From 818497003bb8f47c71cce940bbe02522301801b1 Mon Sep 17 00:00:00 2001
From: Frede Hundewadt <noreply@wonky.codeberg.org>
Date: Sun, 30 Apr 2023 10:27:33 +0200
Subject: [PATCH] ean format validator added

---
 EanFormatValidator.cs | 73 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 EanFormatValidator.cs

diff --git a/EanFormatValidator.cs b/EanFormatValidator.cs
new file mode 100644
index 0000000..1da7394
--- /dev/null
+++ b/EanFormatValidator.cs
@@ -0,0 +1,73 @@
+// ***********************************************************************
+// Assembly         : FCS.Lib.Utility
+// Author           : inno
+// Created          : 2023 04 25 09:01
+// 
+// Last Modified By : inno
+// Last Modified On : 2023 04 30 10:25
+// ***********************************************************************
+// <copyright file="EanFormatValidator.cs" company="FCS">
+//     Copyright (C) 2023-2023 FCS Frede's Computer Services.
+//     This program is free software: you can redistribute it and/or modify
+//     it under the terms of the GNU Affero General Public License as
+//     published by the Free Software Foundation, either version 3 of the
+//     License, or (at your option) any later version.
+// 
+//     This program is distributed in the hope that it will be useful,
+//     but WITHOUT ANY WARRANTY; without even the implied warranty of
+//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//     GNU Affero General Public License for more details.
+// 
+//     You should have received a copy of the GNU Affero General Public License
+//     along with this program.  If not, see [https://www.gnu.org/licenses]
+// </copyright>
+// <summary></summary>
+// ***********************************************************************
+
+using System.Collections.Generic;
+
+namespace FCS.Lib.Utility;
+
+public class EanFormatValidator
+{
+    private const int Ean13Size = 12;
+
+    public static bool ValidateIan13(string number)
+    {
+        if (number.Length != Ean13Size + 1) return false;
+
+        return number == ParsedNumber(number.Substring(0, Ean13Size));
+    }
+
+    private static string CalculateIan13(IReadOnlyList<int> firstDigits)
+    {
+        var subResult = 0;
+
+        for (var idx = 0; idx < Ean13Size; idx++)
+        {
+            var alt = idx % 2 == 0 ? 1 : 3;
+
+            var digit = firstDigits[idx];
+
+            subResult += digit * alt;
+        }
+
+        var checkDigit = 10 - subResult % 10 == 10 ? 0 : 10 - subResult % 10;
+
+        return string.Join("", firstDigits) + checkDigit;
+    }
+
+    private static string ParsedNumber(string number)
+    {
+        var firstDigits = new int[Ean13Size];
+        if ((number.Length != Ean13Size) | !long.TryParse(number, out _))
+            return null;
+        for (var idx = 0; idx < Ean13Size; idx++)
+        {
+            var digit = int.Parse(number[idx].ToString());
+            firstDigits[idx] = digit;
+        }
+
+        return CalculateIan13(firstDigits);
+    }
+}
\ No newline at end of file