import scala.reflect.runtime.universe.{NoSymbol, TermName}
import scala.reflect.{classTag, ClassTag}

object ReflectionUtils {

  def defaultValues[T: ClassTag]: Map[String, Any] = {
    import scala.reflect.runtime.currentMirror

    val classSymbol = currentMirror.classSymbol(classTag[T].runtimeClass)
    val moduleMirror = currentMirror.reflectModule(classSymbol.companion.asModule)
    val instanceMirror = currentMirror.reflect(moduleMirror.instance)
    val instanceTypeSignature = instanceMirror.symbol.typeSignature
    val applyMirror = instanceTypeSignature.member(TermName("apply")).asMethod

    applyMirror.paramLists.flatten.zipWithIndex
      .map {
        case (arg, index) =>
          arg.name.toString -> instanceTypeSignature.member(TermName(s"apply$$default$$${index + 1}"))
      }
      .filterNot(_._2 == NoSymbol)
      .map { case (name, value) => name -> instanceMirror.reflectMethod(value.asMethod)() }
      .toMap
  }

  def instantiate[T: ClassTag](values: Map[String, Any]): T = {
    import scala.reflect.runtime.currentMirror

    val classSymbol = currentMirror.classSymbol(classTag[T].runtimeClass)
    val moduleMirror = currentMirror.reflectModule(classSymbol.companion.asModule)
    val instanceMirror = currentMirror.reflect(moduleMirror.instance)
    val instanceTypeSignature = instanceMirror.symbol.typeSignature
    val applyMirror = instanceTypeSignature.member(TermName("apply")).asMethod

    val args = applyMirror.paramLists.flatten.zipWithIndex.map {
      case (arg, index) =>
        val name = arg.name.toString

        if (values.contains(name))
          values(name)
        else
          instanceTypeSignature.member(TermName(s"apply$$default$$${index + 1}")) match {
            case NoSymbol =>
              throw new Exception(s"Missing value for argument $name")
            case value: Any =>
              instanceMirror.reflectMethod(value.asMethod)()
          }
    }

    instanceMirror.reflectMethod(applyMirror)(args: _*).asInstanceOf[T]
  }

}