I am attempting to create a generic service that should take a 'given' Entity to perform basic CRUD operations.

Thus far, I have tried:

export type UserEntity<E> = { new (): E } | Function;

class AuthenticationService<E> {
  private userEntity: UserEntity<E>;

  constructor(userEntity: UserEntity<E>) {
    this.userEntity = userEntity;
  }

  async login(email: string, password: string) {
    // const user = await getRepository(this.userEntity).findOneOrFail({ email });
    const user = await this.userEntity?.findOneOrFail({ email });

    const validPassword = argon2.verify(user?.password, password);
    if (!validPassword) {
      throw new ErrorHandler(401, ErrorMessage.INVALID_EMAIL_PASSWORD);
    }

    const accessToken = JWTHelpers.generateToken(user, {
      secret: config.ACCESS_TOKEN_SECRET,
      expiry: '300s',
    });

    const refreshToken = JWTHelpers.generateToken(user, {
      secret: config.REFRESH_TOKEN_SECRET,
      expiry: '1y',
    });

    user.tokens = user.tokens.concat(refreshToken);
    await user.save();

    Reflect.deleteProperty(user, 'password');

    return { accessToken, refreshToken };
  }

This approach doesn't seem to work and as a result, compiler throws various types of errors - for instance:

1. Property 'findOneOrFail' does not exist on type 'UserEntity<E>'. Property 'findOneOrFail' does not exist on type 'Function'.

   Which is thrown from this declaration: const user: E = await this.userEntity?.findOneOrFail({ email });

2. Property 'password' does not exist on type 'NonNullable<E>'. - thrown at: const validPassword = argon2.verify(user?.password, password);

I am very open to suggestions on how to best approach / fix these issues.

Thanks in advance.