C# - Create a set of classes designed to help libraries track which books they own and whether they are available or checked out

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace LearningActivity1
{
	public class Book
	{
		public string Name { get; set; }
		public string Author { get; set; }
		public int ISBN { get; set; }
		public bool Rented { get; private set; }

		public Book( string Name, string Author, int ISBN )
		{
			this.Name = Name;
			this.Author = Author;
			this.ISBN = ISBN;
		}

		public override string ToString()
		{
			String status = Rented ? "UNAVAILABLE" : "AVAILABLE";
			return $"{ISBN} - {Name} by {Author} - {status}";
		}

		public void Rent()
		{
			if (Rented)
			{
				Console.WriteLine("This book is already rented.");
				return;
			}

			Rented = true;
			Console.WriteLine($"Book {Name} successfully rented to new reader.");
		}

		public void Return()
		{
			if (!Rented)
			{
				Console.WriteLine("This book is already returned.");
				return;
			}

			Rented = false;
			Console.WriteLine($"Book {Name} successfully rented to new reader.");
		}
	}

	public class Library
	{
		private List<Book> Books = new List<Book>();

		public void AddBook(Book book)
		{
			Books.Add(book);
		}

		public Book FindABookByISBN( int ISBN )
		{
			return Books.Find(book => book.ISBN == ISBN);
		}

		public void SearchBooks( string keyword )
		{
			List<Book> matched = Books.FindAll(book =>
				book.Name.ToLower().Contains(keyword.ToLower())
				|| book.Author.ToLower().Contains(keyword.ToLower()));

			foreach (Book book in matched)
			{
				Console.WriteLine(book);
			}
		}

		public void ListBooks()
		{
			foreach (Book book in Books)
			{
				Console.WriteLine(book);
			}
		}

		public void Checkout( int ISBN )
		{
			Book book = FindABookByISBN(ISBN);

			if (null == book)
			{
				Console.WriteLine("This book is not available in the registery.");
				return;
			}

			book.Rent();
		}

		public void Return(int ISBN)
		{
			Book book = FindABookByISBN(ISBN);

			if (null == book) {
				Console.WriteLine("This book is not available in the registery.");
			}

			book.Return();
		}

		public void HandleCommand( String[] parts )
		{
			String command = "", argument = "";

			for ( int i=0; i<parts.Length; i++)
			{
				if ( 0 == i )
				{
					command = parts[i];
				} else
				{
					argument += (String.IsNullOrEmpty(argument) ? "" : " ") + parts[i];
				}
			}

			switch ( command.ToLower() )
			{
				case "list-all":
					ListBooks();
					break;

				case "search":
					SearchBooks(argument);
					break;

				case "checkout":
				case "return":
					int ISBN;

					if ( int.TryParse(argument, out ISBN))
					{
						if ("return" == command.ToLower())
						{
							Return(ISBN);
						}
						else
						{
							Checkout(ISBN);
						}
					} else
					{
						Console.WriteLine($"Invalid ISBN supplied: {argument}");
					}

					break;

				default:
					Console.WriteLine($"c: {command}, a: {argument}");
					break;
			}
		}
	}

	public class CliClient
	{
		public CliClient( Library library )
		{
			string line;

			StdinHint();

			while ((line = Console.ReadLine()) != null)
			{
				string[] parts = line.Trim().Split(' ').Where(s => ! String.IsNullOrWhiteSpace(s)).ToArray();

				if (parts.Length < 2 && ! ( parts.Length == 1 && (
					"list-all" == parts[0].ToLower()
					|| "help" == parts[0].ToLower()
					|| "exit" == parts[0].ToLower()
					) ))
				{
					Console.WriteLine("Please type a command and at least 1 argument. For a list of commands, type: help");
					StdinHint();
					continue;
				}

				switch ( parts[0].ToLower() )
				{
					case "help":
						Help();
						break;

					case "list-all":
					case "search":
					case "checkout":
					case "return":
						library.HandleCommand( parts );
						break;

					case "exit":
						return;

					default:
						Console.WriteLine("Unknown command. For a list of commands, type: help");
						break;
				}

				StdinHint();
			}
		}

		public void Help()
		{
			Console.WriteLine("Available commands:\n list-all\n search keyword\n checkout ISBN\n return ISBN\n help\n exit");
		}

		public void StdinHint()
		{
			Console.Write("> ");
		}
	}

	class Program
	{
		static void Main(string[] args)
		{
			Library library = new Library();

			// add a list of books
			library.AddBook(new Book("Science Of Storytelling", "Will Storr", 1));
			library.AddBook(new Book("Steve Jobs", "Walter Isaacson", 2));
			library.AddBook(new Book("How We Got to Now", "Steven Johnson", 3));
			library.AddBook(new Book("The Big Nine", "Amy Webb", 4));
			library.AddBook(new Book("Deviced", "Doreen Dodgen-Magee", 5));
			library.AddBook(new Book("The Truth About Your Future", "Eric Edelman", 6));
			library.AddBook(new Book("Digital", "Joshua J Omojuwa", 7));
			library.AddBook(new Book("How to Be Good at Science, Technology, and Engineering", "DK", 8));
			library.AddBook(new Book("A World Without Work", "Daniel Susskind", 9));

			new CliClient(library);
		}
	}
}