Add project files.

Books.ConsoleApp/SearchByAuthor.cs

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+using System;
+using System.Collections.Generic;
+using System.Data.SqlTypes;
+using System.Linq;
+using System.Text;
+
+namespace Books.ConsoleApp
+{
+    public static  class SearchByAuthor
+    {
+        public static IEnumerable<string> MatchBy(
+            IEnumerable<Book> books, string searchCriteria)
+        {
+            return books
+                .ExtractAuthors()
+                .ListAuthorsMatching(searchCriteria);
+        }
+
+        public static IEnumerable<string> SuggestAuthors(
+            IEnumerable<Book> books, int suggestionLength = 5)
+        {
+            return books
+                .ExtractAuthors()
+                .RandomizeOrder()
+                .Take(suggestionLength);
+        }
+
+        public static IEnumerable<Book> ListBooks(IEnumerable<Book> books, string author)
+        {
+            return books
+                .CatalogueByAuthor()
+                .BooksBy(author);
+        }
+
+        public static AuthorCatalogue CatalogueByAuthor(this IEnumerable<Book> books)
+        {
+            return books
+                    .ToLookup(b => b.author)
+                // Mark Twain : {The Adventures of Huckleberry Finn},
+                // Shakespeare: {Othello, Hamlet, ...}
+                // ...
+                ;
+        }
+
+
+        public static IEnumerable<Book> BooksBy(this AuthorCatalogue catalogue, string author)
+        {
+            return catalogue.Contains(author)
+                ? catalogue[author]
+                : Enumerable.Empty<Book>();
+        }
+
+        public static IEnumerable<string> ExtractAuthors(this IEnumerable<Book> books)
+        {
+            return books.Select(b =>
+            {
+                //do stuff here
+                return b.author;
+
+            }).Distinct();
+        }
+
+        public static IEnumerable<string> ListAuthorsMatching(
+            this IEnumerable<string> authors, string searchCriteria)
+        {
+            var partOfNameLower = searchCriteria.ToLower();
+            return authors.Where(a => a.ToLower().Contains(partOfNameLower));
+        }
+
+        private static IOrderedEnumerable<string> RandomizeOrder(this IEnumerable<string> authors)
+        {
+            return authors.OrderBy(_ => Guid.NewGuid());
+        }
+
+    }
+
+    public class AuthorCatalogue
+    {
+    }
+
+    public class Book
+    {
+
+    }
+}