package webutility
  
  type QSortDirection int
  
  const (

  	QSortAscending QSortDirection = iota
  	QSortDescending

  )
  
  // QuickSortable is an interface for quicksorting slices.
  type QuickSortable interface {
  	Swap(i, j int)
  	Compare(i, j int) int
  	Len() int
  }
  
  // Quicksort quicksorts que.
  func Quicksort(que QuickSortable, low, high int, dir QSortDirection) {
  	if low >= high {
  		return
  	}
  
  	if dir != QSortAscending && dir != QSortDescending {
  		return
  	}
  
  	index := partition(que, low, high, dir)
  	Quicksort(que, low, index-1, dir)
  	Quicksort(que, index+1, high, dir)
  }
  
  func partition(que QuickSortable, low, high int, dir QSortDirection) int {

  	swap := 0
  	// -1 -> i > j
  	//  1 -> i < j
  	if dir == QSortDescending {
  		swap = -1
  	} else {
  		swap = 1
  	}

  	i := low - 1
  	for j := low; j <= high-1; j++ {

  		if que.Compare(j, high) == swap {
  			i++
  			que.Swap(i, j)

  		}

  		continue

  	}
  	que.Swap(i+1, high)
  	return i + 1
  }