EM code

// Mažeika EImantas IFF- 9/3 K1-pavyzdinis P175B118
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;


namespace BookStore
{
    class Program
    {
        static void Main(string[] args)
        {
            BookStore books = InOut.InputBooks("Knyga.txt");

            InOut.Print(books, "rezultatai.txt", "Knygynas");


            List<Book> soldBooksList = InOut.InputSoldBooks("Parduota.txt");

            BookStore Soldbooks = new BookStore(soldBooksList);

            InOut.Print(Soldbooks, "rezultatai.txt", "Pardavimas");

            books.AddSalePrice(soldBooksList);
            BookStore FilledSoldbooks = new BookStore(soldBooksList);

            InOut.Print(FilledSoldbooks, "rezultatai.txt", "Parduota");

            InOut.AppendStringToFile(String.Format("Reikia dar surinkti {0} pinigu", books.Sum() - FilledSoldbooks.Sum()), "rezultatai.txt");
            //Stall the program
            Console.ReadKey();
        }
    }

    class Book
    {
        public string Name { get; set; }
        public string Seller { get; set; }
        public int AmountAvailable { get; set; }
        public decimal Price { get; set; }

        public Book(string seller, string name, int amount, decimal price)
        {
            this.Name = name;
            this.Seller = seller;
            this.AmountAvailable = amount;
            this.Price = price;
        }

        public Book(string Name)
        {
            this.Name = Name;
            this.Seller = "";
            this.Price = 0;
            this.AmountAvailable = 1;
        }

        public override string ToString()
        {
            string str = string.Format("{0, -20} {1, -20} {2, 10} {3, 10}", Seller, Name, AmountAvailable, Price);
            return str;
        }

        public static bool operator >=(Book obj1, Book obj2)
        {
            if (obj1.Name == obj2.Name && obj1.Price >= obj2.Price)
                return true;
            else
                return false;
        }

        public static bool operator <=(Book obj1, Book obj2)
        {
            if (obj1.Name == obj2.Name && obj1.Price <= obj2.Price)
                return true;
            else
                return false;
        }
    }

    class BookStore
    {
        private List<Book> allBooks = new List<Book>();
        public BookStore(List<Book> books)
        {
            foreach (Book book in books)
            {
                allBooks.Add(book);
            }
        }
        public void AddEntry(Book book)
        {
            allBooks.Add(book);
        }
        public Book GetEntry(int index)
        {
            if (index < GetCount())
                return allBooks[index];
            else
                return null;
        }
        public int GetCount()
        {
            return allBooks.Count;
        }
        public decimal Sum()
        {
            decimal sum = 0;
            foreach (Book book in allBooks)
            {
                sum += book.AmountAvailable * book.Price;
            }
            return sum;
        }

        public decimal MaximumPrice(Book book)
        {
            decimal maxPrice = -9999;
            foreach (Book bookFromList in allBooks)
            {
                if (bookFromList >= book)
                {
                    maxPrice = bookFromList.Price;
                }
            }
            return maxPrice;
        }


        public void AddSalePrice(List<Book> soldBooks)
        {
            foreach (Book book in soldBooks)
            {
                decimal price = MaximumPrice(book);
                book.Price = price;
            }
        }




    }

    class InOut
    {
        public static BookStore InputBooks(string fileName)
        {
            string[] lines = File.ReadAllLines(fileName);
            List<Book> allBooks = new List<Book>();

            foreach (string line in lines)
            {
                string[] values = line.Split(';');
                string seller = values[0];
                string bookName = values[1];
                int amount = int.Parse(values[2]);
                decimal price = decimal.Parse(values[3]);

                allBooks.Add(new Book(seller, bookName, amount, price));
            }
            return new BookStore(allBooks);
        }

        public static List<Book> InputSoldBooks(string fileName)
        {
            List<Book> soldBooks = new List<Book>();

            string[] lines = File.ReadAllLines(fileName);

            foreach (string line in lines)
            {
                soldBooks.Add(new Book(line));
            }

            return soldBooks;
        }

        public static void Print(BookStore books, string fileName, string header)
        {
            string[] lines = new string[books.GetCount() * 2 + 4];
            lines[0] = header;
            lines[1] = new string('-', 100);
            lines[2] = string.Format("{0, -20} {1, -20} {2, 10} {3, 10}", "Seller", "Name", "Available", "Price");
            for (int i=0;i<books.GetCount();i++)
            {
                lines[i * 2 + 3] = new string('-', 100);
                lines[i * 2 + 4] = (books.GetEntry(i)).ToString();
            }

            File.AppendAllLines(fileName, lines);

        }

        public static void AppendStringToFile(string s, string fileName)
        {
            string[] str = new string[1];
            str[0] = s;
            File.AppendAllLines(fileName, str);

        }


    }
}