import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:provider/provider.dart';
import 'package:shared_preferences/shared_preferences.dart';

import 'package:fuel_tax_tracker/screens/ui_settings_screen.dart';
import 'package:fuel_tax_tracker/services/app_state.dart';

/// Covers the light/dark/system theme toggle on the Settings > UI screen —
/// defaults to System, selecting a segment updates [AppState.themeMode]
/// and persists it to SharedPreferences (so it survives a cold start).
///
/// Deliberately doesn't round-trip through a second [AppState.init] to
/// verify persistence — that pulls in unrelated subsystems (connectivity
/// listening, cloud-restore) with no test-environment platform mocks,
/// which hangs rather than failing fast. Reading the pref back directly
/// verifies the same thing without that baggage.
void main() {
  setUp(() {
    SharedPreferences.setMockInitialValues({});
  });

  testWidgets('defaults to System and switches to Dark/Light on tap', (tester) async {
    final appState = AppState()..isLoading = false;

    await tester.pumpWidget(
      ChangeNotifierProvider.value(
        value: appState,
        child: const MaterialApp(home: UiSettingsScreen()),
      ),
    );

    expect(appState.themeMode, ThemeMode.system);

    await tester.tap(find.text('Dark'));
    await tester.pumpAndSettle();
    expect(appState.themeMode, ThemeMode.dark);

    await tester.tap(find.text('Light'));
    await tester.pumpAndSettle();
    expect(appState.themeMode, ThemeMode.light);
  });

  testWidgets('persists the choice to SharedPreferences', (tester) async {
    final appState = AppState()..isLoading = false;

    await tester.pumpWidget(
      ChangeNotifierProvider.value(
        value: appState,
        child: const MaterialApp(home: UiSettingsScreen()),
      ),
    );

    await tester.tap(find.text('Dark'));
    await tester.pumpAndSettle();

    final prefs = await SharedPreferences.getInstance();
    // Mirrors the private `_prefsKeyThemeMode` key in app_state.dart —
    // a black-box persistence check necessarily has to know the storage
    // key, and this doubles as a guardrail against silently breaking
    // already-persisted user settings by renaming it there.
    expect(prefs.getString('theme_mode'), 'dark');
  });
}