import 'package:flutter/material.dart';
import 'package:google_mobile_ads/google_mobile_ads.dart';
import 'package:provider/provider.dart';

import '../estado/estado_entitlement.dart';
import '../servicios/servicio_anuncios.dart';

/// Entitlement-aware top-banner slot (Design ADR-6, ad-display spec
/// "Persistent Top Banner, Never Overlapping Content"). Collapses to
/// `SizedBox.shrink()` — zero reserved space, zero layout impact — whenever
/// the user is premium OR no ad has finished loading yet; only a
/// successfully loaded [BannerAd] renders a sized box around an [AdWidget].
/// Callers place this as a plain sibling in a `Column` ABOVE the existing
/// body (`app.dart`'s `_PaginaPrincipalState.build`) — this widget itself
/// never wraps its parent in a `Stack`/overlay.
class BannerAnuncioSuperior extends StatefulWidget {
  const BannerAnuncioSuperior({super.key, this.alIntentarCargar});

  /// Test-only hook (FIX 7, code review): fires exactly once per REAL load
  /// ATTEMPT (`BannerAd(...).load()` call), independent of the load's
  /// eventual outcome — lets a widget test count load attempts without a
  /// real AdMob platform channel. Always `null` in production.
  @visibleForTesting
  final VoidCallback? alIntentarCargar;

  @override
  State<BannerAnuncioSuperior> createState() => _BannerAnuncioSuperiorState();
}

class _BannerAnuncioSuperiorState extends State<BannerAnuncioSuperior> {
  BannerAd? _bannerAd;
  bool _cargado = false;

  /// FIX 7 (code review): explicit "load already attempted" flag. Before
  /// this, the guard was `_bannerAd == null`, which stays `null` until a
  /// load actually SUCCEEDS — so every `notifyListeners()` from ANY
  /// provider this widget watches (`EstadoEntitlement` during a
  /// purchase/restore in progress) plus theme/locale/`MediaQuery` changes
  /// re-ran `didChangeDependencies` and spawned ANOTHER `BannerAd` +
  /// `load()` call. Only the LAST loaded ad was ever disposed, leaking
  /// every in-flight duplicate before it.
  ///
  /// Retry policy (documented decision): a FAILED load is never retried
  /// automatically — this flag is set once and never reset. Retrying on
  /// every rebuild is exactly the bug this flag fixes; the next natural
  /// retry opportunity is a fresh app session, which is an adequate cadence
  /// for a non-critical, collapse-to-nothing UI element.
  bool _cargaIntentada = false;

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    final servicio = context.read<ServicioAnuncios>();
    if (!_cargaIntentada && servicio.debeMostrarBanner) {
      _cargaIntentada = true;
      _cargarBanner();
    }
  }

  void _cargarBanner() {
    widget.alIntentarCargar?.call();
    // Fire-and-forget: a failure (no plugin channel in `flutter test`, no
    // fill, offline) leaves `_bannerAd` `null` forever, which keeps this
    // widget collapsed — exactly the same degrade-to-shrink path a genuine
    // load failure takes in production. Never throws out of this method.
    final anuncio = BannerAd(
      size: AdSize.banner,
      adUnitId: bannerAdUnitId,
      request: const AdRequest(),
      listener: BannerAdListener(
        onAdLoaded: (ad) {
          if (!mounted) {
            ad.dispose();
            return;
          }
          setState(() {
            _bannerAd = ad as BannerAd;
            _cargado = true;
          });
        },
        onAdFailedToLoad: (ad, error) {
          ad.dispose();
        },
      ),
    );
    anuncio.load().catchError((_) {});
  }

  @override
  void dispose() {
    _bannerAd?.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final entitlement = context.watch<EstadoEntitlement>();
    if (entitlement.esPremium) return const SizedBox.shrink();
    // Instant vanish-on-purchase (ad-display spec "Ads Vanish Immediately
    // On Purchase"): even a banner that finished loading BEFORE this
    // transition is dropped, never shown to a now-premium user.
    if (!_cargado || _bannerAd == null) return const SizedBox.shrink();
    final ad = _bannerAd!;
    // FIX 1 (code review): the top-inset `SafeArea` now lives HERE, applied
    // ONLY when an ad is actually about to render. `SafeArea` reserves
    // `MediaQuery.padding.top` regardless of its child's own size — even a
    // zero-size `SizedBox.shrink()` child — so the OLD unconditional
    // `app.dart`-level `SafeArea(bottom: false, child: BannerAnuncioSuperior())`
    // wrapper left a permanent blank status-bar-height strip both for
    // premium users and for free users before the first ad finished
    // loading. Collapsing (the two early returns above) now returns a
    // TRULY zero-height widget, including no reserved padding.
    return SafeArea(
      bottom: false,
      child: SizedBox(
        width: ad.size.width.toDouble(),
        height: ad.size.height.toDouble(),
        child: AdWidget(ad: ad),
      ),
    );
  }
}