//Create an invoice as a txt file with the name of the company and with an unique number.
        private void SaveInvoiceBtn_Click(object sender, RoutedEventArgs e)
        {
            if (PartnerNames.SelectedItem == null || DateOfDeliveryBox.SelectedDate == null || TermOfPaymentBox.SelectedDate == null || CurrencyList.SelectedItem == null || MethodOfPaymentList.SelectedItem == null || ItemHandler.GetItems().Count == 0)
            {
                MessageBox.Show("Hiányzó adatok!", "Hiba", MessageBoxButton.OK, MessageBoxImage.Error);
                return;
            }

            long    n = long.Parse(DateTime.Now.ToString("yyyyMMddHHmmss"));
            Partner selectedPartner = PartnerNames.SelectedItem as Partner;
            string  date            = n.ToString();
            string  path            = $"{PartnerNames.SelectedItem.ToString()}\\{PartnerNames.SelectedItem.ToString().Replace(".", "")}{date}";

            using (FileStream file = File.Open(path + ".txt", FileMode.Create))
            {
                List <string> datas = new List <string>();

                datas.Add(string.Format("E-szamla{0,85}{1}", "", InfoHandler.ownCompany.Name));
                datas.Add(string.Format("{0,60} {1,40}", "", InfoHandler.ownCompany.Address));
                datas.Add(string.Format("{0,60} {1,-15}{2,-30}", "", "Adoszam:", InfoHandler.ownCompany.TaxNumber));
                datas.Add(string.Format("{0,60} {1,-15}{2,-30}", "", "Bankszamlaszam:", InfoHandler.ownCompany.AccountNumber));
                datas.Add(drawLine());
                datas.Add("Vevo adatai: ");
                datas.Add("Vevo neve:" + selectedPartner.Name);
                datas.Add("Vevo címe:" + selectedPartner.Address);
                datas.Add("Szamlaszam: " + selectedPartner.BankAccountNumber);
                datas.Add("Szamla kelte: " + DateTime.Now.ToString("yyyy.MM.dd"));
                datas.Add("Teljesites idopontja: " + ((DateTime)DateOfDeliveryBox.SelectedDate).ToString("yyyy.MM.dd"));
                datas.Add("Fizetesi hatarido: " + ((DateTime)TermOfPaymentBox.SelectedDate).ToString("yyyy.MM.dd"));
                datas.Add("Szamla szama: " + n);
                datas.Add(drawLine());
                string header = string.Format("{0}{1,15}{2,15}{3,15}{4,15}{5,15}{6,15}{7,15}", "Megnevezes", "Penznem", "Egysegar", "Mennyiseg", "Netto ar", "AFA%", "AFA", "Brutto ar");
                datas.Add(header);
                double finalPrice = 0;
                string currency   = ItemHandler.GetItems()[0].Currency;
                foreach (var item in ItemHandler.GetItems())
                {
                    string datasUnderHeader = string.Format("{0}{1,15}{2,15}{3,15}{4,15}{5,15}{6,15}{7,15}", item.Name, item.Currency, item.Price, item.Amount, item.NetPrice, item.Tax, item.TaxAmount, item.BruttoPrice);
                    datas.Add(datasUnderHeader);
                    finalPrice += item.BruttoPrice;
                }
                datas.Add(drawLine());


                datas.Add(string.Format("Fizetendo:{0,60} {1}.", finalPrice, currency));

                string[] dataArray = datas.ToArray();
                for (int i = 0; i < dataArray.Length; i++)
                {
                    dataArray[i] = CharacterReplacer.replaceAccentuatedLetters(dataArray[i]);
                }
                using (StreamWriter writer = new StreamWriter(file))
                {
                    int counter = 0;
                    foreach (var item in dataArray)
                    {
                        writer.WriteLine(item);
                        writer.WriteLine();
                        writer.WriteLine();
                        if (counter == 0 || counter == 3)
                        {
                            writer.WriteLine();
                            writer.WriteLine();
                            writer.WriteLine();
                        }
                        counter++;
                    }
                }
                PdfConverter.GeneratePdf(path);
            }
            MessageBox.Show("Sikeres mentés!", "Mentve", MessageBoxButton.OK, MessageBoxImage.Information);
            this.Close();
        }