/*
 * 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.hudi

import org.apache.hudi.common.table.{HoodieTableMetaClient, TableSchemaResolver}
import org.apache.spark.rdd.RDD
import org.apache.spark.sql.sources.{BaseRelation, TableScan}
import org.apache.spark.sql.types.StructType
import org.apache.spark.sql.{Row, SQLContext}

import scala.util.control.NonFatal

/**
 * BaseRelation representing empty RDD.
 * @param sqlContext instance of SqlContext.
 */
class EmptyRelation(val sqlContext: SQLContext, metaClient: HoodieTableMetaClient) extends BaseRelation with TableScan {

  override def schema: StructType = {
    // do the best to find the table schema.
    val schemaResolver = new TableSchemaResolver(metaClient)
    try {
      val avroSchema = schemaResolver.getTableAvroSchema
      AvroConversionUtils.convertAvroSchemaToStructType(avroSchema)
    } catch {
      case NonFatal(e) =>
        StructType(Nil)
    }
  }

  override def buildScan(): RDD[Row] = {
    sqlContext.sparkContext.emptyRDD[Row]
  }
}
