measure/src/main/scala/org/apache/griffin/measure/step/builder/dsl/expr/SelectExpr.scala

/*
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.griffin.measure.step.builder.dsl.expr

trait HeadExpr extends Expr with AliasableExpr {
  def alias: Option[String] = None
}

case class DataSourceHeadExpr(name: String) extends HeadExpr {
  def desc: String = s"`${name}`"
  def coalesceDesc: String = desc
}

case class FieldNameHeadExpr(field: String) extends HeadExpr {
  def desc: String = s"`${field}`"
  def coalesceDesc: String = desc
  override def alias: Option[String] = Some(field)
}

case class AllSelectHeadExpr() extends HeadExpr {
  def desc: String = "*"
  def coalesceDesc: String = desc
}

case class OtherHeadExpr(expr: Expr) extends HeadExpr {

  addChild(expr)

  def desc: String = expr.desc
  def coalesceDesc: String = expr.coalesceDesc
  override def alias: Option[String] = Some(expr.desc)

  override def map(func: (Expr) => Expr): OtherHeadExpr = {
    OtherHeadExpr(func(expr))
  }
}

// -------------

trait SelectExpr extends Expr with AliasableExpr {
}

case class AllFieldsSelectExpr() extends SelectExpr {
  def desc: String = ".*"
  def coalesceDesc: String = desc
  def alias: Option[String] = None
}

case class FieldSelectExpr(field: String) extends SelectExpr {
  def desc: String = s".`${field}`"
  def coalesceDesc: String = desc
  override def alias: Option[String] = Some(field)
}

case class IndexSelectExpr(index: Expr) extends SelectExpr {

  addChild(index)

  def desc: String = s"[${index.desc}]"
  def coalesceDesc: String = desc
  def alias: Option[String] = Some(index.desc)

  override def map(func: (Expr) => Expr): IndexSelectExpr = {
    IndexSelectExpr(func(index))
  }
}

case class FunctionSelectExpr(functionName: String, args: Seq[Expr]) extends SelectExpr {

  addChildren(args)

  def desc: String = ""
  def coalesceDesc: String = desc
  def alias: Option[String] = Some(functionName)

  override def map(func: (Expr) => Expr): FunctionSelectExpr = {
    FunctionSelectExpr(functionName, args.map(func(_)))
  }
}

// -------------

case class SelectionExpr(head: HeadExpr, selectors: Seq[SelectExpr], aliasOpt: Option[String])
  extends SelectExpr {

  addChildren(head +: selectors)

  def desc: String = {
    selectors.foldLeft(head.desc) { (hd, sel) =>
      sel match {
        case FunctionSelectExpr(funcName, args) =>
          val nargs = hd +: args.map(_.desc)
          s"${funcName}(${nargs.mkString(", ")})"
        case _ => s"${hd}${sel.desc}"
      }
    }
  }
  def coalesceDesc: String = {
    selectors.lastOption match {
      case None => desc
      case Some(sel: FunctionSelectExpr) => desc
      case _ => s"coalesce(${desc}, '')"
    }
  }
  def alias: Option[String] = {
    if (aliasOpt.isEmpty) {
      val aliasSeq = (head +: selectors).flatMap(_.alias)
      if (aliasSeq.size > 0) Some(aliasSeq.mkString("_")) else None
    } else aliasOpt
  }

  override def map(func: (Expr) => Expr): SelectionExpr = {
    SelectionExpr(func(head).asInstanceOf[HeadExpr],
      selectors.map(func(_).asInstanceOf[SelectExpr]), aliasOpt)
  }
}