object SystemPropertyClosure {
		trait PropertyProxy {
			def setProperty(key: String, value: String): String
			def clearProperty(key: String): String

			def setProperty(key: String, value: Option[String]): Option[String] = value match {
				case Some(value) => Option { setProperty(key, value) }
				case None => Option { clearProperty(key) }
			}
		}

		private def restoreProperties(history: Seq[(String, Option[String])]) {
			for {
				// get the FIRST value of each property set to restore it
				(key, value) <- history.groupBy(_._1).mapValues(_.head)
			} {
				value match {
					case Some(value) => System.setProperty(key, value)
					case None => System.clearProperty(key)
				}
			}
		}

		def apply[T](body: PropertyProxy => T) = {
			val history = Seq.newBuilder[(String, Option[String])]

			object propertyProxy extends PropertyProxy {
				private def wrapInteraction(key: String, action: => String) = {
					val last = action
					history += key -> Option(last)
					last
				}

				def setProperty(key: String, value: String) = wrapInteraction(key, System.setProperty(key, value))
				def clearProperty(key: String) = wrapInteraction(key, System.clearProperty(key))
			}

			val res = body(propertyProxy)
			restoreProperties(history.result)
			res
		}
	}