From 212ad739d200d51525e71d1140cffb8e8cd24de5 Mon Sep 17 00:00:00 2001
From: John O'Keefe <jokeefe@fastmail.com>
Date: Fri, 8 Dec 2023 10:46:19 -0500
Subject: [PATCH] fixed even digit bug

---
 main.go | 52 ++++++++++++++++++++++++++++++++++------------------
 1 file changed, 34 insertions(+), 18 deletions(-)

diff --git a/main.go b/main.go
index cce1d60..d0ca72d 100644
--- a/main.go
+++ b/main.go
@@ -43,39 +43,55 @@ func main() {
 		// Take all the digits in even positions (except for the last one) and add to the number you got above
 		// Divide that number by 10 and take the remainder
 		// If the remainder is not 0, subtract it from 10
+		//
+		// 12/8/2023: New git updates from https://www.gs1.org/services/how-calculate-check-digit-manually
 
 		oddNumber := 0
 		evenNumber := 0
 		var remainder int
 
-		if upcLength < 10 {
-			gtins = append(gtins, "Cannot process upcs less than 10 digits")
+		if upcLength < 8 {
+			gtins = append(gtins, "Cannot process upcs less than 8 digits")
 			continue
 		}
 
-		if upcLength == 10 {
-			upc = "0" + upc
+		if upcLength > 17 {
+			gtins = append(gtins, "Invalid barcode")
+			continue
 		}
 
-		if upcLength > 13 {
-			gtins = append(gtins, "GTINs longer than 14 digits are not valid")
-		}
-
-		for i, num := range upc {
-			if i%2 == 0 {
-				oddString, err := strconv.Atoi(string(num))
-				Error(err)
-				oddNumber += oddString
-			} else {
-				if upcLength-1 > i {
-					evenString, err := strconv.Atoi(string(num))
+		if upcLength%2 == 0 {
+			for i, num := range upc {
+				if i%2 != 0 {
+					convertedOddNumber, err := strconv.Atoi(string(num))
 					Error(err)
-					evenNumber += evenString
+					convertedOddNumber = convertedOddNumber * 3
+					oddNumber += convertedOddNumber
+				} else {
+					if upcLength-1 > i {
+						convertedEvenNumber, err := strconv.Atoi(string(num))
+						Error(err)
+						evenNumber += convertedEvenNumber
+					}
+				}
+			}
+		} else {
+			for i, num := range upc {
+				if i%2 == 0 {
+					convertedOddNumber, err := strconv.Atoi(string(num))
+					Error(err)
+					convertedOddNumber = convertedOddNumber * 3
+					oddNumber += convertedOddNumber
+				} else {
+					if upcLength-1 > i {
+						convertedEvenNumber, err := strconv.Atoi(string(num))
+						Error(err)
+						evenNumber += convertedEvenNumber
+					}
 				}
 			}
 		}
 
-		oddNumber = oddNumber * 3
 		remainder = (oddNumber + evenNumber) % 10
 		if remainder != 0 {
 			remainder = 10 - remainder