added vat utils

Properties/AssemblyInfo.cs

@@ -16,5 +16,5 @@ using System.Runtime.InteropServices;
 [assembly: ComVisible(false)]
 [assembly: Guid("aaf08873-14e5-411d-8ec8-629782ac8f03")]
 
-[assembly: AssemblyVersion("2.1.22074.1600")]
-[assembly: AssemblyFileVersion("2.1.22074.1600")]
+[assembly: AssemblyVersion("2.1.22090.1256")]
+[assembly: AssemblyFileVersion("2.1.22090.1256")]

VatUtils.cs

@@ -0,0 +1,164 @@
+using System;
+using System.Collections.Generic;
+using System.Configuration;
+using System.Linq;
+using System.Security.Cryptography.X509Certificates;
+
+namespace FCS.Lib.Utility
+{
+    public class VatUtils
+    {
+        public static bool CheckVat(string countryCode, string vatNumber)
+        {
+            return countryCode.ToUpperInvariant() switch
+            {
+                "DK" => CheckVatNumberDenmark(vatNumber),
+                "NO" => CheckVatNumberNorway(vatNumber),
+                "SE" => CheckVatNumberSweden(vatNumber),
+                _ => false
+            };
+        }
+
+        private static bool CheckVatNumberNorway(string vatNumber)
+        {
+            // https://wiki.scn.sap.com/wiki/display/CRM/Norway
+            // 12 digits
+            // C1..C8 random 0 to 9
+            // C9 Check MOD11
+            // C10 C11 C12 chars == MVA
+            return vatNumber.Length >= 9 && ValidateMod11(vatNumber.Substring(0, 8));
+        }
+
+        private static bool CheckVatNumberDenmark(string vatNumber)
+        {
+            // https://wiki.scn.sap.com/wiki/display/CRM/Denmark
+            // 8 digits 0 to 9
+            // C1..C7
+            // C8 Modulo 11 check digit
+            // C1 > 0
+            // R = (2*C1 + 7*C2 + 6*C3 + 5*C4 + 4*C5 + 3*C6 + 2*C7 + C8)
+            if ((int)char.GetNumericValue(vatNumber[0]) < 1 || vatNumber.Length > 8)
+                return false;
+            return ValidateMod11(vatNumber);
+        }
+
+        private static bool CheckVatNumberSweden(string vatNumber)
+        {
+            // https://wiki.scn.sap.com/wiki/display/CRM/Sweden
+            // 12 digits 0 to 9
+            // C1 = (10 - (R + C2 + C4 + C6 + C8) modulo 10) modulo 10
+            // R = S1 + S3 + S5 + S7 + S9
+            // Si = int(Ci/5) + (Ci*2) modulo 10)
+            // C11 C12 >= 01 <= 94
+            //
+            // Validate full string using Luhn algoritm
+            // 12 chars
+            if (vatNumber.Length != 12)
+                return false;
+            // validate if number
+            if (!int.TryParse(vatNumber, out var result))
+                return false;
+            //validate char 11 and 12
+            var valid = int.TryParse(vatNumber.Substring(10, 2), out var v2);
+            if(valid && v2 is < 1 or > 94 )
+                return false;
+            // check vatnumber
+            return CheckLuhn(vatNumber);
+        }
+
+        public static bool ValidateMod11(string number)
+        {
+            if (long.Parse(number) == 0)
+                return false;
+
+            var sum = 0;
+            for (int i = number.Length - 1, multiplier = 1; i >= 0; i--)
+            {
+                Console.WriteLine($"char: {number[i]} multiplier: {multiplier}");
+                sum += (int)char.GetNumericValue(number[i]) * multiplier;
+                if (++multiplier > 7) multiplier = 2;
+            }
+            return sum % 11 == 0;
+        }
+
+        public static bool ValidateMod10(string number)
+        {
+            if (long.Parse(number) == 0)
+                return false;
+
+            var nDigits = number.Length;
+            var nSum = 0;
+            var isSecond = false;
+            for (var i = nDigits - 1; i >= 0; i--)
+            {
+                var d = (int)char.GetNumericValue(number[i]) - '0';
+                if (isSecond)
+                    d *= 2;
+                nSum += d / 10;
+                nSum += d % 10;
+                isSecond = !isSecond;
+            }
+            return (nSum % 10 == 0);
+        }
+
+        public static bool CheckLuhn(string vatNumber)
+        {
+            // https://www.geeksforgeeks.org/luhn-algorithm/
+            
+            var nDigits = vatNumber.Length;
+            var nSum = 0;
+            var isSecond = false;
+            for (var i = nDigits - 1; i >= 0; i--)
+            {
+                var d = (int)char.GetNumericValue(vatNumber[i]) - '0';
+                if (isSecond)
+                    d *= 2;
+                // We add two digits to handle
+                // cases that make two digits
+                // after doubling
+                nSum += d / 10;
+                nSum += d % 10;
+ 
+                isSecond = !isSecond;
+            }
+            return (nSum % 10 == 0);
+        }
+
+        public static string GetMod10CheckDigit(string number)
+        {
+            var sum = 0;
+            var alt = true;
+            var digits = number.ToCharArray();
+            for (int i = digits.Length - 1; i >= 0; i--)
+            {
+                var curDigit = digits[i] - 48;
+                if (alt)
+                {
+                    curDigit *= 2;
+                    if (curDigit > 9)
+                        curDigit -= 9;
+                }
+                sum += curDigit;
+                alt = !alt;
+            }
+            return sum % 10 == 0 ? "0" : (10 - sum % 10).ToString();
+        }
+
+        public static string AddSelfCheckDigit(string number)
+        {
+            return number + GetMod11CheckDigit(number);
+        }
+
+        public static string GetMod11CheckDigit(string number)
+        {
+            var sum = 0;
+            for (int i = number.Length - 1, multiplier = 2; i >= 0; i--)
+            {
+                sum += (int)char.GetNumericValue(number[i]) * multiplier;
+                if (++multiplier > 7) multiplier = 2;
+            }
+            var modulo = (sum % 11);
+            return modulo is 0 or 1 ? "0" : (11 - modulo).ToString();
+        }
+    }
+}