gistfile1.scala

import org.json4s._
import org.json4s.native.JsonMethods._
import shapeless._
import poly._
import ops.hlist._
import syntax.singleton._
import record._

object Record {
  def keyAsString[F, V](f: FieldType[F, V])(implicit wk: shapeless.Witness.Aux[F]) =
    wk.value.toString
}

object JSON {
  def compact[A](a: A)(implicit st: toJSON.Case[A] { type Result <: JValue }): String = 
    org.json4s.native.JsonMethods.compact(render(st(a)))
 
  def pretty[A](a: A)(implicit st: toJSON.Case[A] { type Result <: JValue }): String = 
    org.json4s.native.JsonMethods.pretty(render(st(a)))
}

object toJSON extends Poly1 { // Pullback1[JValue]  {
  implicit def nullToJSON = at[Null](_ => JNull)
  implicit def doubleToJSON = at[Double](JDouble(_))
  implicit def bigIntToJSON = at[BigInt](JInt(_))
  implicit def bigDecimalToJSON = at[BigDecimal](JDecimal(_))
  implicit def numToJSON[V <% Long] = at[V](i => JInt(BigInt(i)))
  implicit def stringToJSON = at[String](s => if (s == null) JNull else JString(s))
  implicit def boolToJSON = at[Boolean](JBool(_))
  implicit def jsonToJSON[V <: JValue] = at[V](identity)
 
  implicit def dateToJSON[V <: java.util.Date](implicit f: Formats) = 
    at[V](s => if (s == null) JNull else JString(f.dateFormat.format(s)))
 
  implicit def traversableToJSON[V, C[V] <: Traversable[V]](implicit st: Case.Aux[V, JValue]) = 
    at[C[V]](l => JArray(l.toList.map(v => toJSON(v))))
  
  implicit def recordToJSON[R <: HList, F, V](r: R)
    (implicit folderttl2: MapFolder[R, List[JField], fieldToJSON.type]) =
      JObject(r.foldMap(Nil: List[JField])(fieldToJSON)(_ ::: _))
}

object fieldToJSON extends Poly1 {
  implicit def f[F, V](implicit tjf: toJSON.Case[V] { type Result <: JValue }, wk: shapeless.Witness.Aux[F]) = at[FieldType[F, V]] {
    f => (Record.keyAsString(f), tjf(f : V) : JValue) :: Nil
  }
}

object Test {
  def main(args: Array[String]) {
    val x = ("a" ->> 1) ::
            ("b" ->> "c") :: HNil
    val y = toJSON.recordToJSON(x) // wookie
    println(JSON.pretty(y))
    val z = toJSON(x)              // no wookie
    println(JSON.pretty(z))
  }
}