@spec active_subscription_for(integer()) :: Plausible.Billing.Subscription.t() | nil

@spec check_needs_to_upgrade(Plausible.Auth.User.t()) ::
  {:needs_to_upgrade, :no_trial | :no_active_subscription | :grace_period_ended}
  | :no_upgrade_needed

@spec has_active_subscription?(integer()) :: boolean()

@spec last_two_billing_months_usage(Plausible.Auth.User.t(), Date.t()) ::
  {non_neg_integer(), non_neg_integer()}