CollectionDeser.scala

object ConcreteCollection extends App {

  import scala.reflect.runtime.universe.{typeTag, TypeTag}

  def restoreElement[S <: SType](body: Array[Byte], idx: Int): (Value[_ <: SType], TypeTag[_ <: SType]) = {
    if (body(idx) == 10) (IntConstant(body(idx + 1)), typeTag[SInt.type])
    else if (body(idx) == 11) BooleanConstant.fromBoolean(body(idx + 1) != 0) -> typeTag[SBoolean.type] else ???
  }

  def normalize[S <: SType](elems: (Value[_ <: SType], TypeTag[_ <: SType])*)(t: TypeTag[S]): IndexedSeq[Value[S]] = {
    require(elems.map(_._2).forall(_ == t))
    elems.map(_._1).map(v => v.asInstanceOf[Value[S]]).toIndexedSeq
  }

  def decodeCollection(bs: Array[Byte]): Try[ConcreteCollection[_]] = Try {
    bs.head match {
      case b: Byte if b == 1 =>
        val bt = bs.tail
        val elemsCount = bt.head
        val body = bt.tail
        val elems = (0 until elemsCount).map(i => restoreElement(body, i * 2))

        val seq = normalize(elems: _*)(elems.head._2)
        ConcreteCollection(seq)
      case _ => ???
    }
  }

  assert(decodeCollection(Array[Byte](0, 2, 10, 5, 11, 7)).isFailure)
  assert(decodeCollection(Array[Byte](1, 2, 10, 5, 11, 7)).isFailure)
  assert(decodeCollection(Array[Byte](1, 2, 10, 5, 10, 7)).get == ConcreteCollection(IndexedSeq(IntConstant(5), IntConstant(7))))
  assert(decodeCollection(Array[Byte](1, 2, 10, 5, 10, 7)).get != ConcreteCollection(IndexedSeq(IntConstant(5), IntConstant(8))))
  assert(decodeCollection(Array[Byte](1, 2, 11, 5, 10, 7)).isFailure)
  assert(decodeCollection(Array[Byte](1, 2, 11, 5, 11, 7)).get == ConcreteCollection(IndexedSeq(TrueLeaf, TrueLeaf)))
  assert(decodeCollection(Array[Byte](1, 2, 11, 5, 11, 0)).get == ConcreteCollection(IndexedSeq(TrueLeaf, FalseLeaf)))
  assert(decodeCollection(Array[Byte](1, 3, 11, 5, 11, 0, 10, 1)).isFailure)
}