private void setRegexMatchedTopicsToSourceNodes() {
        if (hasSubscriptionUpdates()) {
            for (final String nodeName : nodeToSourcePatterns.keySet()) {
                final SourceNodeFactory<?, ?> sourceNode = (SourceNodeFactory<?, ?>) nodeFactories.get(nodeName);
                final List<String> sourceTopics = sourceNode.getTopics(subscriptionUpdates);
                //need to update nodeToSourceTopics and sourceTopicNames with topics matched from given regex
                nodeToSourceTopics.put(nodeName, sourceTopics);
                rawSourceTopicNames.addAll(sourceTopics);
            }
            log.debug("Updated nodeToSourceTopics: {}", nodeToSourceTopics);
        }
    }
Returns the map of topic groups keyed by the group id.
A topic group is a group of topics in the same task.

@return groups of topic names
streams/src/main/java/org/apache/kafka/streams/processor/internals/InternalTopologyBuilder.java