From 8bc80c872d140b2c6a1c89c54eba587d4385887b Mon Sep 17 00:00:00 2001
From: sebseb7 <sebgreenbus@gmail.com>
Date: Fri, 18 Jul 2025 16:09:37 +0200
Subject: [PATCH] Enhance GTIN validation in product XML generation: Improved
 the GTIN validation logic in feeds.cjs to include checksum verification,
 ensuring only products with valid GTINs are processed. This update enhances
 data integrity for SEO purposes.

---
 prerender/seo/feeds.cjs | 31 ++++++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/prerender/seo/feeds.cjs b/prerender/seo/feeds.cjs
index 3ecc436..531922b 100644
--- a/prerender/seo/feeds.cjs
+++ b/prerender/seo/feeds.cjs
@@ -343,11 +343,32 @@ const generateProductsXml = (allProductsData = [], baseUrl, config) => {
         return;
       }
       
-      // Validate GTIN format (must be numeric and proper length)
+      // Validate GTIN format and checksum
       const gtinString = product.gtin.toString().trim();
-      const isValidGtin = /^\d{8}$|^\d{12}$|^\d{13}$|^\d{14}$/.test(gtinString);
       
-      if (!isValidGtin) {
+      // Helper function to validate GTIN with proper checksum validation
+      const isValidGTIN = (gtin) => {
+        if (!/^\d{8}$|^\d{12,14}$/.test(gtin)) return false; // Only 8, 12, 13, 14 digits allowed
+
+        const digits = gtin.split('').map(Number);
+        const length = digits.length;
+        let sum = 0;
+
+        for (let i = 0; i < length - 1; i++) {
+          // Even/odd multiplier depends on GTIN length
+          let multiplier = 1;
+          if (length === 8) {
+            multiplier = (i % 2 === 0) ? 3 : 1;
+          } else {
+            multiplier = ((length - i) % 2 === 0) ? 3 : 1;
+          }
+          sum += digits[i] * multiplier;
+        }
+        const checkDigit = (10 - (sum % 10)) % 10;
+        return checkDigit === digits[length - 1];
+      };
+      
+      if (!isValidGTIN(gtinString)) {
         skippedCount++;
         return;
       }
@@ -404,8 +425,8 @@ const generateProductsXml = (allProductsData = [], baseUrl, config) => {
         return;
       }
 
-      // Generate GTIN/EAN if available
-      const gtin = product.gtin ? escapeXml(product.gtin.toString().trim()) : null;
+      // Generate GTIN/EAN if available (use the already validated gtinString)
+      const gtin = gtinString ? escapeXml(gtinString) : null;
 
       // Generate product ID (using articleNumber or seoName)
       const rawProductId = product.articleNumber || product.seoName || `product_${Date.now()}_${Math.random().toString(36).substr(2, 5)}`;