Simple cash register for demo

We’re going to see how far we can get in implementing a supermarket checkout that calculates the total price of a number of items.

In a normal supermarket, things are identified using Stock Keeping Units, or SKUs. In our store, we’ll use individual letters of the alphabet (A, B, C, and so on). Our goods are priced individually.

Our checkout accepts items in any order, so that if we scan a B, an A, and another B, we’ll recognize the two ‘B’s and price them at £6.00 (for a total price so far of £11.00). In addition, some items are multi-priced: buy n of them, and they’ll cost you y pounds.

For example, item A might cost £5.00 individually, but this week we have a special offer: buy three ‘A’s and they’ll cost you £13.00 The price and offer table:

This application is build with .NET core 2.0, the latest version of .NET.

.NET Core is a general purpose, modular, cross-platform and open source implementation of the .NET Platform. It contains many of the same APIs as the .NET Framework (but .NET Core is a smaller set) and includes runtime, framework, compiler and tools components that support a variety of operating systems and chip targets. Microsoft is considering this technology as the future of its development platform.

For this reason CashRegister.Library can be used in every kind of application: web, mobile or desktop. In my implementation I use it for a Console application.

The application has the following components.

This is the important part of this project. This library contains the logic to add new goods in the shopping list.

First of all, you find Interfaces. An interface is defined as a syntactical contract that all the classes inheriting the interface should follow. The interface defines the what part of the syntactical contract and the deriving classes define the how part of the syntactical contract.

Interfaces define properties, methods, and events, which are the members of the interface. Interfaces contain only the declaration of the members. It is the responsibility of the deriving class to define the members. It often helps in providing a standard structure that the deriving classes would follow.

• IBasketManager.cs defines what functions we want to manage a basket
• IGoodsManager.cs defines how to manage your good
• IRepository.cs defines the requirements for a simple repository

BasketManager is responsible for managing your shopping, creating the shopping history and writing your receipt.

When a new item is added in the basker, BasketManager checks if there is any offer for that product and, eventually, calculates the right price and update the receipt.

GoodManager is responsible for managing items in the shopping list.

When you add a new good, there is a validation of your input and a check if this element already exists in the shopping list.

Test-driven development (TDD) is a software development process that relies on the repetition of a very short development cycle: requirements are turned into very specific test cases, then the software is improved to pass the new tests, only. TDD is primarily a developer’s tool to help create well-written unit of code (function, class, or module) that correctly performs a set of operations.

With TDD it cans test all functions and scenarios for CashRegister.Library.

In this project there is the implementation from CashRegister.Library for repository. Basically this module is responsible to read and write on file system the list of goods or a basket. Files are saved in json format in a Data folder in the local directory.

To avoid redundant code or duplicated function, there is a generic GenericRepository that write or read a file in json, serialized or deserialized data with a particular type: for each model there is class that it defines only the name of the function.

To try CashRegister.Library I created a console application. Why? I thought it was a best way to show you how I can work. Under Infrastructures folder, there is my implementation and extension of a basic Console application to build a simple menu interface and also introduce a navigation logic similar to webapplications and mobile applications that never existed in console application.

• Create automatically menus with numbers
• Fluent creation of menus
• Navigation between pages with breadcrumbs
• Input/Output helpers

The base functionality of the library is to provide an easy way to create console menus. A Menu consists of Options that will be presented to a user for selection. An option contains a name, that will be displayed to the user, and a callback function to invoke if the user selects the option. Render the menu in the console using the Display() method.

The infrastructure also provides input and output utilities to abstract the concept of dealing with the Console. The Output class adds helper methods to control the color of text in the console.

The Input class adds helper methods that prompt the user for input. The utility takes care of displaying prompt text and handling parsing logic. For example, non-numeric input will be rejected by ReadInt() and the user will be re-prompted.

All of these features can be put together to create complex programs with nested menus. A console program consists of a main Program class that contains Pages. The Program class is a navigator of pages and will keep a history of pages that a user is navigating through. Think of it as your browser history. To create a program you must subclass the Program class and add any Pages in the constructor.

The list of goods can be created every time manually or loaded from file. To save a list, select option n. 4

You add your items in the basket. When you finish, press 0 and the application shows you your receipt, your basket and all history.