index.html

This artifact contains the complete Flutter source code for the PaperStudy app. Due to the complexity, I'm providing the full project structure with all key files. To run this app:

1. Install Flutter SDK (stable channel)
2. Create a new Flutter project: `flutter create paperstudy`
3. Replace/add the files below
4. Add dependencies to `pubspec.yaml`
5. Run: `flutter run`

## Project Structure

```
paperstudy/
├── android/                     # Android-specific config
├── ios/                         # iOS-specific config (not included)
├── lib/
│   ├── main.dart                # Entry point
│   ├── app.dart                 # App root with theme
│   ├── models/                  # Data models
│   │   ├── subject.dart
│   │   ├── physical_note.dart
│   │   ├── review_item.dart
│   │   ├── review_log.dart
│   │   ├── study_session.dart
│   │   ├── exam.dart
│   │   └── user_settings.dart
│   ├── database/                # SQLite database
│   │   ├── database.dart
│   │   ├── database.g.dart      # Generated by drift
│   │   └── tables.dart
│   ├── services/                # Business logic
│   │   ├── fsrs_service.dart    # FSRS-4.5 algorithm
│   │   ├── review_service.dart
│   │   ├── note_service.dart
│   │   ├── subject_service.dart
│   │   ├── session_service.dart
│   │   ├── exam_service.dart
│   │   ├── ocr_service.dart
│   │   ├── notification_service.dart
│   │   └── sync_service.dart
│   ├── providers/               # Riverpod state management
│   │   ├── app_providers.dart
│   │   ├── review_providers.dart
│   │   ├── note_providers.dart
│   │   ├── subject_providers.dart
│   │   ├── session_providers.dart
│   │   └── settings_providers.dart
│   ├── screens/                 # UI screens
│   │   ├── home_screen.dart
│   │   ├── review_screen.dart
│   │   ├── add_note_screen.dart
│   │   ├── note_detail_screen.dart
│   │   ├── library_screen.dart
│   │   ├── subject_detail_screen.dart
│   │   ├── stats_screen.dart
│   │   ├── settings_screen.dart
│   │   ├── onboarding_screen.dart
│   │   └── exam_mode_screen.dart
│   ├── widgets/                 # Reusable UI components
│   │   ├── review_card.dart
│   │   ├── rating_buttons.dart
│   │   ├── subject_chip.dart
│   │   ├── tag_list.dart
│   │   ├── heatmap_calendar.dart
│   │   ├── progress_ring.dart
│   │   ├── quick_add_fab.dart
│   │   ├── note_list_item.dart
│   │   ├── empty_state.dart
│   │   ├── streak_flame.dart
│   │   └── workload_chart.dart
│   ├── utils/                   # Utilities
│   │   ├── constants.dart
│   │   ├── extensions.dart
│   │   ├── validators.dart
│   │   └── formatters.dart
│   └── theme/                   # Design system
│       ├── app_colors.dart
│       ├── app_typography.dart
│       └── app_spacing.dart
├── test/                        # Unit tests
├── pubspec.yaml
└── README.md
```

## pubspec.yaml

```yaml
name: paperstudy
description: Physical Note Study Tracker & Spaced Repetition Scheduler

publish_to: 'none'

version: 1.0.0+1

environment:
  sdk: '>=3.0.0 <4.0.0'

dependencies:
  flutter:
    sdk: flutter
  
  # State Management
  flutter_riverpod: ^2.4.0
  riverpod_annotation: ^2.2.0
  
  # Database
  drift: ^2.12.0
  sqlite3_flutter_libs: ^0.5.18
  path_provider: ^2.1.1
  path: ^1.8.3
  
  # Local Storage
  hive: ^2.2.3
  hive_flutter: ^1.1.0
  
  # Camera & Photos
  camera: ^0.10.5+5
  image_picker: ^1.0.4
  image: ^4.1.3
  
  # OCR
  google_mlkit_text_recognition: ^0.11.0
  
  # Notifications
  flutter_local_notifications: ^16.1.0
  timezone: ^0.9.2
  
  # UI Components
  flutter_svg: ^2.0.9
  fl_chart: ^0.65.0
  shimmer: ^3.0.0
  flutter_slidable: ^3.0.1
  
  # Utilities
  uuid: ^4.2.1
  intl: ^0.18.1
  freezed_annotation: ^2.4.1
  json_annotation: ^4.8.1
  collection: ^1.18.0
  
  # Share/Export
  share_plus: ^7.2.1
  file_picker: ^6.1.1
  csv: ^5.1.1
  
  # Permissions
  permission_handler: ^11.0.1
  
  # Deep Links
  uni_links: ^0.5.1

dev_dependencies:
  flutter_test:
    sdk: flutter
  flutter_lints: ^3.0.1
  build_runner: ^2.4.7
  drift_dev: ^2.12.0
  riverpod_generator: ^2.3.5
  freezed: ^2.4.5
  json_serializable: ^6.7.1
  custom_lint: ^0.5.3
  riverpod_lint: ^2.3.7

flutter:
  uses-material-design: true
  
  assets:
    - assets/icons/
    - assets/images/
  
  fonts:
    - family: Inter
      fonts:
        - asset: assets/fonts/Inter-Regular.ttf
        - asset: assets/fonts/Inter-Medium.ttf
          weight: 500
        - asset: assets/fonts/Inter-SemiBold.ttf
          weight: 600
        - asset: assets/fonts/Inter-Bold.ttf
          weight: 700
    - family: OpenDyslexic
      fonts:
        - asset: assets/fonts/OpenDyslexic-Regular.otf
```

## lib/main.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:hive_flutter/hive_flutter.dart';
import 'package:paperstudy/app.dart';
import 'package:paperstudy/services/notification_service.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  
  // Initialize Hive for local settings
  await Hive.initFlutter();
  await Hive.openBox('settings');
  await Hive.openBox('user_data');
  
  // Initialize notifications
  final notificationService = NotificationService();
  await notificationService.initialize();
  
  runApp(
    ProviderScope(
      child: PaperStudyApp(),
    ),
  );
}
```

## lib/app.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/providers/settings_providers.dart';
import 'package:paperstudy/screens/home_screen.dart';
import 'package:paperstudy/screens/onboarding_screen.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_typography.dart';

class PaperStudyApp extends ConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final settings = ref.watch(userSettingsProvider);
    final hasCompletedOnboarding = ref.watch(onboardingCompleteProvider);

    return MaterialApp(
      title: 'PaperStudy',
      debugShowCheckedModeBanner: false,
      theme: _buildLightTheme(),
      darkTheme: _buildDarkTheme(),
      themeMode: settings.themeMode,
      home: hasCompletedOnboarding ? const HomeScreen() : const OnboardingScreen(),
    );
  }

  ThemeData _buildLightTheme() {
    return ThemeData(
      useMaterial3: true,
      brightness: Brightness.light,
      colorScheme: ColorScheme.fromSeed(
        seedColor: AppColors.primary,
        brightness: Brightness.light,
        primary: AppColors.primary,
        secondary: AppColors.primaryDark,
        error: AppColors.error,
        surface: AppColors.surface,
        background: AppColors.background,
      ),
      textTheme: TextTheme(
        displayLarge: AppTypography.displayLarge,
        headlineMedium: AppTypography.headline,
        bodyLarge: AppTypography.body,
        bodyMedium: AppTypography.body.copyWith(fontSize: 14),
        labelSmall: AppTypography.caption,
      ),
      cardTheme: CardTheme(
        elevation: 2,
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(16),
        ),
      ),
      elevatedButtonTheme: ElevatedButtonThemeData(
        style: ElevatedButton.styleFrom(
          minimumSize: const Size(64, 48),
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(12),
          ),
        ),
      ),
      bottomNavigationBarTheme: const BottomNavigationBarThemeData(
        type: BottomNavigationBarType.fixed,
        selectedItemColor: AppColors.primary,
        unselectedItemColor: AppColors.textSecondary,
      ),
      fontFamily: 'Inter',
    );
  }

  ThemeData _buildDarkTheme() {
    return ThemeData(
      useMaterial3: true,
      brightness: Brightness.dark,
      colorScheme: ColorScheme.fromSeed(
        seedColor: AppColors.primary,
        brightness: Brightness.dark,
        primary: AppColors.primary,
        secondary: AppColors.primaryDark,
        error: AppColors.error,
      ),
      fontFamily: 'Inter',
    );
  }
}
```

## lib/theme/app_colors.dart

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

class AppColors {
  // Primary
  static const primary = Color(0xFF6366F1);
  static const primaryDark = Color(0xFF4F46E5);
  static const primaryLight = Color(0xFFE0E7FF);
  
  // Semantic
  static const success = Color(0xFF22C55E);
  static const warning = Color(0xFFF59E0B);
  static const error = Color(0xFFEF4444);
  
  // Ratings
  static const again = Color(0xFFEF4444);
  static const hard = Color(0xFFF59E0B);
  static const good = Color(0xFF22C55E);
  static const easy = Color(0xFF3B82F6);
  
  // Neutrals
  static const background = Color(0xFFF8FAFC);
  static const surface = Color(0xFFFFFFFF);
  static const textPrimary = Color(0xFF0F172A);
  static const textSecondary = Color(0xFF64748B);
  static const divider = Color(0xFFE2E8F0);
  
  // Dark mode
  static const darkBackground = Color(0xFF0F172A);
  static const darkSurface = Color(0xFF1E293B);
  static const darkTextPrimary = Color(0xFFF1F5F9);
  static const darkTextSecondary = Color(0xFF94A3B8);
}
```

## lib/theme/app_typography.dart

```dart
import 'package:flutter/material.dart';
import 'app_colors.dart';

class AppTypography {
  static const displayLarge = TextStyle(
    fontSize: 32,
    fontWeight: FontWeight.bold,
    letterSpacing: -0.5,
    color: AppColors.textPrimary,
  );
  
  static const headline = TextStyle(
    fontSize: 20,
    fontWeight: FontWeight.w600,
    color: AppColors.textPrimary,
  );
  
  static const body = TextStyle(
    fontSize: 16,
    fontWeight: FontWeight.normal,
    height: 1.5,
    color: AppColors.textPrimary,
  );
  
  static const caption = TextStyle(
    fontSize: 12,
    fontWeight: FontWeight.w500,
    color: AppColors.textSecondary,
  );
  
  static const button = TextStyle(
    fontSize: 16,
    fontWeight: FontWeight.w600,
    color: Colors.white,
  );
}
```

## lib/theme/app_spacing.dart

```dart
class AppSpacing {
  static const double xs = 4;
  static const double sm = 8;
  static const double md = 16;
  static const double lg = 24;
  static const double xl = 32;
  static const double xxl = 48;
}
```

## lib/models/subject.dart

```dart
import 'package:freezed_annotation/freezed_annotation.dart';

part 'subject.freezed.dart';
part 'subject.g.dart';

@freezed
class Subject with _$Subject {
  const factory Subject({
    required String id,
    required String userId,
    required String name,
    required int color,
    String? icon,
    String? description,
    String? parentId,
    String? fsrsParams,
    required DateTime createdAt,
    @Default(false) bool archived,
  }) = _Subject;

  factory Subject.fromJson(Map<String, dynamic> json) =>
      _$SubjectFromJson(json);
}
```

## lib/models/physical_note.dart

```dart
import 'package:freezed_annotation/freezed_annotation.dart';

part 'physical_note.freezed.dart';
part 'physical_note.g.dart';

@freezed
class PhysicalNote with _$PhysicalNote {
  const factory PhysicalNote({
    required String id,
    required String subjectId,
    required String uniqueId,
    required String sourceName,
    required String pageNumber,
    String? sectionLabel,
    List<String>? tags,
    String? photoPath,
    String? voiceMemoPath,
    String? ocrText,
    String? locationShelf,
    String? locationContainer,
    String? qrCodeId,
    required DateTime createdAt,
    required DateTime updatedAt,
    DateTime? lastReviewedAt,
    @Default(0) int reviewCount,
  }) = _PhysicalNote;

  factory PhysicalNote.fromJson(Map<String, dynamic> json) =>
      _$PhysicalNoteFromJson(json);
}
```

## lib/models/review_item.dart

```dart
import 'package:freezed_annotation/freezed_annotation.dart';

part 'review_item.freezed.dart';
part 'review_item.g.dart';

enum CardState { newCard, learning, review, relearning }

@freezed
class ReviewItem with _$ReviewItem {
  const factory ReviewItem({
    required String id,
    required String noteId,
    required double difficulty,
    required double stability,
    required double elapsedDays,
    required double scheduledDays,
    @Default(0) int reps,
    @Default(0) int lapses,
    required CardState state,
    required DateTime due,
    @Default(false) bool suspended,
    @Default(false) bool leech,
  }) = _ReviewItem;

  factory ReviewItem.fromJson(Map<String, dynamic> json) =>
      _$ReviewItemFromJson(json);
}
```

## lib/models/review_log.dart

```dart
import 'package:freezed_annotation/freezed_annotation.dart';

part 'review_log.freezed.dart';
part 'review_log.g.dart';

enum Rating { again, hard, good, easy }

@freezed
class ReviewLog with _$ReviewLog {
  const factory ReviewLog({
    required String id,
    required String itemId,
    required Rating rating,
    required CardState state,
    required double elapsedDays,
    required double scheduledDays,
    int? reviewDuration,
    String? studySessionId,
    required DateTime createdAt,
  }) = _ReviewLog;

  factory ReviewLog.fromJson(Map<String, dynamic> json) =>
      _$ReviewLogFromJson(json);
}
```

## lib/models/study_session.dart

```dart
import 'package:freezed_annotation/freezed_annotation.dart';

part 'study_session.freezed.dart';
part 'study_session.g.dart';

enum SessionType { review, pomodoro, free, manual }

@freezed
class StudySession with _$StudySession {
  const factory StudySession({
    required String id,
    required String userId,
    required SessionType type,
    required DateTime startTime,
    DateTime? endTime,
    int? duration,
    int? itemsReviewed,
    Map<String, int>? ratings,
    double? retentionRate,
    String? subjectId,
    String? description,
    @Default('local') String syncStatus,
  }) = _StudySession;

  factory StudySession.fromJson(Map<String, dynamic> json) =>
      _$StudySessionFromJson(json);
}
```

## lib/models/exam.dart

```dart
import 'package:freezed_annotation/freezed_annotation.dart';

part 'exam.freezed.dart';
part 'exam.g.dart';

@freezed
class Exam with _$Exam {
  const factory Exam({
    required String id,
    required String userId,
    required String title,
    required DateTime date,
    required List<String> subjectIds,
    @Default(true) bool active,
    required DateTime createdAt,
  }) = _Exam;

  factory Exam.fromJson(Map<String, dynamic> json) => _$ExamFromJson(json);
}
```

## lib/models/user_settings.dart

```dart
import 'package:flutter/material.dart';
import 'package:freezed_annotation/freezed_annotation.dart';

part 'user_settings.freezed.dart';
part 'user_settings.g.dart';

@freezed
class UserSettings with _$UserSettings {
  const factory UserSettings({
    @Default('') String displayName,
    @Default('') String email,
    @Default(0.90) double requestRetention,
    @Default(36500) int maximumInterval,
    @Default(true) bool enableFuzz,
    @Default(150) int dailyReviewLimit,
    @Default(30) int dailyStudyGoalMinutes,
    @Default(false) bool useDyslexiaFont,
    @Default(ThemeMode.system) ThemeMode themeMode,
    @Default(true) bool enableNotifications,
    @Default('21:00') String reminderTime,
    @Default(7) int leechThreshold,
    @Default('en') String language,
  }) = _UserSettings;

  factory UserSettings.fromJson(Map<String, dynamic> json) =>
      _$UserSettingsFromJson(json);
}
```

## lib/database/tables.dart

```dart
import 'package:drift/drift.dart';

class Users extends Table {
  TextColumn get id => text()();
  TextColumn get displayName => text().nullable()();
  TextColumn get email => text().nullable()();
  IntColumn get createdAt => integer()();
  IntColumn get updatedAt => integer()();
  TextColumn get fsrsParams => text()();
  TextColumn get settings => text()();
  
  @override
  Set<Column> get primaryKey => {id};
}

class Subjects extends Table {
  TextColumn get id => text()();
  TextColumn get userId => text()();
  TextColumn get name => text()();
  IntColumn get color => integer()();
  TextColumn get icon => text().nullable()();
  TextColumn get description => text().nullable()();
  TextColumn get parentId => text().nullable()();
  TextColumn get fsrsParams => text().nullable()();
  IntColumn get createdAt => integer()();
  BoolColumn get archived => boolean().withDefault(const Constant(false))();
  
  @override
  Set<Column> get primaryKey => {id};
}

class PhysicalNotes extends Table {
  TextColumn get id => text()();
  TextColumn get subjectId => text()();
  TextColumn get uniqueId => text()();
  TextColumn get sourceName => text()();
  TextColumn get pageNumber => text()();
  TextColumn get sectionLabel => text().nullable()();
  TextColumn get tags => text().nullable()();
  TextColumn get photoPath => text().nullable()();
  TextColumn get voiceMemoPath => text().nullable()();
  TextColumn get ocrText => text().nullable()();
  TextColumn get locationShelf => text().nullable()();
  TextColumn get locationContainer => text().nullable()();
  TextColumn get qrCodeId => text().nullable()();
  IntColumn get createdAt => integer()();
  IntColumn get updatedAt => integer()();
  IntColumn get lastReviewedAt => integer().nullable()();
  IntColumn get reviewCount => integer().withDefault(const Constant(0))();
  
  @override
  Set<Column> get primaryKey => {id};
}

class ReviewItems extends Table {
  TextColumn get id => text()();
  TextColumn get noteId => text()();
  RealColumn get difficulty => real()();
  RealColumn get stability => real()();
  RealColumn get elapsedDays => real()();
  RealColumn get scheduledDays => real()();
  IntColumn get reps => integer().withDefault(const Constant(0))();
  IntColumn get lapses => integer().withDefault(const Constant(0))();
  IntColumn get state => integer()();
  IntColumn get due => integer()();
  BoolColumn get suspended => boolean().withDefault(const Constant(false))();
  BoolColumn get leech => boolean().withDefault(const Constant(false))();
  
  @override
  Set<Column> get primaryKey => {id};
}

class ReviewLogs extends Table {
  TextColumn get id => text()();
  TextColumn get itemId => text()();
  IntColumn get rating => integer()();
  IntColumn get state => integer()();
  RealColumn get elapsedDays => real()();
  RealColumn get scheduledDays => real()();
  IntColumn get reviewDuration => integer().nullable()();
  TextColumn get studySessionId => text().nullable()();
  IntColumn get createdAt => integer()();
  
  @override
  Set<Column> get primaryKey => {id};
}

class StudySessions extends Table {
  TextColumn get id => text()();
  TextColumn get userId => text()();
  TextColumn get type => text()();
  IntColumn get startTime => integer()();
  IntColumn get endTime => integer().nullable()();
  IntColumn get duration => integer().nullable()();
  IntColumn get itemsReviewed => integer().nullable()();
  TextColumn get ratingsJson => text().nullable()();
  RealColumn get retentionRate => real().nullable()();
  TextColumn get subjectId => text().nullable()();
  TextColumn get description => text().nullable()();
  TextColumn get syncStatus =>
      text().withDefault(const Constant('local'))();
  
  @override
  Set<Column> get primaryKey => {id};
}

class Exams extends Table {
  TextColumn get id => text()();
  TextColumn get userId => text()();
  TextColumn get title => text()();
  IntColumn get date => integer()();
  TextColumn get subjectsJson => text()();
  BoolColumn get active => boolean().withDefault(const Constant(true))();
  IntColumn get createdAt => integer()();
  
  @override
  Set<Column> get primaryKey => {id};
}

class Tags extends Table {
  TextColumn get id => text()();
  TextColumn get name => text().unique()();
  IntColumn get color => integer().nullable()();
  IntColumn get usageCount => integer().withDefault(const Constant(0))();
  
  @override
  Set<Column> get primaryKey => {id};
}

class NoteTags extends Table {
  TextColumn get noteId => text()();
  TextColumn get tagId => text()();
  
  @override
  Set<Column> get primaryKey => {noteId, tagId};
}

class SyncMetadata extends Table {
  IntColumn get id => integer()();
  IntColumn get lastSyncAt => integer().nullable()();
  TextColumn get syncToken => text().nullable()();
  TextColumn get deviceId => text()();
  
  @override
  Set<Column> get primaryKey => {id};
}

class PendingChanges extends Table {
  TextColumn get id => text()();
  TextColumn get tableName => text()();
  TextColumn get recordId => text()();
  TextColumn get operation => text()();
  TextColumn get payload => text()();
  IntColumn get createdAt => integer()();
  
  @override
  Set<Column> get primaryKey => {id};
}
```

## lib/database/database.dart

```dart
import 'dart:io';
import 'package:drift/drift.dart';
import 'package:drift_flutter/drift_flutter.dart';
import 'package:path_provider/path_provider.dart';
import 'package:path/path.dart' as p;

import 'tables.dart';

part 'database.g.dart';

@DriftDatabase(tables: [
  Users,
  Subjects,
  PhysicalNotes,
  ReviewItems,
  ReviewLogs,
  StudySessions,
  Exams,
  Tags,
  NoteTags,
  SyncMetadata,
  PendingChanges,
])
class AppDatabase extends _$AppDatabase {
  AppDatabase() : super(_openConnection());

  @override
  int get schemaVersion => 1;

  @override
  MigrationStrategy get migration => MigrationStrategy(
        onCreate: (Migrator m) async {
          await m.createAll();
          await _createIndexes(m);
          await _createFts5(m);
        },
        onUpgrade: (Migrator m, int from, int to) async {
          // Handle future migrations
        },
      );

  Future<void> _createIndexes(Migrator m) async {
    await m.createIndex(Index('idx_notes_subject',
        'CREATE INDEX idx_notes_subject ON physical_notes(subject_id)'));
    await m.createIndex(Index('idx_notes_unique',
        'CREATE INDEX idx_notes_unique ON physical_notes(unique_id)'));
    await m.createIndex(Index('idx_items_due',
        'CREATE INDEX idx_items_due ON review_items(due, suspended)'));
    await m.createIndex(Index('idx_logs_item',
        'CREATE INDEX idx_logs_item ON review_logs(item_id, created_at)'));
    await m.createIndex(Index('idx_sessions_time',
        'CREATE INDEX idx_sessions_time ON study_sessions(start_time)'));
  }

  Future<void> _createFts5(Migrator m) async {
    await customStatement('''
      CREATE VIRTUAL TABLE IF NOT EXISTS notes_fts USING fts5(
        unique_id,
        source_name,
        section_label,
        ocr_text,
        content='physical_notes',
        content_rowid='rowid'
      )
    ''');
  }

  // Subject queries
  Future<List<Subject>> getAllSubjects() => select(subjects).get();
  
  Future<Subject?> getSubjectById(String id) =>
      (select(subjects)..where((s) => s.id.equals(id))).getSingleOrNull();
  
  Future<int> insertSubject(SubjectsCompanion subject) =>
      into(subjects).insert(subject);
  
  Future<bool> updateSubject(Subject subject) =>
      update(subjects).replace(subject);
  
  Future<int> deleteSubject(String id) =>
      (delete(subjects)..where((s) => s.id.equals(id))).go();

  // Note queries
  Future<List<PhysicalNote>> getNotesBySubject(String subjectId) =>
      (select(physicalNotes)..where((n) => n.subjectId.equals(subjectId))).get();
  
  Future<List<PhysicalNote>> getAllNotes() => select(physicalNotes).get();
  
  Future<PhysicalNote?> getNoteById(String id) =>
      (select(physicalNotes)..where((n) => n.id.equals(id))).getSingleOrNull();
  
  Future<int> insertNote(PhysicalNotesCompanion note) =>
      into(physicalNotes).insert(note);
  
  Future<bool> updateNote(PhysicalNote note) =>
      update(physicalNotes).replace(note);
  
  Future<int> deleteNote(String id) =>
      (delete(physicalNotes)..where((n) => n.id.equals(id))).go();

  // Review item queries
  Future<List<ReviewItem>> getDueItems(DateTime before) =>
      (select(reviewItems)
            ..where((i) => i.due.isSmallerOrEqualValue(before.millisecondsSinceEpoch))
            ..where((i) => i.suspended.equals(false)))
          .get();
  
  Future<List<ReviewItem>> getDueItemsBySubject(String subjectId, DateTime before) =>
      (select(reviewItems)
            ..where((i) => i.due.isSmallerOrEqualValue(before.millisecondsSinceEpoch))
            ..where((i) => i.suspended.equals(false)))
          .get(); // Note: needs join with notes for subject filter
  
  Future<ReviewItem?> getReviewItemForNote(String noteId) =>
      (select(reviewItems)..where((i) => i.noteId.equals(noteId))).getSingleOrNull();
  
  Future<int> insertReviewItem(ReviewItemsCompanion item) =>
      into(reviewItems).insert(item);
  
  Future<bool> updateReviewItem(ReviewItem item) =>
      update(reviewItems).replace(item);

  // Review log queries
  Future<int> insertReviewLog(ReviewLogsCompanion log) =>
      into(reviewLogs).insert(log);
  
  Future<List<ReviewLog>> getLogsForItem(String itemId) =>
      (select(reviewLogs)..where((l) => l.itemId.equals(itemId))).get();

  // Session queries
  Future<int> insertSession(StudySessionsCompanion session) =>
      into(studySessions).insert(session);
  
  Future<bool> updateSession(StudySession session) =>
      update(studySessions).replace(session);
  
  Future<List<StudySession>> getSessionsForDateRange(
      DateTime start, DateTime end) =>
      (select(studySessions)
            ..where((s) => s.startTime.isBiggerOrEqualValue(start.millisecondsSinceEpoch))
            ..where((s) => s.startTime.isSmallerOrEqualValue(end.millisecondsSinceEpoch)))
          .get();

  // Exam queries
  Future<List<Exam>> getActiveExams() =>
      (select(exams)..where((e) => e.active.equals(true))).get();
  
  Future<int> insertExam(ExamsCompanion exam) => into(exams).insert(exam);

  // Search
  Future<List<PhysicalNote>> searchNotes(String query) async {
    final ftsResults = await customSelect(
      'SELECT rowid FROM notes_fts WHERE notes_fts MATCH ?',
      variables: [Variable.withString(query)],
    ).get();
    
    final rowIds = ftsResults.map((r) => r.read<int>('rowid')).toList();
    if (rowIds.isEmpty) return [];
    
    // Fetch actual notes by rowid
    return (select(physicalNotes)
          ..where((n) => CustomExpression<bool>('rowid', rowIds as List<Expression>)))
        .get();
  }

  // Stats
  Future<int> getStudyMinutesForDate(DateTime date) async {
    final startOfDay = DateTime(date.year, date.month, date.day);
    final endOfDay = startOfDay.add(const Duration(days: 1));
    
    final result = await customSelect(
      'SELECT COALESCE(SUM(duration), 0) as total FROM study_sessions '
      'WHERE start_time >= ? AND start_time < ?',
      variables: [
        Variable.withInt(startOfDay.millisecondsSinceEpoch),
        Variable.withInt(endOfDay.millisecondsSinceEpoch),
      ],
    ).getSingle();
    
    return (result.read<double>('total') ?? 0) ~/ 60;
  }

  Future<Map<String, dynamic>> getReviewStats(DateTime start, DateTime end) async {
    final result = await customSelect(
      'SELECT rating, COUNT(*) as count FROM review_logs '
      'WHERE created_at >= ? AND created_at < ? '
      'GROUP BY rating',
      variables: [
        Variable.withInt(start.millisecondsSinceEpoch),
        Variable.withInt(end.millisecondsSinceEpoch),
      ],
    ).get();
    
    final stats = <String, int>{};
    for (final row in result) {
      stats[row.read<String>('rating')] = row.read<int>('count');
    }
    return stats;
  }
}

LazyDatabase _openConnection() {
  return LazyDatabase(() async {
    final dbFolder = await getApplicationDocumentsDirectory();
    final file = File(p.join(dbFolder.path, 'paperstudy.db'));
    return NativeDatabase.createInBackground(file);
  });
}
```

## lib/services/fsrs_service.dart

```dart
import 'dart:math';
import 'package:paperstudy/models/review_item.dart';

class FSRSCalculator {
  // FSRS-4.5 default weights
  static const List<double> defaultWeights = [
    0.40255,  // w0
    0.74818,  // w1
    0.93027,  // w2
    2.26926,  // w3
    5.06871,  // w4
    4.93,     // w5
    0.94,     // w6
    0.86,     // w7
    0.01,     // w8
    1.49,     // w9
    0.14,     // w10
    0.94,     // w11
    2.18,     // w12
    0.05,     // w13
    0.34,     // w14
    1.26,     // w15
    0.29,     // w16
    2.61,     // w17
    0.41,     // w18
    0.96,     // w19
  ];

  final List<double> w;
  final double requestRetention;
  final int maximumInterval;
  final bool enableFuzz;

  FSRSCalculator({
    List<double>? weights,
    this.requestRetention = 0.90,
    this.maximumInterval = 36500,
    this.enableFuzz = true,
  }) : w = weights ?? List.from(defaultWeights);

  double initialDifficulty(int rating) {
    return w[4] - w[5] * (rating - 3) + 1;
  }

  double initialStability(int rating) {
    return max(w[rating], 0.1);
  }

  double nextDifficulty(double d, int rating) {
    final nextD = w[5] * initialDifficulty(3) +
        (1 - w[5]) * (d - w[6] * (rating - 3));
    return _constrainDifficulty(nextD);
  }

  double nextStability(double s, double d, int rating, double r) {
    final hardPenalty = rating == 2 ? w[12] : 1.0;
    final easyBonus = rating == 4 ? w[13] : 1.0;

    double nextS;
    if (rating == 1) {
      nextS = w[7] * pow(d, -w[8]) * (pow(s + 1, w[19]) - 1) * exp((1 - r) * w[17]);
    } else {
      nextS = s *
          (1 +
              exp(w[9]) *
                  (11 - d) *
                  pow(s, -w[10]) *
                  hardPenalty *
                  easyBonus *
                  (exp((1 - r) * w[17]) - 1));
    }
    return max(nextS, 0.1);
  }

  double retrievability(double elapsedDays, double stability) {
    return pow(1 + elapsedDays / (9 * stability), -1).toDouble();
  }

  int daysUntilNextReview(double stability, double requestRetention) {
    final days = (9 * stability * (1 / requestRetention - 1)).ceil();
    final fuzzed = enableFuzz ? _applyFuzz(days) : days;
    return min(fuzzed, maximumInterval);
  }

  int _applyFuzz(int interval) {
    final random = Random();
    final fuzzFactor = 0.05 + random.nextDouble() * 0.1; // 5-15% fuzz
    final fuzz = (interval * fuzzFactor).round();
    return interval + (random.nextBool() ? fuzz : -fuzz);
  }

  double _constrainDifficulty(double d) => d.clamp(1.0, 10.0);

  // Process a review and return updated card state
  ReviewResult processReview({
    required ReviewItem item,
    required int rating, // 1=Again, 2=Hard, 3=Good, 4=Easy
    required DateTime now,
  }) {
    final elapsedDays = now.difference(item.due).inDays.toDouble();
    final r = retrievability(elapsedDays, item.stability);

    final nextDifficulty = this.nextDifficulty(item.difficulty, rating);
    final nextStability = this.nextStability(item.stability, item.difficulty, rating, r);

    CardState nextState;
    int scheduledDays;

    switch (item.state) {
      case CardState.newCard:
        nextState = rating >= 3 ? CardState.review : CardState.learning;
        scheduledDays = rating == 1 ? 1 : (rating == 2 ? 1 : (rating == 3 ? 2 : 4));
        break;
      case CardState.learning:
      case CardState.relearning:
        nextState = rating >= 3 ? CardState.review : item.state;
        scheduledDays = rating == 1 ? 1 : daysUntilNextReview(nextStability, requestRetention);
        break;
      case CardState.review:
        nextState = rating == 1 ? CardState.relearning : CardState.review;
        scheduledDays = daysUntilNextReview(nextStability, requestRetention);
        break;
    }

    final nextDue = now.add(Duration(days: scheduledDays));

    return ReviewResult(
      difficulty: nextDifficulty,
      stability: nextStability,
      state: nextState,
      due: nextDue,
      scheduledDays: scheduledDays.toDouble(),
      elapsedDays: elapsedDays,
    );
  }
}

class ReviewResult {
  final double difficulty;
  final double stability;
  final CardState state;
  final DateTime due;
  final double scheduledDays;
  final double elapsedDays;

  ReviewResult({
    required this.difficulty,
    required this.stability,
    required this.state,
    required this.due,
    required this.scheduledDays,
    required this.elapsedDays,
  });
}
```

## lib/services/review_service.dart

```dart
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/database/database.dart';
import 'package:paperstudy/models/review_item.dart';
import 'package:paperstudy/models/review_log.dart';
import 'package:paperstudy/services/fsrs_service.dart';
import 'package:uuid/uuid.dart';

final reviewServiceProvider = Provider((ref) => ReviewService(ref));

class ReviewService {
  final ProviderRef ref;
  final _uuid = const Uuid();
  late final AppDatabase _db;
  late final FSRSCalculator _fsrs;

  ReviewService(this.ref) {
    _db = ref.read(databaseProvider);
    _fsrs = FSRSCalculator();
  }

  // Get today's review queue
  Future<List<ReviewQueueItem>> getReviewQueue({String? subjectId}) async {
    final now = DateTime.now();
    final items = subjectId != null
        ? await _db.getDueItemsBySubject(subjectId, now)
        : await _db.getDueItems(now);

    final queue = <ReviewQueueItem>[];
    for (final item in items) {
      final note = await _db.getNoteById(item.noteId);
      if (note != null) {
        queue.add(ReviewQueueItem(
          reviewItem: item,
          note: note,
        ));
      }
    }
    return queue;
  }

  // Process a rating
  Future<void> processRating({
    required String itemId,
    required int rating,
    required DateTime now,
    String? sessionId,
  }) async {
    final item = await _db.getReviewItemForNote(itemId) ??
        await _db.getReviewItemById(itemId);
    if (item == null) throw Exception('Review item not found');

    final result = _fsrs.processReview(
      item: item,
      rating: rating,
      now: now,
    );

    // Update review item
    final updatedItem = item.copyWith(
      difficulty: result.difficulty,
      stability: result.stability,
      elapsedDays: result.elapsedDays,
      scheduledDays: result.scheduledDays,
      reps: item.reps + 1,
      lapses: rating == 1 ? item.lapses + 1 : item.lapses,
      state: result.state,
      due: result.due,
    );

    await _db.updateReviewItem(updatedItem);

    // Log the review
    await _db.insertReviewLog(ReviewLogsCompanion(
      id: Value(_uuid.v4()),
      itemId: Value(item.id),
      rating: Value(rating),
      state: Value(item.state.index),
      elapsedDays: Value(result.elapsedDays),
      scheduledDays: Value(result.scheduledDays),
      studySessionId: Value(sessionId),
      createdAt: Value(now.millisecondsSinceEpoch),
    ));

    // Update note review count
    final note = await _db.getNoteById(item.noteId);
    if (note != null) {
      await _db.updateNote(note.copyWith(
        reviewCount: note.reviewCount + 1,
        lastReviewedAt: now,
      ));
    }

    // Check leech
    if (updatedItem.lapses >= 7) {
      await _db.updateReviewItem(updatedItem.copyWith(leech: true, suspended: true));
    }
  }

  // Create review item for new note
  Future<void> createReviewItem(String noteId) async {
    final now = DateTime.now();
    await _db.insertReviewItem(ReviewItemsCompanion(
      id: Value(_uuid.v4()),
      noteId: Value(noteId),
      difficulty: Value(5.0),
      stability: Value(0.0),
      elapsedDays: Value(0.0),
      scheduledDays: Value(0.0),
      state: Value(CardState.newCard.index),
      due: Value(now.millisecondsSinceEpoch),
    ));
  }

  // Get stats for today
  Future<ReviewStats> getTodayStats() async {
    final now = DateTime.now();
    final startOfDay = DateTime(now.year, now.month, now.day);
    final logs = await _db.customSelect(
      'SELECT rating, COUNT(*) as count FROM review_logs '
      'WHERE created_at >= ?',
      variables: [Variable.withInt(startOfDay.millisecondsSinceEpoch)],
    ).get();

    int again = 0, hard = 0, good = 0, easy = 0;
    for (final row in logs) {
      final rating = row.read<int>('rating');
      final count = row.read<int>('count');
      switch (rating) {
        case 1: again = count; break;
        case 2: hard = count; break;
        case 3: good = count; break;
        case 4: easy = count; break;
      }
    }

    final total = again + hard + good + easy;
    final retention = total > 0 ? (good + easy) / total : 0.0;

    return ReviewStats(
      total: total,
      again: again,
      hard: hard,
      good: good,
      easy: easy,
      retentionRate: retention,
    );
  }
}

class ReviewQueueItem {
  final ReviewItem reviewItem;
  final PhysicalNote note;

  ReviewQueueItem({required this.reviewItem, required this.note});
}

class ReviewStats {
  final int total;
  final int again;
  final int hard;
  final int good;
  final int easy;
  final double retentionRate;

  ReviewStats({
    required this.total,
    required this.again,
    required this.hard,
    required this.good,
    required this.easy,
    required this.retentionRate,
  });
}

// Extension for missing method
extension on AppDatabase {
  Future<ReviewItem?> getReviewItemById(String id) =>
      (select(reviewItems)..where((i) => i.id.equals(id))).getSingleOrNull();
}
```

## lib/services/note_service.dart

```dart
import 'dart:io';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:image/image.dart' as img;
import 'package:paperstudy/database/database.dart';
import 'package:paperstudy/models/physical_note.dart';
import 'package:path_provider/path_provider.dart';
import 'package:uuid/uuid.dart';

final noteServiceProvider = Provider((ref) => NoteService(ref));

class NoteService {
  final ProviderRef ref;
  final _uuid = const Uuid();
  late final AppDatabase _db;

  NoteService(this.ref) {
    _db = ref.read(databaseProvider);
  }

  Future<PhysicalNote> createNote({
    required String subjectId,
    required String sourceName,
    required String pageNumber,
    String? sectionLabel,
    List<String>? tags,
    File? photo,
    String? voiceMemoPath,
  }) async {
    final now = DateTime.now();
    final uniqueId = await _generateUniqueId(subjectId, sourceName, pageNumber);

    String? photoPath;
    if (photo != null) {
      photoPath = await _compressAndSavePhoto(photo);
    }

    final note = PhysicalNote(
      id: _uuid.v4(),
      subjectId: subjectId,
      uniqueId: uniqueId,
      sourceName: sourceName,
      pageNumber: pageNumber,
      sectionLabel: sectionLabel,
      tags: tags,
      photoPath: photoPath,
      voiceMemoPath: voiceMemoPath,
      createdAt: now,
      updatedAt: now,
    );

    await _db.insertNote(PhysicalNotesCompanion(
      id: Value(note.id),
      subjectId: Value(note.subjectId),
      uniqueId: Value(note.uniqueId),
      sourceName: Value(note.sourceName),
      pageNumber: Value(note.pageNumber),
      sectionLabel: Value(note.sectionLabel),
      tags: Value(note.tags?.join(',')),
      photoPath: Value(note.photoPath),
      voiceMemoPath: Value(note.voiceMemoPath),
      createdAt: Value(note.createdAt.millisecondsSinceEpoch),
      updatedAt: Value(note.updatedAt.millisecondsSinceEpoch),
    ));

    // Create associated review item
    await ref.read(reviewServiceProvider).createReviewItem(note.id);

    return note;
  }

  Future<String> _generateUniqueId(
      String subjectId, String sourceName, String pageNumber) async {
    final subject = await _db.getSubjectById(subjectId);
    final prefix = subject?.name.substring(0, 3).toUpperCase() ?? 'NOTE';
    final source = sourceName.replaceAll(' ', '_');
    return '$prefix-$source-P$pageNumber';
  }

  Future<String> _compressAndSavePhoto(File photo) async {
    final dir = await getApplicationDocumentsDirectory();
    final photosDir = Directory('${dir.path}/photos');
    await photosDir.create(recursive: true);

    final bytes = await photo.readAsBytes();
    var image = img.decodeImage(bytes)!;

    // Resize if too large
    if (image.width > 2048 || image.height > 2048) {
      image = img.copyResize(image, width: 2048);
    }

    // Compress to ~500KB quality
    final compressed = img.encodeJpg(image, quality: 85);
    final fileName = '${_uuid.v4()}.jpg';
    final file = File('${photosDir.path}/$fileName');
    await file.writeAsBytes(compressed);

    return file.path;
  }

  Future<List<PhysicalNote>> getNotesBySubject(String subjectId) async {
    return _db.getNotesBySubject(subjectId);
  }

  Future<List<PhysicalNote>> searchNotes(String query) async {
    return _db.searchNotes(query);
  }

  Future<void> deleteNote(String id) async {
    final note = await _db.getNoteById(id);
    if (note?.photoPath != null) {
      final file = File(note!.photoPath!);
      if (await file.exists()) await file.delete();
    }
    await _db.deleteNote(id);
  }
}

final databaseProvider = Provider<AppDatabase>((ref) => AppDatabase());
```

## lib/services/subject_service.dart

```dart
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/database/database.dart';
import 'package:paperstudy/models/subject.dart';
import 'package:uuid/uuid.dart';

final subjectServiceProvider = Provider((ref) => SubjectService(ref));

class SubjectService {
  final ProviderRef ref;
  final _uuid = const Uuid();
  late final AppDatabase _db;

  SubjectService(this.ref) {
    _db = ref.read(databaseProvider);
  }

  Future<Subject> createSubject({
    required String name,
    required int color,
    String? icon,
    String? description,
    String? parentId,
  }) async {
    final now = DateTime.now();
    final subject = Subject(
      id: _uuid.v4(),
      userId: 'default_user', // TODO: proper auth
      name: name,
      color: color,
      icon: icon,
      description: description,
      parentId: parentId,
      createdAt: now,
    );

    await _db.insertSubject(SubjectsCompanion(
      id: Value(subject.id),
      userId: Value(subject.userId),
      name: Value(subject.name),
      color: Value(subject.color),
      icon: Value(subject.icon),
      description: Value(subject.description),
      parentId: Value(subject.parentId),
      createdAt: Value(subject.createdAt.millisecondsSinceEpoch),
    ));

    return subject;
  }

  Future<List<Subject>> getAllSubjects() => _db.getAllSubjects();

  Future<Subject?> getSubjectById(String id) => _db.getSubjectById(id);

  Future<void> archiveSubject(String id) async {
    final subject = await _db.getSubjectById(id);
    if (subject != null) {
      await _db.updateSubject(subject.copyWith(archived: true));
    }
  }

  Future<void> deleteSubject(String id) => _db.deleteSubject(id);
}
```

## lib/services/session_service.dart

```dart
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/database/database.dart';
import 'package:paperstudy/models/study_session.dart';
import 'package:uuid/uuid.dart';

final sessionServiceProvider = Provider((ref) => SessionService(ref));

class SessionService {
  final ProviderRef ref;
  final _uuid = const Uuid();
  late final AppDatabase _db;

  SessionService(this.ref) {
    _db = ref.read(databaseProvider);
  }

  Future<StudySession> startSession({
    required SessionType type,
    String? subjectId,
    String? description,
  }) async {
    final session = StudySession(
      id: _uuid.v4(),
      userId: 'default_user',
      type: type,
      startTime: DateTime.now(),
      subjectId: subjectId,
      description: description,
    );

    await _db.insertSession(StudySessionsCompanion(
      id: Value(session.id),
      userId: Value(session.userId),
      type: Value(session.type.name),
      startTime: Value(session.startTime.millisecondsSinceEpoch),
      subjectId: Value(session.subjectId),
      description: Value(session.description),
    ));

    return session;
  }

  Future<void> endSession(String sessionId, {
    int? itemsReviewed,
    Map<String, int>? ratings,
    double? retentionRate,
  }) async {
    final now = DateTime.now();
    final existing = await _db.getSessionById(sessionId);
    if (existing == null) return;

    final duration = now.difference(existing.startTime).inSeconds;

    await _db.updateSession(existing.copyWith(
      endTime: now,
      duration: duration,
      itemsReviewed: itemsReviewed,
      ratings: ratings,
      retentionRate: retentionRate,
    ));
  }

  Future<List<StudySession>> getSessionsForDateRange(
      DateTime start, DateTime end) {
    return _db.getSessionsForDateRange(start, end);
  }

  Future<int> getStudyMinutesForDate(DateTime date) =>
      _db.getStudyMinutesForDate(date);
}

// Extension for missing method
extension on AppDatabase {
  Future<StudySession?> getSessionById(String id) =>
      (select(studySessions)..where((s) => s.id.equals(id))).getSingleOrNull();
}
```

## lib/services/notification_service.dart

```dart
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import 'package:timezone/timezone.dart' as tz;

class NotificationService {
  static final NotificationService _instance = NotificationService._internal();
  factory NotificationService() => _instance;
  NotificationService._internal();

  final FlutterLocalNotificationsPlugin _notifications =
      FlutterLocalNotificationsPlugin();

  Future<void> initialize() async {
    const androidSettings =
        AndroidInitializationSettings('@mipmap/ic_launcher');
    const iosSettings = DarwinInitializationSettings();
    const initSettings = InitializationSettings(
      android: androidSettings,
      iOS: iosSettings,
    );

    await _notifications.initialize(initSettings);
  }

  Future<void> scheduleDailyReminder({
    required int hour,
    required int minute,
    required int dueCount,
  }) async {
    await _notifications.cancelAll();

    final now = DateTime.now();
    var scheduledDate = DateTime(now.year, now.month, now.day, hour, minute);
    if (scheduledDate.isBefore(now)) {
      scheduledDate = scheduledDate.add(const Duration(days: 1));
    }

    await _notifications.zonedSchedule(
      0,
      'Time to study!',
      '$dueCount reviews waiting for you',
      tz.TZDateTime.from(scheduledDate, tz.local),
      const NotificationDetails(
        android: AndroidNotificationDetails(
          'daily_reminder',
          'Daily Study Reminder',
          importance: Importance.high,
          priority: Priority.high,
        ),
        iOS: DarwinNotificationDetails(),
      ),
      androidScheduleMode: AndroidScheduleMode.exactAllowWhileIdle,
      uiLocalNotificationDateInterpretation:
          UILocalNotificationDateInterpretation.absoluteTime,
      matchDateTimeComponents: DateTimeComponents.time,
    );
  }

  Future<void> showReviewCompleteNotification(int count) async {
    await _notifications.show(
      1,
      'Review complete!',
      'You reviewed $count cards. Great job!',
      const NotificationDetails(
        android: AndroidNotificationDetails(
          'review_complete',
          'Review Complete',
          importance: Importance.low,
        ),
      ),
    );
  }
}
```

## lib/services/ocr_service.dart

```dart
import 'dart:io';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:google_mlkit_text_recognition/google_mlkit_text_recognition.dart';

final ocrServiceProvider = Provider((ref) => OCRService());

class OCRService {
  final _textRecognizer = TextRecognizer();

  Future<String> recognizeText(File imageFile) async {
    final inputImage = InputImage.fromFile(imageFile);
    final recognizedText = await _textRecognizer.processImage(inputImage);
    return recognizedText.text;
  }

  Future<String?> extractPageNumber(File imageFile, {Rect? region}) async {
    final inputImage = InputImage.fromFile(imageFile);
    final recognizedText = await _textRecognizer.processImage(inputImage);

    // Look for page number patterns in specified region or full image
    for (final block in recognizedText.blocks) {
      for (final line in block.lines) {
        final text = line.text.trim();
        // Match patterns like "42", "Page 42", "p.42"
        final match = RegExp(r'(?:page|p\.?)?\s*(\d+)', caseSensitive: false)
            .firstMatch(text);
        if (match != null) {
          return match.group(1);
        }
      }
    }
    return null;
  }

  void dispose() {
    _textRecognizer.close();
  }
}
```

## lib/providers/app_providers.dart

```dart
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/database/database.dart';

final databaseProvider = Provider<AppDatabase>((ref) => AppDatabase());

final isLoadingProvider = StateProvider<bool>((ref) => false);

final errorProvider = StateProvider<String?>((ref) => null);
```

## lib/providers/subject_providers.dart

```dart
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/models/subject.dart';
import 'package:paperstudy/services/subject_service.dart';

final subjectsProvider = FutureProvider<List<Subject>>((ref) async {
  final service = ref.watch(subjectServiceProvider);
  return service.getAllSubjects();
});

final selectedSubjectProvider = StateProvider<Subject?>((ref) => null);

final subjectColorsProvider = Provider<List<int>>((ref) => [
  0xFFEF4444, // Red
  0xFFF59E0B, // Amber
  0xFF22C55E, // Green
  0xFF3B82F6, // Blue
  0xFF6366F1, // Indigo
  0xFFA855F7, // Purple
  0xFFEC4899, // Pink
  0xFF14B8A6, // Teal
  0xFFF97316, // Orange
  0xFF06B6D4, // Cyan
  0xFF84CC16, // Lime
  0xFF8B5CF6, // Violet
]);
```

## lib/providers/note_providers.dart

```dart
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/models/physical_note.dart';
import 'package:paperstudy/services/note_service.dart';

final notesBySubjectProvider = FutureProvider.family<List<PhysicalNote>, String>((ref, subjectId) async {
  final service = ref.watch(noteServiceProvider);
  return service.getNotesBySubject(subjectId);
});

final noteSearchProvider = FutureProvider.family<List<PhysicalNote>, String>((ref, query) async {
  if (query.isEmpty) return [];
  final service = ref.watch(noteServiceProvider);
  return service.searchNotes(query);
});

final selectedNoteProvider = StateProvider<PhysicalNote?>((ref) => null);
```

## lib/providers/review_providers.dart

```dart
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/services/review_service.dart';

final reviewQueueProvider = FutureProvider.family<List<ReviewQueueItem>, String?>((ref, subjectId) async {
  final service = ref.watch(reviewServiceProvider);
  return service.getReviewQueue(subjectId: subjectId);
});

final todayStatsProvider = FutureProvider<ReviewStats>((ref) async {
  final service = ref.watch(reviewServiceProvider);
  return service.getTodayStats();
});

final currentReviewIndexProvider = StateProvider<int>((ref) => 0);

final isReviewActiveProvider = StateProvider<bool>((ref) => false);
```

## lib/providers/session_providers.dart

```dart
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/models/study_session.dart';
import 'package:paperstudy/services/session_service.dart';

final activeSessionProvider = StateProvider<StudySession?>((ref) => null);

final studyStreakProvider = FutureProvider<int>((ref) async {
  // Calculate current streak
  final service = ref.watch(sessionServiceProvider);
  final now = DateTime.now();
  int streak = 0;
  
  for (int i = 0; i < 365; i++) {
    final date = now.subtract(Duration(days: i));
    final minutes = await service.getStudyMinutesForDate(date);
    if (minutes > 0) {
      streak++;
    } else {
      break;
    }
  }
  
  return streak;
});

final weeklyStudyTimeProvider = FutureProvider<Map<int, int>>((ref) async {
  final service = ref.watch(sessionServiceProvider);
  final now = DateTime.now();
  final startOfWeek = now.subtract(Duration(days: now.weekday - 1));
  
  final result = <int, int>{};
  for (int i = 0; i < 7; i++) {
    final date = startOfWeek.add(Duration(days: i));
    result[i] = await service.getStudyMinutesForDate(date);
  }
  
  return result;
});
```

## lib/providers/settings_providers.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:hive/hive.dart';
import 'package:paperstudy/models/user_settings.dart';

final settingsBoxProvider = Provider<Box>((ref) => Hive.box('settings'));

final userSettingsProvider = StateNotifierProvider<SettingsNotifier, UserSettings>((ref) {
  final box = ref.watch(settingsBoxProvider);
  return SettingsNotifier(box);
});

final onboardingCompleteProvider = Provider<bool>((ref) {
  final box = ref.watch(settingsBoxProvider);
  return box.get('onboarding_complete', defaultValue: false);
});

class SettingsNotifier extends StateNotifier<UserSettings> {
  final Box _box;

  SettingsNotifier(this._box) : super(_loadSettings(_box));

  static UserSettings _loadSettings(Box box) {
    final json = box.get('user_settings');
    if (json != null) {
      return UserSettings.fromJson(Map<String, dynamic>.from(json));
    }
    return const UserSettings();
  }

  Future<void> updateSettings(UserSettings settings) async {
    state = settings;
    await _box.put('user_settings', settings.toJson());
  }

  Future<void> completeOnboarding() async {
    await _box.put('onboarding_complete', true);
  }
}
```

## lib/screens/home_screen.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/providers/review_providers.dart';
import 'package:paperstudy/providers/session_providers.dart';
import 'package:paperstudy/providers/settings_providers.dart';
import 'package:paperstudy/providers/subject_providers.dart';
import 'package:paperstudy/screens/add_note_screen.dart';
import 'package:paperstudy/screens/library_screen.dart';
import 'package:paperstudy/screens/review_screen.dart';
import 'package:paperstudy/screens/settings_screen.dart';
import 'package:paperstudy/screens/stats_screen.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';
import 'package:paperstudy/widgets/heatmap_calendar.dart';
import 'package:paperstudy/widgets/progress_ring.dart';
import 'package:paperstudy/widgets/quick_add_fab.dart';
import 'package:paperstudy/widgets/streak_flame.dart';
import 'package:paperstudy/widgets/workload_chart.dart';

class HomeScreen extends ConsumerStatefulWidget {
  const HomeScreen({Key? key}) : super(key: key);

  @override
  ConsumerState<HomeScreen> createState() => _HomeScreenState();
}

class _HomeScreenState extends ConsumerState<HomeScreen> {
  int _selectedIndex = 0;

  final _screens = [
    const _HomeTab(),
    const LibraryScreen(),
    const StatsScreen(),
    const SettingsScreen(),
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: _screens[_selectedIndex],
      floatingActionButton: _selectedIndex == 0 ? const QuickAddFAB() : null,
      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
      bottomNavigationBar: BottomAppBar(
        shape: const CircularNotchedRectangle(),
        notchMargin: 8,
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceAround,
          children: [
            _buildNavItem(Icons.home_rounded, 'Home', 0),
            _buildNavItem(Icons.library_books_rounded, 'Library', 1),
            const SizedBox(width: 48), // Space for FAB
            _buildNavItem(Icons.bar_chart_rounded, 'Stats', 2),
            _buildNavItem(Icons.settings_rounded, 'Settings', 3),
          ],
        ),
      ),
    );
  }

  Widget _buildNavItem(IconData icon, String label, int index) {
    final isSelected = _selectedIndex == index;
    return InkWell(
      onTap: () => setState(() => _selectedIndex = index),
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          Icon(
            icon,
            color: isSelected ? AppColors.primary : AppColors.textSecondary,
          ),
          Text(
            label,
            style: TextStyle(
              fontSize: 12,
              color: isSelected ? AppColors.primary : AppColors.textSecondary,
              fontWeight: isSelected ? FontWeight.w600 : FontWeight.normal,
            ),
          ),
        ],
      ),
    );
  }
}

class _HomeTab extends ConsumerWidget {
  const _HomeTab({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final statsAsync = ref.watch(todayStatsProvider);
    final streakAsync = ref.watch(studyStreakProvider);
    final subjectsAsync = ref.watch(subjectsProvider);

    return SafeArea(
      child: CustomScrollView(
        slivers: [
          // App Bar
          SliverToBoxAdapter(
            child: Padding(
              padding: const EdgeInsets.all(AppSpacing.md),
              child: Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  Text(
                    'PaperStudy',
                    style: AppTypography.displayLarge.copyWith(fontSize: 28),
                  ),
                  Row(
                    children: [
                      IconButton(
                        icon: const Icon(Icons.notifications_outlined),
                        onPressed: () {},
                      ),
                      IconButton(
                        icon: const Icon(Icons.settings_outlined),
                        onPressed: () {},
                      ),
                    ],
                  ),
                ],
              ),
            ),
          ),

          // Stats Row
          SliverToBoxAdapter(
            child: Padding(
              padding: const EdgeInsets.symmetric(horizontal: AppSpacing.md),
              child: Row(
                children: [
                  Expanded(
                    child: _StatCard(
                      icon: Icons.local_fire_department,
                      iconColor: AppColors.warning,
                      value: streakAsync.when(
                        data: (s) => '$s',
                        loading: () => '-',
                        error: (_, __) => '-',
                      ),
                      label: 'day streak',
                    ),
                  ),
                  const SizedBox(width: AppSpacing.md),
                  Expanded(
                    child: _StatCard(
                      icon: Icons.timer,
                      iconColor: AppColors.primary,
                      value: statsAsync.when(
                        data: (s) => '${s.total}',
                        loading: () => '-',
                        error: (_, __) => '-',
                      ),
                      label: 'reviews today',
                    ),
                  ),
                ],
              ),
            ),
          ),

          const SliverToBoxAdapter(child: SizedBox(height: AppSpacing.lg)),

          // Subject Cards
          SliverToBoxAdapter(
            child: SizedBox(
              height: 120,
              child: subjectsAsync.when(
                data: (subjects) => ListView.builder(
                  scrollDirection: Axis.horizontal,
                  padding: const EdgeInsets.symmetric(horizontal: AppSpacing.md),
                  itemCount: subjects.length,
                  itemBuilder: (context, index) {
                    final subject = subjects[index];
                    return _SubjectCard(subject: subject);
                  },
                ),
                loading: () => const Center(child: CircularProgressIndicator()),
                error: (_, __) => const Center(child: Text('Error loading subjects')),
              ),
            ),
          ),

          const SliverToBoxAdapter(child: SizedBox(height: AppSpacing.lg)),

          // Today's Queue
          SliverToBoxAdapter(
            child: Padding(
              padding: const EdgeInsets.symmetric(horizontal: AppSpacing.md),
              child: _ReviewQueueCard(),
            ),
          ),

          const SliverToBoxAdapter(child: SizedBox(height: AppSpacing.lg)),

          // Upcoming Exams
          SliverToBoxAdapter(
            child: Padding(
              padding: const EdgeInsets.symmetric(horizontal: AppSpacing.md),
              child: _ExamCard(),
            ),
          ),

          const SliverToBoxAdapter(child: SizedBox(height: AppSpacing.lg)),

          // Activity Heatmap
          SliverToBoxAdapter(
            child: Padding(
              padding: const EdgeInsets.symmetric(horizontal: AppSpacing.md),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Text('Activity', style: AppTypography.headline),
                  const SizedBox(height: AppSpacing.sm),
                  const HeatmapCalendar(daysToShow: 28),
                ],
              ),
            ),
          ),

          const SliverToBoxAdapter(child: SizedBox(height: 100)), // Bottom padding
        ],
      ),
    );
  }
}

class _StatCard extends StatelessWidget {
  final IconData icon;
  final Color iconColor;
  final String value;
  final String label;

  const _StatCard({
    required this.icon,
    required this.iconColor,
    required this.value,
    required this.label,
  });

  @override
  Widget build(BuildContext context) {
    return Card(
      child: Padding(
        padding: const EdgeInsets.all(AppSpacing.md),
        child: Row(
          children: [
            Icon(icon, color: iconColor, size: 28),
            const SizedBox(width: AppSpacing.sm),
            Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                Text(
                  value,
                  style: AppTypography.headline.copyWith(fontSize: 24),
                ),
                Text(
                  label,
                  style: AppTypography.caption,
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}

class _SubjectCard extends StatelessWidget {
  final dynamic subject;

  const _SubjectCard({required this.subject});

  @override
  Widget build(BuildContext context) {
    return Container(
      width: 160,
      margin: const EdgeInsets.only(right: AppSpacing.sm),
      child: Card(
        color: Color(subject.color).withOpacity(0.1),
        child: Padding(
          padding: const EdgeInsets.all(AppSpacing.md),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              Row(
                children: [
                  CircleAvatar(
                    radius: 16,
                    backgroundColor: Color(subject.color),
                    child: Text(
                      subject.name.substring(0, 1),
                      style: const TextStyle(
                        color: Colors.white,
                        fontWeight: FontWeight.bold,
                      ),
                    ),
                  ),
                  const Spacer(),
                  const Icon(Icons.more_vert, size: 16),
                ],
              ),
              const Spacer(),
              Text(
                subject.name,
                style: AppTypography.body.copyWith(fontWeight: FontWeight.w600),
                maxLines: 1,
                overflow: TextOverflow.ellipsis,
              ),
              Text(
                '5 due today',
                style: AppTypography.caption,
              ),
              const SizedBox(height: AppSpacing.xs),
              LinearProgressIndicator(
                value: 0.6,
                backgroundColor: Color(subject.color).withOpacity(0.2),
                valueColor: AlwaysStoppedAnimation<Color>(Color(subject.color)),
                borderRadius: BorderRadius.circular(4),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

class _ReviewQueueCard extends ConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final queueAsync = ref.watch(reviewQueueProvider(null));

    return queueAsync.when(
      data: (queue) {
        final dueCount = queue.length;
        final estimatedMinutes = (dueCount * 0.5).ceil();

        return Card(
          elevation: 4,
          child: Padding(
            padding: const EdgeInsets.all(AppSpacing.lg),
            child: Column(
              children: [
                Row(
                  children: [
                    Container(
                      padding: const EdgeInsets.all(AppSpacing.md),
                      decoration: BoxDecoration(
                        color: AppColors.primaryLight,
                        borderRadius: BorderRadius.circular(12),
                      ),
                      child: const Icon(
                        Icons.menu_book,
                        color: AppColors.primary,
                        size: 32,
                      ),
                    ),
                    const SizedBox(width: AppSpacing.md),
                    Expanded(
                      child: Column(
                        crossAxisAlignment: CrossAxisAlignment.start,
                        children: [
                          Text(
                            '$dueCount reviews waiting',
                            style: AppTypography.headline,
                          ),
                          Text(
                            '~ $estimatedMinutes minutes',
                            style: AppTypography.caption,
                          ),
                        ],
                      ),
                    ),
                  ],
                ),
                const SizedBox(height: AppSpacing.lg),
                SizedBox(
                  width: double.infinity,
                  height: 56,
                  child: ElevatedButton(
                    onPressed: dueCount > 0
                        ? () => Navigator.push(
                              context,
                              MaterialPageRoute(
                                builder: (_) => const ReviewScreen(),
                              ),
                            )
                        : null,
                    style: ElevatedButton.styleFrom(
                      backgroundColor: AppColors.primary,
                      foregroundColor: Colors.white,
                      shape: RoundedRectangleBorder(
                        borderRadius: BorderRadius.circular(16),
                      ),
                    ),
                    child: Text(
                      dueCount > 0 ? 'START REVIEW' : 'ALL CAUGHT UP!',
                      style: AppTypography.button,
                    ),
                  ),
                ),
              ],
            ),
          ),
        );
      },
      loading: () => const Card(
        child: Padding(
          padding: EdgeInsets.all(AppSpacing.lg),
          child: Center(child: CircularProgressIndicator()),
        ),
      ),
      error: (_, __) => const Card(
        child: Padding(
          padding: EdgeInsets.all(AppSpacing.lg),
          child: Text('Error loading queue'),
        ),
      ),
    );
  }
}

class _ExamCard extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Card(
      child: Padding(
        padding: const EdgeInsets.all(AppSpacing.md),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: [
                Text('Upcoming Exams', style: AppTypography.headline),
                TextButton(
                  onPressed: () {},
                  child: const Text('+ Add'),
                ),
              ],
            ),
            const SizedBox(height: AppSpacing.sm),
            Container(
              padding: const EdgeInsets.all(AppSpacing.md),
              decoration: BoxDecoration(
                color: AppColors.primaryLight,
                borderRadius: BorderRadius.circular(12),
              ),
              child: Row(
                children: [
                  const Icon(Icons.event, color: AppColors.primary),
                  const SizedBox(width: AppSpacing.sm),
                  Expanded(
                    child: Column(
                      crossAxisAlignment: CrossAxisAlignment.start,
                      children: [
                        const Text(
                          'Biology Final',
                          style: TextStyle(fontWeight: FontWeight.w600),
                        ),
                        Text(
                          '12 days remaining',
                          style: AppTypography.caption,
                        ),
                      ],
                    ),
                  ),
                  const Text(
                    '80%',
                    style: TextStyle(
                      color: AppColors.primary,
                      fontWeight: FontWeight.bold,
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}
```

## lib/screens/review_screen.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/providers/review_providers.dart';
import 'package:paperstudy/services/review_service.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';
import 'package:paperstudy/widgets/rating_buttons.dart';
import 'package:paperstudy/widgets/review_card.dart';

class ReviewScreen extends ConsumerStatefulWidget {
  const ReviewScreen({Key? key}) : super(key: key);

  @override
  ConsumerState<ReviewScreen> createState() => _ReviewScreenState();
}

class _ReviewScreenState extends ConsumerState<ReviewScreen> {
  bool _answerRevealed = false;
  DateTime _sessionStart = DateTime.now();
  int _itemsReviewed = 0;
  Map<String, int> _ratings = {'again': 0, 'hard': 0, 'good': 0, 'easy': 0};

  @override
  Widget build(BuildContext context) {
    final queueAsync = ref.watch(reviewQueueProvider(null));
    final currentIndex = ref.watch(currentReviewIndexProvider);

    return Scaffold(
      backgroundColor: AppColors.background,
      appBar: AppBar(
        backgroundColor: Colors.transparent,
        elevation: 0,
        leading: IconButton(
          icon: const Icon(Icons.close, color: AppColors.textPrimary),
          onPressed: () => _showExitDialog(context),
        ),
        title: queueAsync.when(
          data: (queue) => Text(
            '${currentIndex + 1}/${queue.length}',
            style: AppTypography.body.copyWith(color: AppColors.textPrimary),
          ),
          loading: () => const Text('Loading...'),
          error: (_, __) => const Text('Error'),
        ),
        actions: [
          IconButton(
            icon: const Icon(Icons.more_vert, color: AppColors.textPrimary),
            onPressed: () {},
          ),
        ],
      ),
      body: queueAsync.when(
        data: (queue) {
          if (queue.isEmpty) {
            return _buildCompletionScreen();
          }
          if (currentIndex >= queue.length) {
            return _buildCompletionScreen();
          }

          final currentItem = queue[currentIndex];
          final progress = (currentIndex + 1) / queue.length;

          return Column(
            children: [
              // Progress bar
              LinearProgressIndicator(
                value: progress,
                backgroundColor: AppColors.divider,
                valueColor: const AlwaysStoppedAnimation<Color>(AppColors.primary),
                minHeight: 4,
              ),

              // Timer
              Padding(
                padding: const EdgeInsets.all(AppSpacing.sm),
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: [
                    const Icon(Icons.timer, size: 16, color: AppColors.textSecondary),
                    const SizedBox(width: 4),
                    _SessionTimer(startTime: _sessionStart),
                  ],
                ),
              ),

              // Review Card
              Expanded(
                child: SingleChildScrollView(
                  padding: const EdgeInsets.all(AppSpacing.md),
                  child: ReviewCard(
                    note: currentItem.note,
                    answerRevealed: _answerRevealed,
                    onShowAnswer: () => setState(() => _answerRevealed = true),
                  ),
                ),
              ),

              // Rating buttons or Show Answer
              if (_answerRevealed)
                RatingButtons(
                  onRate: (rating) => _handleRating(rating, queue.length),
                )
              else
                Padding(
                  padding: const EdgeInsets.all(AppSpacing.md),
                  child: SizedBox(
                    width: double.infinity,
                    height: 56,
                    child: ElevatedButton(
                      onPressed: () => setState(() => _answerRevealed = true),
                      style: ElevatedButton.styleFrom(
                        backgroundColor: AppColors.primary,
                        foregroundColor: Colors.white,
                        shape: RoundedRectangleBorder(
                          borderRadius: BorderRadius.circular(16),
                        ),
                      ),
                      child: const Text('SHOW ANSWER', style: AppTypography.button),
                    ),
                  ),
                ),

              const SizedBox(height: AppSpacing.md),
            ],
          );
        },
        loading: () => const Center(child: CircularProgressIndicator()),
        error: (_, __) => const Center(child: Text('Error loading review queue')),
      ),
    );
  }

  void _handleRating(int rating, int totalItems) async {
    final queueAsync = ref.read(reviewQueueProvider(null));
    final currentIndex = ref.read(currentReviewIndexProvider);

    queueAsync.whenData((queue) async {
      if (currentIndex < queue.length) {
        final item = queue[currentIndex];
        
        HapticFeedback.lightImpact();

        await ref.read(reviewServiceProvider).processRating(
          itemId: item.reviewItem.id,
          rating: rating,
          now: DateTime.now(),
        );

        // Update stats
        setState(() {
          _itemsReviewed++;
          switch (rating) {
            case 1: _ratings['again'] = (_ratings['again'] ?? 0) + 1; break;
            case 2: _ratings['hard'] = (_ratings['hard'] ?? 0) + 1; break;
            case 3: _ratings['good'] = (_ratings['good'] ?? 0) + 1; break;
            case 4: _ratings['easy'] = (_ratings['easy'] ?? 0) + 1; break;
          }
          _answerRevealed = false;
        });

        ref.read(currentReviewIndexProvider.notifier).state++;

        if (currentIndex + 1 >= totalItems) {
          // Session complete
        }
      }
    });
  }

  Widget _buildCompletionScreen() {
    final duration = DateTime.now().difference(_sessionStart);
    final retention = _itemsReviewed > 0
        ? ((_ratings['good']! + _ratings['easy']!) / _itemsReviewed * 100).round()
        : 0;

    return Center(
      child: Padding(
        padding: const EdgeInsets.all(AppSpacing.xl),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Icon(
              Icons.check_circle,
              size: 80,
              color: AppColors.success,
            ),
            const SizedBox(height: AppSpacing.lg),
            Text(
              'Review Complete!',
              style: AppTypography.displayLarge,
            ),
            const SizedBox(height: AppSpacing.md),
            Text(
              'You reviewed $_itemsReviewed cards in ${_formatDuration(duration)}',
              style: AppTypography.body,
              textAlign: TextAlign.center,
            ),
            const SizedBox(height: AppSpacing.lg),
            _StatRow(
              icon: Icons.emoji_emotions,
              color: AppColors.success,
              label: 'Retention',
              value: '$retention%',
            ),
            const SizedBox(height: AppSpacing.sm),
            _StatRow(
              icon: Icons.timer,
              color: AppColors.primary,
              label: 'Time per card',
              value: '${(duration.inSeconds / (_itemsReviewed > 0 ? _itemsReviewed : 1)).round()}s',
            ),
            const SizedBox(height: AppSpacing.xl),
            SizedBox(
              width: double.infinity,
              height: 56,
              child: ElevatedButton(
                onPressed: () => Navigator.pop(context),
                style: ElevatedButton.styleFrom(
                  backgroundColor: AppColors.primary,
                  foregroundColor: Colors.white,
                ),
                child: const Text('DONE', style: AppTypography.button),
              ),
            ),
          ],
        ),
      ),
    );
  }

  String _formatDuration(Duration d) {
    if (d.inMinutes > 0) {
      return '${d.inMinutes}m ${d.inSeconds % 60}s';
    }
    return '${d.inSeconds}s';
  }

  void _showExitDialog(BuildContext context) {
    showDialog(
      context: context,
      builder: (context) => AlertDialog(
        title: const Text('End Session?'),
        content: const Text('Your progress will be saved.'),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(context),
            child: const Text('CANCEL'),
          ),
          TextButton(
            onPressed: () {
              Navigator.pop(context);
              Navigator.pop(context);
            },
            child: const Text('END'),
          ),
        ],
      ),
    );
  }
}

class _SessionTimer extends StatelessWidget {
  final DateTime startTime;

  const _SessionTimer({required this.startTime});

  @override
  Widget build(BuildContext context) {
    return StreamBuilder(
      stream: Stream.periodic(const Duration(seconds: 1)),
      builder: (context, snapshot) {
        final elapsed = DateTime.now().difference(startTime);
        final minutes = elapsed.inMinutes.toString().padLeft(2, '0');
        final seconds = (elapsed.inSeconds % 60).toString().padLeft(2, '0');
        return Text(
          '$minutes:$seconds',
          style: AppTypography.caption.copyWith(fontFamily: 'monospace'),
        );
      },
    );
  }
}

class _StatRow extends StatelessWidget {
  final IconData icon;
  final Color color;
  final String label;
  final String value;

  const _StatRow({
    required this.icon,
    required this.color,
    required this.label,
    required this.value,
  });

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Icon(icon, color: color, size: 20),
        const SizedBox(width: AppSpacing.sm),
        Text('$label: ', style: AppTypography.body),
        Text(value, style: AppTypography.body.copyWith(fontWeight: FontWeight.bold)),
      ],
    );
  }
}
```

## lib/screens/add_note_screen.dart

```dart
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:image_picker/image_picker.dart';
import 'package:paperstudy/providers/note_providers.dart';
import 'package:paperstudy/providers/subject_providers.dart';
import 'package:paperstudy/services/note_service.dart';
import 'package:paperstudy/services/ocr_service.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';

class AddNoteScreen extends ConsumerStatefulWidget {
  const AddNoteScreen({Key? key}) : super(key: key);

  @override
  ConsumerState<AddNoteScreen> createState() => _AddNoteScreenState();
}

class _AddNoteScreenState extends ConsumerState<AddNoteScreen> {
  final _sourceController = TextEditingController();
  final _pageController = TextEditingController();
  final _topicController = TextEditingController();
  final _tagsController = TextEditingController();
  
  File? _photo;
  String? _detectedPageNumber;
  bool _isProcessing = false;

  @override
  Widget build(BuildContext context) {
    final subjectsAsync = ref.watch(subjectsProvider);
    final selectedSubject = ref.watch(selectedSubjectProvider);

    return Scaffold(
      appBar: AppBar(
        title: const Text('Add Note'),
        actions: [
          TextButton(
            onPressed: _saveNote,
            child: const Text('SAVE', style: TextStyle(color: AppColors.primary)),
          ),
        ],
      ),
      body: SingleChildScrollView(
        padding: const EdgeInsets.all(AppSpacing.md),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            // Subject selector
            subjectsAsync.when(
              data: (subjects) => DropdownButtonFormField<String>(
                value: selectedSubject?.id,
                decoration: const InputDecoration(
                  labelText: 'Subject',
                  prefixIcon: Icon(Icons.folder),
                ),
                items: subjects.map((s) {
                  return DropdownMenuItem(
                    value: s.id,
                    child: Row(
                      children: [
                        CircleAvatar(
                          radius: 8,
                          backgroundColor: Color(s.color),
                        ),
                        const SizedBox(width: 8),
                        Text(s.name),
                      ],
                    ),
                  );
                }).toList(),
                onChanged: (value) {
                  final subject = subjects.firstWhere((s) => s.id == value);
                  ref.read(selectedSubjectProvider.notifier).state = subject;
                },
              ),
              loading: () => const CircularProgressIndicator(),
              error: (_, __) => const Text('Error loading subjects'),
            ),

            const SizedBox(height: AppSpacing.lg),

            // Photo capture
            GestureDetector(
              onTap: _takePhoto,
              child: Container(
                height: 200,
                decoration: BoxDecoration(
                  color: AppColors.background,
                  borderRadius: BorderRadius.circular(16),
                  border: Border.all(color: AppColors.divider),
                ),
                child: _photo != null
                    ? ClipRRect(
                        borderRadius: BorderRadius.circular(16),
                        child: Image.file(_photo!, fit: BoxFit.cover, width: double.infinity),
                      )
                    : Column(
                        mainAxisAlignment: MainAxisAlignment.center,
                        children: const [
                          Icon(Icons.camera_alt, size: 48, color: AppColors.textSecondary),
                          SizedBox(height: AppSpacing.sm),
                          Text('Tap to add photo', style: AppTypography.caption),
                        ],
                      ),
              ),
            ),

            const SizedBox(height: AppSpacing.lg),

            // Source name
            TextField(
              controller: _sourceController,
              decoration: const InputDecoration(
                labelText: 'Notebook/Source Name',
                hintText: 'e.g., Biology Notebook 1',
                prefixIcon: Icon(Icons.book),
              ),
            ),

            const SizedBox(height: AppSpacing.md),

            // Page number
            Row(
              children: [
                Expanded(
                  child: TextField(
                    controller: _pageController,
                    decoration: InputDecoration(
                      labelText: 'Page Number',
                      hintText: '42',
                      prefixIcon: const Icon(Icons.format_list_numbered),
                      suffixIcon: _detectedPageNumber != null
                          ? Chip(
                              label: Text('Auto: $_detectedPageNumber'),
                              backgroundColor: AppColors.success.withOpacity(0.2),
                            )
                          : null,
                    ),
                    keyboardType: TextInputType.number,
                  ),
                ),
                if (_isProcessing)
                  const Padding(
                    padding: EdgeInsets.only(left: AppSpacing.sm),
                    child: SizedBox(
                      width: 24,
                      height: 24,
                      child: CircularProgressIndicator(strokeWidth: 2),
                    ),
                  ),
              ],
            ),

            const SizedBox(height: AppSpacing.md),

            // Topic/Section
            TextField(
              controller: _topicController,
              decoration: const InputDecoration(
                labelText: 'Topic (optional)',
                hintText: 'e.g., Mitosis Diagram',
                prefixIcon: Icon(Icons.label),
              ),
            ),

            const SizedBox(height: AppSpacing.md),

            // Tags
            TextField(
              controller: _tagsController,
              decoration: const InputDecoration(
                labelText: 'Tags (comma separated)',
                hintText: 'cell, division, biology',
                prefixIcon: Icon(Icons.tag),
              ),
            ),

            const SizedBox(height: AppSpacing.xl),

            // Quick add button
            SizedBox(
              width: double.infinity,
              height: 56,
              child: ElevatedButton.icon(
                onPressed: _saveNote,
                icon: const Icon(Icons.add),
                label: const Text('ADD NOTE', style: AppTypography.button),
              ),
            ),

            const SizedBox(height: AppSpacing.md),

            // Add another option
            Center(
              child: TextButton(
                onPressed: () {
                  _saveNote();
                  _clearForm();
                },
                child: const Text('Save & Add Another'),
              ),
            ),
          ],
        ),
      ),
    );
  }

  Future<void> _takePhoto() async {
    final picker = ImagePicker();
    final picked = await picker.pickImage(source: ImageSource.camera);
    if (picked != null) {
      setState(() {
        _photo = File(picked.path);
        _isProcessing = true;
      });

      // Auto-detect page number
      final ocrService = ref.read(ocrServiceProvider);
      final pageNumber = await ocrService.extractPageNumber(_photo!);
      
      setState(() {
        _detectedPageNumber = pageNumber;
        if (pageNumber != null) {
          _pageController.text = pageNumber;
        }
        _isProcessing = false;
      });
    }
  }

  Future<void> _saveNote() async {
    final subject = ref.read(selectedSubjectProvider);
    if (subject == null) {
      ScaffoldMessenger.of(context).showSnackBar(
        const SnackBar(content: Text('Please select a subject')),
      );
      return;
    }

    if (_sourceController.text.isEmpty || _pageController.text.isEmpty) {
      ScaffoldMessenger.of(context).showSnackBar(
        const SnackBar(content: Text('Please fill in source and page number')),
      );
      return;
    }

    setState(() => _isProcessing = true);

    try {
      final tags = _tagsController.text.isEmpty
          ? null
          : _tagsController.text.split(',').map((t) => t.trim()).toList();

      await ref.read(noteServiceProvider).createNote(
        subjectId: subject.id,
        sourceName: _sourceController.text,
        pageNumber: _pageController.text,
        sectionLabel: _topicController.text.isEmpty ? null : _topicController.text,
        tags: tags,
        photo: _photo,
      );

      if (mounted) {
        Navigator.pop(context);
        ScaffoldMessenger.of(context).showSnackBar(
          const SnackBar(content: Text('Note added successfully!')),
        );
      }
    } catch (e) {
      if (mounted) {
        ScaffoldMessenger.of(context).showSnackBar(
          SnackBar(content: Text('Error: $e')),
        );
      }
    } finally {
      setState(() => _isProcessing = false);
    }
  }

  void _clearForm() {
    _sourceController.clear();
    _pageController.clear();
    _topicController.clear();
    _tagsController.clear();
    setState(() {
      _photo = null;
      _detectedPageNumber = null;
    });
  }

  @override
  void dispose() {
    _sourceController.dispose();
    _pageController.dispose();
    _topicController.dispose();
    _tagsController.dispose();
    super.dispose();
  }
}
```

## lib/screens/library_screen.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/providers/note_providers.dart';
import 'package:paperstudy/providers/subject_providers.dart';
import 'package:paperstudy/screens/add_note_screen.dart';
import 'package:paperstudy/screens/subject_detail_screen.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';
import 'package:paperstudy/widgets/note_list_item.dart';

class LibraryScreen extends ConsumerWidget {
  const LibraryScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final subjectsAsync = ref.watch(subjectsProvider);
    final searchQuery = ref.watch(noteSearchProvider);

    return Scaffold(
      appBar: AppBar(
        title: const Text('Library'),
        actions: [
          IconButton(
            icon: const Icon(Icons.search),
            onPressed: () {
              showSearch(
                context: context,
                delegate: NoteSearchDelegate(ref),
              );
            },
          ),
          IconButton(
            icon: const Icon(Icons.sort),
            onPressed: () {},
          ),
        ],
      ),
      body: subjectsAsync.when(
        data: (subjects) {
          if (subjects.isEmpty) {
            return _buildEmptyState(context);
          }

          return ListView.builder(
            padding: const EdgeInsets.all(AppSpacing.md),
            itemCount: subjects.length,
            itemBuilder: (context, index) {
              final subject = subjects[index];
              return _SubjectListItem(subject: subject);
            },
          );
        },
        loading: () => const Center(child: CircularProgressIndicator()),
        error: (_, __) => const Center(child: Text('Error loading library')),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => Navigator.push(
          context,
          MaterialPageRoute(builder: (_) => const AddNoteScreen()),
        ),
        child: const Icon(Icons.add),
      ),
    );
  }

  Widget _buildEmptyState(BuildContext context) {
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Icon(
            Icons.folder_open,
            size: 80,
            color: AppColors.textSecondary.withOpacity(0.5),
          ),
          const SizedBox(height: AppSpacing.md),
          Text(
            'No subjects yet',
            style: AppTypography.headline,
          ),
          const SizedBox(height: AppSpacing.sm),
          Text(
            'Create a subject to start adding notes',
            style: AppTypography.caption,
          ),
          const SizedBox(height: AppSpacing.lg),
          ElevatedButton.icon(
            onPressed: () => _showCreateSubjectDialog(context),
            icon: const Icon(Icons.add),
            label: const Text('Create Subject'),
          ),
        ],
      ),
    );
  }

  void _showCreateSubjectDialog(BuildContext context) {
    // Implementation for creating subject
  }
}

class _SubjectListItem extends ConsumerWidget {
  final dynamic subject;

  const _SubjectListItem({required this.subject});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    return Card(
      margin: const EdgeInsets.only(bottom: AppSpacing.sm),
      child: ListTile(
        leading: CircleAvatar(
          backgroundColor: Color(subject.color),
          child: Text(
            subject.name.substring(0, 1),
            style: const TextStyle(color: Colors.white),
          ),
        ),
        title: Text(subject.name),
        subtitle: Text(
          subject.description ?? 'No description',
          maxLines: 1,
          overflow: TextOverflow.ellipsis,
        ),
        trailing: const Icon(Icons.chevron_right),
        onTap: () {
          ref.read(selectedSubjectProvider.notifier).state = subject;
          Navigator.push(
            context,
            MaterialPageRoute(
              builder: (_) => SubjectDetailScreen(subjectId: subject.id),
            ),
          );
        },
      ),
    );
  }
}

class NoteSearchDelegate extends SearchDelegate {
  final WidgetRef ref;

  NoteSearchDelegate(this.ref);

  @override
  List<Widget>? buildActions(BuildContext context) => [
        IconButton(
          icon: const Icon(Icons.clear),
          onPressed: () => query = '',
        ),
      ];

  @override
  Widget? buildLeading(BuildContext context) => IconButton(
        icon: const Icon(Icons.arrow_back),
        onPressed: () => close(context, null),
      );

  @override
  Widget buildResults(BuildContext context) {
    return _buildSearchResults();
  }

  @override
  Widget buildSuggestions(BuildContext context) {
    if (query.isEmpty) return const Center(child: Text('Type to search notes'));
    return _buildSearchResults();
  }

  Widget _buildSearchResults() {
    final results = ref.watch(noteSearchProvider(query));
    return results.when(
      data: (notes) => ListView.builder(
        itemCount: notes.length,
        itemBuilder: (context, index) => NoteListItem(note: notes[index]),
      ),
      loading: () => const Center(child: CircularProgressIndicator()),
      error: (_, __) => const Center(child: Text('Search error')),
    );
  }
}
```

## lib/screens/stats_screen.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/providers/session_providers.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';
import 'package:paperstudy/widgets/heatmap_calendar.dart';
import 'package:fl_chart/fl_chart.dart';

class StatsScreen extends ConsumerWidget {
  const StatsScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final weeklyTimeAsync = ref.watch(weeklyStudyTimeProvider);
    final streakAsync = ref.watch(studyStreakProvider);

    return Scaffold(
      appBar: AppBar(
        title: const Text('Statistics'),
      ),
      body: SingleChildScrollView(
        padding: const EdgeInsets.all(AppSpacing.md),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            // Header stats
            Row(
              children: [
                Expanded(
                  child: _BigStatCard(
                    title: 'Current Streak',
                    value: streakAsync.when(
                      data: (s) => '$s days',
                      loading: () => '-',
                      error: (_, __) => '-',
                    ),
                    icon: Icons.local_fire_department,
                    color: AppColors.warning,
                  ),
                ),
                const SizedBox(width: AppSpacing.md),
                Expanded(
                  child: _BigStatCard(
                    title: 'Total Reviews',
                    value: '1,247',
                    icon: Icons.check_circle,
                    color: AppColors.success,
                  ),
                ),
              ],
            ),

            const SizedBox(height: AppSpacing.lg),

            // Weekly study time chart
            Text('Study Time This Week', style: AppTypography.headline),
            const SizedBox(height: AppSpacing.md),
            SizedBox(
              height: 200,
              child: weeklyTimeAsync.when(
                data: (data) => _buildBarChart(data),
                loading: () => const Center(child: CircularProgressIndicator()),
                error: (_, __) => const Text('Error loading data'),
              ),
            ),

            const SizedBox(height: AppSpacing.lg),

            // Retention rate
            Text('Retention Rate', style: AppTypography.headline),
            const SizedBox(height: AppSpacing.md),
            _buildRetentionCard(),

            const SizedBox(height: AppSpacing.lg),

            // Heatmap
            Text('Activity', style: AppTypography.headline),
            const SizedBox(height: AppSpacing.md),
            const HeatmapCalendar(daysToShow: 365),

            const SizedBox(height: AppSpacing.lg),

            // Subject breakdown
            Text('By Subject', style: AppTypography.headline),
            const SizedBox(height: AppSpacing.md),
            _buildSubjectBreakdown(),
          ],
        ),
      ),
    );
  }

  Widget _buildBarChart(Map<int, int> data) {
    final spots = data.entries.map((e) {
      return BarChartGroupData(
        x: e.key,
        barRods: [
          BarChartRodData(
            toY: e.value.toDouble(),
            color: AppColors.primary,
            width: 16,
            borderRadius: BorderRadius.circular(4),
          ),
        ],
      );
    }).toList();

    return BarChart(
      BarChartData(
        barGroups: spots,
        gridData: FlGridData(show: false),
        titlesData: FlTitlesData(
          bottomTitles: AxisTitles(
            sideTitles: SideTitles(
              showTitles: true,
              getTitlesWidget: (value, meta) {
                const days = ['M', 'T', 'W', 'T', 'F', 'S', 'S'];
                return Text(days[value.toInt()]);
              },
            ),
          ),
          leftTitles: AxisTitles(
            sideTitles: SideTitles(showTitles: true, reservedSize: 40),
          ),
          topTitles: AxisTitles(sideTitles: SideTitles(showTitles: false)),
          rightTitles: AxisTitles(sideTitles: SideTitles(showTitles: false)),
        ),
        borderData: FlBorderData(show: false),
      ),
    );
  }

  Widget _buildRetentionCard() {
    return Card(
      child: Padding(
        padding: const EdgeInsets.all(AppSpacing.lg),
        child: Column(
          children: [
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: [
                _RetentionStat('87%', 'Overall', AppColors.primary),
                _RetentionStat('92%', 'Biology', AppColors.success),
                _RetentionStat('78%', 'History', AppColors.warning),
              ],
            ),
            const SizedBox(height: AppSpacing.md),
            const LinearProgressIndicator(
              value: 0.87,
              backgroundColor: AppColors.divider,
              valueColor: AlwaysStoppedAnimation<Color>(AppColors.primary),
              minHeight: 8,
              borderRadius: BorderRadius.all(Radius.circular(4)),
            ),
          ],
        ),
      ),
    );
  }

  Widget _buildSubjectBreakdown() {
    final subjects = [
      _SubjectStat('Biology', 0.92, AppColors.success),
      _SubjectStat('History', 0.78, AppColors.warning),
      _SubjectStat('Chemistry', 0.85, AppColors.primary),
    ];

    return Column(
      children: subjects.map((s) => _SubjectBar(subject: s)).toList(),
    );
  }
}

class _BigStatCard extends StatelessWidget {
  final String title;
  final String value;
  final IconData icon;
  final Color color;

  const _BigStatCard({
    required this.title,
    required this.value,
    required this.icon,
    required this.color,
  });

  @override
  Widget build(BuildContext context) {
    return Card(
      child: Padding(
        padding: const EdgeInsets.all(AppSpacing.lg),
        child: Column(
          children: [
            Icon(icon, color: color, size: 32),
            const SizedBox(height: AppSpacing.sm),
            Text(value, style: AppTypography.headline.copyWith(fontSize: 24)),
            Text(title, style: AppTypography.caption),
          ],
        ),
      ),
    );
  }
}

class _RetentionStat extends StatelessWidget {
  final String value;
  final String label;
  final Color color;

  const _RetentionStat(this.value, this.label, this.color);

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text(
          value,
          style: AppTypography.headline.copyWith(color: color, fontSize: 28),
        ),
        Text(label, style: AppTypography.caption),
      ],
    );
  }
}

class _SubjectStat {
  final String name;
  final double rate;
  final Color color;

  _SubjectStat(this.name, this.rate, this.color);
}

class _SubjectBar extends StatelessWidget {
  final _SubjectStat subject;

  const _SubjectBar({required this.subject});

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.only(bottom: AppSpacing.sm),
      child: Row(
        children: [
          SizedBox(
            width: 100,
            child: Text(subject.name, style: AppTypography.body),
          ),
          Expanded(
            child: LinearProgressIndicator(
              value: subject.rate,
              backgroundColor: AppColors.divider,
              valueColor: AlwaysStoppedAnimation<Color>(subject.color),
              minHeight: 12,
              borderRadius: BorderRadius.circular(6),
            ),
          ),
          SizedBox(
            width: 50,
            child: Text(
              '${(subject.rate * 100).round()}%',
              style: AppTypography.body.copyWith(fontWeight: FontWeight.bold),
              textAlign: TextAlign.right,
            ),
          ),
        ],
      ),
    );
  }
}
```

## lib/screens/settings_screen.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/models/user_settings.dart';
import 'package:paperstudy/providers/settings_providers.dart';
import 'package:paperstudy/theme/app_colors.dart';

class SettingsScreen extends ConsumerWidget {
  const SettingsScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, ref) {
    final settings = ref.watch(userSettingsProvider);

    return Scaffold(
      appBar: AppBar(
        title: const Text('Settings'),
      ),
      body: ListView(
        children: [
          _SectionHeader('Study Preferences'),
          _SettingsTile(
            icon: Icons.timer,
            title: 'Daily Review Limit',
            subtitle: '${settings.dailyReviewLimit} cards',
            onTap: () => _showNumberPicker(context, ref, 'Daily Review Limit',
                settings.dailyReviewLimit, (v) {
              ref.read(userSettingsProvider.notifier).updateSettings(
                    settings.copyWith(dailyReviewLimit: v),
                  );
            }),
          ),
          _SettingsTile(
            icon: Icons.track_changes,
            title: 'Target Retention',
            subtitle: '${(settings.requestRetention * 100).round()}%',
            onTap: () {},
          ),
          _SettingsTile(
            icon: Icons.access_time,
            title: 'Daily Study Goal',
            subtitle: '${settings.dailyStudyGoalMinutes} minutes',
            onTap: () {},
          ),

          _SectionHeader('Notifications'),
          SwitchListTile(
            secondary: const Icon(Icons.notifications),
            title: const Text('Enable Reminders'),
            value: settings.enableNotifications,
            onChanged: (v) => ref.read(userSettingsProvider.notifier).updateSettings(
                  settings.copyWith(enableNotifications: v),
                ),
          ),
          _SettingsTile(
            icon: Icons.schedule,
            title: 'Reminder Time',
            subtitle: settings.reminderTime,
            onTap: () {},
          ),

          _SectionHeader('Appearance'),
          _SettingsTile(
            icon: Icons.dark_mode,
            title: 'Theme',
            subtitle: settings.themeMode.name,
            onTap: () => _showThemePicker(context, ref, settings),
          ),
          SwitchListTile(
            secondary: const Icon(Icons.font_download),
            title: const Text('Dyslexia-Friendly Font'),
            subtitle: const Text('Use OpenDyslexic font'),
            value: settings.useDyslexiaFont,
            onChanged: (v) => ref.read(userSettingsProvider.notifier).updateSettings(
                  settings.copyWith(useDyslexiaFont: v),
                ),
          ),

          _SectionHeader('Data & Backup'),
          _SettingsTile(
            icon: Icons.backup,
            title: 'Export Data',
            subtitle: 'JSON backup file',
            onTap: () {},
          ),
          _SettingsTile(
            icon: Icons.file_upload,
            title: 'Import Data',
            subtitle: 'Restore from backup',
            onTap: () {},
          ),
          _SettingsTile(
            icon: Icons.delete,
            title: 'Clear All Data',
            subtitle: 'Permanently delete everything',
            onTap: () => _showClearDataDialog(context),
            textColor: AppColors.error,
          ),

          const SizedBox(height: 48),
          Center(
            child: Text(
              'PaperStudy v1.0.0',
              style: TextStyle(color: AppColors.textSecondary),
            ),
          ),
          const SizedBox(height: 24),
        ],
      ),
    );
  }

  void _showNumberPicker(BuildContext context, WidgetRef ref, String title,
      int current, Function(int) onChanged) {
    // Implementation
  }

  void _showThemePicker(BuildContext context, WidgetRef ref, UserSettings settings) {
    showDialog(
      context: context,
      builder: (context) => AlertDialog(
        title: const Text('Choose Theme'),
        content: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            ListTile(
              title: const Text('System'),
              leading: const Icon(Icons.brightness_auto),
              onTap: () {
                ref.read(userSettingsProvider.notifier).updateSettings(
                      settings.copyWith(themeMode: ThemeMode.system),
                    );
                Navigator.pop(context);
              },
            ),
            ListTile(
              title: const Text('Light'),
              leading: const Icon(Icons.brightness_7),
              onTap: () {
                ref.read(userSettingsProvider.notifier).updateSettings(
                      settings.copyWith(themeMode: ThemeMode.light),
                    );
                Navigator.pop(context);
              },
            ),
            ListTile(
              title: const Text('Dark'),
              leading: const Icon(Icons.brightness_2),
              onTap: () {
                ref.read(userSettingsProvider.notifier).updateSettings(
                      settings.copyWith(themeMode: ThemeMode.dark),
                    );
                Navigator.pop(context);
              },
            ),
          ],
        ),
      ),
    );
  }

  void _showClearDataDialog(BuildContext context) {
    showDialog(
      context: context,
      builder: (context) => AlertDialog(
        title: const Text('Clear All Data?'),
        content: const Text('This will permanently delete all your notes, reviews, and settings. This action cannot be undone.'),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(context),
            child: const Text('CANCEL'),
          ),
          TextButton(
            onPressed: () {
              // Clear data
              Navigator.pop(context);
            },
            style: TextButton.styleFrom(foregroundColor: AppColors.error),
            child: const Text('DELETE'),
          ),
        ],
      ),
    );
  }
}

class _SectionHeader extends StatelessWidget {
  final String title;

  const _SectionHeader(this.title);

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.fromLTRB(16, 24, 16, 8),
      child: Text(
        title,
        style: TextStyle(
          color: AppColors.primary,
          fontWeight: FontWeight.w600,
          fontSize: 14,
        ),
      ),
    );
  }
}

class _SettingsTile extends StatelessWidget {
  final IconData icon;
  final String title;
  final String subtitle;
  final VoidCallback onTap;
  final Color? textColor;

  const _SettingsTile({
    required this.icon,
    required this.title,
    required this.subtitle,
    required this.onTap,
    this.textColor,
  });

  @override
  Widget build(BuildContext context) {
    return ListTile(
      leading: Icon(icon),
      title: Text(title),
      subtitle: Text(subtitle),
      trailing: const Icon(Icons.chevron_right),
      onTap: onTap,
      textColor: textColor,
    );
  }
}
```

## lib/screens/onboarding_screen.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/providers/settings_providers.dart';
import 'package:paperstudy/providers/subject_providers.dart';
import 'package:paperstudy/screens/home_screen.dart';
import 'package:paperstudy/services/subject_service.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';

class OnboardingScreen extends StatefulWidget {
  const OnboardingScreen({Key? key}) : super(key: key);

  @override
  State<OnboardingScreen> createState() => _OnboardingScreenState();
}

class _OnboardingScreenState extends State<OnboardingScreen> {
  int _currentPage = 0;
  final _pageController = PageController();

  final _pages = [
    _OnboardingPage(
      image: Icons.menu_book,
      title: 'Track your physical notes',
      description: 'Snap a photo, add page number, done. No need to type everything out.',
    ),
    _OnboardingPage(
      image: Icons.calendar_today,
      title: 'Spaced repetition scheduling',
      description: 'We intelligently schedule when to review each page for maximum retention.',
    ),
    _OnboardingPage(
      image: Icons.trending_up,
      title: 'Study smarter, not harder',
      description: 'Track time, retention, and streaks. Build habits that last.',
    ),
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Column(
          children: [
            Expanded(
              child: PageView.builder(
                controller: _pageController,
                onPageChanged: (index) => setState(() => _currentPage = index),
                itemCount: _pages.length,
                itemBuilder: (context, index) => _pages[index],
              ),
            ),

            // Page indicators
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: List.generate(
                _pages.length,
                (index) => Container(
                  width: 8,
                  height: 8,
                  margin: const EdgeInsets.symmetric(horizontal: 4),
                  decoration: BoxDecoration(
                    shape: BoxShape.circle,
                    color: index == _currentPage
                        ? AppColors.primary
                        : AppColors.divider,
                  ),
                ),
              ),
            ),

            const SizedBox(height: AppSpacing.lg),

            // Navigation buttons
            Padding(
              padding: const EdgeInsets.all(AppSpacing.md),
              child: Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  TextButton(
                    onPressed: () => _skipOnboarding(),
                    child: const Text('SKIP'),
                  ),
                  ElevatedButton(
                    onPressed: _currentPage == _pages.length - 1
                        ? _completeOnboarding
                        : () => _pageController.nextPage(
                              duration: const Duration(milliseconds: 300),
                              curve: Curves.easeInOut,
                            ),
                    style: ElevatedButton.styleFrom(
                      backgroundColor: AppColors.primary,
                      foregroundColor: Colors.white,
                      padding: const EdgeInsets.symmetric(
                        horizontal: 32,
                        vertical: 16,
                      ),
                    ),
                    child: Text(
                      _currentPage == _pages.length - 1 ? 'GET STARTED' : 'NEXT',
                      style: AppTypography.button,
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }

  void _skipOnboarding() {
    _pageController.jumpToPage(_pages.length - 1);
  }

  void _completeOnboarding() {
    // Navigate to create first subject
    Navigator.pushReplacement(
      context,
      MaterialPageRoute(builder: (_) => const _CreateFirstSubjectScreen()),
    );
  }

  @override
  void dispose() {
    _pageController.dispose();
    super.dispose();
  }
}

class _OnboardingPage extends StatelessWidget {
  final IconData image;
  final String title;
  final String description;

  const _OnboardingPage({
    required this.image,
    required this.title,
    required this.description,
  });

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(AppSpacing.xl),
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Icon(
            image,
            size: 120,
            color: AppColors.primary,
          ),
          const SizedBox(height: AppSpacing.xl),
          Text(
            title,
            style: AppTypography.displayLarge,
            textAlign: TextAlign.center,
          ),
          const SizedBox(height: AppSpacing.md),
          Text(
            description,
            style: AppTypography.body.copyWith(color: AppColors.textSecondary),
            textAlign: TextAlign.center,
          ),
        ],
      ),
    );
  }
}

class _CreateFirstSubjectScreen extends ConsumerStatefulWidget {
  const _CreateFirstSubjectScreen({Key? key}) : super(key: key);

  @override
  ConsumerState<_CreateFirstSubjectScreen> createState() => _CreateFirstSubjectScreenState();
}

class _CreateFirstSubjectScreenState extends ConsumerState<_CreateFirstSubjectScreen> {
  final _nameController = TextEditingController();
  int _selectedColor = 0xFF6366F1;

  final _suggestions = [
    'Biology',
    'History',
    'Chemistry',
    'Physics',
    'Mathematics',
    'Spanish',
    'MCAT',
    'Law',
  ];

  @override
  Widget build(BuildContext context) {
    final colors = ref.watch(subjectColorsProvider);

    return Scaffold(
      appBar: AppBar(
        title: const Text('Create Your First Subject'),
        automaticallyImplyLeading: false,
      ),
      body: SingleChildScrollView(
        padding: const EdgeInsets.all(AppSpacing.md),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Text(
              'What are you studying?',
              style: AppTypography.headline,
            ),
            const SizedBox(height: AppSpacing.sm),
            Text(
              'You can add more subjects later',
              style: AppTypography.caption,
            ),
            const SizedBox(height: AppSpacing.lg),

            // Suggestions
            Wrap(
              spacing: AppSpacing.sm,
              runSpacing: AppSpacing.sm,
              children: _suggestions.map((s) {
                return ActionChip(
                  label: Text(s),
                  onPressed: () => _nameController.text = s,
                );
              }).toList(),
            ),

            const SizedBox(height: AppSpacing.lg),

            // Name input
            TextField(
              controller: _nameController,
              decoration: const InputDecoration(
                labelText: 'Subject Name',
                hintText: 'e.g., Biology',
                prefixIcon: Icon(Icons.folder),
              ),
            ),

            const SizedBox(height: AppSpacing.lg),

            // Color picker
            Text('Choose a color', style: AppTypography.body),
            const SizedBox(height: AppSpacing.sm),
            Wrap(
              spacing: AppSpacing.sm,
              runSpacing: AppSpacing.sm,
              children: colors.map((color) {
                final isSelected = color == _selectedColor;
                return GestureDetector(
                  onTap: () => setState(() => _selectedColor = color),
                  child: Container(
                    width: 48,
                    height: 48,
                    decoration: BoxDecoration(
                      color: Color(color),
                      shape: BoxShape.circle,
                      border: isSelected
                          ? Border.all(color: Colors.white, width: 3)
                          : null,
                      boxShadow: isSelected
                          ? [
                              BoxShadow(
                                color: Color(color).withOpacity(0.4),
                                blurRadius: 8,
                                spreadRadius: 2,
                              ),
                            ]
                          : null,
                    ),
                    child: isSelected
                        ? const Icon(Icons.check, color: Colors.white)
                        : null,
                  ),
                );
              }).toList(),
            ),

            const SizedBox(height: AppSpacing.xl),

            SizedBox(
              width: double.infinity,
              height: 56,
              child: ElevatedButton(
                onPressed: _createSubject,
                style: ElevatedButton.styleFrom(
                  backgroundColor: AppColors.primary,
                  foregroundColor: Colors.white,
                ),
                child: const Text('CREATE SUBJECT', style: AppTypography.button),
              ),
            ),
          ],
        ),
      ),
    );
  }

  Future<void> _createSubject() async {
    if (_nameController.text.isEmpty) return;

    final subject = await ref.read(subjectServiceProvider).createSubject(
      name: _nameController.text,
      color: _selectedColor,
    );

    ref.read(selectedSubjectProvider.notifier).state = subject;
    await ref.read(userSettingsProvider.notifier).completeOnboarding();

    if (mounted) {
      Navigator.pushReplacement(
        context,
        MaterialPageRoute(builder: (_) => const HomeScreen()),
      );
    }
  }

  @override
  void dispose() {
    _nameController.dispose();
    super.dispose();
  }
}
```

## lib/widgets/review_card.dart

```dart
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:paperstudy/models/physical_note.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';

class ReviewCard extends StatelessWidget {
  final PhysicalNote note;
  final bool answerRevealed;
  final VoidCallback onShowAnswer;

  const ReviewCard({
    Key? key,
    required this.note,
    required this.answerRevealed,
    required this.onShowAnswer,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Card(
      elevation: 2,
      margin: const EdgeInsets.all(AppSpacing.md),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          // Photo
          if (note.photoPath != null)
            GestureDetector(
              onTap: () => _showFullImage(context),
              child: AspectRatio(
                aspectRatio: 4 / 3,
                child: ClipRRect(
                  borderRadius: const BorderRadius.vertical(
                    top: Radius.circular(16),
                  ),
                  child: Image.file(
                    File(note.photoPath!),
                    fit: BoxFit.cover,
                  ),
                ),
              ),
            ),

          // Info section
          Padding(
            padding: const EdgeInsets.all(AppSpacing.md),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                // Subject chip
                Container(
                  padding: const EdgeInsets.symmetric(
                    horizontal: AppSpacing.sm,
                    vertical: 4,
                  ),
                  decoration: BoxDecoration(
                    color: AppColors.primaryLight,
                    borderRadius: BorderRadius.circular(8),
                  ),
                  child: Text(
                    'Biology', // TODO: Get subject name
                    style: TextStyle(
                      color: AppColors.primary,
                      fontSize: 12,
                      fontWeight: FontWeight.w600,
                    ),
                  ),
                ),

                const SizedBox(height: AppSpacing.sm),

                // Source and page
                Row(
                  children: [
                    const Icon(Icons.book, size: 16, color: AppColors.textSecondary),
                    const SizedBox(width: 4),
                    Text(
                      note.sourceName,
                      style: AppTypography.body,
                    ),
                  ],
                ),

                const SizedBox(height: AppSpacing.xs),

                Row(
                  children: [
                    const Icon(Icons.description, size: 16, color: AppColors.textSecondary),
                    const SizedBox(width: 4),
                    Text(
                      'Page ${note.pageNumber}',
                      style: AppTypography.body,
                    ),
                  ],
                ),

                if (note.sectionLabel != null) ...[
                  const SizedBox(height: AppSpacing.xs),
                  Text(
                    note.sectionLabel!,
                    style: AppTypography.caption,
                  ),
                ],

                if (note.tags != null && note.tags!.isNotEmpty) ...[
                  const SizedBox(height: AppSpacing.sm),
                  Wrap(
                    spacing: 4,
                    runSpacing: 4,
                    children: note.tags!.map((tag) {
                      return Chip(
                        label: Text(tag, style: const TextStyle(fontSize: 12)),
                        padding: EdgeInsets.zero,
                        materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
                      );
                    }).toList(),
                  ),
                ],

                const SizedBox(height: AppSpacing.lg),

                // Instruction text
                if (!answerRevealed)
                  Container(
                    padding: const EdgeInsets.all(AppSpacing.md),
                    decoration: BoxDecoration(
                      color: AppColors.background,
                      borderRadius: BorderRadius.circular(12),
                    ),
                    child: Row(
                      children: [
                        const Icon(Icons.info, color: AppColors.primary),
                        const SizedBox(width: AppSpacing.sm),
                        Expanded(
                          child: Text(
                            'Study this page in your notebook, then tap "Show Answer" to rate your recall',
                            style: AppTypography.body.copyWith(fontSize: 14),
                          ),
                        ),
                      ],
                    ),
                  ),
              ],
            ),
          ),
        ],
      ),
    );
  }

  void _showFullImage(BuildContext context) {
    showDialog(
      context: context,
      builder: (context) => Dialog(
        child: InteractiveViewer(
          child: Image.file(File(note.photoPath!)),
        ),
      ),
    );
  }
}
```

## lib/widgets/rating_buttons.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';

class RatingButtons extends StatelessWidget {
  final Function(int rating) onRate;

  const RatingButtons({Key? key, required this.onRate}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(AppSpacing.md),
      child: Column(
        children: [
          Text(
            'How well did you recall?',
            style: AppTypography.body.copyWith(fontWeight: FontWeight.w600),
          ),
          const SizedBox(height: AppSpacing.md),
          Row(
            children: [
              Expanded(
                child: _RatingButton(
                  label: 'AGAIN',
                  sublabel: '< 1 min',
                  color: AppColors.again,
                  onPressed: () {
                    HapticFeedback.heavyImpact();
                    onRate(1);
                  },
                ),
              ),
              const SizedBox(width: AppSpacing.sm),
              Expanded(
                child: _RatingButton(
                  label: 'HARD',
                  sublabel: '< 10 min',
                  color: AppColors.hard,
                  onPressed: () {
                    HapticFeedback.mediumImpact();
                    onRate(2);
                  },
                ),
              ),
            ],
          ),
          const SizedBox(height: AppSpacing.sm),
          Row(
            children: [
              Expanded(
                child: _RatingButton(
                  label: 'GOOD',
                  sublabel: '3 days',
                  color: AppColors.good,
                  onPressed: () {
                    HapticFeedback.lightImpact();
                    onRate(3);
                  },
                ),
              ),
              const SizedBox(width: AppSpacing.sm),
              Expanded(
                child: _RatingButton(
                  label: 'EASY',
                  sublabel: '5 days',
                  color: AppColors.easy,
                  onPressed: () {
                    HapticFeedback.lightImpact();
                    onRate(4);
                  },
                ),
              ),
            ],
          ),
          const SizedBox(height: AppSpacing.md),
          // Secondary actions
          Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              TextButton.icon(
                onPressed: () {},
                icon: const Icon(Icons.edit, size: 16),
                label: const Text('Needs Rewriting'),
              ),
              const SizedBox(width: AppSpacing.md),
              TextButton.icon(
                onPressed: () {},
                icon: const Icon(Icons.skip_next, size: 16),
                label: const Text('Skip'),
              ),
            ],
          ),
        ],
      ),
    );
  }
}

class _RatingButton extends StatelessWidget {
  final String label;
  final String sublabel;
  final Color color;
  final VoidCallback onPressed;

  const _RatingButton({
    required this.label,
    required this.sublabel,
    required this.color,
    required this.onPressed,
  });

  @override
  Widget build(BuildContext context) {
    return Material(
      color: color,
      borderRadius: BorderRadius.circular(12),
      child: InkWell(
        onTap: onPressed,
        borderRadius: BorderRadius.circular(12),
        child: Container(
          height: 72,
          padding: const EdgeInsets.all(AppSpacing.sm),
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Text(
                label,
                style: AppTypography.button.copyWith(
                  fontSize: 16,
                  fontWeight: FontWeight.bold,
                ),
              ),
              const SizedBox(height: 2),
              Text(
                sublabel,
                style: const TextStyle(
                  color: Colors.white70,
                  fontSize: 12,
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}
```

## lib/widgets/quick_add_fab.dart

```dart
import 'package:flutter/material.dart';
import 'package:paperstudy/screens/add_note_screen.dart';
import 'package:paperstudy/theme/app_colors.dart';

class QuickAddFAB extends StatelessWidget {
  const QuickAddFAB({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return FloatingActionButton.extended(
      onPressed: () => Navigator.push(
        context,
        MaterialPageRoute(builder: (_) => const AddNoteScreen()),
      ),
      backgroundColor: AppColors.primary,
      foregroundColor: Colors.white,
      icon: const Icon(Icons.add),
      label: const Text('Add Note'),
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(16),
      ),
    );
  }
}
```

## lib/widgets/heatmap_calendar.dart

```dart
import 'package:flutter/material.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';

class HeatmapCalendar extends StatelessWidget {
  final int daysToShow;

  const HeatmapCalendar({
    Key? key,
    this.daysToShow = 28,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    // Generate dummy data for demo
    final now = DateTime.now();
    final cells = <Widget>[];

    for (int i = daysToShow - 1; i >= 0; i--) {
      final date = now.subtract(Duration(days: i));
      final intensity = _getIntensity(date);
      cells.add(_DayCell(
        date: date,
        intensity: intensity,
      ));
    }

    return Container(
      padding: const EdgeInsets.all(AppSpacing.md),
      decoration: BoxDecoration(
        color: AppColors.surface,
        borderRadius: BorderRadius.circular(16),
        border: Border.all(color: AppColors.divider),
      ),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          // Month labels
          Row(
            children: [
              Text(
                _getMonthLabel(now.subtract(Duration(days: daysToShow))),
                style: const TextStyle(fontSize: 12, color: AppColors.textSecondary),
              ),
            ],
          ),
          const SizedBox(height: AppSpacing.sm),
          // Grid
          Wrap(
            spacing: 4,
            runSpacing: 4,
            children: cells,
          ),
          const SizedBox(height: AppSpacing.sm),
          // Legend
          Row(
            mainAxisAlignment: MainAxisAlignment.end,
            children: [
              const Text('Less', style: TextStyle(fontSize: 10, color: AppColors.textSecondary)),
              const SizedBox(width: 4),
              ...List.generate(5, (i) {
                return Container(
                  width: 12,
                  height: 12,
                  margin: const EdgeInsets.symmetric(horizontal: 1),
                  decoration: BoxDecoration(
                    color: _intensityColor(i / 4),
                    borderRadius: BorderRadius.circular(2),
                  ),
                );
              }),
              const SizedBox(width: 4),
              const Text('More', style: TextStyle(fontSize: 10, color: AppColors.textSecondary)),
            ],
          ),
        ],
      ),
    );
  }

  double _getIntensity(DateTime date) {
    // TODO: Replace with actual study data
    // Return random intensity for demo
    return (date.day % 5) / 4;
  }

  Color _intensityColor(double intensity) {
    if (intensity <= 0) return AppColors.divider.withOpacity(0.3);
    if (intensity < 0.25) return AppColors.primary.withOpacity(0.2);
    if (intensity < 0.5) return AppColors.primary.withOpacity(0.4);
    if (intensity < 0.75) return AppColors.primary.withOpacity(0.6);
    return AppColors.primary;
  }

  String _getMonthLabel(DateTime date) {
    const months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
    return months[date.month - 1];
  }
}

class _DayCell extends StatelessWidget {
  final DateTime date;
  final double intensity;

  const _DayCell({
    required this.date,
    required this.intensity,
  });

  @override
  Widget build(BuildContext context) {
    return Tooltip(
      message: '${date.month}/${date.day}: ${(intensity * 100).round()}% intensity',
      child: Container(
        width: 14,
        height: 14,
        decoration: BoxDecoration(
          color: _intensityColor(intensity),
          borderRadius: BorderRadius.circular(3),
        ),
      ),
    );
  }

  Color _intensityColor(double intensity) {
    if (intensity <= 0) return AppColors.divider.withOpacity(0.3);
    if (intensity < 0.25) return AppColors.primary.withOpacity(0.2);
    if (intensity < 0.5) return AppColors.primary.withOpacity(0.4);
    if (intensity < 0.75) return AppColors.primary.withOpacity(0.6);
    return AppColors.primary;
  }
}
```

## lib/widgets/progress_ring.dart

```dart
import 'package:flutter/material.dart';
import 'dart:math';

class ProgressRing extends StatelessWidget {
  final double progress;
  final double size;
  final Color color;
  final double strokeWidth;
  final Widget? child;

  const ProgressRing({
    Key? key,
    required this.progress,
    this.size = 80,
    this.color = Colors.blue,
    this.strokeWidth = 8,
    this.child,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      width: size,
      height: size,
      child: CustomPaint(
        painter: _RingPainter(
          progress: progress,
          color: color,
          strokeWidth: strokeWidth,
        ),
        child: Center(child: child),
      ),
    );
  }
}

class _RingPainter extends CustomPainter {
  final double progress;
  final Color color;
  final double strokeWidth;

  _RingPainter({
    required this.progress,
    required this.color,
    required this.strokeWidth,
  });

  @override
  void paint(Canvas canvas, Size size) {
    final center = Offset(size.width / 2, size.height / 2);
    final radius = (size.width - strokeWidth) / 2;

    // Background circle
    final bgPaint = Paint()
      ..color = color.withOpacity(0.2)
      ..style = PaintingStyle.stroke
      ..strokeWidth = strokeWidth
      ..strokeCap = StrokeCap.round;

    canvas.drawCircle(center, radius, bgPaint);

    // Progress arc
    final progressPaint = Paint()
      ..color = color
      ..style = PaintingStyle.stroke
      ..strokeWidth = strokeWidth
      ..strokeCap = StrokeCap.round;

    final sweepAngle = 2 * pi * progress;
    canvas.drawArc(
      Rect.fromCircle(center: center, radius: radius),
      -pi / 2,
      sweepAngle,
      false,
      progressPaint,
    );
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}
```

## lib/widgets/streak_flame.dart

```dart
import 'package:flutter/material.dart';
import 'package:paperstudy/theme/app_colors.dart';

class StreakFlame extends StatelessWidget {
  final int streak;
  final double size;

  const StreakFlame({
    Key? key,
    required this.streak,
    this.size = 24,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisSize: MainAxisSize.min,
      children: [
        Icon(
          Icons.local_fire_department,
          color: streak > 0 ? AppColors.warning : AppColors.textSecondary,
          size: size,
        ),
        const SizedBox(width: 4),
        Text(
          '$streak',
          style: TextStyle(
            fontWeight: FontWeight.bold,
            color: streak > 0 ? AppColors.warning : AppColors.textSecondary,
            fontSize: size * 0.6,
          ),
        ),
      ],
    );
  }
}
```

## lib/widgets/workload_chart.dart

```dart
import 'package:flutter/material.dart';
import 'package:fl_chart/fl_chart.dart';
import 'package:paperstudy/theme/app_colors.dart';

class WorkloadChart extends StatelessWidget {
  final List<int> dailyCounts;

  const WorkloadChart({
    Key? key,
    required this.dailyCounts,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final spots = dailyCounts.asMap().entries.map((e) {
      return BarChartGroupData(
        x: e.key,
        barRods: [
          BarChartRodData(
            toY: e.value.toDouble(),
            color: e.value > 50 ? AppColors.warning : AppColors.primary,
            width: 12,
            borderRadius: BorderRadius.circular(4),
          ),
        ],
      );
    }).toList();

    return SizedBox(
      height: 150,
      child: BarChart(
        BarChartData(
          barGroups: spots,
          gridData: FlGridData(show: false),
          titlesData: FlTitlesData(
            bottomTitles: AxisTitles(
              sideTitles: SideTitles(showTitles: false),
            ),
            leftTitles: AxisTitles(
              sideTitles: SideTitles(showTitles: false),
            ),
            topTitles: AxisTitles(
              sideTitles: SideTitles(showTitles: false),
            ),
            rightTitles: AxisTitles(
              sideTitles: SideTitles(showTitles: false),
            ),
          ),
          borderData: FlBorderData(show: false),
        ),
      ),
    );
  }
}
```

## lib/widgets/note_list_item.dart

```dart
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:paperstudy/models/physical_note.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';

class NoteListItem extends StatelessWidget {
  final PhysicalNote note;

  const NoteListItem({Key? key, required this.note}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Card(
      margin: const EdgeInsets.only(bottom: AppSpacing.sm),
      child: ListTile(
        leading: note.photoPath != null
            ? ClipRRect(
                borderRadius: BorderRadius.circular(8),
                child: Image.file(
                  File(note.photoPath!),
                  width: 48,
                  height: 48,
                  fit: BoxFit.cover,
                ),
              )
            : const CircleAvatar(
                child: Icon(Icons.note),
              ),
        title: Text('${note.sourceName} - Page ${note.pageNumber}'),
        subtitle: note.sectionLabel != null ? Text(note.sectionLabel!) : null,
        trailing: const Icon(Icons.chevron_right),
        onTap: () {
          // Navigate to note detail
        },
      ),
    );
  }
}
```

## lib/widgets/empty_state.dart

```dart
import 'package:flutter/material.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';

class EmptyState extends StatelessWidget {
  final IconData icon;
  final String title;
  final String? subtitle;
  final String? actionLabel;
  final VoidCallback? onAction;

  const EmptyState({
    Key? key,
    required this.icon,
    required this.title,
    this.subtitle,
    this.actionLabel,
    this.onAction,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Padding(
        padding: const EdgeInsets.all(AppSpacing.xl),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Icon(
              icon,
              size: 80,
              color: AppColors.textSecondary.withOpacity(0.5),
            ),
            const SizedBox(height: AppSpacing.md),
            Text(title, style: AppTypography.headline),
            if (subtitle != null) ...[
              const SizedBox(height: AppSpacing.sm),
              Text(
                subtitle!,
                style: AppTypography.caption,
                textAlign: TextAlign.center,
              ),
            ],
            if (actionLabel != null && onAction != null) ...[
              const SizedBox(height: AppSpacing.lg),
              ElevatedButton(
                onPressed: onAction,
                child: Text(actionLabel!),
              ),
            ],
          ],
        ),
      ),
    );
  }
}
```

## lib/screens/subject_detail_screen.dart

```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:paperstudy/providers/note_providers.dart';
import 'package:paperstudy/providers/subject_providers.dart';
import 'package:paperstudy/screens/add_note_screen.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';
import 'package:paperstudy/widgets/note_list_item.dart';

class SubjectDetailScreen extends ConsumerWidget {
  final String subjectId;

  const SubjectDetailScreen({
    Key? key,
    required this.subjectId,
  }) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final subjectAsync = ref.watch(subjectByIdProvider(subjectId));
    final notesAsync = ref.watch(notesBySubjectProvider(subjectId));

    return Scaffold(
      appBar: AppBar(
        title: subjectAsync.when(
          data: (subject) => Text(subject?.name ?? 'Subject'),
          loading: () => const Text('Loading...'),
          error: (_, __) => const Text('Error'),
        ),
        actions: [
          IconButton(
            icon: const Icon(Icons.edit),
            onPressed: () {},
          ),
          IconButton(
            icon: const Icon(Icons.more_vert),
            onPressed: () {},
          ),
        ],
      ),
      body: notesAsync.when(
        data: (notes) {
          if (notes.isEmpty) {
            return _buildEmptyState(context);
          }

          return ListView.builder(
            padding: const EdgeInsets.all(AppSpacing.md),
            itemCount: notes.length,
            itemBuilder: (context, index) {
              return NoteListItem(note: notes[index]);
            },
          );
        },
        loading: () => const Center(child: CircularProgressIndicator()),
        error: (_, __) => const Center(child: Text('Error loading notes')),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => Navigator.push(
          context,
          MaterialPageRoute(builder: (_) => const AddNoteScreen()),
        ),
        child: const Icon(Icons.add),
      ),
    );
  }

  Widget _buildEmptyState(BuildContext context) {
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Icon(
            Icons.note_add,
            size: 80,
            color: AppColors.textSecondary.withOpacity(0.5),
          ),
          const SizedBox(height: AppSpacing.md),
          Text('No notes yet', style: AppTypography.headline),
          const SizedBox(height: AppSpacing.sm),
          Text(
            'Add your first note to this subject',
            style: AppTypography.caption,
          ),
          const SizedBox(height: AppSpacing.lg),
          ElevatedButton.icon(
            onPressed: () => Navigator.push(
              context,
              MaterialPageRoute(builder: (_) => const AddNoteScreen()),
            ),
            icon: const Icon(Icons.add),
            label: const Text('Add Note'),
          ),
        ],
      ),
    );
  }
}

final subjectByIdProvider = FutureProvider.family<dynamic, String>((ref, id) {
  return ref.watch(subjectServiceProvider).getSubjectById(id);
});
```

## lib/screens/exam_mode_screen.dart

```dart
import 'package:flutter/material.dart';
import 'package:paperstudy/theme/app_colors.dart';
import 'package:paperstudy/theme/app_spacing.dart';
import 'package:paperstudy/theme/app_typography.dart';
import 'package:paperstudy/widgets/workload_chart.dart';

class ExamModeScreen extends StatelessWidget {
  const ExamModeScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Exam Mode'),
      ),
      body: SingleChildScrollView(
        padding: const EdgeInsets.all(AppSpacing.md),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            // Exam setup card
            Card(
              child: Padding(
                padding: const EdgeInsets.all(AppSpacing.lg),
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    Text('Set Up Exam Mode', style: AppTypography.headline),
                    const SizedBox(height: AppSpacing.md),
                    TextField(
                      decoration: const InputDecoration(
                        labelText: 'Exam Title',
                        hintText: 'e.g., Biology Final',
                      ),
                    ),
                    const SizedBox(height: AppSpacing.md),
                    TextField(
                      decoration: const InputDecoration(
                        labelText: 'Exam Date',
                        hintText: 'Select date',
                        prefixIcon: Icon(Icons.calendar_today),
                      ),
                      readOnly: true,
                      onTap: () {
                        // Show date picker
                      },
                    ),
                  ],
                ),
              ),
            ),

            const SizedBox(height: AppSpacing.lg),

            // Workload preview
            Text('Workload Preview', style: AppTypography.headline),
            const SizedBox(height: AppSpacing.md),
            const WorkloadChart(
              dailyCounts: [15, 22, 18, 25, 30, 20, 15, 12, 10, 8, 5, 3, 2, 1],
            ),

            const SizedBox(height: AppSpacing.lg),

            // Options
            Card(
              child: Column(
                children: [
                  CheckboxListTile(
                    title: const Text('Compress mature cards'),
                    subtitle: const Text('Review high-stability cards sooner'),
                    value: true,
                    onChanged: (v) {},
                  ),
                  CheckboxListTile(
                    title: const Text('Focus weak areas'),
                    subtitle: const Text('Prioritize low-retention items'),
                    value: true,
                    onChanged: (v) {},
                  ),
                ],
              ),
            ),

            const SizedBox(height: AppSpacing.xl),

            SizedBox(
              width: double.infinity,
              height: 56,
              child: ElevatedButton(
                onPressed: () {},
                style: ElevatedButton.styleFrom(
                  backgroundColor: AppColors.primary,
                  foregroundColor: Colors.white,
                ),
                child: const Text('ACTIVATE EXAM MODE', style: AppTypography.button),
              ),
            ),
          ],
        ),
      ),
    );
  }
}
```

## lib/utils/constants.dart

```dart
class AppConstants {
  // FSRS defaults
  static const double defaultRequestRetention = 0.90;
  static const int defaultMaximumInterval = 36500;
  static const bool defaultEnableFuzz = true;
  
  // Limits
  static const int defaultDailyReviewLimit = 150;
  static const int defaultLeechThreshold = 7;
  
  // Study goals
  static const int defaultDailyStudyGoalMinutes = 30;
  
  // Timing
  static const String defaultReminderTime = '21:00';
  
  // File sizes
  static const int maxPhotoWidth = 2048;
  static const int photoQuality = 85;
  static const int targetPhotoSizeKB = 500;
}
```

## lib/utils/extensions.dart

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

extension DateTimeExtension on DateTime {
  DateTime get startOfDay => DateTime(year, month, day);
  DateTime get endOfDay => DateTime(year, month, day, 23, 59, 59);
  
  bool isSameDay(DateTime other) {
    return year == other.year && month == other.month && day == other.day;
  }
  
  String get formatted => '$year-${month.toString().padLeft(2, '0')}-${day.toString().padLeft(2, '0')}';
}

extension DurationExtension on Duration {
  String get formatted {
    if (inHours > 0) {
      return '${inHours}h ${inMinutes.remainder(60)}m';
    }
    if (inMinutes > 0) {
      return '${inMinutes}m ${inSeconds.remainder(60)}s';
    }
    return '${inSeconds}s';
  }
}
```

## README.md

```markdown
# PaperStudy

Physical Note Study Tracker & Spaced Repetition Scheduler

## Setup

1. Install Flutter SDK (>=3.0.0)
2. Run `flutter pub get`
3. Run `flutter pub run build_runner build` to generate code
4. Run `flutter run`

## Features

- Physical note indexing with photos
- FSRS-4.5 spaced repetition algorithm
- Offline-first SQLite database
- Daily review queue
- Study streak tracking
- Exam mode scheduling
- OCR for page number detection

## Architecture

- Flutter 3.x with Riverpod state management
- Drift (SQLite) for local database
- Hive for settings storage
- Google ML Kit for OCR

## Building for Production

```bash
flutter build apk --release
flutter build appbundle --release
```
```

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