TrueRate - Smart GST Calculator & Scanner

TrueRate is a robust Android application designed to simplify GST (Goods and Services Tax) calculations for everyday products. It features a smart, crowdsourced barcode scanner that automatically identifies products, retrieves their details, and calculates the precise tax breakdown based on Indian GST laws.

Built with performance in mind, the app utilizes an Offline-First approach and a Parallel Network architecture to ensure users get results instantly, regardless of network conditions.

🚀 Key Features

⚡ Hybrid Parallel Scanning

The app employs a sophisticated "Race Logic" to retrieve product data with minimal latency. It simultaneously queries four different sources:

1. Cloud Firestore: Our proprietary crowdsourced database (Fastest).
2. OpenFoodFacts API: For food and beverage items.
3. OpenBeautyFacts API: For cosmetics and personal care.
4. UPCItemDB: A reliable backup for general retail items.

The first source to return valid data "wins" the race, cancelling the other requests to conserve resources.

☁️ Crowdsourcing Engine

TrueRate gets smarter with every use. If a product is not found in our databases, users can manually enter the details. This data is instantly uploaded to the cloud, making the product recognizable for all future users.

🏢 Dynamic Tax Slabs

The app supports configurable tax categories based on current GST standards:

• Exempt (0%): Essentials like milk, bread, and fresh vegetables.
• Essential (5%): Daily-use items like oil, tea, and medicines.
• Standard (18%): Electronics and home appliances.
• Luxury (40%): Sin goods like tobacco and aerated drinks.

💾 Offline Persistence

Powered by the Room Persistence Library, TrueRate caches your scan history locally. You can access your previous scans and calculations even without an active internet connection.

📷 Advanced Scanning

Integrated with Google ML Kit and CameraX, the app offers instant and accurate barcode detection directly from the device's camera.

🧪 Quality Assurance

This project adheres to strict engineering standards with a robust and comprehensive test suite ensuring reliability and accuracy.

• 100+ Unit Tests: Rigorous testing of all core business logic including:
  • Tax Engine: Verifies accurate calculation of Exempt (0%), Essential (5%), Standard (18%), and Luxury (40%) tax slabs with precise floating-point math.
  • Barcode Router: Validates routing logic for Indian Retail (890), Books (978), and Global products.
  • Data Parsing: Ensures resilience against null values, missing fields, and API inconsistencies.
• Integration Tests: Validates the persistence layer, ensuring that the Room Database correctly saves, retrieves, and maintains data integrity for scan history.
• UI/Espresso Tests: Automated verification of key user flows, including navigation, dialog interactions, and screen visibility on physical devices.
• Performance: Achieved a 100% Pass Rate across all test modules (Unit, Integration, and UI).

🛠️ Technical Architecture

• Language: Java
• Architecture pattern: MVC (Model-View-Controller) with Repository Pattern
• Database:
  • Local: Room Database (SQLite) for history and caching.
  • Cloud: Firebase Firestore (NoSQL) for crowdsourced data.
• Networking: Retrofit 2 with Gson for API communication.
• Concurrency: Parallel Execution using ExecutorService and Atomic Boolean Locks.
• Hardware Integration: CameraX + ML Kit Vision API.
• UI/UX: Material Design Components.

📸 How It Works

1. Scan: Point the camera at any product barcode.
2. Identify: The app checks the Cloud Cache first. If missing, it initiates a parallel API race to find the product globally.
3. Calculate: Once identified, the app applies the correct GST slab.
4. Contribute: If the product is unknown, your manual entry contributes to the global database.

📝 Setup Instructions

1. Clone the Repository:

   git clone https://github.com/blackspade1901/Tax_calculator.git

2. Firebase Configuration:
   • Create a project in the Firebase Console.
   • Download the google-services.json file.
   • Place it in the /app directory of the project.
3. Build: Open the project in Android Studio and sync Gradle.
4. Run: Deploy the app to a physical device or emulator.

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Built as a Master of Computer Applications (MCA) project at Goa University.