DecodeTWithDefault.scala

import scalaz._

import Scalaz._
import argonaut._
import Argonaut._

/**
 * Created by tldeti on 14-9-23.
 */
object Tags {

  sealed trait WithDefault

  def TWIthDefault[A](a: A): A @@ WithDefault = Tag[A, WithDefault](a)


}

import Tags._

object Decodes {
  implicit val stringDefaultDecode: DecodeJson[String @@ WithDefault] = DecodeJson(
    h =>
      h.as[String].map(x =>
        Tags.TWIthDefault(
          if (x.trim.isEmpty)
            "not Supplied"
          else
            x
        )
      )
  )
}

import Decodes._

object test extends App {

  case class Eg(a:String,b:String)
  val tt = Eg("","x")
  val ttt = Eg("x","")

  implicit val decodeA:DecodeJson[Eg] = DecodeJson(
    h=>
      for{
        a <- (h --\ "a").as[String @@ WithDefault]
        b <- (h --\ "b").as[String]
      } yield Eg(Tag.unwrap(a),b)
  )

  implicit val encodeA:EncodeJson[Eg] =
    jencode2L((p: Eg) => (p.a, p.b))("a", "b")

  tt.asJson.as[Eg].fold((x,y)=> throw new RuntimeException("eror"),m=>
    assert(Eg("not Supplied","x") == m)
  )

  ttt.asJson.as[Eg].fold((x,y)=> throw new RuntimeException("eror"),m=>
    assert(Eg("x","") == m)
  )


}