/// Quick sort
/// @author Sam Richards
/// @param {List} $list - list to sort
/// @param {List} $order ($default-order) - order to use for sorting
/// @return {List}
/// @require {function} _str-compare
@function quick-sort($list, $order: $default-order) {
  $less:  ();
  $equal: ();
  $large: ();

  @if length($list) > 1 {
    $seed: nth($list, ceil(length($list) / 2));

    @each $item in $list {
      @if $item == $seed {
        $equal: append($equal, $item, list-separator($list));
      } @else if _str-compare($item, $seed, $order) {
        $less: append($less, $item, list-separator($list));
      } @else if not _str-compare($item, $seed, $order) {
        $large: append($large, $item, list-separator($list));
      }
    }

    @return join(join(quick-sort($less, $order), $equal), quick-sort($large, $order));
  }

  @return $list;
}