GraphQL en Flutter: ejercicio resuelto con graphql_flutter, queries y mutaciones

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dependencies:
  graphql_flutter: ^5.2.0-beta.7

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import 'package:flutter/material.dart';
import 'package:graphql_flutter/graphql_flutter.dart';

// ── Configuración del cliente GraphQL ─────────────────────────────────────────
ValueNotifier<GraphQLClient> _buildClient() {
  final httpLink = HttpLink('https://countries.trevorblades.com/');
  return ValueNotifier(
    GraphQLClient(
      link: httpLink,
      cache: GraphQLCache(store: InMemoryStore()),
    ),
  );
}

// ── Queries y mutaciones ───────────────────────────────────────────────────────

/// Lista países filtrables por continente
const _listCountries = r'''
  query ListCountries($continent: String) {
    countries(filter: { continent: { eq: $continent } }) {
      code
      name
      emoji
      capital
      continent {
        name
      }
      languages {
        name
      }
    }
  }
''';

/// Detalle de un continente
const _getContinents = r'''
  query GetContinents {
    continents {
      code
      name
    }
  }
''';

// ── Tipos de dominio ───────────────────────────────────────────────────────────
class Country {
  final String code;
  final String name;
  final String emoji;
  final String? capital;
  final String continent;
  final List<String> languages;

  const Country({
    required this.code,
    required this.name,
    required this.emoji,
    required this.capital,
    required this.continent,
    required this.languages,
  });

  factory Country.fromJson(Map<String, dynamic> json) => Country(
        code: json['code'] as String,
        name: json['name'] as String,
        emoji: json['emoji'] as String,
        capital: json['capital'] as String?,
        continent: (json['continent'] as Map<String, dynamic>)['name'] as String,
        languages: (json['languages'] as List)
            .map((l) => l['name'] as String)
            .toList(),
      );
}

class Continent {
  final String code;
  final String name;
  const Continent({required this.code, required this.name});
  factory Continent.fromJson(Map<String, dynamic> json) =>
      Continent(code: json['code'] as String, name: json['name'] as String);
}

// ── App ────────────────────────────────────────────────────────────────────────
void main() async {
  await initHiveForFlutter(); // inicializa Hive para caché persistente opcional
  runApp(GraphQLProvider(
    client: _buildClient(),
    child: const MaterialApp(home: CountriesScreen()),
  ));
}

// ── Pantalla principal ─────────────────────────────────────────────────────────
class CountriesScreen extends StatefulWidget {
  const CountriesScreen({super.key});
  @override
  State<CountriesScreen> createState() => _CountriesScreenState();
}

class _CountriesScreenState extends State<CountriesScreen> {
  String? _selectedContinent; // null = todos los continentes
  String? _favoriteCountry;   // guardado localmente (sin backend real)
  String _search = '';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('GraphQL + graphql_flutter'),
        bottom: PreferredSize(
          preferredSize: const Size.fromHeight(96),
          child: Padding(
            padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 4),
            child: Column(
              children: [
                // Filtro por continente
                _ContinentFilter(
                  selected: _selectedContinent,
                  onChanged: (code) =>
                      setState(() => _selectedContinent = code),
                ),
                const SizedBox(height: 4),
                // Búsqueda local
                TextField(
                  decoration: const InputDecoration(
                    hintText: 'Buscar país...',
                    prefixIcon: Icon(Icons.search),
                    isDense: true,
                    border: OutlineInputBorder(),
                    fillColor: Colors.white,
                    filled: true,
                  ),
                  onChanged: (v) => setState(() => _search = v.toLowerCase()),
                ),
              ],
            ),
          ),
        ),
      ),
      body: Query(
        options: QueryOptions(
          document: gql(_listCountries),
          variables: {
            if (_selectedContinent != null) 'continent': _selectedContinent,
          },
          fetchPolicy: FetchPolicy.cacheAndNetwork,
        ),
        builder: (result, {fetchMore, refetch}) {
          // ── Estado de carga ───────────────────────────────────────────
          if (result.isLoading && result.data == null) {
            return const Center(child: CircularProgressIndicator());
          }

          // ── Estado de error ───────────────────────────────────────────
          if (result.hasException) {
            return _ErrorView(
              message: result.exception.toString(),
              onRetry: refetch,
            );
          }

          // ── Datos vacíos ──────────────────────────────────────────────
          final rawList = result.data?['countries'] as List? ?? [];
          var countries =
              rawList.map((e) => Country.fromJson(e as Map<String, dynamic>)).toList();

          if (_search.isNotEmpty) {
            countries = countries
                .where((c) =>
                    c.name.toLowerCase().contains(_search) ||
                    c.capital?.toLowerCase().contains(_search) == true)
                .toList();
          }

          if (countries.isEmpty) {
            return const Center(child: Text('No se encontraron países'));
          }

          // ── Lista de países ───────────────────────────────────────────
          return RefreshIndicator(
            onRefresh: () async => refetch?.call(),
            child: ListView.builder(
              itemCount: countries.length,
              itemBuilder: (context, i) {
                final c = countries[i];
                final isFav = _favoriteCountry == c.code;
                return ListTile(
                  leading: Text(c.emoji, style: const TextStyle(fontSize: 28)),
                  title: Text(c.name),
                  subtitle: Text(
                    '${c.capital ?? 'Sin capital'} · ${c.continent}',
                    style: const TextStyle(fontSize: 12),
                  ),
                  trailing: IconButton(
                    icon: Icon(
                      isFav ? Icons.favorite : Icons.favorite_border,
                      color: isFav ? Colors.red : null,
                    ),
                    onPressed: () =>
                        setState(() => _favoriteCountry = isFav ? null : c.code),
                    tooltip: isFav ? 'Quitar favorito' : 'Marcar favorito',
                  ),
                  onTap: () => _showDetail(context, c),
                );
              },
            ),
          );
        },
      ),
    );
  }

  void _showDetail(BuildContext context, Country c) {
    showModalBottomSheet(
      context: context,
      builder: (_) => _CountryDetail(country: c),
    );
  }
}

// ── Filtro de continentes (usa su propia Query) ────────────────────────────────
class _ContinentFilter extends StatelessWidget {
  final String? selected;
  final ValueChanged<String?> onChanged;

  const _ContinentFilter({required this.selected, required this.onChanged});

  @override
  Widget build(BuildContext context) {
    return Query(
      options: QueryOptions(
        document: gql(_getContinents),
        fetchPolicy: FetchPolicy.cacheFirst,
      ),
      builder: (result, {fetchMore, refetch}) {
        if (result.isLoading) return const SizedBox(height: 28);
        final raw = result.data?['continents'] as List? ?? [];
        final continents =
            raw.map((e) => Continent.fromJson(e as Map<String, dynamic>)).toList();

        return SizedBox(
          height: 28,
          child: ListView(
            scrollDirection: Axis.horizontal,
            children: [
              ChoiceChip(
                label: const Text('Todos', style: TextStyle(fontSize: 11)),
                selected: selected == null,
                onSelected: (_) => onChanged(null),
                padding: EdgeInsets.zero,
                visualDensity: VisualDensity.compact,
              ),
              ...continents.map((cont) => Padding(
                    padding: const EdgeInsets.only(left: 4),
                    child: ChoiceChip(
                      label: Text(cont.name, style: const TextStyle(fontSize: 11)),
                      selected: selected == cont.code,
                      onSelected: (_) =>
                          onChanged(selected == cont.code ? null : cont.code),
                      padding: EdgeInsets.zero,
                      visualDensity: VisualDensity.compact,
                    ),
                  )),
            ],
          ),
        );
      },
    );
  }
}

// ── Detalle de país ────────────────────────────────────────────────────────────
class _CountryDetail extends StatelessWidget {
  final Country country;
  const _CountryDetail({required this.country});

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(24),
      child: Column(
        mainAxisSize: MainAxisSize.min,
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          Row(
            children: [
              Text(country.emoji, style: const TextStyle(fontSize: 48)),
              const SizedBox(width: 16),
              Expanded(
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    Text(country.name,
                        style: Theme.of(context).textTheme.headlineSmall),
                    Text(country.continent,
                        style: const TextStyle(color: Colors.grey)),
                  ],
                ),
              ),
            ],
          ),
          const Divider(height: 24),
          if (country.capital != null) ...[
            _DetailRow(Icons.location_city, 'Capital', country.capital!),
            const SizedBox(height: 8),
          ],
          _DetailRow(Icons.language, 'Idiomas', country.languages.join(', ')),
          _DetailRow(Icons.code, 'Código', country.code),
        ],
      ),
    );
  }
}

class _DetailRow extends StatelessWidget {
  final IconData icon;
  final String label;
  final String value;
  const _DetailRow(this.icon, this.label, this.value);

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        Icon(icon, size: 18, color: Colors.grey),
        const SizedBox(width: 8),
        Text('$label: ', style: const TextStyle(fontWeight: FontWeight.bold)),
        Expanded(child: Text(value)),
      ],
    );
  }
}

// ── Vista de error ─────────────────────────────────────────────────────────────
class _ErrorView extends StatelessWidget {
  final String message;
  final VoidCallback? onRetry;
  const _ErrorView({required this.message, this.onRetry});

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Padding(
        padding: const EdgeInsets.all(24),
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            const Icon(Icons.wifi_off, size: 48, color: Colors.red),
            const SizedBox(height: 16),
            Text(
              'Error de red',
              style: Theme.of(context).textTheme.titleMedium,
            ),
            const SizedBox(height: 8),
            Text(
              message,
              textAlign: TextAlign.center,
              style: const TextStyle(color: Colors.grey, fontSize: 12),
            ),
            const SizedBox(height: 16),
            if (onRetry != null)
              FilledButton.icon(
                onPressed: onRetry,
                icon: const Icon(Icons.refresh),
                label: const Text('Reintentar'),
              ),
          ],
        ),
      ),
    );
  }
}