package webutility
  
  type QSortDirection int
  
  const (
  	QSortAscending  = 0
  	QSortDescending = 1
  )
  
  // 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 {
  	i := low - 1
  	for j := low; j <= high-1; j++ {
  		if dir == QSortAscending {
  			if que.Compare(j, high) == -1 {
  				i++
  				que.Swap(i, j)
  			}
  		} else if dir == QSortDescending {
  			if que.Compare(j, high) == 1 {
  				i++
  				que.Swap(i, j)
  			}
  		}
  	}
  	que.Swap(i+1, high)
  	return i + 1
  }