E-Commerce System

Project Structure

ECommerceSystem/
├── Interfaces/
│   └── IShippable.cs           # Interface for products requiring shipping
├── Models/
│   ├── Product.cs              # Abstract base product class
│   ├── PerishableProduct.cs    # Base class for expiring products
│   ├── Customer.cs             # Customer with balance management
│   ├── CartItem.cs             # Individual cart item
│   ├── ShoppingCart.cs         # Shopping cart functionality
│   └── CheckoutResult.cs       # Checkout result data
├── Products/
│   ├── Cheese.cs               # Perishable, shippable product
│   ├── Biscuits.cs             # Perishable, non-shippable product
│   ├── Television.cs           # Non-perishable, shippable product
│   └── MobileScratchCard.cs    # Non-perishable, non-shippable product
├── Services/
│   ├── ShippingService.cs      # Shipping cost calculations
│   └── CheckoutService.cs      # Order processing and validation
└── Program.cs                  # Demo application

Architecture

Core Classes

• Product: Abstract base class for all products
• PerishableProduct: Extends Product with expiration date functionality
• IShippable: Interface for products that require shipping
• Customer: Manages customer information and balance
• ShoppingCart: Handles product selection and quantity management
• CheckoutService: Processes orders and coordinates payment
• ShippingService: Calculates shipping costs for shippable items

Product Types

1. Cheese: Perishable product that requires shipping
2. Biscuits: Perishable product that doesn't require shipping
3. Television: Non-perishable product that requires shipping
4. MobileScratchCard: Non-perishable product that doesn't require shipping

Business Rules

• Products can be perishable (with expiration dates) or non-perishable
• Some products require shipping and have weight for shipping calculations
• Customers cannot purchase more items than available in stock
• Expired products cannot be purchased
• Customers must have sufficient balance to complete purchases
• Shipping costs are calculated based on base fee plus weight-based charges

Error Handling

The system handles the following error scenarios:

• Empty cart checkout attempts
• Insufficient customer balance
• Out of stock products
• Expired products
• Invalid quantities

Running the Application

dotnet run

The application will demonstrate:

1. Adding products to cart
2. Successful checkout process
3. Error scenario testing