refactor: reorganize packages into a domain-based layered structure

internal/account/service.go

@@ -0,0 +1,46 @@
+package account
+
+type UserService struct {
+	userRepository *UserRepository
+}
+
+func NewUserService(userRepository *UserRepository) *UserService {
+	return &UserService{userRepository: userRepository}
+}
+
+func (us *UserService) CreateUser(user *User) error {
+	if err := us.userRepository.CreateUser(user); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (us *UserService) RenameByID(id uint, newUsername string) error {
+	if err := us.userRepository.RenameByID(id, newUsername); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (us *UserService) ChangePassword(id uint, newPassword string) error {
+	if err := us.userRepository.ChangePassword(id, newPassword); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (us *UserService) FindByID(id uint) (*User, error) {
+	if user, err := us.userRepository.FindByID(id); err != nil {
+		return nil, err
+	} else {
+		return user, nil
+	}
+}
+
+func (us *UserService) FindByUsername(username string) (*User, error) {
+	if user, err := us.userRepository.FindByUsername(username); err != nil {
+		return nil, err
+	} else {
+		return user, nil
+	}
+}