Segment Allow List Implementation

SegmentAllowList.scala

import org.http4s.RequestPrelude
import org.typelevel.ci.CIString


object SegmentAllowList {

  def fromAllowList(set: Set[CIString])(req: RequestPrelude): String = {
    classifier(req)((s: String) => if (set.contains(CIString(s))) SegmentFilter.LeaveAsIs else SegmentFilter.star)
  }

  private val SLASH = "/"
  sealed trait SegmentFilter{

    def &&(that: => SegmentFilter): SegmentFilter = this match {
      case SegmentFilter.LeaveAsIs => that
      case otherwise => otherwise
    }
  }
  object SegmentFilter {
    def fromBool(b: Boolean) = b match {
      case false => star
      case true => LeaveAsIs
    }

    final case class TurnToSanitizedSymbol(symbol: String) extends SegmentFilter
    case object LeaveAsIs extends SegmentFilter
    val star: SegmentFilter = TurnToSanitizedSymbol("*")
  }
 
  private def classifier[F[_]](r: RequestPrelude)(segmentFilter: String => SegmentFilter): String = {
    val p = r.uri.path.renderString
    val uriBaseArray = p.split('/')
    if (uriBaseArray.size <= 1){
      SLASH
    } else {
      val base = uriBaseArray.drop(1)
        .foldLeft(new StringBuilder("/")){ case (builder, s) =>
          builder
            .append(
                segmentFilter(s) match {
                  case SegmentFilter.LeaveAsIs => s
                  case SegmentFilter.TurnToSanitizedSymbol(symbol) => symbol
                }
            )
            .append(SLASH)
        }
        val b2 = if (p.endsWith(SLASH)) base else base.dropRight(1)
        b2.result()
    }
  }
}