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

import '../di/injector.dart';
import '../i18n/strings.g.dart';
import '../services/export_import_service.dart';
import '../services/locale_store.dart';
import 'backup_section.dart';
import 'theme.dart';

/// Basic settings: app language, backup (export/import) and an "about"
/// section. [exportImport] and [localeStore] are injectable so widget tests can
/// pass fakes; the app resolves them lazily from the service locator.
class SettingsScreen extends StatelessWidget {
  const SettingsScreen({this.exportImport, this.localeStore, super.key});

  final ExportImportService? exportImport;
  final LocaleStore? localeStore;

  @override
  Widget build(BuildContext context) {
    final t = context.t;
    return Scaffold(
      appBar: AppBar(title: Text(t.menu.settings)),
      body: ListView(
        children: [
          _SectionHeader(t.settings.language),
          _LanguageSelector(localeStore: localeStore),
          const Divider(),
          _SectionHeader(t.backup.title),
          BackupSection(service: exportImport),
          const Divider(),
          _SectionHeader(t.settings.about),
          ListTile(
            leading: Image.asset('assets/logo.png', width: 32),
            title: Text(t.settings.aboutOpen),
            subtitle: Text(t.settings.aboutText),
            trailing: const Icon(Icons.chevron_right),
            onTap: () => context.push('/about'),
          ),
          ListTile(
            leading: const Icon(Icons.privacy_tip_outlined, color: seedGreen),
            title: Text(t.legal.title),
            trailing: const Icon(Icons.chevron_right),
            onTap: () => context.push('/legal'),
          ),
        ],
      ),
    );
  }
}

/// The full ordered list of app languages, paired with their endonym label.
/// One source of truth for both the current-choice subtitle and the picker.
List<(AppLocale, String)> _languages(Translations t) => [
  (AppLocale.es, t.settings.langEs),
  (AppLocale.ast, t.settings.langAst),
  (AppLocale.en, t.settings.langEn),
  (AppLocale.pt, t.settings.langPt),
  (AppLocale.fr, t.settings.langFr),
  (AppLocale.de, t.settings.langDe),
  (AppLocale.ja, t.settings.langJa),
];

/// A single tile showing the active language; tapping opens a picker with all
/// languages plus "System language" (follow the device). A `null` saved value
/// means the user follows the device language — the app still resolves to some
/// concrete locale, but the picker must show "System language" as the choice.
class _LanguageSelector extends StatefulWidget {
  const _LanguageSelector({this.localeStore});

  final LocaleStore? localeStore;

  @override
  State<_LanguageSelector> createState() => _LanguageSelectorState();
}

class _LanguageSelectorState extends State<_LanguageSelector> {
  /// Prefer the injected store; otherwise fall back to the locator, but only if
  /// it actually has one registered — widget tests may pump this screen with no
  /// DI set up, and reading the current language must not crash there.
  LocaleStore? get _store =>
      widget.localeStore ??
      (getIt.isRegistered<LocaleStore>() ? getIt<LocaleStore>() : null);

  /// The user's explicit choice, or null when following the device language.
  AppLocale? _saved;
  bool _loaded = false;

  @override
  void initState() {
    super.initState();
    _store?.saved().then((locale) {
      if (!mounted) return;
      setState(() {
        _saved = locale;
        _loaded = true;
      });
    });
  }

  Future<void> _select(AppLocale? locale) async {
    final store = _store;
    if (store == null) return;
    if (locale == null) {
      await store.useDeviceLocale();
    } else {
      await store.setLocale(locale);
    }
    if (mounted) setState(() => _saved = locale);
  }

  @override
  Widget build(BuildContext context) {
    final t = context.t;
    // The tile shows the current language by its endonym. When following the
    // device language, the title is still the resolved language and a subtitle
    // makes the "System language" mode explicit.
    final resolved = TranslationProvider.of(context).locale;
    final isDevice = _loaded && _saved == null;
    final label = _labelFor(t, _loaded && _saved != null ? _saved! : resolved);
    return ListTile(
      key: const Key('settings.language'),
      leading: const Icon(Icons.translate, color: seedGreen),
      title: Text(label),
      subtitle: isDevice ? Text(t.settings.systemLanguage) : null,
      trailing: const Icon(Icons.chevron_right),
      onTap: () => _openPicker(context),
    );
  }

  String _labelFor(Translations t, AppLocale locale) {
    for (final (l, label) in _languages(t)) {
      if (l == locale) return label;
    }
    return locale.languageCode;
  }

  Future<void> _openPicker(BuildContext context) async {
    final t = context.t;
    final selection = await showModalBottomSheet<Object?>(
      context: context,
      showDragHandle: true,
      builder: (context) {
        return SafeArea(
          child: ListView(
            shrinkWrap: true,
            children: [
              for (final (locale, label) in _languages(t))
                ListTile(
                  title: Text(label),
                  trailing: _saved == locale
                      ? const Icon(Icons.check, color: seedGreen)
                      : null,
                  onTap: () => Navigator.pop(context, locale),
                ),
              const Divider(),
              ListTile(
                leading: const Icon(Icons.smartphone_outlined),
                title: Text(t.settings.systemLanguage),
                trailing: _saved == null
                    ? const Icon(Icons.check, color: seedGreen)
                    : null,
                // Use a sentinel so "System language" (null) is distinct from
                // "nothing tapped" (also null from a dismissed sheet).
                onTap: () => Navigator.pop(context, _deviceSentinel),
              ),
            ],
          ),
        );
      },
    );
    if (selection == null) return; // dismissed without choosing
    await _select(
      identical(selection, _deviceSentinel) ? null : selection as AppLocale,
    );
  }
}

/// Distinguishes an explicit "System language" pick from a dismissed sheet,
/// since both would otherwise arrive as `null`.
const Object _deviceSentinel = Object();

class _SectionHeader extends StatelessWidget {
  const _SectionHeader(this.text);

  final String text;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.fromLTRB(16, 16, 16, 4),
      child: Text(
        text,
        style: Theme.of(context).textTheme.titleSmall?.copyWith(
          color: seedGreen,
          fontWeight: FontWeight.w600,
          letterSpacing: 0.4,
        ),
      ),
    );
  }
}