refac: atomic merge, lost-update race, RunPurge cost, duplicated walks

internal/domain/image/imageDomain.go

@@ -246,3 +246,52 @@ type Image struct {
 	CreatedAt    time.Time `json:"created_at"`
 	UpdatedAt    time.Time `json:"updated_at"`
 }
+
+func isStoredNameByte(char byte) bool {
+	return char == '-' || char == '_' || char == '.' || char >= '0' && char <= '9' || char >= 'a' && char <= 'z' || char >= 'A' && char <= 'Z'
+}
+
+func continuesName(body string, end int) bool {
+	if end >= len(body) || !isStoredNameByte(body[end]) {
+		return false
+	}
+	return body[end] != '.' || end+1 < len(body) && isStoredNameByte(body[end+1])
+}
+
+func storedNameMatches(body string, name string) []int {
+	var starts []int
+	if name == "" {
+		return starts
+	}
+	for from := 0; from < len(body); {
+		found := strings.Index(body[from:], name)
+		if found < 0 {
+			break
+		}
+		start := from + found
+		end := start + len(name)
+		from = start + 1
+		if start > 0 && isStoredNameByte(body[start-1]) || continuesName(body, end) {
+			continue
+		}
+		starts = append(starts, start)
+		from = end
+	}
+	return starts
+}
+
+func ContainsStoredName(body string, name string) bool {
+	return len(storedNameMatches(body, name)) > 0
+}
+
+func ReplaceStoredName(body string, from string, to string) string {
+	var rewritten strings.Builder
+	last := 0
+	for _, start := range storedNameMatches(body, from) {
+		rewritten.WriteString(body[last:start])
+		rewritten.WriteString(to)
+		last = start + len(from)
+	}
+	rewritten.WriteString(body[last:])
+	return rewritten.String()
+}