userSchema.pre('save', async function (next) {
    try {
        const user = this;
        if (user.isModified('password')) {
            const salt = await bcrypt.genSalt(SALT_ROUNDS);
            user.password = await bcrypt.hash(user.password, salt);

            next();
        } else {
            next();
        }
    } catch (error) {
        next(error);
    }
});