private void ImportButton_Click(object sender, RoutedEventArgs e)
        {
            var screen = new OpenFileDialog();

            screen.Filter = "Excel files|*.xls;*.xlsx";

            if (screen.ShowDialog() == true)
            {
                var workbook = new Workbook(screen.FileName);

                var sheet = workbook.Worksheets[0];

                var col = "A";
                var row = 2;

                var cell = sheet.Cells[$"{col}{row}"];

                while (cell.Value != null)
                {
                    var categoryid = sheet.Cells[$"C{row}"].StringValue;
                    var name       = sheet.Cells[$"B{row}"].StringValue;

                    bool has = MainWindow.db.Categories.ToList().Any(cus => cus.ID == categoryid);
                    if (has == true)
                    {
                        var price     = sheet.Cells[$"D{row}"].DoubleValue;
                        var weight    = sheet.Cells[$"E{row}"].DoubleValue;
                        var imageName = sheet.Cells[$"F{row}"].StringValue;

                        var imageSourceInfo     = new FileInfo(screen.FileName);
                        var imageSourceFullPath = $"{imageSourceInfo.DirectoryName}\\images\\{imageName}";
                        var imageSourceFileInfo = new FileInfo(imageSourceFullPath);

                        var uniqueName = $"{Guid.NewGuid()}.{imageSourceFileInfo.Extension}";

                        var baseDirectory   = AppDomain.CurrentDomain.BaseDirectory;
                        var destinationPath = $"{baseDirectory}image\\{uniqueName}";

                        File.Copy(imageSourceFullPath, destinationPath);

                        var newProduct = new Product()
                        {
                            ID   = IDGenerator.createID("P"),
                            Name = name,
                            //CategoryID = (from category in MainWindow.db.Categories where category.Name == categoryid select category.ID).Single(),
                            CategoryID = categoryid,
                            Price      = price,
                            Weight     = weight,
                            isDeleted  = false,
                            Picture    = uniqueName,
                        };

                        MainWindow.db.Products.Add(newProduct);
                        MainWindow.db.SaveChanges();

                        row++;
                        cell = sheet.Cells[$"{col}{row}"];
                    }
                    else
                    {
                        string message = "The category with ID \"" + categoryid + "\" in product \"" + name + "\" does not exist.\nDo you want to add a new category? You can skip importing this product by clicking \"No\".";

                        if (MessageBox.Show(message, "Warning", MessageBoxButton.YesNo, MessageBoxImage.Warning) == MessageBoxResult.Yes)
                        {
                            var newCategory = new AddCategoryWindow();

                            if (newCategory.ShowDialog() == true)
                            {
                                if (newCategory.CT_Name != null)
                                {
                                    var category = new Category()
                                    {
                                        ID        = categoryid,
                                        Name      = newCategory.CT_Name,
                                        isDeleted = false,
                                    };

                                    MainWindow.db.Categories.Add(category);
                                    MainWindow.db.SaveChanges();
                                    CategoryControl.category_notification.CategoryChange = true;

                                    var price     = sheet.Cells[$"D{row}"].DoubleValue;
                                    var weight    = sheet.Cells[$"E{row}"].DoubleValue;
                                    var imageName = sheet.Cells[$"F{row}"].StringValue;

                                    var imageSourceInfo     = new FileInfo(screen.FileName);
                                    var imageSourceFullPath = $"{imageSourceInfo.DirectoryName}\\images\\{imageName}";
                                    var imageSourceFileInfo = new FileInfo(imageSourceFullPath);

                                    var uniqueName = $"{Guid.NewGuid()}.{imageSourceFileInfo.Extension}";

                                    var baseDirectory   = AppDomain.CurrentDomain.BaseDirectory;
                                    var destinationPath = $"{baseDirectory}image\\{uniqueName}";

                                    File.Copy(imageSourceFullPath, destinationPath);

                                    var newProduct = new Product()
                                    {
                                        ID         = IDGenerator.createID("P"),
                                        Name       = name,
                                        CategoryID = categoryid,
                                        Price      = price,
                                        Weight     = weight,
                                        isDeleted  = false,
                                        Picture    = uniqueName,
                                    };

                                    MainWindow.db.Products.Add(newProduct);
                                    MainWindow.db.SaveChanges();
                                }
                            }

                            row++;
                            cell = sheet.Cells[$"{col}{row}"];
                        }
                        else
                        {
                            row++;
                            cell = sheet.Cells[$"{col}{row}"];
                        }
                    }
                }

                MessageBox.Show("Import completed!", "Message");

                productDataGrid.ItemsSource = MainWindow.db.Products.ToList();
            }
        }