Firebase

// pubspec.yaml
// dependencies:
//   firebase_core: ^2.31.0
//   firebase_auth: ^4.20.0
//   cloud_firestore: ^4.17.5
//   firebase_crashlytics: ^3.5.7
//   firebase_app_check: ^0.2.2
//   google_sign_in: ^6.2.1   # for Google sign in
// dev_dependencies:
//   flutterfire_cli: ^1.0.0

// 1) One-time setup
//    npm i -g firebase-tools && firebase login
//    dart pub global activate flutterfire_cli
//    flutterfire configure   # generates lib/firebase_options.dart

// 2) main.dart
import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_crashlytics/firebase_crashlytics.dart';
import 'package:firebase_app_check/firebase_app_check.dart';
import 'firebase_options.dart';

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp(options: DefaultFirebaseOptions.currentPlatform);

  // 3) App Check before any Auth/Firestore call
  await FirebaseAppCheck.instance.activate(
    androidProvider: AndroidProvider.playIntegrity,
    appleProvider:   AppleProvider.deviceCheck,
  );

  // 4) Pipe errors to Crashlytics
  await FirebaseCrashlytics.instance.setCrashlyticsCollectionEnabled(!kDebugMode);
  FlutterError.onError = FirebaseCrashlytics.instance.recordFlutterFatalError;
  PlatformDispatcher.instance.onError = (error, stack) {
    FirebaseCrashlytics.instance.recordError(error, stack, fatal: true);
    return true;
  };

  runApp(const ShopApp());
}

class ShopApp extends StatelessWidget {
  const ShopApp({super.key});
  @override
  Widget build(BuildContext context) => MaterialApp(home: const AuthGate());
}

// 5) Auth gate — switches between sign-in and main screen
class AuthGate extends StatelessWidget {
  const AuthGate({super.key});
  @override
  Widget build(BuildContext context) => StreamBuilder<User?>(
    stream: FirebaseAuth.instance.authStateChanges(),
    builder: (context, snap) {
      if (snap.connectionState != ConnectionState.active) {
        return const Scaffold(body: Center(child: CircularProgressIndicator()));
      }
      return snap.data == null ? const SignInScreen() : const HomeScreen();
    },
  );
}

class SignInScreen extends StatelessWidget {
  const SignInScreen({super.key});
  @override
  Widget build(BuildContext context) => Scaffold(
    body: Center(
      child: ElevatedButton.icon(
        icon: const Icon(Icons.person_outline),
        label: const Text('Continue as guest'),
        onPressed: () async {
          await FirebaseAuth.instance.signInAnonymously();
        },
      ),
    ),
  );
}

// 6) Home — read + write a Firestore collection scoped to the user
class HomeScreen extends StatelessWidget {
  const HomeScreen({super.key});

  CollectionReference<Map<String, dynamic>> get _notes =>
    FirebaseFirestore.instance.collection('notes');

  @override
  Widget build(BuildContext context) {
    final uid = FirebaseAuth.instance.currentUser!.uid;

    return Scaffold(
      appBar: AppBar(title: const Text('Notes')),
      body: StreamBuilder<QuerySnapshot<Map<String, dynamic>>>(
        stream: _notes.where('uid', isEqualTo: uid)
                      .orderBy('createdAt', descending: true)
                      .limit(50)
                      .snapshots(),
        builder: (context, snap) {
          if (!snap.hasData) return const Center(child: CircularProgressIndicator());
          final docs = snap.data!.docs;
          return ListView(children: [
            for (final d in docs) ListTile(
              title: Text(d.data()['body'] ?? ''),
              trailing: IconButton(
                icon: const Icon(Icons.delete_outline),
                onPressed: () => d.reference.delete(),
              ),
            ),
          ]);
        },
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () async {
          await _notes.add({
            'uid': uid,
            'body': 'hello at ${DateTime.now()}',
            'createdAt': FieldValue.serverTimestamp(),
          });
        },
        child: const Icon(Icons.add),
      ),
    );
  }
}

// 7) Firestore security rules — paste in firestore.rules
// rules_version = '2';
// service cloud.firestore {
//   match /databases/{db}/documents {
//     match /notes/{id} {
//       allow read, update, delete: if request.auth != null && resource.data.uid == request.auth.uid;
//       allow create: if request.auth != null
//                     && request.resource.data.uid == request.auth.uid;
//     }
//   }
// }

// 8) Add Crashlytics user id + custom keys for richer crash context
FirebaseCrashlytics.instance.setUserIdentifier(uid);
FirebaseCrashlytics.instance.setCustomKey('build', '1.4.0+142');

// 9) Decision matrix
// - Real-time data sync                          -> Firestore + snapshots
// - Tiny key/value config                         -> Remote Config
// - Push notifications                            -> Firebase Cloud Messaging
// - Crash + non-fatal reports                     -> Crashlytics
// - Files (images, audio)                         -> Cloud Storage
// - Background jobs / webhooks                    -> Cloud Functions
// - Per-user analytics                            -> Analytics (auto-exports to BigQuery)

// 10) Pitfalls
// - Skipping App Check -> instant scraper / abuse on launch
// - 'allow read, write: if true' shipped from a tutorial
// - Loading 10k docs into memory; paginate with cursors
// - Crashlytics missing dSYMs (iOS) / mapping (Android) -> unresolved stacks

// pubspec.yaml: firebase_core, firebase_auth, cloud_firestore
await Firebase.initializeApp();
final u = await FirebaseAuth.instance.signInAnonymously();
await FirebaseFirestore.instance.collection('events').add({'kind': 'open'});