package service

import (
	"errors"

	"homework-manager/internal/models"
	"homework-manager/internal/repository"

	"golang.org/x/crypto/bcrypt"
)

var (
	ErrUserNotFound       = errors.New("user not found")
	ErrEmailAlreadyExists = errors.New("email already exists")
	ErrInvalidCredentials = errors.New("invalid credentials")
)

type AuthService struct {
	userRepo *repository.UserRepository
}

func NewAuthService() *AuthService {
	return &AuthService{
		userRepo: repository.NewUserRepository(),
	}
}

func (s *AuthService) Register(email, password, name string) (*models.User, error) {
	// Check if email already exists
	_, err := s.userRepo.FindByEmail(email)
	if err == nil {
		return nil, ErrEmailAlreadyExists
	}

	// Hash password
	hashedPassword, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
	if err != nil {
		return nil, err
	}

	// Determine role (first user is admin)
	role := "user"
	count, _ := s.userRepo.Count()
	if count == 0 {
		role = "admin"
	}

	user := &models.User{
		Email:        email,
		PasswordHash: string(hashedPassword),
		Name:         name,
		Role:         role,
	}

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

	return user, nil
}

func (s *AuthService) Login(email, password string) (*models.User, error) {
	user, err := s.userRepo.FindByEmail(email)
	if err != nil {
		return nil, ErrInvalidCredentials
	}

	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(password)); err != nil {
		return nil, ErrInvalidCredentials
	}

	return user, nil
}

func (s *AuthService) GetUserByID(id uint) (*models.User, error) {
	return s.userRepo.FindByID(id)
}

func (s *AuthService) ChangePassword(userID uint, oldPassword, newPassword string) error {
	user, err := s.userRepo.FindByID(userID)
	if err != nil {
		return ErrUserNotFound
	}

	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(oldPassword)); err != nil {
		return ErrInvalidCredentials
	}

	hashedPassword, err := bcrypt.GenerateFromPassword([]byte(newPassword), bcrypt.DefaultCost)
	if err != nil {
		return err
	}

	user.PasswordHash = string(hashedPassword)
	return s.userRepo.Update(user)
}

func (s *AuthService) UpdateProfile(userID uint, name string) error {
	user, err := s.userRepo.FindByID(userID)
	if err != nil {
		return ErrUserNotFound
	}

	user.Name = name
	return s.userRepo.Update(user)
}