using System;

using System.Threading;

using System.Threading.Tasks;

using System.Collections.Generic;

using System.Linq;

​

namespace HelloWorld

{

    public class Book

    {

        public string Name { get; set; }

        public string Author { get; set; }

    }

​

    public class Program

    {

        public static List<Book> OrderByAuthorAndBookName()

        {

            return Books.OrderBy(book => book.Author).ThenBy(book => book.Name).ToList();

        }

​

        public static string[] GetAuthorsBookCount()

        {

            return Books.GroupBy(book => book.Author)

                        .Select(group => $"{group.Key} - Book count {group.Count()}")

                        .ToArray();

        }

​

        public static Task<Book[]> GetBooksByAuthor(string author)

        {

            return Task.Run(() =>

            {

                return Books.Where(book => book.Author == author).ToArray();

            });

        }

​

        public static void DeleteAuthor(string authorName)

        {

            Books.RemoveAll(book => book.Author == authorName);

        }

​

        public static List<Book> Books { get; set; } = new List<Book>

        {

            new Book { Name = "Book1", Author = "Author1" },

            new Book { Name = "Book3", Author = "Author3" },

            new Book { Name = "Book4", Author = "Author3" },

            new Book { Name = "Book1", Author = "Author2" },

            new Book { Name = "Book3", Author = "Author1" },

            new Book { Name = "Book1", Author = "Author3" },

            new Book { Name = "Book2", Author = "Author2" },

            new Book { Name = "Book2", Author = "Author1" },

            new Book { Name = "Book2", Author = "Author3" },

            new Book { Name = "Book3", Author = "Author2" },

        };

​

        public static void Main(string[] args)

        {

            // Predefined data for validation

            var expectedOrderedBooks = new List<Book>

            {

                new Book { Name = "Book1", Author = "Author1" },

                new Book { Name = "Book2", Author = "Author1" },

                new Book { Name = "Book3", Author = "Author1" },

                new Book { Name = "Book1", Author = "Author2" },

                new Book { Name = "Book2", Author = "Author2" },

                new Book { Name = "Book3", Author = "Author2" },

                new Book { Name = "Book1", Author = "Author3" },

                new Book { Name = "Book2", Author = "Author3" },

                new Book { Name = "Book3", Author = "Author3" },

                new Book { Name = "Book4", Author = "Author3" },

            };

​

            var expectedAuthorBookCounts = new[]

            {

                "Author1 - Book count 3",

                "Author3 - Book count 4",

                "Author2 - Book count 3",

            };

​

            var expectedBooksByAuthor1 = new[]

            {

                new Book { Name = "Book1", Author = "Author1" },

                new Book { Name = "Book3", Author = "Author1" },

                new Book { Name = "Book2", Author = "Author1" },

            };

​

            var expectedBooksAfterDeletion = new List<Book>

            {

                new Book { Name = "Book1", Author = "Author1" },

                new Book { Name = "Book3", Author = "Author3" },

                new Book { Name = "Book4", Author = "Author3" },

                new Book { Name = "Book3", Author = "Author1" },

                new Book { Name = "Book1", Author = "Author3" },

                new Book { Name = "Book2", Author = "Author1" },

                new Book { Name = "Book2", Author = "Author3" },

            };

​

            // Call methods

            var orderedBooks = OrderByAuthorAndBookName();

            Console.WriteLine("Ordered Books Validation:");

            Console.WriteLine(orderedBooks.SequenceEqual(expectedOrderedBooks, new BookComparer()) ? "PASSED" : "FAILED");

​

            var authorBookCounts = GetAuthorsBookCount();

            Console.WriteLine("\nAuthor Book Counts Validation:");

            Console.WriteLine(authorBookCounts.ToHashSet().SetEquals(expectedAuthorBookCounts) ? "PASSED" : "FAILED");

​

            var booksByAuthor1 = GetBooksByAuthor("Author1").Result;

            Console.WriteLine("\nBooks by Author1 Validation:");

            Console.WriteLine(booksByAuthor1.ToHashSet(new BookComparer()).SetEquals(expectedBooksByAuthor1) ? "PASSED" : "FAILED");

​

            DeleteAuthor("Author2");

            Console.WriteLine("\nBooks After Deleting Author2 Validation:");

            Console.WriteLine(Books.ToHashSet(new BookComparer()).SetEquals(expectedBooksAfterDeletion) ? "PASSED" : "FAILED");

        }

​

        // Comparer to check equality of Book objects

        public class BookComparer : IEqualityComparer<Book>

        {

            public bool Equals(Book x, Book y)

            {

                return x.Name == y.Name && x.Author == y.Author;

            }

​

            public int GetHashCode(Book obj)

            {

                return (obj.Name, obj.Author).GetHashCode();

            }

        }

    }

}

​

​

​