📘 Bookshop Discount Management System (BDMS)

University of Sri Jayewardenepura - Object-Oriented Programming (OOP) Assignment

A comprehensive JavaFX application demonstrating core OOP principles, secure data handling, and modern UI design.

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🧠 Project Overview

The Bookshop Discount Management System (BDMS) is a robust desktop application designed to solve a real-world business challenge: managing complex, multi-tiered discount structures in a retail environment. Built with Java 11, JavaFX 17, and Maven, this project serves as a practical demonstration of Object-Oriented Programming (OOP) concepts, software architecture, and secure coding practices.

❓ The Problem

Bookshops often struggle with manual discount calculations, leading to:

• Human Error: Mistakes in calculating bulk discounts or VIP rates.
• Inefficiency: Slow checkout processes.
• Inconsistency: Different discounts applied to similar customers.
• Security Risks: Unsecured data storage and weak authentication.

✅ The Solution

BDMS automates the entire process by:

1. Dynamic Pricing: Automatically applying quantity-based bulk discounts.
2. Customer Tiers: Distinguishing between Regular and VIP customers (VIPs get an extra 5% off).
3. Secure Access: Role-based login (Manager vs. Cashier) with BCrypt password hashing.
4. Data Integrity: Using file locking to prevent data corruption in CSV storage.

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⚙️ Key Features

🔐 Security & Reliability

• BCrypt Hashing: User passwords are never stored in plain text. They are hashed using the industry-standard BCrypt algorithm.
• Input Sanitization: All user inputs are sanitized to prevent CSV Injection attacks.
• Concurrency Control: Implemented File Locking (FileChannel.lock) to ensure safe concurrent writes to data files.
• Strict Validation: Robust validation for customer data (e.g., phone number format).

💻 Modern User Interface

• Cashier Portal: A responsive, grid-based POS interface with real-time product filtering.
• Auto-Search: Instant product and customer lookup without manual "Search" buttons.
• Live Cart: Dynamic shopping cart with real-time subtotal and discount updates.

🛠 Architecture

• MVC Pattern: Separation of concerns using Model-View-Controller architecture.
• Service Layer: Business logic is encapsulated in Service classes (AuthService, ProductService, CustomerService).
• File-Based Persistence: Lightweight CSV storage (users.csv, products.csv, customers.csv) making the app portable and database-free.

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📚 OOP Principles Demonstrated

This project is built upon the four pillars of Object-Oriented Programming:

1️⃣ Encapsulation

Data is hidden within classes and accessed only through public methods, ensuring data integrity.

public class Product {
    private String productId;
    private double realPrice;
    
    // Controlled access via getters and setters
    public double getRealPrice() { return realPrice; }
    public void setRealPrice(double price) {
        if (price < 0) throw new IllegalArgumentException("Price cannot be negative");
        this.realPrice = price;
    }
}

2️⃣ Inheritance

Specialized classes inherit behavior from generalized classes to promote code reuse.

// Base class
public abstract class Customer {
    protected String name;
    public abstract double getBaseDiscountRate();
}

// Derived class
public class VIPCustomer extends Customer {
    @Override
    public double getBaseDiscountRate() {
        return 0.05; // VIPs get 5% base discount
    }
}

3️⃣ Polymorphism

The system treats different objects (Regular vs. VIP) uniformly but they behave differently at runtime.

Customer customer = new VIPCustomer("John");
// The system doesn't need to know it's a VIP; it just asks for the rate.
double discount = total * customer.getBaseDiscountRate(); 

4️⃣ Abstraction

Complex logic is hidden behind simple interfaces. The FileHandler utility abstracts away the low-level details of file I/O, locking, and parsing.

// High-level usage
FileHandler.writeCsv("data/products.csv", lines);

// Low-level implementation (hidden)
// - Opens FileChannel
// - Acquires FileLock
// - Writes ByteBuffers
// - Handles IOExceptions

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📂 Project Structure

BookshopDiscountSystem/
├── src/main/java/bookshop/
│   ├── controllers/      # UI Logic (CashierController, AdminController)
│   ├── model/            # Data Classes (Product, Customer, User)
│   ├── service/          # Business Logic (AuthService, ProductService)
│   └── util/             # Helpers (FileHandler, PasswordMigrator)
├── src/main/resources/
│   ├── FXML/             # UI Layouts (.fxml)
│   └── Styles/           # CSS Styling
├── data/                 # CSV Data Storage
├── docs/                 # Documentation & Security Audit
├── BookshopDiscountSystem-linux.sh    # Linux executable script

└── pom.xml               # Maven Dependencies

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🚀 Installation & Setup

Prerequisites

• Java JDK 11 or higher.
• Maven 3.6+.

Steps to Run

1. Clone the Repository:

   git clone https://github.com/Chamath-Adithya/Bookshop-Discount-Management-System.git
   cd BookshopDiscountSystem

2. Build the Project:

   mvn clean install

3. Run the Application:

   mvn javafx:run

Default Credentials

• Admin/Manager: Creates new users.
• Worker/Cashier: Handles sales.
• (Note: Default users are stored in data/users.csv with hashed passwords)

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🧪 Usage Scenarios

Scenario 1: VIP Checkout

1. Cashier logs in.
2. Searches for "Pen" (Price: Rs.100).
3. Adds 10 Pens (Bulk discount applies -> Rs.80/each).
4. Selects Customer "John" (VIP).
5. System Calculation:
   • Subtotal: 10 * 100 = Rs.1000
   • Bulk Price: 10 * 80 = Rs.800
   • VIP Discount: 5% of Rs.800 = Rs.40
   • Final Total: Rs.760

Scenario 2: Security Check

1. Malicious user tries to edit customers.csv to inject a spreadsheet formula (=cmd|...).
2. System Defense: The application detects the special character and sanitizes the input by prepending a ', rendering the formula harmless.

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👨‍💻 Contributors

• Chamath-Adithya - Lead Developer, Core Models & Project Foundation
• yasaruhashen - Customer Hierarchy & Service
• prabandisathsarani080-ai - User Roles & Data Management Services
• IOICybErIOI - Main Application & Billing Logic
• kaveesha-tharindi5 - Validation, Exceptions & Testing

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This project was developed for the Object-Oriented Programming Module at the University of Sri Jayewardenepura.

Executable Files

• Linux: Run ./BookshopDiscountSystem-linux.sh
• Windows: Run target/BookshopDiscountSystem.exe

Generating Windows Executable

To generate the .exe file for Windows, run the following command:

MAVEN_OPTS="--add-opens java.base/java.util=ALL-UNNAMED --add-opens java.base/java.lang.reflect=ALL-UNNAMED --add-opens java.base/java.text=ALL-UNNAMED --add-opens java.desktop/java.awt.font=ALL-UNNAMED" mvn clean package

Ensure Java 11+ is installed.