fix: move implementation to "internal" package

internal/service/default.go

@@ -0,0 +1,25 @@
+package service
+
+import (
+	"fmt"
+	"regexp"
+)
+
+const (
+	DECIMALS_MULTIPLIER = 100
+)
+
+var (
+	safeInputRegex = regexp.MustCompile(`^[a-zA-Z0-9ÄÖÜäöüß,&'" -]+$`)
+)
+
+func validateString(value string, fieldName string) error {
+	switch {
+	case value == "":
+		return fmt.Errorf("field \"%s\" needs to be set: %w", fieldName, ErrBadRequest)
+	case !safeInputRegex.MatchString(value):
+		return fmt.Errorf("use only letters, dashes and spaces for \"%s\": %w", fieldName, ErrBadRequest)
+	default:
+		return nil
+	}
+}