public class LoginPresenter implements LoginPresenterInterface, IListener<User> {

  LoginView iLoginView;
  LoginServiceInterface iLoginService;

  public LoginPresenter(LoginView loginView){
    iLoginView = loginView;
    iLoginService = new LoginService();
  }

  @Override
  public void validateCredentials(){
    String username = iLoginView.getUsername();
    /**
     * Check if username is empty or not
     */
    if(username.isEmpty()){
      iLoginView.showError("Username cannot be empty");
      return;
    }

    String password = iLoginView.getPassword();
    /**
     * Check if password is empty or not
     */
    if(password.isEmpty()){
      iLoginView.showError("Password cannot be empty");
      return;
    }

    /**
     * Call login service to authenticate user credentials from the backend
     */
    iLoginService.validateCredentialsFromBackendService(username, password, this);
  }

  @Override
  public void onSuccess(User user){
    /**
     * After successful authentication take the user to the main activity
     */
    iLoginView.navigateToMainActivity();
  }

  @Override
  public void onFailure(String errorMessage){
    /**
     * Show error message if the authentication fails
     */
    iLoginView.showError(errorMessage);
  }

}