LensApp/App.tsx

import React, {useState, useCallback, useEffect} from 'react';
import {Alert, BackHandler} from 'react-native';
import HomeScreen from './src/screens/HomeScreen';
import ScanScreen from './src/screens/ScanScreen';
import ReviewScreen from './src/screens/ReviewScreen';
import ViewerScreen from './src/screens/ViewerScreen';
import {useDocumentStore} from './src/hooks/useDocumentStore';
import {ScannedDocument, ScannedPage, FilterMode} from './src/types';

type Screen = 'home' | 'scan' | 'review' | 'viewer';

export default function App() {
  const {documents, createDocument, deleteDocument, renameDocument} =
    useDocumentStore();

  const [screen, setScreen] = useState<Screen>('home');
  const [pendingPages, setPendingPages] = useState<ScannedPage[]>([]);
  const [viewingDoc, setViewingDoc] = useState<ScannedDocument | null>(null);

  const goHome = useCallback(() => {
    setScreen('home');
    setPendingPages([]);
    setViewingDoc(null);
  }, []);

  const handleScanComplete = useCallback((pages: ScannedPage[]) => {
    setPendingPages(pages);
    setScreen('review');
  }, []);

  const handleSaveDocument = useCallback(
    (pages: ScannedPage[], _filter: FilterMode) => {
      const doc = createDocument(pages);
      setPendingPages([]);
      setViewingDoc(doc);
      setScreen('viewer');
    },
    [createDocument],
  );

  const confirmDiscardReview = useCallback(() => {
    Alert.alert('Discard scan?', 'Going back will discard all scanned pages.', [
      {text: 'Stay', style: 'cancel'},
      {text: 'Discard', style: 'destructive', onPress: goHome},
    ]);
  }, [goHome]);

  const handleView = useCallback((doc: ScannedDocument) => {
    setViewingDoc(doc);
    setScreen('viewer');
  }, []);

  useEffect(() => {
    if (screen === 'home') return;
    const sub = BackHandler.addEventListener('hardwareBackPress', () => {
      if (screen === 'scan') {
        goHome();
        return true;
      }
      if (screen === 'review') {
        confirmDiscardReview();
        return true;
      }
      if (screen === 'viewer') {
        goHome();
        return true;
      }
      return false;
    });
    return () => sub.remove();
  }, [screen, goHome, confirmDiscardReview]);

  const handleRenameFromViewer = useCallback(
    (name: string) => {
      if (viewingDoc) renameDocument(viewingDoc.id, name);
    },
    [viewingDoc, renameDocument],
  );

  if (screen === 'scan') {
    return (
      <ScanScreen
        onComplete={handleScanComplete}
        onCancel={goHome}
      />
    );
  }

  if (screen === 'review') {
    return (
      <ReviewScreen
        pages={pendingPages}
        onSave={handleSaveDocument}
        onAddMore={() => setScreen('scan')}
        onCancel={confirmDiscardReview}
      />
    );
  }

  if (screen === 'viewer' && viewingDoc) {
    const fresh = documents.find(d => d.id === viewingDoc.id) ?? viewingDoc;
    return (
      <ViewerScreen
        document={fresh}
        onBack={goHome}
        onDelete={() => {
          deleteDocument(fresh.id);
          goHome();
        }}
        onRename={handleRenameFromViewer}
      />
    );
  }

  return (
    <HomeScreen
      documents={documents}
      onScan={() => setScreen('scan')}
      onView={handleView}
      onDelete={deleteDocument}
      onRename={renameDocument}
    />
  );
}