using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public class Book {

        public int BookId { get; set; }

        public string Title { get; set; }

    }

    public class BookLoan {

        public int BookId { get; set; }

        public DateTime CheckedOutOn { get; set; }

        public DateTime? ReturnedOn { get; set; }

        public DateTime DueOn { get; set; }

    }

    public class BookViewModel {

        public int BookId { get; set; }

        public string Title { get; set; }

        public bool IsAvailable { get; set; }

        public DateTime? AvailableOn { get; set; }

    } 

    public static void Main()

    {

        var books = new List<Book> {

            new Book { BookId = 1, Title = "Book 1" },

            new Book { BookId = 2, Title = "Book 2" },

            new Book { BookId = 3, Title = "Book 3" }

        };

        var loans = new List<BookLoan> {

            new BookLoan { BookId = 1, CheckedOutOn = new DateTime(2016, 1, 3), DueOn = new DateTime(2016, 2, 4), ReturnedOn = new DateTime(2016, 2, 3)},

            new BookLoan { BookId = 1, CheckedOutOn = new DateTime(2016, 6, 9), DueOn = new DateTime(2016, 7, 4), ReturnedOn = null },

            new BookLoan { BookId = 2, CheckedOutOn = new DateTime(2016, 4, 5), DueOn = new DateTime(2016, 5, 3), ReturnedOn = new DateTime(2016, 5, 23)},

            new BookLoan { BookId = 2, CheckedOutOn = new DateTime(2016, 6, 1), DueOn = new DateTime(2016, 8, 4), ReturnedOn = new DateTime(2016, 7, 5)},

            new BookLoan { BookId = 3, CheckedOutOn = new DateTime(2016, 1, 9), DueOn = new DateTime(2016, 2, 4), ReturnedOn = null }

        };

        var viewModel = from book in books

            join loan in loans.Where(x => !x.ReturnedOn.HasValue) on book.BookId equals loan.BookId into result

            from loanWithDefault in result.DefaultIfEmpty()

            select new BookViewModel { 

                BookId = book.BookId,

                Title = book.Title,

                IsAvailable = loanWithDefault == null,

                AvailableOn = loanWithDefault == null ? (DateTime?) null : loanWithDefault.DueOn

            };

        Console.WriteLine("Available: ");

        viewModel.Where(x => x.IsAvailable).ToList().ForEach(x => Console.WriteLine(x.Title));

        Console.WriteLine("\nUnavailable: ");

        viewModel.Where(x => !x.IsAvailable).ToList().ForEach(x => Console.WriteLine(x.Title + " - available " + x.AvailableOn));

    }

}