React
Native

export class UserRepositoryImpl implements IUserRepository {
  constructor(
    private api: UserApiService,
    private db: Database,
  ) {}

  async getUser(id: string): Promise<User> {
    // 1. Try local cache first
    const local = await this.db.collections
      .get<UserModel>('users').find(id);
    if (local) return toDomain(local);

    // 2. Fetch from network
    const remote = await this.api.getUser(id);

    // 3. Persist to local DB
    await this.db.write(async () => {
      await this.db.collections
        .get<UserModel>('users')
        .create(u => { u._raw.id = remote.id; u.name = remote.name; });
    });
    return remote;
  }
}

// TanStack Query persistence setup
const mmkvPersister = createMMKVStoragePersister({ storage: mmkv });
persistQueryClient({ queryClient, persister: mmkvPersister, maxAge: Infinity });

import * as Keychain from 'react-native-keychain';

const SERVICE = 'com.app.tokens';

export const secureStorage = {
  async saveTokens(access: string, refresh: string) {
    await Keychain.setGenericPassword(
      'tokens',
      JSON.stringify({ access, refresh }),
      {
        service: SERVICE,
        accessControl: Keychain.ACCESS_CONTROL.BIOMETRY_ANY_OR_DEVICE_PASSCODE,
        accessible: Keychain.ACCESSIBLE.WHEN_UNLOCKED_THIS_DEVICE_ONLY,
      }
    );
  },

  async getAccessToken(): Promise<string | null> {
    const creds = await Keychain.getGenericPassword({ service: SERVICE });
    if (!creds) return null;
    return JSON.parse(creds.password).access;
  },

  async clearTokens() {
    await Keychain.resetGenericPassword({ service: SERVICE });
  },
};

// MMKV — typed wrapper for non-sensitive values
const storage = new MMKV({ id: 'app-prefs' });
export const prefs = {
  setTheme: (mode: 'light' | 'dark') => storage.set('theme', mode),
  getTheme: () => storage.getString('theme'),
  setOnboarded: () => storage.set('onboarded', true),
  isOnboarded: () => storage.getBoolean('onboarded') ?? false,
};

import Aes from 'react-native-aes-crypto';

class EncryptionService {
  private sessionKey: string | null = null;

  async initSessionKey(serverPublicKey: string) {
    // ECDH: derive shared secret, store in Keychain
    this.sessionKey = await deriveECDHSecret(serverPublicKey);
    await secureStorage.saveKey(this.sessionKey);
  }

  async encryptPayload(data: unknown): Promise<string> {
    const key = await this.getKey();
    const iv = await Aes.randomKey(16); // 128-bit IV
    const plaintext = JSON.stringify(data);
    const cipher = await Aes.encrypt(plaintext, key, iv, 'aes-256-gcm');
    // Pack as base64: iv.cipher (server splits on first 32 chars)
    return `${iv}.${cipher}`;
  }

  async decryptPayload(packed: string): Promise<unknown> {
    const [iv, cipher] = packed.split('.');
    const key = await this.getKey();
    const plaintext = await Aes.decrypt(cipher, key, iv, 'aes-256-gcm');
    return JSON.parse(plaintext);
  }
}

import Voice, { SpeechResultsEvent } from '@react-native-voice/voice';
import * as Speech from 'expo-speech';

export const useSpeech = () => {
  const [transcript, setTranscript] = useState('');
  const [isListening, setListening] = useState(false);

  useEffect(() => {
    Voice.onSpeechPartialResults = (e: SpeechResultsEvent) =>
      setTranscript(e.value?.[0] ?? '');

    Voice.onSpeechResults = (e: SpeechResultsEvent) => {
      setTranscript(e.value?.[0] ?? '');
      setListening(false);
    };
    return () => { Voice.destroy().then(Voice.removeAllListeners); };
  }, []);

  const startListening = async (locale = 'en-US') => {
    setTranscript('');
    setListening(true);
    await Voice.start(locale);
  };

  const stopListening = async () => {
    await Voice.stop();
    setListening(false);
  };

  const speak = (text: string, language = 'en-US') =>
    Speech.speak(text, { language, pitch: 1.0, rate: 0.9 });

  return { transcript, isListening, startListening, stopListening, speak };
};

import { io, Socket } from 'socket.io-client';

interface ServerToClientEvents {
  notification: (payload: { title: string; body: string }) => void;
  data_update:  (payload: { entity: string; id: string }) => void;
}

let socket: Socket<ServerToClientEvents> | null = null;

export const connectSocket = (token: string) => {
  socket = io(AppConfig.WS_URL, {
    auth: { token },
    reconnection: true,
    reconnectionDelay: 1000,
    reconnectionDelayMax: 30_000,
    reconnectionAttempts: Infinity,
    transports: ['websocket'],
  });

  socket.on('connect', () => useSocketStore.getState().setConnected(true));
  socket.on('disconnect', () => useSocketStore.getState().setConnected(false));

  socket.on('data_update', ({ entity, id }) => {
    queryClient.invalidateQueries({ queryKey: [entity, id] });
  });
};

// Hook for component-level subscriptions
export const useWebSocket = <K extends keyof ServerToClientEvents>(
  event: K, handler: ServerToClientEvents[K]
) => {
  useEffect(() => {
    socket?.on(event, handler as any);
    return () => { socket?.off(event, handler as any); };
  }, [event, handler]);
};

import Animated, {
  FadeInDown, FadeOutUp,
  useAnimatedStyle, useSharedValue,
  withSpring, withTiming, interpolateColor
} from 'react-native-reanimated';

export const AnimatedListItem = ({ item, index }: Props) => {
  const pressed = useSharedValue(0);

  const animStyle = useAnimatedStyle(() => ({
    transform: [{ scale: withSpring(pressed.value ? 0.96 : 1, { damping: 15 }) }],
    backgroundColor: interpolateColor(
      pressed.value, [0, 1],
      ['transparent', 'rgba(251,191,36,0.08)']
    ),
  }));

  return (
    <Animated.View
      entering={FadeInDown.delay(index * 40).springify().damping(14)}
      exiting={FadeOutUp.duration(200)}
      style={animStyle}
    >
      <Pressable
        onPressIn={() => { pressed.value = 1; }}
        onPressOut={() => { pressed.value = 0; }}
      >
        <Text>{item.title}</Text>
      </Pressable>
    </Animated.View>
  );
};

// List screen — tag the shared element
import { SharedElement } from 'react-native-shared-element';

<SharedElement id={`user.avatar.${user.id}`}>
  <Image source={{ uri: user.avatarUrl }} style={styles.avatar} />
</SharedElement>

// Detail screen — same id, Reanimated handles the morph
<SharedElement id={`user.avatar.${userId}`}>
  <Image source={{ uri: user.avatarUrl }} style={styles.heroBanner} />
</SharedElement>