Building Dracula: A Privacy-First Blood Sugar Tracking App

Hey fellow developers and health enthusiasts! Today, I’m excited to share the complete development journey of Dracula, my privacy-first blood sugar and health tracking app built with Flutter. This isn’t just a project showcase—it’s a deep dive into building a production-ready health app from scratch, complete with MVPs, technical challenges, and lessons learned. Let’s dive in!

What is Dracula?

Dracula is a cross-platform mobile app designed for people managing diabetes or monitoring blood sugar levels. What sets it apart? Zero telemetry, local-only storage, and comprehensive nutrition tracking. Built with Flutter and SQLite, it runs on both Android and iOS with a sleek Dracula-inspired dark theme.

The app started as a simple logging tool but evolved into a full-featured health companion. Here’s how it happened.

MVP 1: Core Offline Functionality

Every great app starts simple. For Dracula, MVP 1 focused on the essentials:

Blood Sugar Logging: Users can add, edit, and delete readings with before/after meal flags
Custom Categories: Flexible categorization for different types of readings (e.g., fasting, post-meal)
Smart Settings: Unit conversion (mg/dL vs mmol/L), timezone display, and CSV export
Secure Storage: SQLite database with offline-first design
Privacy by Design: No cloud storage, no data sharing—everything stays on the device

The tech stack was straightforward: Flutter with Provider for state management (later evolved), and sqflite for database operations. I implemented a clean architecture with models, services, and screens.

class BloodSugarLog {
  final int? id;
  final double bloodSugar;
  final bool isBeforeMeal;
  final DateTime createdAt;
  // ... more fields
}

MVP 2: Analytics & User Experience

Once the core logging worked, it was time to make it useful. MVP 2 brought data visualization and usability improvements:

Interactive Charts: Beautiful line charts using fl_chart showing trends over days/weeks
Statistical Insights: Average readings, high/low alerts, and trend analysis
Daily Reminders: Customizable notifications with flutter_local_notifications
Security Features: Biometric app lock using local_auth
Enhanced UI: Material 3 components, smooth animations, and responsive design

This phase taught me a lot about Flutter’s animation system and notification scheduling. The charts were particularly challenging—getting the data aggregation right while maintaining performance.

MVP 3 & The Nutrition Revolution

The latest evolution added comprehensive meal tracking, turning Dracula from a blood sugar logger into a full nutrition-blood sugar correlation tool:

Meal Tracking System

Macro Nutrients: Carbs, protein, fat, and calories
Micro Nutrients: Fiber, sugar, sodium, vitamins, and minerals
Premade Meals: Quick-select common foods for convenience
Custom Entries: Full nutrition data input for detailed logging

Blood Sugar-Meal Correlation

The killer feature: When logging blood sugar “before meal,” users can select the meal they’re about to eat. This creates powerful correlations for better health insights.

// Database schema evolution
if (oldVersion < 4) {
  // Create meals table with all nutrient fields
}
if (oldVersion < 5) {
  // Add mealId to blood sugar logs
}

Technical Deep Dive: Challenges & Solutions

Database Evolution

Managing schema changes across app versions was tricky. I implemented proper migration logic:

Future _upgradeDB(Database db, int oldVersion, int newVersion) async {
  if (oldVersion < 2) {
    await db.execute('DROP TABLE IF EXISTS blood_sugar_logs');
    await _createDB(db, newVersion);
  }
  // ... more migrations
}

Testing Strategy

Following TDD principles, I built comprehensive tests:

Unit Tests: Model serialization, business logic
Widget Tests: UI interactions, form validation
Integration Tests: End-to-end workflows

The meal-blood sugar correlation required careful testing of the linked data relationships.

Cross-Platform Headaches

Supporting Android and iOS meant handling platform-specific quirks:

File picker implementations vary by platform
Notification permissions differ
Biometric authentication APIs have different capabilities

Lessons Learned

Start Simple, Scale Smart: MVP 1 proved the core concept; each iteration added value without overcomplicating.
Privacy Matters: Users trust health apps with sensitive data. Building privacy-first from day one was crucial.
Testing Saves Time: Early test failures caught bugs before they became user issues.
Database Design is Forever: Plan your schema carefully—migrations are painful!
User Experience is Everything: The app’s success depends on how intuitive and helpful it feels.

What’s Next?

Dracula is feature-complete for core use cases, but the roadmap includes:

Health data sync with wearables
Advanced AI-powered insights
Multi-language support expansion
Performance monitoring and optimization

Conclusion

Building Dracula was an incredible journey from concept to production-ready app. It taught me Flutter best practices, health app development nuances, and the importance of user privacy.

The app is now fully functional with comprehensive testing and documentation. If you’re managing blood sugar or building health apps, I’d love to hear your thoughts!

Have you built any health-related apps? What challenges did you face? Drop a comment below!

Disclaimer: Dracula is a personal project and not medical advice. Consult healthcare professionals for diabetes management.