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.connect.transforms;
  
  import org.apache.kafka.common.cache.Cache;
  import org.apache.kafka.common.cache.LRUCache;
  import org.apache.kafka.common.cache.SynchronizedCache;
  import org.apache.kafka.common.config.ConfigDef;
  import org.apache.kafka.common.utils.AppInfoParser;
  import org.apache.kafka.connect.components.Versioned;
  import org.apache.kafka.connect.connector.ConnectRecord;
  import org.apache.kafka.connect.data.Field;
  import org.apache.kafka.connect.data.Schema;
  import org.apache.kafka.connect.data.SchemaBuilder;
  import org.apache.kafka.connect.data.Struct;
  import org.apache.kafka.connect.errors.DataException;
  import org.apache.kafka.connect.transforms.util.NonEmptyListValidator;
  import org.apache.kafka.connect.transforms.util.SimpleConfig;
  
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import static org.apache.kafka.connect.transforms.util.Requirements.requireMap;
  import static org.apache.kafka.connect.transforms.util.Requirements.requireStruct;
  
  public class ValueToKey<R extends ConnectRecord<R>> implements Transformation<R>, Versioned {
  
      public static final String OVERVIEW_DOC = "Replace the record key with a new key formed from a subset of fields in the record value.";
  
      public static final String FIELDS_CONFIG = "fields";
      public static final String REPLACE_NULL_WITH_DEFAULT_CONFIG = "replace.null.with.default";
  
      public static final ConfigDef CONFIG_DEF = new ConfigDef()
              .define(FIELDS_CONFIG, ConfigDef.Type.LIST, ConfigDef.NO_DEFAULT_VALUE, new NonEmptyListValidator(), ConfigDef.Importance.HIGH,
                      "Field names on the record value to extract as the record key.")
              .define(REPLACE_NULL_WITH_DEFAULT_CONFIG, ConfigDef.Type.BOOLEAN, true, ConfigDef.Importance.MEDIUM,
                      "Whether to replace fields that have a default value and that are null to the default value. When set to true, the default value is used, otherwise null is used.");
  
      private static final String PURPOSE = "copying fields from value to key";
  
      private List<String> fields;
      private boolean replaceNullWithDefault;
  
      private Cache<Schema, Schema> valueToKeySchemaCache;
  
      @Override
      public String version() {
          return AppInfoParser.getVersion();
      }
  
      @Override
      public void configure(Map<String, ?> configs) {
          final SimpleConfig config = new SimpleConfig(CONFIG_DEF, configs);
          fields = config.getList(FIELDS_CONFIG);
          replaceNullWithDefault = config.getBoolean(REPLACE_NULL_WITH_DEFAULT_CONFIG);
          valueToKeySchemaCache = new SynchronizedCache<>(new LRUCache<>(16));
      }
  
      @Override
      public R apply(R record) {
          if (record.valueSchema() == null) {
              return applySchemaless(record);
          } else {
              return applyWithSchema(record);
          }
      }
  
      private R applySchemaless(R record) {
          final Map<String, Object> value = requireMap(record.value(), PURPOSE);
          final Map<String, Object> key = new HashMap<>(fields.size());
          for (String field : fields) {
              key.put(field, value.get(field));
          }
          return record.newRecord(record.topic(), record.kafkaPartition(), null, key, record.valueSchema(), record.value(), record.timestamp());
      }
  
      private R applyWithSchema(R record) {
          final Struct value = requireStruct(record.value(), PURPOSE);
  
          Schema keySchema = valueToKeySchemaCache.get(value.schema());
          if (keySchema == null) {
              final SchemaBuilder keySchemaBuilder = SchemaBuilder.struct();
              for (String field : fields) {
                  final Field fieldFromValue = value.schema().field(field);
                  if (fieldFromValue == null) {
                      throw new DataException("Field does not exist: " + field);
                  }
                  keySchemaBuilder.field(field, fieldFromValue.schema());
              }
              keySchema = keySchemaBuilder.build();
              valueToKeySchemaCache.put(value.schema(), keySchema);
          }
  
          final Struct key = new Struct(keySchema);
          for (String field : fields) {
              key.put(field, replaceNullWithDefault ? value.get(field) : value.getWithoutDefault(field));
          }
  
          return record.newRecord(record.topic(), record.kafkaPartition(), keySchema, key, value.schema(), value, record.timestamp());
      }
  
      @Override
      public ConfigDef config() {
          return CONFIG_DEF;
      }
  
      @Override
      public void close() {
          valueToKeySchemaCache = null;
      }
  
  }
  