	permissionService *PermissionService
	jwtManager        *auth.JWTManager
	passHasher        *security.PasswordHasher
	encryptor         *security.Encryptor
}

// NewAuthService creates a new auth service
func NewAuthService(
	userRepo repositories.UserRepository,
	groupRepo repositories.GroupRepository,
	providerRepo repositories.AuthProviderRepository,
	linkRepo repositories.UserProviderLinkRepository,
	recoveryRepo repositories.AccountRecoveryRepository,
	featureFlagRepo repositories.FeatureFlagRepository,
	permissionService *PermissionService,
	jwtManager *auth.JWTManager,
	passHasher *security.PasswordHasher,
	encryptor *security.Encryptor,
) *AuthService {
	return &AuthService{
		userRepo:          userRepo,
		groupRepo:         groupRepo,
		providerRepo:      providerRepo,
		linkRepo:          linkRepo,
		recoveryRepo:      recoveryRepo,
		featureFlagRepo:   featureFlagRepo,
		permissionService: permissionService,
		jwtManager:        jwtManager,
		passHasher:        passHasher,
		encryptor:         encryptor,
	}
}

// Register registers a new user
func (s *AuthService) Register(ctx context.Context, req *dto.RegisterRequest) (*dto.LoginResponse, error) {
	flags, err := s.GetFeatureFlags(ctx)
	if err != nil {
		return nil, err
	}
	if !flags.RegistrationEnabled {
		return nil, errors.New("registration is currently disabled")
	}

	req.Email = strings.ToLower(strings.TrimSpace(req.Email))
	req.Username = strings.TrimSpace(req.Username)

	// Check if email already exists
	_, err = s.userRepo.GetUserByEmail(ctx, req.Email)
	if err == nil {
		return nil, errors.New("email already registered")
	}

	// Check if username already exists
	_, err = s.userRepo.GetUserByUsername(ctx, req.Username)
	if err == nil {
		return nil, errors.New("username already taken")
	}

	// Hash password
	hashedPassword, err := s.passHasher.HashPassword(req.Password)
	if err != nil {
		return nil, err
	}

	// Create user
	user := &entities.User{
		Email:         req.Email,
		Username:      req.Username,
		PasswordHash:  hashedPassword,
		FirstName:     req.FirstName,
		LastName:      req.LastName,
		IsActive:      true,
		EmailVerified: false, // Should verify email in production
	}

	if err := s.userRepo.CreateUser(ctx, user); err != nil {
		return nil, err
	}

	if s.permissionService != nil {
		if err := s.permissionService.UpdateUserEffectivePermissions(ctx, user); err != nil {
			return nil, err
		}
	}

	// Generate tokens
	accessToken, err := s.jwtManager.GenerateAccessToken(user.ID.Hex(), user.Email, user.Username)
	if err != nil {
		return nil, err
	}

	refreshToken, err := s.jwtManager.GenerateRefreshToken(user.ID.Hex())
	if err != nil {
		return nil, err
	}

	return &dto.LoginResponse{
		AccessToken:  accessToken,
		RefreshToken: refreshToken,
		User:         dto.NewUserDTO(user),
		ExpiresIn:    3600, // 1 hour
	}, nil
}

// Login authenticates a user
func (s *AuthService) Login(ctx context.Context, req *dto.LoginRequest) (*dto.LoginResponse, error) {
	req.Email = strings.ToLower(strings.TrimSpace(req.Email))

	// Get user by email
	user, err := s.userRepo.GetUserByEmail(ctx, req.Email)
	if err != nil {
		return nil, errors.New("invalid credentials")
	}

	if !user.IsActive {
		return nil, errors.New("account is inactive")
	}

	// Verify password
	match, err := s.passHasher.VerifyPassword(req.Password, user.PasswordHash)
	if err != nil || !match {
		return nil, errors.New("invalid credentials")
	}

	// Update last login
	now := time.Now()
	user.LastLoginAt = &now
	if s.permissionService != nil {
		if err := s.permissionService.UpdateUserEffectivePermissions(ctx, user); err != nil {
			return nil, err
		}
	}
	if err := s.userRepo.UpdateUser(ctx, user); err != nil {
		// Log error but don't fail the login
	}

	// Generate tokens
	accessToken, err := s.jwtManager.GenerateAccessToken(user.ID.Hex(), user.Email, user.Username)
	if err != nil {
		return nil, err
	}

	refreshToken, err := s.jwtManager.GenerateRefreshToken(user.ID.Hex())
	if err != nil {
		return nil, err
	}

	return &dto.LoginResponse{
		AccessToken:  accessToken,
		RefreshToken: refreshToken,
		User:         dto.NewUserDTO(user),
		ExpiresIn:    3600,
	}, nil
}

// RefreshAccessToken refreshes an access token
func (s *AuthService) RefreshAccessToken(ctx context.Context, refreshToken string) (string, error) {
	claims, err := s.jwtManager.VerifyRefreshToken(refreshToken)
	if err != nil {
		return "", err
	}

	user, err := s.userRepo.GetUserByID(ctx, mustParseObjectID(claims.UserID))
	if err != nil {
		return "", err
	}

	return s.jwtManager.GenerateAccessToken(user.ID.Hex(), user.Email, user.Username)
}

// RequestPasswordReset initiates password reset flow
func (s *AuthService) RequestPasswordReset(ctx context.Context, email string) error {
	user, err := s.userRepo.GetUserByEmail(ctx, email)
	if err != nil {
		// Don't reveal if email exists (security best practice)
		return nil
	}

	token, err := auth.GenerateRandomToken(32)
	if err != nil {
		return err
	}

	recovery := &entities.AccountRecovery{
		UserID:    user.ID,
		Token:     token,
		Type:      "password_reset",
		ExpiresAt: time.Now().Add(1 * time.Hour),
	}

	// Save recovery token
	// This would need AccountRecoveryRepository implementation
	_ = recovery

	// In production: send email with reset link containing token
	return nil
}

// mustParseObjectID parses a string to ObjectID, panics on error
func mustParseObjectID(id string) bson.ObjectID {
	objID, _ := bson.ObjectIDFromHex(id)
	return objID
}

// ListProviders returns all active OAuth/OIDC providers.
func (s *AuthService) ListProviders(ctx context.Context) ([]*dto.AuthProviderDTO, error) {
	flags, err := s.GetFeatureFlags(ctx)
	if err != nil {
		return nil, err
	}
	if !flags.ProviderLoginEnabled {
		return []*dto.AuthProviderDTO{}, nil
	}

	if s.providerRepo == nil {
		return []*dto.AuthProviderDTO{}, nil
	}

	providers, err := s.providerRepo.GetAllProviders(ctx)
	if err != nil {
		return nil, err
	}

	result := make([]*dto.AuthProviderDTO, 0, len(providers))
	for _, provider := range providers {
		result = append(result, dto.NewAuthProviderDTO(provider))
	}

	return result, nil
}

// GetFeatureFlags returns current app-wide feature flags.
func (s *AuthService) GetFeatureFlags(ctx context.Context) (*dto.FeatureFlagsDTO, error) {
	if s.featureFlagRepo == nil {
		return dto.NewFeatureFlagsDTO(nil), nil
	}

	flags, err := s.featureFlagRepo.GetFeatureFlags(ctx)
	if err != nil {
		return nil, err
	}

	return dto.NewFeatureFlagsDTO(flags), nil
}

// CreateProvider stores a new OAuth/OIDC provider.
func (s *AuthService) CreateProvider(ctx context.Context, req *dto.CreateAuthProviderRequest) (*dto.AuthProviderDTO, error) {
	if s.providerRepo == nil || s.encryptor == nil {
		return nil, errors.New("provider configuration unavailable")
	}

	providerType := strings.ToLower(strings.TrimSpace(req.Type))
	if providerType != "oidc" && providerType != "oauth2" {
		return nil, errors.New("provider type must be oidc or oauth2")
	}

	name := strings.TrimSpace(req.Name)
	clientID := strings.TrimSpace(req.ClientID)
	clientSecret := strings.TrimSpace(req.ClientSecret)
	authorizationURL := strings.TrimSpace(req.AuthorizationURL)
	tokenURL := strings.TrimSpace(req.TokenURL)
	if name == "" || clientID == "" || clientSecret == "" || authorizationURL == "" || tokenURL == "" {
		return nil, errors.New("missing required provider fields")
	}

	encryptedSecret, err := s.encryptor.Encrypt(clientSecret)
	if err != nil {
		return nil, err
	}

	provider := &entities.AuthProvider{
		Name:             name,
		Type:             providerType,
		ClientID:         clientID,
		ClientSecret:     encryptedSecret,
		AuthorizationURL: authorizationURL,
		TokenURL:         tokenURL,
		UserInfoURL:      strings.TrimSpace(req.UserInfoURL),
		Scopes:           normalizeScopes(req.Scopes, providerType),
		IDTokenClaim:     strings.TrimSpace(req.IDTokenClaim),
		IsActive:         req.IsActive,
	}

	if err := s.providerRepo.CreateProvider(ctx, provider); err != nil {
		return nil, err
	}

	return dto.NewAuthProviderDTO(provider), nil
}

// UpdateProvider updates an existing OAuth/OIDC provider.
// If ClientSecret is empty, the existing encrypted secret is preserved.
func (s *AuthService) UpdateProvider(ctx context.Context, providerID bson.ObjectID, req *dto.UpdateAuthProviderRequest) (*dto.AuthProviderDTO, error) {
	if s.providerRepo == nil || s.encryptor == nil {
		return nil, errors.New("provider configuration unavailable")
	}

	existing, err := s.providerRepo.GetProviderByID(ctx, providerID)
	if err != nil {
		return nil, err
	}

	providerType := strings.ToLower(strings.TrimSpace(req.Type))
	if providerType != "oidc" && providerType != "oauth2" {
		return nil, errors.New("provider type must be oidc or oauth2")
	}

	name := strings.TrimSpace(req.Name)
	clientID := strings.TrimSpace(req.ClientID)
	authorizationURL := strings.TrimSpace(req.AuthorizationURL)
	tokenURL := strings.TrimSpace(req.TokenURL)
	if name == "" || clientID == "" || authorizationURL == "" || tokenURL == "" {
		return nil, errors.New("missing required provider fields")
	}

	existing.Name = name
	existing.Type = providerType
	existing.ClientID = clientID
	existing.AuthorizationURL = authorizationURL
	existing.TokenURL = tokenURL
	existing.UserInfoURL = strings.TrimSpace(req.UserInfoURL)
	existing.Scopes = normalizeScopes(req.Scopes, providerType)
	existing.IDTokenClaim = strings.TrimSpace(req.IDTokenClaim)
	existing.IsActive = req.IsActive

	clientSecret := strings.TrimSpace(req.ClientSecret)
	if clientSecret != "" {
		encrypted, err := s.encryptor.Encrypt(clientSecret)
		if err != nil {
			return nil, err
		}
		existing.ClientSecret = encrypted
	}

	if err := s.providerRepo.UpdateProvider(ctx, existing); err != nil {
		return nil, err
	}

	return dto.NewAuthProviderDTO(existing), nil
}

// BuildProviderAuthorizationURL constructs a provider authorization URL.
func (s *AuthService) BuildProviderAuthorizationURL(ctx context.Context, providerID bson.ObjectID, redirectURI, state string) (string, error) {
	flags, err := s.GetFeatureFlags(ctx)
	if err != nil {
		return "", err
	}
	if !flags.ProviderLoginEnabled {
		return "", errors.New("provider login is currently disabled")
	}

	provider, secret, err := s.getProviderConfig(ctx, providerID)
	if err != nil {
		return "", err
	}

	config := oauth2.Config{
		ClientID:     provider.ClientID,
		ClientSecret: secret,
		RedirectURL:  redirectURI,
		Scopes:       normalizeScopes(provider.Scopes, provider.Type),
		Endpoint: oauth2.Endpoint{
			AuthURL:  provider.AuthorizationURL,
			TokenURL: provider.TokenURL,
		},
	}

	return config.AuthCodeURL(state, oauth2.AccessTypeOffline), nil
}

// CompleteProviderLogin exchanges an auth code and creates a user session.
func (s *AuthService) CompleteProviderLogin(ctx context.Context, providerID bson.ObjectID, code, redirectURI string) (*dto.LoginResponse, error) {
	if s.providerRepo == nil || s.linkRepo == nil {
		return nil, errors.New("provider login unavailable")
	}

	flags, err := s.GetFeatureFlags(ctx)
	if err != nil {
		return nil, err
	}
	if !flags.ProviderLoginEnabled {
		return nil, errors.New("provider login is currently disabled")
	}

	provider, secret, err := s.getProviderConfig(ctx, providerID)
	if err != nil {
		return nil, err
	}

	config := oauth2.Config{
		ClientID:     provider.ClientID,
		ClientSecret: secret,
		RedirectURL:  redirectURI,
		Scopes:       normalizeScopes(provider.Scopes, provider.Type),
		Endpoint: oauth2.Endpoint{
			AuthURL:  provider.AuthorizationURL,
			TokenURL: provider.TokenURL,
		},
	}

	token, err := config.Exchange(ctx, code)
	if err != nil {
		return nil, err
	}

	profile, err := s.fetchProviderProfile(ctx, provider, token.AccessToken, token.Extra(provider.IDTokenClaim))
	if err != nil {
		return nil, err
	}

	user, err := s.findOrCreateOAuthUser(ctx, provider, profile)
	if err != nil {
		return nil, err
	}

	accessToken, err := s.jwtManager.GenerateAccessToken(user.ID.Hex(), user.Email, user.Username)
	if err != nil {
		return nil, err
	}

	refreshToken, err := s.jwtManager.GenerateRefreshToken(user.ID.Hex())
	if err != nil {
		return nil, err
	}

	return &dto.LoginResponse{AccessToken: accessToken, RefreshToken: refreshToken, User: dto.NewUserDTO(user), ExpiresIn: 3600}, nil
}

type providerProfile struct {
	ProviderUserID string
	Email          string
	Username       string
	FirstName      string
	LastName       string
}

func (s *AuthService) getProviderConfig(ctx context.Context, providerID bson.ObjectID) (*entities.AuthProvider, string, error) {
	provider, err := s.providerRepo.GetProviderByID(ctx, providerID)
	if err != nil {
		return nil, "", err
	}
	if !provider.IsActive {
		return nil, "", errors.New("provider is inactive")
	}

	secret, err := s.encryptor.Decrypt(provider.ClientSecret)
	if err != nil {
		return nil, "", err
	}

	return provider, secret, nil
}

func (s *AuthService) fetchProviderProfile(ctx context.Context, provider *entities.AuthProvider, accessToken string, rawIDToken any) (*providerProfile, error) {
	payload := map[string]any{}

	if provider.UserInfoURL != "" {
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, provider.UserInfoURL, nil)
		if err != nil {
			return nil, err
		}
		req.Header.Set("Authorization", "Bearer "+accessToken)

		resp, err := http.DefaultClient.Do(req)
		if err != nil {
			return nil, err
		}
		defer resp.Body.Close()

		if resp.StatusCode >= 400 {
			body, _ := io.ReadAll(resp.Body)
			return nil, fmt.Errorf("provider userinfo request failed: %s", string(body))
		}

		if err := json.NewDecoder(resp.Body).Decode(&payload); err != nil {
			return nil, err
		}
	} else if idToken, ok := rawIDToken.(string); ok && idToken != "" {
		payload = decodeJWTWithoutVerify(idToken)
	} else {
		return nil, errors.New("provider must define userinfo_url or return id_token")
	}

	profile := &providerProfile{
		ProviderUserID: firstNonEmpty(asString(payload["sub"]), asString(payload["id"]), asString(payload["user_id"])),
		Email:          strings.ToLower(strings.TrimSpace(firstNonEmpty(asString(payload["email"]), asString(payload["upn"])))),
		Username:       firstNonEmpty(asString(payload["preferred_username"]), asString(payload["login"]), asString(payload["name"])),
		FirstName:      firstNonEmpty(asString(payload["given_name"]), asString(payload["first_name"])),
		LastName:       firstNonEmpty(asString(payload["family_name"]), asString(payload["last_name"])),
	}

	if profile.ProviderUserID == "" {
		return nil, errors.New("provider user info missing subject identifier")
	}
	if profile.Email == "" {
		profile.Email = fmt.Sprintf("%s@%s.oauth.local", sanitizeUsername(profile.ProviderUserID), sanitizeUsername(provider.Name))
	}
	if profile.Username == "" {
		profile.Username = strings.Split(profile.Email, "@")[0]
	}
	profile.Username = sanitizeUsername(profile.Username)

	return profile, nil
}

func (s *AuthService) findOrCreateOAuthUser(ctx context.Context, provider *entities.AuthProvider, profile *providerProfile) (*entities.User, error) {
	if link, err := s.linkRepo.GetLinkByProviderUserID(ctx, provider.ID, profile.ProviderUserID); err == nil {
		return s.userRepo.GetUserByID(ctx, link.UserID)
	}

	user, err := s.userRepo.GetUserByEmail(ctx, profile.Email)
	if err != nil {
		username, err := s.generateUniqueUsername(ctx, profile.Username)
		if err != nil {
			return nil, err
		}

		user = &entities.User{Email: profile.Email, Username: username, PasswordHash: "", FirstName: profile.FirstName, LastName: profile.LastName, IsActive: true, EmailVerified: true}
		if err := s.userRepo.CreateUser(ctx, user); err != nil {
			return nil, err
		}
	}

	if _, err := s.linkRepo.GetLink(ctx, user.ID, provider.ID); err != nil {
		if err := s.linkRepo.CreateLink(ctx, &entities.UserProviderLink{UserID: user.ID, ProviderID: provider.ID, ProviderUserID: profile.ProviderUserID, Email: profile.Email}); err != nil {
			return nil, err
		}
	}

	return user, nil
}

func (s *AuthService) generateUniqueUsername(ctx context.Context, base string) (string, error) {
	base = sanitizeUsername(base)
	candidates := []string{base}
	for i := 0; i < 5; i++ {
		token, err := auth.GenerateRandomToken(2)
		if err != nil {
			return "", err
		}
		candidates = append(candidates, fmt.Sprintf("%s-%s", base, token[:4]))
	}

	for _, candidate := range candidates {
		if _, err := s.userRepo.GetUserByUsername(ctx, candidate); err != nil {
			return candidate, nil
		}
	}

	return fmt.Sprintf("%s-%d", base, time.Now().Unix()), nil
}

func normalizeScopes(scopes []string, providerType string) []string {
	if len(scopes) == 0 {
		if providerType == "oidc" {
			return []string{"openid", "profile", "email"}
		}
		return []string{"profile", "email"}
	}

	result := make([]string, 0, len(scopes))
	for _, scope := range scopes {
		scope = strings.TrimSpace(scope)
		if scope != "" {
			result = append(result, scope)
		}
	}
	return result
}

func decodeJWTWithoutVerify(token string) map[string]any {
	parts := strings.Split(token, ".")
	if len(parts) < 2 {
		return map[string]any{}
	}

	decoded, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return map[string]any{}
	}

	claims := map[string]any{}
	if err := json.Unmarshal(decoded, &claims); err != nil {
		return map[string]any{}
	}
	return claims
}

func asString(value any) string {
	if str, ok := value.(string); ok {
		return strings.TrimSpace(str)
	}
	return ""
}

func firstNonEmpty(values ...string) string {
	for _, value := range values {
		if value != "" {
			return value
		}
	}
	return ""
}

func sanitizeUsername(value string) string {
	cleaned := regexp.MustCompile(`[^a-zA-Z0-9_-]+`).ReplaceAllString(strings.ToLower(strings.TrimSpace(value)), "-")
	cleaned = strings.Trim(cleaned, "-")
	if cleaned == "" {
		return "user"
	}
	return cleaned
}