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import language.experimental.macros
import scala.reflect.macros.Context
trait Iso[T, U] {
def to(t : T) : U
// def from(u : U) : T
}
object Iso {
implicit def materializeIso[T, U]: Iso[T, U] = macro impl[T, U]
def impl[T: c.WeakTypeTag, U: c.WeakTypeTag](c: Context): c.Expr[Iso[T, U]] = {
import c.universe._
import definitions._
import Flag._
val sym = c.weakTypeOf[T].typeSymbol
if (!sym.isClass || !sym.asClass.isCaseClass) c.abort(c.enclosingPosition, s"$sym is not a case class")
val fields = sym.typeSignature.declarations.toList.collect{ case x: TermSymbol if x.isVal && x.isCaseAccessor => x }
def mkTpt() = {
val core = Ident(TupleClass(fields.length) orElse UnitClass)
if (fields.length == 0) core
else AppliedTypeTree(core, fields map (f => TypeTree(f.typeSignature)))
}
def mkFrom() = {
if (fields.length == 0) Literal(Constant(Unit))
else Apply(Ident(newTermName("Tuple" + fields.length)), fields map (f => Select(Ident(newTermName("f")), newTermName(f.name.toString.trim))))
}
val evidenceClass = ClassDef(Modifiers(FINAL), newTypeName("$anon"), List(), Template(
List(AppliedTypeTree(Ident(newTypeName("Iso")), List(Ident(sym), mkTpt()))),
emptyValDef,
List(
DefDef(Modifiers(), nme.CONSTRUCTOR, List(), List(List()), TypeTree(), Block(List(Apply(Select(Super(This(tpnme.EMPTY), tpnme.EMPTY), nme.CONSTRUCTOR), List())), Literal(Constant(())))),
DefDef(Modifiers(), newTermName("to"), List(), List(List(ValDef(Modifiers(PARAM), newTermName("f"), Ident(sym), EmptyTree))), TypeTree(), mkFrom()))))
c.Expr[Iso[T, U]](Block(List(evidenceClass), Apply(Select(New(Ident(newTypeName("$anon"))), nme.CONSTRUCTOR), List())))
}
}
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