shapeless-csv.scala

import shapeless._
import shapeless.record._
import shapeless.ops.hlist.Mapper
import shapeless.ops.hlist.ToTraversable
import shapeless.ops.record.{Keys, Fields}

import org.joda.time.format.DateTimeFormatter
import org.joda.time.LocalDate

object ShapelessCsv {
  trait MkColumn[C] {
    def apply(col: C): String
  }

  object MkColumn {
    implicit val stringMkColumn: MkColumn[String] = new MkColumn[String] { def apply(col: String): String = col }
    implicit val intMkColumn: MkColumn[Int] = new MkColumn[Int] { def apply(col: Int): String = col.toString }
    implicit def optionMkColumn[A](implicit ev: MkColumn[A]): MkColumn[Option[A]] = new MkColumn[Option[A]] {
      def apply(col: Option[A]): String = col.map(ev(_)).getOrElse("")
    }

    trait FormattedLocalDate[FMT <: DateTimeFormatter] extends Any {
      def date: LocalDate
    }
    implicit def formattedDateMkColumn[FMT <: DateTimeFormatter, A <: FormattedLocalDate[FMT]](implicit w: Witness.Aux[FMT]): MkColumn[A] =
      new MkColumn[A] {
        def apply(col: A): String = w.value.print(col.date)
      }
  }

  object toColumn extends Poly1 {
    implicit def caseMkColumn[C, W](implicit mkColumn: MkColumn[C]) = at[(Symbol with W, C)]{case (h, c) => h.name -> mkColumn(c)}
  }

  trait MkRow[R] {
    def header: Array[String]
    def toRow(row: R): Map[String, String]
  }

  object MkRow {
    def apply[R: MkRow]: MkRow[R] = implicitly[MkRow[R]]

    implicit def row[R, Repr <: HList, Fs <: HList, KVs <: HList, Ks <: HList](implicit
      lg: LabelledGeneric.Aux[R, Repr],
      ks: Keys.Aux[Repr, Ks],
      ksLub: ToTraversable.Aux[Ks, List, Symbol],
      fs: Fields.Aux[Repr, Fs],
      mp: Mapper.Aux[toColumn.type, Fs, KVs],
      tt: ToTraversable.Aux[KVs, List, (String, String)]
    ): MkRow[R] = new MkRow[R] {
      val header = ks().toList.map(_.toString).toArray
      def toRow(row: R): Map[String, String] = lg.to(row).fields.map(toColumn).toList.toMap
    }
  }
}