lucasbru commented on code in PR #18442:
URL: https://github.com/apache/kafka/pull/18442#discussion_r1922100063


##########
group-coordinator/src/test/java/org/apache/kafka/coordinator/group/streams/TopicMetadataTest.java:
##########
@@ -0,0 +1,104 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.coordinator.group.streams;
+
+import org.apache.kafka.common.Uuid;
+import 
org.apache.kafka.coordinator.group.generated.StreamsGroupPartitionMetadataValue;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class TopicMetadataTest {
+
+    @Test
+    public void testConstructorWithZeroUuid() {
+        Exception exception = assertThrows(IllegalArgumentException.class, () 
->
+            new TopicMetadata(Uuid.ZERO_UUID, "valid-topic", 3, new 
HashMap<>()));
+        assertEquals("Topic id cannot be ZERO_UUID.", exception.getMessage());
+    }
+
+    @Test
+    public void testConstructorWithNullUuid() {
+        assertThrows(NullPointerException.class, () ->
+            new TopicMetadata(null, "valid-topic", 3, new HashMap<>()));
+    }
+
+    @Test
+    public void testConstructorWithNullName() {
+        assertThrows(NullPointerException.class, () ->
+            new TopicMetadata(Uuid.randomUuid(), null, 3, new HashMap<>()));
+    }
+
+    @Test
+    public void testConstructorWithEmptyName() {
+        Exception exception = assertThrows(IllegalArgumentException.class, () 
->
+            new TopicMetadata(Uuid.randomUuid(), "", 3, new HashMap<>()));
+        assertEquals("Topic name cannot be empty.", exception.getMessage());
+    }
+
+    @Test
+    public void testConstructorWithNegativeNumPartitions() {

Review Comment:
   Hmm, actually not sure why the implementation allows this. I changed it to 
require positive, let's see if it breaks anything.



##########
group-coordinator/src/test/java/org/apache/kafka/coordinator/group/streams/TopicMetadataTest.java:
##########
@@ -0,0 +1,104 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.coordinator.group.streams;
+
+import org.apache.kafka.common.Uuid;
+import 
org.apache.kafka.coordinator.group.generated.StreamsGroupPartitionMetadataValue;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class TopicMetadataTest {
+
+    @Test
+    public void testConstructorWithZeroUuid() {

Review Comment:
   Done



##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/topics/InternalTopicManager.java:
##########
@@ -0,0 +1,290 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.coordinator.group.streams.topics;
+
+import org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopic;
+import 
org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopicConfig;
+import 
org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopicConfigCollection;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.coordinator.group.generated.StreamsGroupTopologyValue;
+import org.apache.kafka.coordinator.group.streams.StreamsTopology;
+import org.apache.kafka.coordinator.group.streams.TopicMetadata;
+
+import org.slf4j.Logger;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Optional;
+import java.util.OptionalInt;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * Responsible for configuring internal topics for a given topology.
+ */
+public class InternalTopicManager {
+
+    /**
+     * Configures the internal topics for the given topology. Given a topology 
and the topic metadata, this method determines the number of
+     * partitions for all internal topics and returns a {@link 
ConfiguredTopology} object.
+     *
+     * @param logContext    The log context.
+     * @param topology      The topology.
+     * @param topicMetadata The topic metadata.
+     * @return The configured topology.
+     */
+    public static ConfiguredTopology configureTopics(LogContext logContext,
+                                                     StreamsTopology topology,
+                                                     Map<String, 
TopicMetadata> topicMetadata) {
+        final Logger log = logContext.logger(InternalTopicManager.class);
+        final Collection<StreamsGroupTopologyValue.Subtopology> subtopologies 
= topology.subtopologies().values();
+
+        final Map<String, Collection<Set<String>>> 
copartitionGroupsBySubtopology =
+            subtopologies.stream()
+                .collect(Collectors.toMap(
+                    StreamsGroupTopologyValue.Subtopology::subtopologyId,
+                    
InternalTopicManager::copartitionGroupsFromPersistedSubtopology)
+                );
+
+        try {
+            Optional<TopicConfigurationException> topicConfigurationException 
= Optional.empty();
+
+            throwOnMissingSourceTopics(topology, topicMetadata);
+
+            Map<String, Integer> decidedPartitionCountsForInternalTopics =
+                decidePartitionCounts(logContext, topology, topicMetadata, 
copartitionGroupsBySubtopology, log);
+
+            final Map<String, ConfiguredSubtopology> configuredSubtopologies =
+                subtopologies.stream()
+                    .collect(Collectors.toMap(
+                        StreamsGroupTopologyValue.Subtopology::subtopologyId,
+                        x -> fromPersistedSubtopology(x, 
decidedPartitionCountsForInternalTopics))
+                    );
+
+            Map<String, CreatableTopic> internalTopicsToCreate = 
missingInternalTopics(configuredSubtopologies, topicMetadata);
+            if (!internalTopicsToCreate.isEmpty()) {
+                topicConfigurationException = 
Optional.of(TopicConfigurationException.missingInternalTopics(
+                    "Internal topics are missing: " + 
internalTopicsToCreate.keySet()
+                ));
+                log.info("Valid topic configuration found, but internal topics 
are missing for topology epoch {}: {}",
+                    topology.topologyEpoch(), 
topicConfigurationException.get().toString());
+            } else {
+                log.info("Valid topic configuration found, topology epoch {} 
is now initialized.", topology.topologyEpoch());
+            }
+
+            return new ConfiguredTopology(
+                topology.topologyEpoch(),
+                Optional.of(configuredSubtopologies),
+                internalTopicsToCreate,
+                topicConfigurationException
+            );
+
+        } catch (TopicConfigurationException e) {
+            log.warn("Topic configuration failed for topology epoch {}: {} ",
+                topology.topologyEpoch(), e.toString());
+            return new ConfiguredTopology(
+                topology.topologyEpoch(),
+                Optional.empty(),
+                Map.of(),
+                Optional.of(e)
+            );
+        }
+    }
+
+    private static void throwOnMissingSourceTopics(final StreamsTopology 
topology,
+                                                   final Map<String, 
TopicMetadata> topicMetadata) {
+        TreeSet<String> sortedMissingTopics = new TreeSet<>();
+        for (StreamsGroupTopologyValue.Subtopology subtopology : 
topology.subtopologies().values()) {
+            for (String sourceTopic : subtopology.sourceTopics()) {
+                if (!topicMetadata.containsKey(sourceTopic)) {
+                    sortedMissingTopics.add(sourceTopic);
+                }
+            }
+        }
+        if (!sortedMissingTopics.isEmpty()) {
+            throw TopicConfigurationException.missingSourceTopics(
+                "Source topics " + String.join(", ", sortedMissingTopics) + " 
are missing.");
+        }
+    }
+
+    private static Map<String, Integer> decidePartitionCounts(final LogContext 
logContext,
+                                                              final 
StreamsTopology topology,
+                                                              final 
Map<String, TopicMetadata> topicMetadata,
+                                                              final 
Map<String, Collection<Set<String>>> copartitionGroupsBySubtopology,
+                                                              final Logger 
log) {
+        final Map<String, Integer> decidedPartitionCountsForInternalTopics = 
new HashMap<>();
+        final Function<String, OptionalInt> topicPartitionCountProvider =
+            topic -> getPartitionCount(topicMetadata, topic, 
decidedPartitionCountsForInternalTopics);
+        final RepartitionTopics repartitionTopics = new RepartitionTopics(
+            logContext,
+            topology.subtopologies().values(),
+            topicPartitionCountProvider);
+        final CopartitionedTopicsEnforcer copartitionedTopicsEnforcer = new 
CopartitionedTopicsEnforcer(
+            logContext,
+            topicPartitionCountProvider);
+        final ChangelogTopics changelogTopics = new ChangelogTopics(logContext,
+            topology.subtopologies().values(),
+            topicPartitionCountProvider);
+
+        
decidedPartitionCountsForInternalTopics.putAll(repartitionTopics.setup());
+
+        final Set<String> fixedRepartitionTopics =
+            topology.subtopologies().values().stream().flatMap(x ->
+                x.repartitionSourceTopics().stream().filter(y -> 
y.partitions() != 0)
+            
).map(StreamsGroupTopologyValue.TopicInfo::name).collect(Collectors.toSet());
+        final Set<String> flexibleRepartitionTopics =
+            topology.subtopologies().values().stream().flatMap(x ->
+                x.repartitionSourceTopics().stream().filter(y -> 
y.partitions() == 0)
+            
).map(StreamsGroupTopologyValue.TopicInfo::name).collect(Collectors.toSet());
+
+        if (fixedRepartitionTopics.isEmpty() && 
flexibleRepartitionTopics.isEmpty()) {
+            log.info("Skipping the repartition topic validation since there 
are no repartition topics.");
+        } else {
+            // ensure the co-partitioning topics within the group have the 
same number of partitions,
+            // and enforce the number of partitions for those repartition 
topics to be the same if they
+            // are co-partitioned as well.
+            for (Collection<Set<String>> copartitionGroups : 
copartitionGroupsBySubtopology.values()) {
+                for (Set<String> copartitionGroup : copartitionGroups) {
+                    decidedPartitionCountsForInternalTopics.putAll(
+                        copartitionedTopicsEnforcer.enforce(copartitionGroup, 
fixedRepartitionTopics, flexibleRepartitionTopics));
+                }
+            }
+        }
+
+        
decidedPartitionCountsForInternalTopics.putAll(changelogTopics.setup());
+
+        return decidedPartitionCountsForInternalTopics;
+    }
+
+    private static Map<String, CreatableTopic> 
missingInternalTopics(Map<String, ConfiguredSubtopology> subtopologyMap,
+                                                                     
Map<String, TopicMetadata> topicMetadata) {
+
+        final Map<String, CreatableTopic> topicsToCreate = new HashMap<>();
+        for (ConfiguredSubtopology subtopology : subtopologyMap.values()) {
+            subtopology.repartitionSourceTopics().values()
+                .forEach(x -> topicsToCreate.put(x.name(), 
toCreatableTopic(x)));
+            subtopology.stateChangelogTopics().values()
+                .forEach(x -> topicsToCreate.put(x.name(), 
toCreatableTopic(x)));
+        }
+        for (Map.Entry<String, TopicMetadata> topic : 
topicMetadata.entrySet()) {
+            final TopicMetadata existingTopic = topic.getValue();
+            final CreatableTopic expectedTopic = 
topicsToCreate.remove(topic.getKey());
+            if (expectedTopic != null) {
+                if (existingTopic.numPartitions() != 
expectedTopic.numPartitions()) {
+                    throw 
TopicConfigurationException.incorrectlyPartitionedTopics("Existing topic " + 
topic.getKey() + " has different"
+                        + " number of partitions: expected " + 
expectedTopic.numPartitions() + ", found " + existingTopic.numPartitions());
+                }
+            }
+        }
+        return topicsToCreate;
+    }
+
+    private static OptionalInt getPartitionCount(Map<String, TopicMetadata> 
topicMetadata,
+                                                 String topic,
+                                                 Map<String, Integer> 
decidedPartitionCountsForInternalTopics) {
+        final TopicMetadata metadata = topicMetadata.get(topic);
+        if (metadata == null) {
+            if (decidedPartitionCountsForInternalTopics.containsKey(topic)) {
+                return 
OptionalInt.of(decidedPartitionCountsForInternalTopics.get(topic));
+            } else {
+                return OptionalInt.empty();
+            }
+        } else {
+            return OptionalInt.of(metadata.numPartitions());
+        }
+    }
+
+    private static CreatableTopic toCreatableTopic(final 
ConfiguredInternalTopic config) {
+
+        final CreatableTopic creatableTopic = new CreatableTopic();
+
+        creatableTopic.setName(config.name());
+        creatableTopic.setNumPartitions(config.numberOfPartitions());
+
+        if (config.replicationFactor().isPresent() && 
config.replicationFactor().get() != 0) {
+            
creatableTopic.setReplicationFactor(config.replicationFactor().get());
+        } else {
+            creatableTopic.setReplicationFactor((short) -1);
+        }
+
+        final CreatableTopicConfigCollection topicConfigs = new 
CreatableTopicConfigCollection();
+
+        config.topicConfigs().forEach((k, v) -> {
+            final CreatableTopicConfig topicConfig = new 
CreatableTopicConfig();
+            topicConfig.setName(k);
+            topicConfig.setValue(v);
+            topicConfigs.add(topicConfig);
+        });
+
+        creatableTopic.setConfigs(topicConfigs);
+
+        return creatableTopic;
+    }
+
+    private static ConfiguredSubtopology fromPersistedSubtopology(
+        final StreamsGroupTopologyValue.Subtopology subtopology,
+        Map<String, Integer> decidedPartitionCountsForInternalTopics
+    ) {
+        return new ConfiguredSubtopology(
+            new HashSet<>(subtopology.sourceTopics()),
+            subtopology.repartitionSourceTopics().stream()
+                .map(x -> fromPersistedTopicInfo(x, 
decidedPartitionCountsForInternalTopics))
+                .collect(Collectors.toMap(ConfiguredInternalTopic::name, x -> 
x)),
+            new HashSet<>(subtopology.repartitionSinkTopics()),
+            subtopology.stateChangelogTopics().stream()
+                .map(x -> fromPersistedTopicInfo(x, 
decidedPartitionCountsForInternalTopics))
+                .collect(Collectors.toMap(ConfiguredInternalTopic::name, x -> 
x))
+        );
+    }
+
+    private static ConfiguredInternalTopic fromPersistedTopicInfo(
+        final StreamsGroupTopologyValue.TopicInfo topicInfo,
+        Map<String, Integer> decidedPartitionCountsForInternalTopics) {

Review Comment:
   Done



##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/topics/InternalTopicManager.java:
##########
@@ -0,0 +1,290 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.coordinator.group.streams.topics;
+
+import org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopic;
+import 
org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopicConfig;
+import 
org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopicConfigCollection;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.coordinator.group.generated.StreamsGroupTopologyValue;
+import org.apache.kafka.coordinator.group.streams.StreamsTopology;
+import org.apache.kafka.coordinator.group.streams.TopicMetadata;
+
+import org.slf4j.Logger;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Optional;
+import java.util.OptionalInt;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * Responsible for configuring internal topics for a given topology.
+ */
+public class InternalTopicManager {
+
+    /**
+     * Configures the internal topics for the given topology. Given a topology 
and the topic metadata, this method determines the number of
+     * partitions for all internal topics and returns a {@link 
ConfiguredTopology} object.
+     *
+     * @param logContext    The log context.
+     * @param topology      The topology.
+     * @param topicMetadata The topic metadata.
+     * @return The configured topology.
+     */
+    public static ConfiguredTopology configureTopics(LogContext logContext,
+                                                     StreamsTopology topology,
+                                                     Map<String, 
TopicMetadata> topicMetadata) {
+        final Logger log = logContext.logger(InternalTopicManager.class);
+        final Collection<StreamsGroupTopologyValue.Subtopology> subtopologies 
= topology.subtopologies().values();
+
+        final Map<String, Collection<Set<String>>> 
copartitionGroupsBySubtopology =
+            subtopologies.stream()
+                .collect(Collectors.toMap(
+                    StreamsGroupTopologyValue.Subtopology::subtopologyId,
+                    
InternalTopicManager::copartitionGroupsFromPersistedSubtopology)
+                );
+
+        try {
+            Optional<TopicConfigurationException> topicConfigurationException 
= Optional.empty();
+
+            throwOnMissingSourceTopics(topology, topicMetadata);
+
+            Map<String, Integer> decidedPartitionCountsForInternalTopics =
+                decidePartitionCounts(logContext, topology, topicMetadata, 
copartitionGroupsBySubtopology, log);
+
+            final Map<String, ConfiguredSubtopology> configuredSubtopologies =
+                subtopologies.stream()
+                    .collect(Collectors.toMap(
+                        StreamsGroupTopologyValue.Subtopology::subtopologyId,
+                        x -> fromPersistedSubtopology(x, 
decidedPartitionCountsForInternalTopics))
+                    );
+
+            Map<String, CreatableTopic> internalTopicsToCreate = 
missingInternalTopics(configuredSubtopologies, topicMetadata);
+            if (!internalTopicsToCreate.isEmpty()) {
+                topicConfigurationException = 
Optional.of(TopicConfigurationException.missingInternalTopics(
+                    "Internal topics are missing: " + 
internalTopicsToCreate.keySet()
+                ));
+                log.info("Valid topic configuration found, but internal topics 
are missing for topology epoch {}: {}",
+                    topology.topologyEpoch(), 
topicConfigurationException.get().toString());
+            } else {
+                log.info("Valid topic configuration found, topology epoch {} 
is now initialized.", topology.topologyEpoch());
+            }
+
+            return new ConfiguredTopology(
+                topology.topologyEpoch(),
+                Optional.of(configuredSubtopologies),
+                internalTopicsToCreate,
+                topicConfigurationException
+            );
+
+        } catch (TopicConfigurationException e) {
+            log.warn("Topic configuration failed for topology epoch {}: {} ",
+                topology.topologyEpoch(), e.toString());
+            return new ConfiguredTopology(
+                topology.topologyEpoch(),
+                Optional.empty(),
+                Map.of(),
+                Optional.of(e)
+            );
+        }
+    }
+
+    private static void throwOnMissingSourceTopics(final StreamsTopology 
topology,
+                                                   final Map<String, 
TopicMetadata> topicMetadata) {
+        TreeSet<String> sortedMissingTopics = new TreeSet<>();
+        for (StreamsGroupTopologyValue.Subtopology subtopology : 
topology.subtopologies().values()) {
+            for (String sourceTopic : subtopology.sourceTopics()) {
+                if (!topicMetadata.containsKey(sourceTopic)) {
+                    sortedMissingTopics.add(sourceTopic);
+                }
+            }
+        }
+        if (!sortedMissingTopics.isEmpty()) {
+            throw TopicConfigurationException.missingSourceTopics(
+                "Source topics " + String.join(", ", sortedMissingTopics) + " 
are missing.");
+        }
+    }
+
+    private static Map<String, Integer> decidePartitionCounts(final LogContext 
logContext,
+                                                              final 
StreamsTopology topology,
+                                                              final 
Map<String, TopicMetadata> topicMetadata,
+                                                              final 
Map<String, Collection<Set<String>>> copartitionGroupsBySubtopology,
+                                                              final Logger 
log) {
+        final Map<String, Integer> decidedPartitionCountsForInternalTopics = 
new HashMap<>();
+        final Function<String, OptionalInt> topicPartitionCountProvider =
+            topic -> getPartitionCount(topicMetadata, topic, 
decidedPartitionCountsForInternalTopics);
+        final RepartitionTopics repartitionTopics = new RepartitionTopics(
+            logContext,
+            topology.subtopologies().values(),
+            topicPartitionCountProvider);
+        final CopartitionedTopicsEnforcer copartitionedTopicsEnforcer = new 
CopartitionedTopicsEnforcer(
+            logContext,
+            topicPartitionCountProvider);
+        final ChangelogTopics changelogTopics = new ChangelogTopics(logContext,
+            topology.subtopologies().values(),
+            topicPartitionCountProvider);
+
+        
decidedPartitionCountsForInternalTopics.putAll(repartitionTopics.setup());
+
+        final Set<String> fixedRepartitionTopics =
+            topology.subtopologies().values().stream().flatMap(x ->
+                x.repartitionSourceTopics().stream().filter(y -> 
y.partitions() != 0)
+            
).map(StreamsGroupTopologyValue.TopicInfo::name).collect(Collectors.toSet());
+        final Set<String> flexibleRepartitionTopics =
+            topology.subtopologies().values().stream().flatMap(x ->
+                x.repartitionSourceTopics().stream().filter(y -> 
y.partitions() == 0)
+            
).map(StreamsGroupTopologyValue.TopicInfo::name).collect(Collectors.toSet());
+
+        if (fixedRepartitionTopics.isEmpty() && 
flexibleRepartitionTopics.isEmpty()) {
+            log.info("Skipping the repartition topic validation since there 
are no repartition topics.");
+        } else {
+            // ensure the co-partitioning topics within the group have the 
same number of partitions,
+            // and enforce the number of partitions for those repartition 
topics to be the same if they
+            // are co-partitioned as well.
+            for (Collection<Set<String>> copartitionGroups : 
copartitionGroupsBySubtopology.values()) {
+                for (Set<String> copartitionGroup : copartitionGroups) {
+                    decidedPartitionCountsForInternalTopics.putAll(
+                        copartitionedTopicsEnforcer.enforce(copartitionGroup, 
fixedRepartitionTopics, flexibleRepartitionTopics));
+                }
+            }
+        }
+
+        
decidedPartitionCountsForInternalTopics.putAll(changelogTopics.setup());
+
+        return decidedPartitionCountsForInternalTopics;
+    }
+
+    private static Map<String, CreatableTopic> 
missingInternalTopics(Map<String, ConfiguredSubtopology> subtopologyMap,
+                                                                     
Map<String, TopicMetadata> topicMetadata) {
+
+        final Map<String, CreatableTopic> topicsToCreate = new HashMap<>();
+        for (ConfiguredSubtopology subtopology : subtopologyMap.values()) {
+            subtopology.repartitionSourceTopics().values()
+                .forEach(x -> topicsToCreate.put(x.name(), 
toCreatableTopic(x)));
+            subtopology.stateChangelogTopics().values()
+                .forEach(x -> topicsToCreate.put(x.name(), 
toCreatableTopic(x)));
+        }
+        for (Map.Entry<String, TopicMetadata> topic : 
topicMetadata.entrySet()) {
+            final TopicMetadata existingTopic = topic.getValue();
+            final CreatableTopic expectedTopic = 
topicsToCreate.remove(topic.getKey());
+            if (expectedTopic != null) {
+                if (existingTopic.numPartitions() != 
expectedTopic.numPartitions()) {
+                    throw 
TopicConfigurationException.incorrectlyPartitionedTopics("Existing topic " + 
topic.getKey() + " has different"
+                        + " number of partitions: expected " + 
expectedTopic.numPartitions() + ", found " + existingTopic.numPartitions());
+                }
+            }
+        }
+        return topicsToCreate;
+    }
+
+    private static OptionalInt getPartitionCount(Map<String, TopicMetadata> 
topicMetadata,
+                                                 String topic,
+                                                 Map<String, Integer> 
decidedPartitionCountsForInternalTopics) {
+        final TopicMetadata metadata = topicMetadata.get(topic);
+        if (metadata == null) {
+            if (decidedPartitionCountsForInternalTopics.containsKey(topic)) {
+                return 
OptionalInt.of(decidedPartitionCountsForInternalTopics.get(topic));
+            } else {
+                return OptionalInt.empty();
+            }
+        } else {
+            return OptionalInt.of(metadata.numPartitions());
+        }
+    }
+
+    private static CreatableTopic toCreatableTopic(final 
ConfiguredInternalTopic config) {
+
+        final CreatableTopic creatableTopic = new CreatableTopic();
+
+        creatableTopic.setName(config.name());
+        creatableTopic.setNumPartitions(config.numberOfPartitions());
+
+        if (config.replicationFactor().isPresent() && 
config.replicationFactor().get() != 0) {
+            
creatableTopic.setReplicationFactor(config.replicationFactor().get());
+        } else {
+            creatableTopic.setReplicationFactor((short) -1);
+        }
+
+        final CreatableTopicConfigCollection topicConfigs = new 
CreatableTopicConfigCollection();
+
+        config.topicConfigs().forEach((k, v) -> {
+            final CreatableTopicConfig topicConfig = new 
CreatableTopicConfig();
+            topicConfig.setName(k);
+            topicConfig.setValue(v);
+            topicConfigs.add(topicConfig);
+        });
+
+        creatableTopic.setConfigs(topicConfigs);
+
+        return creatableTopic;
+    }
+
+    private static ConfiguredSubtopology fromPersistedSubtopology(
+        final StreamsGroupTopologyValue.Subtopology subtopology,
+        Map<String, Integer> decidedPartitionCountsForInternalTopics
+    ) {
+        return new ConfiguredSubtopology(
+            new HashSet<>(subtopology.sourceTopics()),
+            subtopology.repartitionSourceTopics().stream()
+                .map(x -> fromPersistedTopicInfo(x, 
decidedPartitionCountsForInternalTopics))
+                .collect(Collectors.toMap(ConfiguredInternalTopic::name, x -> 
x)),
+            new HashSet<>(subtopology.repartitionSinkTopics()),
+            subtopology.stateChangelogTopics().stream()
+                .map(x -> fromPersistedTopicInfo(x, 
decidedPartitionCountsForInternalTopics))
+                .collect(Collectors.toMap(ConfiguredInternalTopic::name, x -> 
x))
+        );
+    }
+
+    private static ConfiguredInternalTopic fromPersistedTopicInfo(
+        final StreamsGroupTopologyValue.TopicInfo topicInfo,
+        Map<String, Integer> decidedPartitionCountsForInternalTopics) {
+        if (topicInfo.partitions() == 0 && 
!decidedPartitionCountsForInternalTopics.containsKey(topicInfo.name())) {
+            throw new IllegalStateException("Number of partitions must be set 
for topic " + topicInfo.name());
+        }
+
+        return new ConfiguredInternalTopic(
+            topicInfo.name(),
+            topicInfo.partitions() == 0 ? 
decidedPartitionCountsForInternalTopics.get(topicInfo.name()) : 
topicInfo.partitions(),
+            topicInfo.replicationFactor() == 0 ? Optional.empty()
+                : Optional.of(topicInfo.replicationFactor()),
+            topicInfo.topicConfigs() != null ? 
topicInfo.topicConfigs().stream()
+                
.collect(Collectors.toMap(StreamsGroupTopologyValue.TopicConfig::key,
+                    StreamsGroupTopologyValue.TopicConfig::value))
+                : Collections.emptyMap()
+        );
+    }
+
+    private static Collection<Set<String>> 
copartitionGroupsFromPersistedSubtopology(
+        final StreamsGroupTopologyValue.Subtopology subtopology) {

Review Comment:
   This will make the line too long, and my IDE (based on imported checkstyle 
config) will wrap it the same way.... I added another line break.
   
   I didn't know this was an accepted standard in the streams code that 
everybody follows. Is there something I can do in my IDE to follow this? I 
imported the official Kafka checkstyle configuration, and it produces this kind 
of wrapping. It would be good if our "review nitpicking" and automated 
formatting tools somewhat agree.



##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/TopicMetadata.java:
##########
@@ -0,0 +1,77 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.coordinator.group.streams;
+
+import org.apache.kafka.common.Uuid;
+import 
org.apache.kafka.coordinator.group.generated.StreamsGroupPartitionMetadataValue;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * Immutable topic metadata, representing the current state of a topic in the 
broker.
+ *
+ * @param id             The topic id.
+ * @param name           The topic name.
+ * @param numPartitions  The number of partitions.
+ * @param partitionRacks Map of every partition ID to a set of its rack IDs, 
if they exist. If rack information is unavailable for all
+ *                       partitions, this is an empty map.
+ */
+public record TopicMetadata(Uuid id, String name, int numPartitions, 
Map<Integer, Set<String>> partitionRacks) {
+
+    public TopicMetadata(
+        Uuid id,
+        String name,
+        int numPartitions,
+        Map<Integer, Set<String>> partitionRacks
+    ) {
+        this.id = Objects.requireNonNull(id);
+        if (Uuid.ZERO_UUID.equals(id)) {
+            throw new IllegalArgumentException("Topic id cannot be 
ZERO_UUID.");
+        }
+        this.name = Objects.requireNonNull(name);
+        if (name.isEmpty()) {
+            throw new IllegalArgumentException("Topic name cannot be empty.");
+        }
+        this.numPartitions = numPartitions;
+        if (numPartitions < 0) {
+            throw new IllegalArgumentException("Number of partitions cannot be 
negative.");
+        }
+        this.partitionRacks = Objects.requireNonNull(partitionRacks);
+    }
+
+    public static TopicMetadata fromRecord(
+        StreamsGroupPartitionMetadataValue.TopicMetadata record
+    ) {

Review Comment:
   Done



##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/topics/InternalTopicManager.java:
##########
@@ -0,0 +1,290 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.coordinator.group.streams.topics;
+
+import org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopic;
+import 
org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopicConfig;
+import 
org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopicConfigCollection;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.coordinator.group.generated.StreamsGroupTopologyValue;
+import org.apache.kafka.coordinator.group.streams.StreamsTopology;
+import org.apache.kafka.coordinator.group.streams.TopicMetadata;
+
+import org.slf4j.Logger;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Optional;
+import java.util.OptionalInt;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * Responsible for configuring internal topics for a given topology.
+ */
+public class InternalTopicManager {
+
+    /**
+     * Configures the internal topics for the given topology. Given a topology 
and the topic metadata, this method determines the number of
+     * partitions for all internal topics and returns a {@link 
ConfiguredTopology} object.
+     *
+     * @param logContext    The log context.
+     * @param topology      The topology.
+     * @param topicMetadata The topic metadata.
+     * @return The configured topology.
+     */
+    public static ConfiguredTopology configureTopics(LogContext logContext,
+                                                     StreamsTopology topology,
+                                                     Map<String, 
TopicMetadata> topicMetadata) {
+        final Logger log = logContext.logger(InternalTopicManager.class);
+        final Collection<StreamsGroupTopologyValue.Subtopology> subtopologies 
= topology.subtopologies().values();
+
+        final Map<String, Collection<Set<String>>> 
copartitionGroupsBySubtopology =
+            subtopologies.stream()
+                .collect(Collectors.toMap(
+                    StreamsGroupTopologyValue.Subtopology::subtopologyId,
+                    
InternalTopicManager::copartitionGroupsFromPersistedSubtopology)
+                );
+
+        try {
+            Optional<TopicConfigurationException> topicConfigurationException 
= Optional.empty();
+
+            throwOnMissingSourceTopics(topology, topicMetadata);
+
+            Map<String, Integer> decidedPartitionCountsForInternalTopics =
+                decidePartitionCounts(logContext, topology, topicMetadata, 
copartitionGroupsBySubtopology, log);
+
+            final Map<String, ConfiguredSubtopology> configuredSubtopologies =
+                subtopologies.stream()
+                    .collect(Collectors.toMap(
+                        StreamsGroupTopologyValue.Subtopology::subtopologyId,
+                        x -> fromPersistedSubtopology(x, 
decidedPartitionCountsForInternalTopics))
+                    );
+
+            Map<String, CreatableTopic> internalTopicsToCreate = 
missingInternalTopics(configuredSubtopologies, topicMetadata);
+            if (!internalTopicsToCreate.isEmpty()) {
+                topicConfigurationException = 
Optional.of(TopicConfigurationException.missingInternalTopics(
+                    "Internal topics are missing: " + 
internalTopicsToCreate.keySet()
+                ));
+                log.info("Valid topic configuration found, but internal topics 
are missing for topology epoch {}: {}",
+                    topology.topologyEpoch(), 
topicConfigurationException.get().toString());
+            } else {
+                log.info("Valid topic configuration found, topology epoch {} 
is now initialized.", topology.topologyEpoch());
+            }
+
+            return new ConfiguredTopology(
+                topology.topologyEpoch(),
+                Optional.of(configuredSubtopologies),
+                internalTopicsToCreate,
+                topicConfigurationException
+            );
+
+        } catch (TopicConfigurationException e) {
+            log.warn("Topic configuration failed for topology epoch {}: {} ",
+                topology.topologyEpoch(), e.toString());
+            return new ConfiguredTopology(
+                topology.topologyEpoch(),
+                Optional.empty(),
+                Map.of(),
+                Optional.of(e)
+            );
+        }
+    }
+
+    private static void throwOnMissingSourceTopics(final StreamsTopology 
topology,
+                                                   final Map<String, 
TopicMetadata> topicMetadata) {
+        TreeSet<String> sortedMissingTopics = new TreeSet<>();
+        for (StreamsGroupTopologyValue.Subtopology subtopology : 
topology.subtopologies().values()) {
+            for (String sourceTopic : subtopology.sourceTopics()) {
+                if (!topicMetadata.containsKey(sourceTopic)) {
+                    sortedMissingTopics.add(sourceTopic);
+                }
+            }
+        }
+        if (!sortedMissingTopics.isEmpty()) {
+            throw TopicConfigurationException.missingSourceTopics(
+                "Source topics " + String.join(", ", sortedMissingTopics) + " 
are missing.");
+        }
+    }
+
+    private static Map<String, Integer> decidePartitionCounts(final LogContext 
logContext,
+                                                              final 
StreamsTopology topology,
+                                                              final 
Map<String, TopicMetadata> topicMetadata,
+                                                              final 
Map<String, Collection<Set<String>>> copartitionGroupsBySubtopology,
+                                                              final Logger 
log) {
+        final Map<String, Integer> decidedPartitionCountsForInternalTopics = 
new HashMap<>();
+        final Function<String, OptionalInt> topicPartitionCountProvider =
+            topic -> getPartitionCount(topicMetadata, topic, 
decidedPartitionCountsForInternalTopics);
+        final RepartitionTopics repartitionTopics = new RepartitionTopics(
+            logContext,
+            topology.subtopologies().values(),
+            topicPartitionCountProvider);
+        final CopartitionedTopicsEnforcer copartitionedTopicsEnforcer = new 
CopartitionedTopicsEnforcer(
+            logContext,
+            topicPartitionCountProvider);
+        final ChangelogTopics changelogTopics = new ChangelogTopics(logContext,
+            topology.subtopologies().values(),
+            topicPartitionCountProvider);
+
+        
decidedPartitionCountsForInternalTopics.putAll(repartitionTopics.setup());
+
+        final Set<String> fixedRepartitionTopics =
+            topology.subtopologies().values().stream().flatMap(x ->
+                x.repartitionSourceTopics().stream().filter(y -> 
y.partitions() != 0)
+            
).map(StreamsGroupTopologyValue.TopicInfo::name).collect(Collectors.toSet());
+        final Set<String> flexibleRepartitionTopics =
+            topology.subtopologies().values().stream().flatMap(x ->
+                x.repartitionSourceTopics().stream().filter(y -> 
y.partitions() == 0)
+            
).map(StreamsGroupTopologyValue.TopicInfo::name).collect(Collectors.toSet());
+
+        if (fixedRepartitionTopics.isEmpty() && 
flexibleRepartitionTopics.isEmpty()) {
+            log.info("Skipping the repartition topic validation since there 
are no repartition topics.");
+        } else {
+            // ensure the co-partitioning topics within the group have the 
same number of partitions,
+            // and enforce the number of partitions for those repartition 
topics to be the same if they
+            // are co-partitioned as well.
+            for (Collection<Set<String>> copartitionGroups : 
copartitionGroupsBySubtopology.values()) {
+                for (Set<String> copartitionGroup : copartitionGroups) {
+                    decidedPartitionCountsForInternalTopics.putAll(
+                        copartitionedTopicsEnforcer.enforce(copartitionGroup, 
fixedRepartitionTopics, flexibleRepartitionTopics));
+                }
+            }
+        }
+
+        
decidedPartitionCountsForInternalTopics.putAll(changelogTopics.setup());
+
+        return decidedPartitionCountsForInternalTopics;
+    }
+
+    private static Map<String, CreatableTopic> 
missingInternalTopics(Map<String, ConfiguredSubtopology> subtopologyMap,
+                                                                     
Map<String, TopicMetadata> topicMetadata) {
+
+        final Map<String, CreatableTopic> topicsToCreate = new HashMap<>();
+        for (ConfiguredSubtopology subtopology : subtopologyMap.values()) {
+            subtopology.repartitionSourceTopics().values()
+                .forEach(x -> topicsToCreate.put(x.name(), 
toCreatableTopic(x)));
+            subtopology.stateChangelogTopics().values()
+                .forEach(x -> topicsToCreate.put(x.name(), 
toCreatableTopic(x)));
+        }
+        for (Map.Entry<String, TopicMetadata> topic : 
topicMetadata.entrySet()) {
+            final TopicMetadata existingTopic = topic.getValue();
+            final CreatableTopic expectedTopic = 
topicsToCreate.remove(topic.getKey());
+            if (expectedTopic != null) {
+                if (existingTopic.numPartitions() != 
expectedTopic.numPartitions()) {
+                    throw 
TopicConfigurationException.incorrectlyPartitionedTopics("Existing topic " + 
topic.getKey() + " has different"
+                        + " number of partitions: expected " + 
expectedTopic.numPartitions() + ", found " + existingTopic.numPartitions());
+                }
+            }
+        }
+        return topicsToCreate;
+    }
+
+    private static OptionalInt getPartitionCount(Map<String, TopicMetadata> 
topicMetadata,
+                                                 String topic,
+                                                 Map<String, Integer> 
decidedPartitionCountsForInternalTopics) {
+        final TopicMetadata metadata = topicMetadata.get(topic);
+        if (metadata == null) {
+            if (decidedPartitionCountsForInternalTopics.containsKey(topic)) {
+                return 
OptionalInt.of(decidedPartitionCountsForInternalTopics.get(topic));
+            } else {
+                return OptionalInt.empty();
+            }
+        } else {
+            return OptionalInt.of(metadata.numPartitions());
+        }
+    }
+
+    private static CreatableTopic toCreatableTopic(final 
ConfiguredInternalTopic config) {
+
+        final CreatableTopic creatableTopic = new CreatableTopic();
+
+        creatableTopic.setName(config.name());
+        creatableTopic.setNumPartitions(config.numberOfPartitions());
+
+        if (config.replicationFactor().isPresent() && 
config.replicationFactor().get() != 0) {
+            
creatableTopic.setReplicationFactor(config.replicationFactor().get());
+        } else {
+            creatableTopic.setReplicationFactor((short) -1);
+        }
+
+        final CreatableTopicConfigCollection topicConfigs = new 
CreatableTopicConfigCollection();
+
+        config.topicConfigs().forEach((k, v) -> {
+            final CreatableTopicConfig topicConfig = new 
CreatableTopicConfig();
+            topicConfig.setName(k);
+            topicConfig.setValue(v);
+            topicConfigs.add(topicConfig);
+        });
+
+        creatableTopic.setConfigs(topicConfigs);
+
+        return creatableTopic;
+    }
+
+    private static ConfiguredSubtopology fromPersistedSubtopology(
+        final StreamsGroupTopologyValue.Subtopology subtopology,
+        Map<String, Integer> decidedPartitionCountsForInternalTopics
+    ) {

Review Comment:
   Done



##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/TopicMetadata.java:
##########
@@ -0,0 +1,77 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.coordinator.group.streams;
+
+import org.apache.kafka.common.Uuid;
+import 
org.apache.kafka.coordinator.group.generated.StreamsGroupPartitionMetadataValue;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * Immutable topic metadata, representing the current state of a topic in the 
broker.
+ *
+ * @param id             The topic id.

Review Comment:
   Done



##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/TopicMetadata.java:
##########
@@ -0,0 +1,77 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.coordinator.group.streams;
+
+import org.apache.kafka.common.Uuid;
+import 
org.apache.kafka.coordinator.group.generated.StreamsGroupPartitionMetadataValue;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * Immutable topic metadata, representing the current state of a topic in the 
broker.
+ *
+ * @param id             The topic id.
+ * @param name           The topic name.
+ * @param numPartitions  The number of partitions.
+ * @param partitionRacks Map of every partition ID to a set of its rack IDs, 
if they exist. If rack information is unavailable for all
+ *                       partitions, this is an empty map.
+ */
+public record TopicMetadata(Uuid id, String name, int numPartitions, 
Map<Integer, Set<String>> partitionRacks) {
+
+    public TopicMetadata(
+        Uuid id,
+        String name,
+        int numPartitions,
+        Map<Integer, Set<String>> partitionRacks
+    ) {

Review Comment:
   Done



##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/topics/InternalTopicManager.java:
##########
@@ -0,0 +1,290 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.coordinator.group.streams.topics;
+
+import org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopic;
+import 
org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopicConfig;
+import 
org.apache.kafka.common.message.CreateTopicsRequestData.CreatableTopicConfigCollection;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.coordinator.group.generated.StreamsGroupTopologyValue;
+import org.apache.kafka.coordinator.group.streams.StreamsTopology;
+import org.apache.kafka.coordinator.group.streams.TopicMetadata;
+
+import org.slf4j.Logger;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Optional;
+import java.util.OptionalInt;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * Responsible for configuring internal topics for a given topology.
+ */
+public class InternalTopicManager {
+
+    /**
+     * Configures the internal topics for the given topology. Given a topology 
and the topic metadata, this method determines the number of
+     * partitions for all internal topics and returns a {@link 
ConfiguredTopology} object.
+     *
+     * @param logContext    The log context.
+     * @param topology      The topology.
+     * @param topicMetadata The topic metadata.
+     * @return The configured topology.
+     */
+    public static ConfiguredTopology configureTopics(LogContext logContext,
+                                                     StreamsTopology topology,
+                                                     Map<String, 
TopicMetadata> topicMetadata) {
+        final Logger log = logContext.logger(InternalTopicManager.class);
+        final Collection<StreamsGroupTopologyValue.Subtopology> subtopologies 
= topology.subtopologies().values();
+
+        final Map<String, Collection<Set<String>>> 
copartitionGroupsBySubtopology =
+            subtopologies.stream()
+                .collect(Collectors.toMap(
+                    StreamsGroupTopologyValue.Subtopology::subtopologyId,
+                    
InternalTopicManager::copartitionGroupsFromPersistedSubtopology)
+                );
+
+        try {
+            Optional<TopicConfigurationException> topicConfigurationException 
= Optional.empty();
+
+            throwOnMissingSourceTopics(topology, topicMetadata);
+
+            Map<String, Integer> decidedPartitionCountsForInternalTopics =
+                decidePartitionCounts(logContext, topology, topicMetadata, 
copartitionGroupsBySubtopology, log);
+
+            final Map<String, ConfiguredSubtopology> configuredSubtopologies =
+                subtopologies.stream()
+                    .collect(Collectors.toMap(
+                        StreamsGroupTopologyValue.Subtopology::subtopologyId,
+                        x -> fromPersistedSubtopology(x, 
decidedPartitionCountsForInternalTopics))
+                    );
+
+            Map<String, CreatableTopic> internalTopicsToCreate = 
missingInternalTopics(configuredSubtopologies, topicMetadata);
+            if (!internalTopicsToCreate.isEmpty()) {
+                topicConfigurationException = 
Optional.of(TopicConfigurationException.missingInternalTopics(
+                    "Internal topics are missing: " + 
internalTopicsToCreate.keySet()
+                ));
+                log.info("Valid topic configuration found, but internal topics 
are missing for topology epoch {}: {}",
+                    topology.topologyEpoch(), 
topicConfigurationException.get().toString());
+            } else {
+                log.info("Valid topic configuration found, topology epoch {} 
is now initialized.", topology.topologyEpoch());
+            }
+
+            return new ConfiguredTopology(
+                topology.topologyEpoch(),
+                Optional.of(configuredSubtopologies),
+                internalTopicsToCreate,
+                topicConfigurationException
+            );
+
+        } catch (TopicConfigurationException e) {
+            log.warn("Topic configuration failed for topology epoch {}: {} ",
+                topology.topologyEpoch(), e.toString());
+            return new ConfiguredTopology(
+                topology.topologyEpoch(),
+                Optional.empty(),
+                Map.of(),
+                Optional.of(e)
+            );
+        }
+    }
+
+    private static void throwOnMissingSourceTopics(final StreamsTopology 
topology,
+                                                   final Map<String, 
TopicMetadata> topicMetadata) {
+        TreeSet<String> sortedMissingTopics = new TreeSet<>();
+        for (StreamsGroupTopologyValue.Subtopology subtopology : 
topology.subtopologies().values()) {
+            for (String sourceTopic : subtopology.sourceTopics()) {
+                if (!topicMetadata.containsKey(sourceTopic)) {
+                    sortedMissingTopics.add(sourceTopic);
+                }
+            }
+        }
+        if (!sortedMissingTopics.isEmpty()) {
+            throw TopicConfigurationException.missingSourceTopics(
+                "Source topics " + String.join(", ", sortedMissingTopics) + " 
are missing.");
+        }
+    }
+
+    private static Map<String, Integer> decidePartitionCounts(final LogContext 
logContext,
+                                                              final 
StreamsTopology topology,
+                                                              final 
Map<String, TopicMetadata> topicMetadata,
+                                                              final 
Map<String, Collection<Set<String>>> copartitionGroupsBySubtopology,
+                                                              final Logger 
log) {
+        final Map<String, Integer> decidedPartitionCountsForInternalTopics = 
new HashMap<>();
+        final Function<String, OptionalInt> topicPartitionCountProvider =
+            topic -> getPartitionCount(topicMetadata, topic, 
decidedPartitionCountsForInternalTopics);
+        final RepartitionTopics repartitionTopics = new RepartitionTopics(
+            logContext,
+            topology.subtopologies().values(),
+            topicPartitionCountProvider);
+        final CopartitionedTopicsEnforcer copartitionedTopicsEnforcer = new 
CopartitionedTopicsEnforcer(
+            logContext,
+            topicPartitionCountProvider);
+        final ChangelogTopics changelogTopics = new ChangelogTopics(logContext,
+            topology.subtopologies().values(),
+            topicPartitionCountProvider);
+
+        
decidedPartitionCountsForInternalTopics.putAll(repartitionTopics.setup());
+
+        final Set<String> fixedRepartitionTopics =
+            topology.subtopologies().values().stream().flatMap(x ->
+                x.repartitionSourceTopics().stream().filter(y -> 
y.partitions() != 0)
+            
).map(StreamsGroupTopologyValue.TopicInfo::name).collect(Collectors.toSet());
+        final Set<String> flexibleRepartitionTopics =
+            topology.subtopologies().values().stream().flatMap(x ->
+                x.repartitionSourceTopics().stream().filter(y -> 
y.partitions() == 0)
+            
).map(StreamsGroupTopologyValue.TopicInfo::name).collect(Collectors.toSet());
+
+        if (fixedRepartitionTopics.isEmpty() && 
flexibleRepartitionTopics.isEmpty()) {
+            log.info("Skipping the repartition topic validation since there 
are no repartition topics.");
+        } else {
+            // ensure the co-partitioning topics within the group have the 
same number of partitions,
+            // and enforce the number of partitions for those repartition 
topics to be the same if they
+            // are co-partitioned as well.
+            for (Collection<Set<String>> copartitionGroups : 
copartitionGroupsBySubtopology.values()) {
+                for (Set<String> copartitionGroup : copartitionGroups) {
+                    decidedPartitionCountsForInternalTopics.putAll(
+                        copartitionedTopicsEnforcer.enforce(copartitionGroup, 
fixedRepartitionTopics, flexibleRepartitionTopics));
+                }
+            }
+        }

Review Comment:
   Done



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