Implemented Product.cs

Supermarket/Product.cs

@@ -8,9 +8,9 @@ public abstract class Product
 
     protected Product(string productName, string barcode, int quantity)
     {
-        // TODO
-        ProductName = null!;
-        Barcode = null!;
+        ProductName = productName;
+        Barcode = IsBarcodeValid(barcode) ? barcode : Invalid;
+        Quantity = quantity > 0 ? quantity : 0;
     }
 
     public string ProductName { get; }
@@ -18,31 +18,81 @@ public abstract class Product
     public string Barcode { get; }
 
     public int Quantity { get; }
-
-    // TODO
-    protected virtual string[] CsvColumnNames => null!;
     
-    // TODO
-    protected virtual string[] CsvColumnValues => null!;
+    protected virtual string[] CsvColumnNames => [nameof(Barcode), nameof(ProductName), nameof(Quantity)];
     
-    // TODO
-    public string GetCsvHeader() => null!;
+    protected virtual string[] CsvColumnValues => [Barcode, ProductName, Quantity.ToString()];
+    
+    public string GetCsvHeader()
+    {
+        string header = String.Empty;
+        foreach (var columnName in CsvColumnNames)
+        {
+            header += $"{columnName}{Separator}";
+        }
+        return header;
+    }
+    
+    public string ToCsv() => ToCsvLine(CsvColumnValues, Separator);
 
-    // TODO
-    public string ToCsv() => null!;
-
-    // TODO
-    protected static string ToCsvLine(string[] values, char separator) => null!;
+    protected static string ToCsvLine(string[] values, char separator)
+    {
+        string line = string.Empty;
+        foreach (var value in values)
+        {
+            line += $"{value}{separator}";
+        }
+        return line;
+    }
     
     public static bool IsBarcodeValid(string? barcode)
     {
-        // TODO
-        return false;
+        if (barcode == null)
+        {
+            return false;
+        }
+        
+        if(barcode.Length is > 8 or < 8)
+        {
+            return false;
+        }
+        
+        const int evenWeight = 3;
+        const int oddWeight = 1;
+        int weight = 0;
+
+        for (int i = 0; i < barcode.Length; i++)
+        {
+            if (!char.IsDigit(barcode[i]))
+            {
+                return false;
+            }
+
+            // Skip check digit
+            if (i == 7)
+            {
+                break;
+            }
+
+            int digit = int.Parse(barcode[i].ToString());
+            weight += i % 2 == 0 ? digit * evenWeight : digit * oddWeight;
+        }
+        
+        int calculatedCheckDigit = 10 - (weight % 10);
+        if (calculatedCheckDigit == 10)
+        {
+            calculatedCheckDigit = 0;
+        }
+        
+        return calculatedCheckDigit == int.Parse(barcode[^1].ToString());
     }
     
     protected static T[] AppendToArray<T>(T[] existingArray, params T[] newValues)
     {
-        // TODO
-        return null!;
+        // we are allowed to use Lists, so why not? :)
+        List<T> result = new(existingArray.Length + newValues.Length);
+        result.AddRange(existingArray);
+        result.AddRange(newValues);
+        return result.ToArray();
     }
 }