Happy New Year 🥳 (seasonal variants + scheduling)

enum AppSurface with PresentumSurface {
  homeHeader,
  popup,
}

enum AppVariant with PresentumVisualVariant {
  snowyBanner,
  confettiCard,
  fullscreenGreeting,
}

@immutable
final class HolidayOption extends PresentumOption<AppSurface, AppVariant> {
  const HolidayOption({
    required this.surface,
    required this.variant,
    required this.isDismissible,
    this.stage,
    this.maxImpressions,
    this.cooldownMinutes,
    this.alwaysOnIfEligible = false,
  });

  @override
  final AppSurface surface;

  @override
  final AppVariant variant;

  @override
  final int? stage;

  @override
  final int? maxImpressions;

  @override
  final int? cooldownMinutes;

  @override
  final bool alwaysOnIfEligible;

  @override
  final bool isDismissible;
}

@immutable
final class HolidayPayload extends PresentumPayload<AppSurface, AppVariant> {
  const HolidayPayload({
    required this.id,
    required this.priority,
    required this.metadata,
    required this.options,
  });

  @override
  final String id;

  @override
  final int priority;

  @override
  final Map<String, Object?> metadata;

  @override
  final List<PresentumOption<AppSurface, AppVariant>> options;

  DateTime get startsAt => DateTime.parse(metadata['startsAt'] as String);
  DateTime get endsAt => DateTime.parse(metadata['endsAt'] as String);
}

@immutable
final class HolidayItem
    extends PresentumItem<HolidayPayload, AppSurface, AppVariant> {
  const HolidayItem({required this.payload, required this.option});

  @override
  final HolidayPayload payload;

  @override
  final PresentumOption<AppSurface, AppVariant> option;
}

final class HolidayCampaignProvider extends ChangeNotifier {
  HolidayCampaignProvider({required this.engine});

  final PresentumEngine<HolidayItem, AppSurface, AppVariant> engine;

  Future<void> syncNewYearCampaign() async {
    final payload = HolidayPayload(
      id: 'holiday:new_year_2026',
      priority: 100,
      metadata: {
        'title': 'Happy New Year!',
        'subtitle': 'Wishing you a year full of wins ✨',
        // Scheduling window (UTC ISO)
        'startsAt': '2025-12-31T18:00:00Z',
        'endsAt': '2026-01-03T23:59:59Z',
      },
      options: const [
        HolidayOption(
          surface: AppSurface.homeHeader,
          variant: AppVariant.snowyBanner,
          isDismissible: true,
          maxImpressions: 3,
          cooldownMinutes: 12 * 60,
          alwaysOnIfEligible: true,
        ),
        HolidayOption(
          surface: AppSurface.popup,
          variant: AppVariant.fullscreenGreeting,
          isDismissible: true,
          stage: 0,
          maxImpressions: 1,
          cooldownMinutes: 24 * 60,
          alwaysOnIfEligible: false,
        ),
      ],
    );

    final items = payload.options
        .map((opt) => HolidayItem(payload: payload, option: opt))
        .toList(growable: false);

    await engine.setCandidatesWithDiff((state) => items);
    notifyListeners();
  }
}

final class SyncSlotsToCandidatesGuard
    extends PresentumGuard<HolidayItem, AppSurface, AppVariant> {
  @override
  PresentumState<HolidayItem, AppSurface, AppVariant> call(
    storage,
    history,
    state,
    candidates,
    context,
  ) {
    final allowed = candidates.map((c) => c.id).toSet();
    state.removeWhere((item) => !allowed.contains(item.id));
    return state;
  }
}

final class HolidayEligibilityGuard
    extends PresentumGuard<HolidayItem, AppSurface, AppVariant> {
  @override
  Future<PresentumState<HolidayItem, AppSurface, AppVariant>> call(
    PresentumStorage<AppSurface, AppVariant> storage,
    history,
    PresentumState$Mutable<HolidayItem, AppSurface, AppVariant> state,
    List<HolidayItem> candidates,
    context,
  ) async {
    final now = DateTime.now().toUtc();

    // Filter candidates
    final eligible = <HolidayItem>[];
    for (final item in candidates) {
      final payload = item.payload;
      if (now.isBefore(payload.startsAt.toUtc())) continue;
      if (now.isAfter(payload.endsAt.toUtc())) continue;

      // If dismissed, skip (you can model “dismissed until” externally if you want)
      final dismissedAt = await storage.getDismissedAt(
        item.id,
        surface: item.surface,
        variant: item.variant,
      );
      if (dismissedAt != null) continue;

      // Cooldown check
      final cooldown = item.option.cooldownMinutes;
      if (cooldown != null) {
        final last = await storage.getLastShown(
          item.id,
          surface: item.surface,
          variant: item.variant,
        );
        if (last != null && now.difference(last.toUtc()).inMinutes < cooldown) {
          continue;
        }
      }

      // Impression cap check (per rolling 365d window for example)
      final cap = item.option.maxImpressions;
      if (cap != null) {
        final shown = await storage.getShownCount(
          item.id,
          period: const Duration(days: 365),
          surface: item.surface,
          variant: item.variant,
        );
        if (shown >= cap) continue;
      }

      eligible.add(item);
    }

    // Deterministic scheduling: per-surface priority order.
    final bySurface = <AppSurface, List<HolidayItem>>{};
    for (final item in eligible) {
      (bySurface[item.surface] ??= []).add(item);
    }
    for (final entry in bySurface.entries) {
      final surface = entry.key;
      final items = entry.value..sort((a, b) => b.priority.compareTo(a.priority));

      state.clearSurface(surface);
      state.addAll(surface, items);
    }

    return state;
  }
}

class HomeHeaderHolidayOutlet extends StatelessWidget {
  const HomeHeaderHolidayOutlet({super.key});

  @override
  Widget build(BuildContext context) {
    return PresentumOutlet<HolidayItem, AppSurface, AppVariant>(
      surface: AppSurface.homeHeader,
      builder: (context, item) {
        switch (item.variant) {
          case AppVariant.snowyBanner:
            return SnowyBanner(
              title: item.payload.metadata['title'] as String,
              subtitle: item.payload.metadata['subtitle'] as String,
              onClose: item.option.isDismissible
                  ? () => context
                      .presentum<HolidayItem, AppSurface, AppVariant>()
                      .markDismissed(item)
                  : null,
            );
          case AppVariant.confettiCard:
            return ConfettiCard(/* ... */);
          case AppVariant.fullscreenGreeting:
            // This variant is intended for the popup host surface.
            return const SizedBox.shrink();
        }
      },
    );
  }
}