NSURL+addPathComponents.swift

extension NSURL {
  /// Appends path components to the receiver, optionally specifying if full path is a directory to avoid filesystem access
  func URLByAppendingPathComponents(pathComponents:[String],lastIsDirectory:Bool? = nil) -> NSURL {
    guard pathComponents.isEmpty == false else { return self }
    var newURL = self
    for idx in pathComponents.startIndex..<pathComponents.endIndex.predecessor() {
      newURL = newURL.URLByAppendingPathComponent(pathComponents[idx], isDirectory: true)
    }
    if let last = pathComponents.last {
      if let lastIsDirectory = lastIsDirectory {
        newURL = newURL.URLByAppendingPathComponent(last, isDirectory: lastIsDirectory)
      }
      else {
        newURL = newURL.URLByAppendingPathComponent(last)
      }
    }
    return newURL
  }
}