gistfile1.scala

package co.aryaapp.macros

import scala.annotation.StaticAnnotation
import scala.language.experimental.macros
import scala.reflect.macros.whitebox

package co.aryaapp.macros

object Util {
  def unCamelCase(s:String):String = {
    (s.head.toLower :: s.tail.flatMap( c =>
        if (c.isUpper)
          '_' :: c.toLower :: Nil
        else c :: Nil
      ) :: Nil).mkString("")
    }
}

object argonautMacro {
  def impl(c: whitebox.Context)(annottees: c.Expr[Any]*): c.Expr[Any] = {
    import c.universe._

    val (className, classFields:List[ValDef]) = annottees(0).tree match {
      case q"case class $name(..$fields)" => (name, fields)
    }
    val fields = classFields.map{ vd:ValDef => (vd.name, vd.tpt) }
    val fieldNamesWithUnderscores = fields.map{ case (name, _) => Util.unCamelCase(name.toString) }
    val casecodecN = TermName("casecodec"+fields.length.toString)
    val reunited = fields.map{ case (name, tpe) => q" $name: $tpe " }
    val cnCodecJson = TermName(s"${className}CodecJson")
    val cn = TermName(className.toString)

    c.Expr[Any](q"""
     case class $className ( ..$reunited )
     object $cn { implicit def $cnCodecJson : CodecJson[ $className ] = $casecodecN ($cn.apply, $cn.unapply)(..$fieldNamesWithUnderscores) }
    """)
  }
}

object Macros {
  class argonaut extends StaticAnnotation {
    def macroTransform(annottees: Any*) = macro argonautMacro.impl
  }

}