/*
 * 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.druid.spark.v2.reader

import org.apache.druid.query.filter.DimFilter
import org.apache.druid.spark.MAPPER
import org.apache.druid.spark.configuration.{Configuration, SerializableHadoopConfiguration}
import org.apache.druid.timeline.DataSegment
import org.apache.spark.sql.SparkSession
import org.apache.spark.sql.sources.v2.reader.{InputPartition, InputPartitionReader}
import org.apache.spark.sql.types.StructType
import org.apache.spark.sql.vectorized.ColumnarBatch

/**
  * Defines a single partition in the dataframe's underlying RDD. This object is generated in the driver and then
  * serialized to the executors where it is responsible for creating the actual ([[InputPartitionReader]]) which
  * does the actual reading.
  */
class DruidColumnarInputPartition(
                                   segment: DataSegment,
                                   schema: StructType,
                                   filter: Option[DimFilter],
                                   columnTypes: Option[Set[String]],
                                   conf: Configuration,
                                   useSparkConfForDeepStorage: Boolean,
                                   useCompactSketches: Boolean,
                                   useDefaultNullHandling: Boolean,
                                   batchSize: Int
                            ) extends InputPartition[ColumnarBatch] {
  // There's probably a better way to do this
  private val session = SparkSession.getActiveSession.get // We're running on the driver, it exists
  private val broadcastConf =
    session.sparkContext.broadcast(
      new SerializableHadoopConfiguration(session.sparkContext.hadoopConfiguration)
    )
  private val serializedSegment: String = MAPPER.writeValueAsString(segment)

  override def createPartitionReader(): InputPartitionReader[ColumnarBatch] = {
    new DruidColumnarInputPartitionReader(
      serializedSegment,
      schema,
      filter,
      columnTypes,
      broadcastConf,
      conf,
      useSparkConfForDeepStorage,
      useCompactSketches,
      useDefaultNullHandling,
      batchSize
    )
  }
}