content: /*
   * 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.streams.kstream.internals;
  
  import org.apache.kafka.common.utils.Bytes;
  import org.apache.kafka.streams.errors.StreamsException;
  import org.apache.kafka.streams.kstream.Reducer;
  import org.apache.kafka.streams.processor.api.Processor;
  import org.apache.kafka.streams.processor.api.ProcessorContext;
  import org.apache.kafka.streams.processor.api.Record;
  import org.apache.kafka.streams.processor.internals.StoreFactory;
  import org.apache.kafka.streams.processor.internals.StoreFactory.FactoryWrappingStoreBuilder;
  import org.apache.kafka.streams.state.KeyValueStore;
  import org.apache.kafka.streams.state.StoreBuilder;
  import org.apache.kafka.streams.state.ValueAndTimestamp;
  import org.apache.kafka.streams.state.internals.KeyValueStoreWrapper;
  
  import java.util.Collections;
  import java.util.Set;
  
  import static org.apache.kafka.streams.state.ValueAndTimestamp.getValueOrNull;
  import static org.apache.kafka.streams.state.VersionedKeyValueStore.PUT_RETURN_CODE_NOT_PUT;
  import static org.apache.kafka.streams.state.internals.KeyValueStoreWrapper.PUT_RETURN_CODE_IS_LATEST;
  
  public class KTableReduce<K, V> implements KTableProcessorSupplier<K, V, K, V> {
  
      private final String storeName;
      private final StoreFactory storeFactory;
      private final Reducer<V> addReducer;
      private final Reducer<V> removeReducer;
  
      private boolean sendOldValues = false;
  
      KTableReduce(final MaterializedInternal<K, V, KeyValueStore<Bytes, byte[]>> materialized,
                   final Reducer<V> addReducer,
                   final Reducer<V> removeReducer) {
          this.storeFactory = new KeyValueStoreMaterializer<>(materialized);
          this.storeName = materialized.storeName();
          this.addReducer = addReducer;
          this.removeReducer = removeReducer;
      }
  
      @Override
      public boolean enableSendingOldValues(final boolean forceMaterialization) {
          // Reduce is always materialized:
          sendOldValues = true;
          return true;
      }
  
      @Override
      public Set<StoreBuilder<?>> stores() {
          return Collections.singleton(new FactoryWrappingStoreBuilder<>(storeFactory));
      }
  
      @Override
      public Processor<K, Change<V>, K, Change<V>> get() {
          return new KTableReduceProcessor();
      }
  
      private class KTableReduceProcessor implements Processor<K, Change<V>, K, Change<V>> {
  
          private KeyValueStoreWrapper<K, V> store;
          private TimestampedTupleForwarder<K, V> tupleForwarder;
  
          @SuppressWarnings("unchecked")
          @Override
          public void init(final ProcessorContext<K, Change<V>> context) {
              store = new KeyValueStoreWrapper<>(context, storeName);
              tupleForwarder = new TimestampedTupleForwarder<>(
                  store.store(),
                  context,
                  new TimestampedCacheFlushListener<>(context),
                  sendOldValues);
          }
  
          /**
           * @throws StreamsException if key is null
           */
          @Override
          public void process(final Record<K, Change<V>> record) {
              // the keys should never be null
              if (record.key() == null) {
                  throw new StreamsException("Record key for KTable reduce operator with state " + storeName + " should not be null.");
              }
  
              final ValueAndTimestamp<V> oldAggAndTimestamp = store.get(record.key());
              final V oldAgg = getValueOrNull(oldAggAndTimestamp);
              final V intermediateAgg;
              long newTimestamp;
  
              // first try to remove the old value
              if (record.value().oldValue != null && oldAgg != null) {
                  intermediateAgg = removeReducer.apply(oldAgg, record.value().oldValue);
                  newTimestamp = Math.max(record.timestamp(), oldAggAndTimestamp.timestamp());
              } else {
                  intermediateAgg = oldAgg;
                  newTimestamp = record.timestamp();
              }
  
              // then try to add the new value
              final V newAgg;
              if (record.value().newValue != null) {
                  if (intermediateAgg == null) {
                      newAgg = record.value().newValue;
                  } else {
                      newAgg = addReducer.apply(intermediateAgg, record.value().newValue);
                      newTimestamp = Math.max(record.timestamp(), oldAggAndTimestamp.timestamp());
                  }
              } else {
                  newAgg = intermediateAgg;
              }
  
              // update the store with the new value
              final long putReturnCode = store.put(record.key(), newAgg, newTimestamp);
              // if not put to store, do not forward downstream either
              if (putReturnCode != PUT_RETURN_CODE_NOT_PUT) {
                  tupleForwarder.maybeForward(
                      record.withValue(new Change<>(newAgg, sendOldValues ? oldAgg : null, putReturnCode == PUT_RETURN_CODE_IS_LATEST))
                          .withTimestamp(newTimestamp));
              }
          }
      }
  
      @Override
      public KTableValueGetterSupplier<K, V> view() {
          return new KTableMaterializedValueGetterSupplier<>(storeName);
      }
  }
  