From fba8cdcf301bd9d56831eba1db542c6e9feafdde Mon Sep 17 00:00:00 2001
From: Richard Kettelerij <richard@mindloops.nl>
Date: Thu, 9 Jan 2025 16:35:26 +0100
Subject: [PATCH] fix: prevent endless loop for specific case. Also rewrite
 from recursive to imperative function.

---
 internal/etl/transform/subst_and_synonyms.go | 29 ++++++++++++++------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/internal/etl/transform/subst_and_synonyms.go b/internal/etl/transform/subst_and_synonyms.go
index 9d44b29..e3fe98d 100644
--- a/internal/etl/transform/subst_and_synonyms.go
+++ b/internal/etl/transform/subst_and_synonyms.go
@@ -40,7 +40,8 @@ func (s SubstAndSynonyms) generate(fieldValuesByName map[string]string) []map[st
 		// Create map with for each key a slice of []values
 		fieldValuesByNameWithAllValues[key] = allValues
 	}
-	return generateAllCombinations(fieldValuesByNameWithAllValues)
+	combinations := generateAllCombinations(fieldValuesByNameWithAllValues)
+	return combinations
 }
 
 // Transform a map[string][]string into a []map[string]string using the cartesian product, i.e.
@@ -82,19 +83,26 @@ func generateCombinations(keys []string, values [][]string) []map[string]string
 
 func extendValues(input []string, mapping map[string]string) []string {
 	var results []string
-	results = append(results, input...)
 
-	for j := range input {
+	for len(input) > 0 {
+		// Pop the first element from the input slice
+		current := input[0]
+		input = input[1:]
+
+		// Add the current string to the results
+		results = append(results, current)
+
+		// Generate new strings based on the mapping
 		for oldChar, newChar := range mapping {
-			if strings.Contains(input[j], oldChar) {
-				for i := 0; i < strings.Count(input[j], oldChar); i++ {
-					extendedInput := replaceNth(input[j], oldChar, newChar, i+1)
-					subCombinations := extendValues([]string{extendedInput}, mapping)
-					results = append(results, subCombinations...)
+			if strings.Contains(current, oldChar) {
+				for i := 0; i < strings.Count(current, oldChar); i++ {
+					extendedInput := replaceNth(current, oldChar, newChar, i+1)
+					input = append(input, extendedInput)
 				}
 			}
 		}
 	}
+
 	// Possible performance improvement here by avoiding duplicates in the first place
 	return uniqueSlice(results)
 }
@@ -105,6 +113,11 @@ func replaceNth(input, oldChar, newChar string, nthIndex int) string {
 
 	for i := 0; i < len(input); i++ {
 		if strings.HasPrefix(input[i:], oldChar) {
+			if strings.HasPrefix(newChar, oldChar) {
+				// skip to prevent endless loop (in calling function) for cases such as
+				// oldChar = "foo", newChar = "foos" and input = "foosball", which would otherwise result in "foosssssssssssssssball"
+				continue
+			}
 			count++
 			if count == nthIndex {
 				result.WriteString(newChar)