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/**
 * 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.config.ConfigDef;
import org.apache.kafka.connect.connector.ConnectRecord;
import org.apache.kafka.connect.data.Schema;
import org.apache.kafka.connect.data.Struct;
import org.apache.kafka.connect.transforms.util.SimpleConfig;

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 abstract class ExtractField> implements Transformation {

    public static final String OVERVIEW_DOC =
            "Extract the specified field from a Struct when schema present, or a Map in the case of schemaless data."
                    + "Use the concrete transformation type designed for the record key (" + Key.class.getCanonicalName() + ") "
                    + "or value (" + Value.class.getCanonicalName() + ").";

    private static final String FIELD_CONFIG = "field";

    public static final ConfigDef CONFIG_DEF = new ConfigDef()
            .define(FIELD_CONFIG, ConfigDef.Type.STRING, ConfigDef.NO_DEFAULT_VALUE, ConfigDef.Importance.MEDIUM, "Field name to extract.");

    private static final String PURPOSE = "field extraction";

    private String fieldName;

    @Override
    public void configure(Map props) {
        final SimpleConfig config = new SimpleConfig(CONFIG_DEF, props);
        fieldName = config.getString(FIELD_CONFIG);
    }

    @Override
    public R apply(R record) {
        final Schema schema = operatingSchema(record);
        if (schema == null) {
            final Map value = requireMap(operatingValue(record), PURPOSE);
            return newRecord(record, null, value.get(fieldName));
        } else {
            final Struct value = requireStruct(operatingValue(record), PURPOSE);
            return newRecord(record, schema.field(fieldName).schema(), value.get(fieldName));
        }
    }

    @Override
    public void close() {
    }

    @Override
    public ConfigDef config() {
        return CONFIG_DEF;
    }

    protected abstract Schema operatingSchema(R record);

    protected abstract Object operatingValue(R record);

    protected abstract R newRecord(R record, Schema updatedSchema, Object updatedValue);

    public static class Key> extends ExtractField {
        @Override
        protected Schema operatingSchema(R record) {
            return record.keySchema();
        }

        @Override
        protected Object operatingValue(R record) {
            return record.key();
        }

        @Override
        protected R newRecord(R record, Schema updatedSchema, Object updatedValue) {
            return record.newRecord(record.topic(), record.kafkaPartition(), updatedSchema, updatedValue, record.valueSchema(), record.value(), record.timestamp());
        }
    }

    public static class Value> extends ExtractField {
        @Override
        protected Schema operatingSchema(R record) {
            return record.valueSchema();
        }

        @Override
        protected Object operatingValue(R record) {
            return record.value();
        }

        @Override
        protected R newRecord(R record, Schema updatedSchema, Object updatedValue) {
            return record.newRecord(record.topic(), record.kafkaPartition(), record.keySchema(), record.key(), updatedSchema, updatedValue, record.timestamp());
        }
    }

}