List imap mail folders with parent and child relationship

ImapFolders.scala

/**
 * List the with parent and child relationship
 */
object ImapFolders extends App {
  val folders = List(
    "mail201.udomain.com.hk.Winway", 
    "mail201.udomain.com.hk.Winway.Quota", 
    "mail201.udomain.com.hk.Winway.Delivery",
    "mail201.udomain.com.hk.Winway.PO",
    "mail201.udomain.com.hk.UA",
    "mail201.udomain.com.hk.UA.Haha",
    "mail201.udomain.com.hk.UA.Lala",
    "mail201.udomain.com.hk.UA.Lala.A",
    "mail201.udomain.com.hk.UA.Lala.B",
    "mail201.udomain.com.hk.UA.Vendor",
    "mail201.udomain.com.hk.UA.Vendor.RSI",
    "mail201.udomain.com.hk.UA.Vendor.American Phil",
    "mail201.udomain.com.hk.UA.Vendor.American Phil.PO",
    "mail201.udomain.com.hk.UA.Vendor.SCI",
    "mail201.udomain.com.hk.UA.Color",
    "mail201.udomain.com.hk.Excellent",
    "mail201.udomain.com.hk.Excellent.PO",
    "mail201.udomain.com.hk.Excellent.Quote",
    "mail201.udomain.com.hk.Maker",
    "mail201.udomain.com.hk.Maker.Maker Factory",
    "mail201.udomain.com.hk.Champion",
    "mail201.udomain.com.hk.Champion.Order",
    "mail201.udomain.com.hk.Champion.Quote",
    "mail201.udomain.com.hk.Champion.Delivery",
    "mail201.udomain.com.hk.TAL",
    "mail201.udomain.com.hk.TAL.Order",
    "mail201.udomain.com.hk.TAL.Quote",
    "mail201.udomain.com.hk.TAL.Account",
    "mail201.udomain.com.hk.GPSS",
    "mail201.udomain.com.hk.Sent Messages",
    "mail201.udomain.com.hk.HSBC",
    "mail201.udomain.com.hk.Drafts",
    "mail201.udomain.com.hk.Other Factory",
    "mail201.udomain.com.hk.Deleted Message",
    "Outbox",
    "Spam",
    "Draft",
    "Trash",
    "OldInbox",
    "INBOX"
  )

  //!--NOTE-- 
  //The gist divide the following steps into two steps for better illustration
  //Actually, step 1 and 2 can be merged together...

  // Step 1:
  // Find grouped folders foreach elemented
  // If the size of a group is one, this means its group member is itself
  val groupedFolders = 
    folders map (x => findGroup(x, folders))

  //groups which have children
  val groupsWithChildren = groupedFolders filter (_.length > 1)

  // Check whether any group it is a child of other groups.
  // If yes, remove it
  val uniqueGroupedFolders = groupedFolders filter { x =>  
    //Loop though all groupsWithChildren
    //Check if any of them contains x,
    // If x is contained in subgroups,
    // need to remove x in this group to avoid duplication
    if(inSubgroup(x, groupsWithChildren)) false
    else true
  }

  uniqueGroupedFolders foreach (println)

  println(uniqueGroupedFolders(6))
  println("-------------------------------")

  
  // Step 2:
  // For each group whose member size is larger than 3, 
  // we need to do similar stuffs recursively since subgroup may exist
  val groupedResult = uniqueGroupedFolders map { grp =>
    if(grp.length >= 3)
      divideSubgroup(grp, 0)
    else
      grp
  }

  groupedResult foreach println


  def divideSubgroup(group: List[String], level:Int):List[Any] = {
    //Remeber that the first elem is parent, So start with the second elem
    val subGroup = group.tail
    val grpedFolders = subGroup map (x => findGroup(x, subGroup))
    
    val grpsWithChildren = grpedFolders filter (_.length > 1)
    val uniqueGrpedFolders = grpedFolders filter { x => 
      if(inSubgroup(x, grpsWithChildren)) false
      else true
    }
    
    //If the group size is 1, means no subgroup
    val children = uniqueGrpedFolders filter (_.length == 1)

    //If the group size > 2, means it is a potential subgroup
    val potentialSubgroups = uniqueGrpedFolders filter (_.length > 1)

    val result:List[Any] = (group.head :: children.map(_.head))

    if(!potentialSubgroups.isEmpty)
      potentialSubgroups.foldLeft(result) { (r, sub) =>
        r ::: List(divideSubgroup(sub, level + 1))
      }
    else
      result
  }

  def inSubgroup(elem:List[String], haystack:List[List[String]]):Boolean = {
    for(compare <- haystack) {
      if(compare.length > elem.length 
        && compare.toSet.intersect(elem.toSet) == elem.toSet)
        return true
    }
    return false
  }
  
  def findGroup(elem: String, haystack: List[String]):List[String] = {
    //Find all elements startWith "elem." in "haystack"
    //e.g. if "elem" is "mail201.udomain.com.hk.TAL", 
    //then mail201.udomain.com.hk.TAL.Order and similar items should be 
    //returned
    return elem :: haystack.filter(_.startsWith(s"$elem."))
  }
}