package services

import (
	"context"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"fmt"
	"log/slog"
	"time"

	"github.com/golang-jwt/jwt/v5"
	"gogs.fxtmmsk.ru/foxtime/photoplaces/backend/internal/log"
	"gogs.fxtmmsk.ru/foxtime/photoplaces/backend/internal/models"
	"gogs.fxtmmsk.ru/foxtime/photoplaces/backend/internal/pointer"
	"gogs.fxtmmsk.ru/foxtime/photoplaces/backend/internal/repository"
	"golang.org/x/crypto/bcrypt"
)

var (
	ErrEmailExists    = errors.New("email already exists")
	ErrInvalidCreds   = errors.New("invalid email or password")
	ErrUserBanned     = errors.New("account is banned")
	ErrInvalidToken   = errors.New("invalid or expired token")
	ErrTokenReused    = errors.New("token reused, possible theft")
)

const (
	AccessTokenExpiry  = 15 * time.Minute
	RefreshTokenExpiry = 30 * 24 * time.Hour
	RefreshTokenBytes  = 32
)

type UserRepo interface {
	Create(ctx context.Context, user *models.User) error
	GetByID(ctx context.Context, id string) (*models.User, error)
	GetByEmail(ctx context.Context, email string) (*models.User, error)
	Update(ctx context.Context, user *models.User) error
	UpdateRole(ctx context.Context, id, role string) error
	UpdateStatus(ctx context.Context, id, status string) error
	List(ctx context.Context, filter models.UserFilter) ([]*models.User, error)
}

type RefreshTokenRepo interface {
	Create(ctx context.Context, userID, plainToken string, expiresAt time.Time) error
	GetValid(ctx context.Context, plainToken string) (*models.RefreshToken, error)
	GetRevoked(ctx context.Context, plainToken string) (*models.RefreshToken, error)
	Revoke(ctx context.Context, tokenHash string) error
	RevokeAllForUser(ctx context.Context, userID string) error
	Delete(ctx context.Context, tokenHash string) error
	ReplaceIfExists(ctx context.Context, tokenHash string) (bool, error)
	CleanupExpired(ctx context.Context) error
}

type AuthService struct {
	userRepo       UserRepo
	refreshTokenRepo RefreshTokenRepo
	jwtSecret      []byte
	refreshSecret  []byte
}

func NewAuthService(userRepo UserRepo, refreshTokenRepo RefreshTokenRepo, jwtSecret, refreshSecret string) *AuthService {
	return &AuthService{
		userRepo:        userRepo,
		refreshTokenRepo: refreshTokenRepo,
		jwtSecret:       []byte(jwtSecret),
		refreshSecret:   []byte(refreshSecret),
	}
}

type AuthResult struct {
	User        *models.User `json:"user"`
	AccessToken string       `json:"access_token"`
}

type RegisterInput struct {
	Email    string
	Password string
	Role     string
	Name     string
}

func (s *AuthService) Register(ctx context.Context, input RegisterInput) (*AuthResult, string, error) {
	logger := log.FromContext(ctx)

	hash, err := bcrypt.GenerateFromPassword([]byte(input.Password), bcrypt.DefaultCost)
	if err != nil {
		logger.ErrorContext(ctx, "password hashing failed", log.WithError(err))
		return nil, "", fmt.Errorf("hash password: %w", err)
	}

	user := &models.User{
		Email:        input.Email,
		PasswordHash: string(hash),
		Role:         input.Role,
		Name:         pointer.Str(input.Name),
	}

	if err := s.userRepo.Create(ctx, user); err != nil {
		if errors.Is(err, repository.ErrEmailExists) {
			logger.WarnContext(ctx, "registration attempt with existing email", slog.String("email", input.Email))
			return nil, "", ErrEmailExists
		}
		logger.ErrorContext(ctx, "user creation failed", log.WithError(err), slog.String("email", input.Email))
		return nil, "", fmt.Errorf("create user: %w", err)
	}

	logger.InfoContext(ctx, "user registered", slog.String("user_id", user.ID), slog.String("email", user.Email), slog.String("role", user.Role))

	return s.generateTokens(ctx, user)
}

type LoginInput struct {
	Email    string
	Password string
}

func (s *AuthService) Login(ctx context.Context, input LoginInput) (*AuthResult, string, error) {
	logger := log.FromContext(ctx)

	user, err := s.userRepo.GetByEmail(ctx, input.Email)
	if err != nil {
		logger.ErrorContext(ctx, "user lookup failed", log.WithError(err), slog.String("email", input.Email))
		return nil, "", fmt.Errorf("get user: %w", err)
	}
	if user == nil {
		logger.WarnContext(ctx, "login attempt for non-existent user", slog.String("email", input.Email))
		return nil, "", ErrInvalidCreds
	}

	if user.Status == "banned" {
		logger.WarnContext(ctx, "login attempt for banned user", slog.String("user_id", user.ID))
		return nil, "", ErrUserBanned
	}

	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(input.Password)); err != nil {
		logger.WarnContext(ctx, "invalid password attempt", slog.String("user_id", user.ID))
		return nil, "", ErrInvalidCreds
	}

	logger.InfoContext(ctx, "user logged in", slog.String("user_id", user.ID), slog.String("role", user.Role))
	return s.generateTokens(ctx, user)
}

type TokenClaims struct {
	UserID string `json:"user_id"`
	Role   string `json:"role"`
	jwt.RegisteredClaims
}

func (s *AuthService) generateTokens(ctx context.Context, user *models.User) (*AuthResult, string, error) {
	now := time.Now()

	accessClaims := TokenClaims{
		UserID: user.ID,
		Role:   user.Role,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(now.Add(AccessTokenExpiry)),
			IssuedAt:  jwt.NewNumericDate(now),
		},
	}
	accessToken, err := jwt.NewWithClaims(jwt.SigningMethodHS256, accessClaims).SignedString(s.jwtSecret)
	if err != nil {
		return nil, "", fmt.Errorf("sign access token: %w", err)
	}

	refreshToken, err := generateSecureToken(RefreshTokenBytes)
	if err != nil {
		return nil, "", fmt.Errorf("generate refresh token: %w", err)
	}

	expiresAt := now.Add(RefreshTokenExpiry)
	if err := s.refreshTokenRepo.Create(ctx, user.ID, refreshToken, expiresAt); err != nil {
		return nil, "", fmt.Errorf("store refresh token: %w", err)
	}

	return &AuthResult{
		User:        user,
		AccessToken: accessToken,
	}, refreshToken, nil
}

func (s *AuthService) ValidateAccessToken(tokenString string) (*TokenClaims, error) {
	token, err := jwt.ParseWithClaims(tokenString, &TokenClaims{}, func(t *jwt.Token) (interface{}, error) {
		return s.jwtSecret, nil
	})
	if err != nil {
		return nil, ErrInvalidToken
	}
	claims, ok := token.Claims.(*TokenClaims)
	if !ok || !token.Valid {
		return nil, ErrInvalidToken
	}
	return claims, nil
}

func (s *AuthService) RefreshSession(ctx context.Context, plainRefreshToken string) (*AuthResult, string, error) {
	logger := log.FromContext(ctx)

	storedToken, err := s.refreshTokenRepo.GetValid(ctx, plainRefreshToken)
	if err != nil {
		logger.ErrorContext(ctx, "refresh token lookup failed", log.WithError(err))
		return nil, "", fmt.Errorf("lookup refresh token: %w", err)
	}
	if storedToken == nil {
		revokedToken, err := s.refreshTokenRepo.GetRevoked(ctx, plainRefreshToken)
		if err != nil {
			logger.ErrorContext(ctx, "revoked token lookup failed", log.WithError(err))
			return nil, "", fmt.Errorf("lookup revoked token: %w", err)
		}
		if revokedToken != nil {
			logger.WarnContext(ctx, "token reuse detected, revoking all user tokens", slog.String("user_id", revokedToken.UserID))
			if revokeErr := s.refreshTokenRepo.RevokeAllForUser(ctx, revokedToken.UserID); revokeErr != nil {
				logger.ErrorContext(ctx, "failed to revoke all user tokens after reuse", log.WithError(revokeErr))
			}
			return nil, "", ErrTokenReused
		}
		logger.WarnContext(ctx, "refresh attempt with invalid/expired token")
		return nil, "", ErrInvalidToken
	}

	user, err := s.userRepo.GetByID(ctx, storedToken.UserID)
	if err != nil {
		logger.ErrorContext(ctx, "user lookup failed during refresh", log.WithError(err), slog.String("user_id", storedToken.UserID))
		return nil, "", fmt.Errorf("get user: %w", err)
	}
	if user == nil {
		logger.WarnContext(ctx, "refresh attempt for deleted user", slog.String("user_id", storedToken.UserID))
		return nil, "", ErrInvalidToken
	}
	if user.Status == "banned" {
		logger.WarnContext(ctx, "refresh attempt for banned user", slog.String("user_id", user.ID))
		return nil, "", ErrUserBanned
	}

	replaced, err := s.refreshTokenRepo.ReplaceIfExists(ctx, storedToken.TokenHash)
	if err != nil {
		logger.ErrorContext(ctx, "failed to replace old refresh token", log.WithError(err))
		return nil, "", fmt.Errorf("replace old refresh token: %w", err)
	}
	if !replaced {
		logger.WarnContext(ctx, "concurrent token rotation detected", slog.String("user_id", user.ID))
		return nil, "", ErrTokenReused
	}

	logger.InfoContext(ctx, "token refreshed", slog.String("user_id", user.ID))
	return s.generateTokens(ctx, user)
}

func (s *AuthService) GetUser(ctx context.Context, userID string) (*models.User, error) {
	return s.userRepo.GetByID(ctx, userID)
}

func (s *AuthService) RevokeSession(ctx context.Context, plainRefreshToken string) error {
	logger := log.FromContext(ctx)

	storedToken, err := s.refreshTokenRepo.GetValid(ctx, plainRefreshToken)
	if err != nil {
		logger.ErrorContext(ctx, "revoke: refresh token lookup failed", log.WithError(err))
		return fmt.Errorf("lookup refresh token: %w", err)
	}
	if storedToken == nil {
		return nil
	}
	logger.InfoContext(ctx, "session revoked", slog.String("user_id", storedToken.UserID))
	return s.refreshTokenRepo.Revoke(ctx, storedToken.TokenHash)
}

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