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Plugins for Google Big Query

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/*
 * Copyright © 2018 Cask Data, Inc.
 *
 * Licensed 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 io.cdap.plugin.gcp.publisher.source;

import io.cdap.cdap.etl.api.streaming.StreamingContext;
import io.cdap.cdap.etl.api.streaming.StreamingSource;
import org.apache.spark.streaming.api.java.JavaDStream;

/**
 * Base implementation of a Realtime source plugin to read from Google PubSub.
 *
 * @param  The type that the PubSubMessage will be mapped to by the mapping function.
 */
public abstract class PubSubSubscriber extends StreamingSource {
  protected final PubSubSubscriberConfig config;
  protected SerializableFunction mappingFunction;

  public PubSubSubscriber(PubSubSubscriberConfig config) {
    this.config = config;
  }

  public PubSubSubscriber(PubSubSubscriberConfig config,
                          SerializableFunction mappingFunction) {
    this.config = config;
    this.mappingFunction = mappingFunction;
  }

  @Override
  public JavaDStream getStream(StreamingContext context) throws Exception {
    if (mappingFunction == null) {
      SerializableFunction serializableFunction = getMappingFunction();
      if (serializableFunction == null) {
        throw new IllegalArgumentException("Mapping Function must be specified for a PubSubSubscriber");
      }
      mappingFunction = serializableFunction;
    }

    return PubSubSubscriberUtil.getStream(context, config, mappingFunction);
  }

  @Override
  public int getRequiredExecutors() {
    return config.getNumberOfReaders();
  }

  /**
   * Get the mapping function
   *
   * @return {@link SerializableFunction}
   */
  public abstract SerializableFunction getMappingFunction();
}