// Policy layer: depends on the interfaces and the entitlement gate — never on an SDK.
sealed class RewardOutcome { const RewardOutcome(); }
final class Rewarded  extends RewardOutcome { const Rewarded(); }
final class Dismissed extends RewardOutcome { const Dismissed(); }   // closed early
final class NoFill    extends RewardOutcome { const NoFill(); }      // no ad existed

class CreditEconomy extends Notifier<CreditState> {
  static const int freeCreditsPerDay = 1;   // the allowance the design assumes
  static const int maxEarnedPerDay = 3;     // the integrity ceiling (rule 4)

  @override
  CreditState build() => const CreditState();

  /// Opt-in earn path. Grants ONLY on `Rewarded`, and only under the daily cap.
  Future<Result<Credit, MonetizationFailure>> watchToEarn() async {
    if (ref.read(isEntitledProvider).valueOrNull ?? false) return _grant(); // no ad at all
    if (state.earnedToday(ref.read(clockProvider)) >= maxEarnedPerDay) {
      return const Err(EarnCapReached());
    }
    return switch (await ref.read(adsServiceProvider).showRewarded()) {
      Rewarded()  => _grant(),
      Dismissed() => const Err(RewardNotEarned()),   // distinct: the user closed it
      NoFill()    => const Err(NoAdAvailable()),     // distinct: nothing to show
    };
  }
}

// Shown only while an ad is genuinely loaded; the free path stays reachable regardless.
final rewardedReadyProvider =
    StreamProvider<bool>((ref) => ref.watch(adsServiceProvider).rewardedAvailability);

if (ref.watch(rewardedReadyProvider).valueOrNull ?? false)
  const WatchToEarnButton(),

Future<void> onTaskCompleted(WidgetRef ref) async {
  if (ref.read(isEntitledProvider).valueOrNull ?? false) return;   // rule 9
  await ref.read(adsServiceProvider).maybeShowInterstitial();      // owns both cap halves
}

// Entitlement first, ads only if the user is not entitled (rule 10).
// Startup-sequence mechanics are owned by `app-startup-and-bootstrap`.
final entitlement = await ref.read(billingServiceProvider).restore();   // failure ⇒ not entitled
if (!entitlement.isEntitled) {
  await ref.read(adsServiceProvider).init();      // consent / tracking prompt happens in here
  await ref.read(adsServiceProvider).preloadRewarded();
}