import scalaz._
import Scalaz._

case class Asset(id: Int, path: String)
case class AssetDependencyChain(assetToDeps: Map[Asset, Set[Asset]]) {
  def getResolvedDependencies(startingAsset: Asset): ValidationNEL[String, Set[Asset]] = {
    def resolve(workingAsset: Asset, workingPath: Vector[Asset]): ValidationNEL[String, Set[Asset]] = {
      if (workingPath.contains(workingAsset)) "Circular dependency discovered with %s and along path %s.".format(workingAsset, workingPath).failNel[Set[Asset]]
      else {
        val workingSet = Set(workingAsset)
        val newWorkingPath = workingPath :+ workingAsset
        assetToDeps.get(workingAsset).map{dependencies =>
          dependencies.foldLeft(workingSet.successNel[String])((left, right) => (left <**> resolve(right, newWorkingPath))(_ ++ _))
        }.getOrElse(workingSet.successNel[String])
      }
    }
    resolve(startingAsset, Vector())
  }
}

object AssetTest extends App {
  val asset1 = new Asset(1, "Asset1")
  val asset2 = new Asset(2, "Asset2")
  val asset3 = new Asset(3, "Asset3")
  val validDepChain = new AssetDependencyChain(Map(asset1 -> Set(asset2), asset2 -> Set(asset3)))
  println(validDepChain.getResolvedDependencies(asset1))
  val invalidDepChain = new AssetDependencyChain(Map(asset1 -> Set(asset2), asset2 -> Set(asset3), asset3 -> Set(asset1)))
  println(invalidDepChain.getResolvedDependencies(asset1))
}