function fv_dragList( name )
  {

  // name of this dragList. Must match the id of the root DIV tag.

  this.dragListRootId = name;

  // array of item offsets

  this.offsetsX = new Array();
  this.offsetsY = new Array();

  }

// ----------------------------------------------

/**
* setup the draglist prior to use
*
* @param string orientation defaults to vert. if set to "horz" renders horizontally.
* @param string itemTagName. if null defaults to "div". Can be "span".
*/

fv_dragList.prototype.setup = function( orientation, itemTagName )
  {

  var horizontal;

  if ( orientation == "horz" )
    horizontal = true;
  else
    horizontal = false;

  this.listRoot = document.getElementById( this.dragListRootId );
  this.listItems = this.getListItems( itemTagName );

  for (var i = 0; i < this.listItems.length; i++) 
    {

    if ( this.listItems[i] == undefined )
      continue;

    if ( horizontal )
      {
      Drag.init(this.listItems[i], null, null, null, 0, 0);
      }
    else
      {
      Drag.init(this.listItems[i], null, 0, 0, null, null);
      }

    // ---------------------------------------------------
    // on drag method

    this.listItems[i].onDrag = function( x, y, thisElem ) 
      {

      x = thisElem.offsetLeft;
      y = thisElem.offsetTop;

      // this is a callback from the dom-drag code. From within this
      // function "this" does not refer to the fv_draglist function.

      draglist = getDragList( thisElem );

      draglist.recalcOffsets( itemTagName );

      var pos = draglist.getCurrentOffset( thisElem, itemTagName );

      //var listItems = this.getListItems( itemTagName );

      // if bottom edge is below top of lower item.

      var testMoveUp;
      var testMoveDown;
      if ( horizontal )
        {
        testMoveUp = (x + draglist.getDivWidth(thisElem) > draglist.offsetsX[pos + 1] + draglist.getDivWidth( draglist.listItems[pos + 1] ));
        testMoveDown = x < draglist.offsetsX[pos - 1];
        }
      else
        {
        testMoveUp = (y + draglist.getDivHeight(thisElem) > draglist.offsetsY[pos + 1] + draglist.getDivHeight( draglist.listItems[pos + 1] ));
        testMoveDown = y < draglist.offsetsY[pos - 1];
        }

      if (( pos != draglist.listItems.length - 1) && testMoveUp )
        { 
        draglist.listRoot.removeChild(thisElem);

        if ( pos + 1 == draglist.listItems.length )
          {
          draglist.listRoot.appendChild( thisElem );
          }
        else
          {
          draglist.listRoot.insertBefore(thisElem, draglist.listItems[pos+1]);
          }

        thisElem.style["top"] = "0px";
        thisElem.style["left"] = "0px";
        }
      else if ( pos != 0 && testMoveDown ) 
        { 
        draglist.listRoot.removeChild(thisElem);
        draglist.listRoot.insertBefore(thisElem, draglist.listItems[pos-1]);
        thisElem.style["top"] = "0px";
        thisElem.style["left"] = "0px";
        }

      };

    this.listItems[i].onDragEnd = function(x,y,thisElem) 
      {
      thisElem.style["top"] = "0px";
      thisElem.style["left"] = "0px";
      }

    }  // end of for loop.

  this.recalcOffsets( itemTagName );

  }  // end of setup.

// ----------------------------------------------


/**
* update the order value fields and submit the form.
*/

fv_dragList.prototype.do_submit = function( formName, dragListRootId )
  {

  var listOrderItems = this.listRoot.getElementsByTagName("input");

  for (var i = 0; i < listOrderItems.length; i++) 
    {
    listOrderItems[i].value = i;
    }

  expr = "document." + formName + ".submit()";

  eval( expr );
  }

// ----------------------------------------------
// "Private" methods.
// ----------------------------------------------

fv_dragList.prototype.recalcOffsets = function( itemTagName ) 
  {
  var listItems = this.getListItems( itemTagName );

  for (var i = 0; i < listItems.length; i++) 
    {
    this.offsetsX[i] = listItems[i].offsetLeft;
    this.offsetsY[i] = listItems[i].offsetTop;
    }
  }

fv_dragList.prototype.getCurrentOffset = function(elem, itemTagName) 
  { 
  var listItems = this.getListItems( itemTagName );

  for (var i = 0; i < listItems.length; i++) 
    {
    if (listItems[i] == elem) 
      { 
      return i;
      }
    }
  }

fv_dragList.prototype.getDivWidth = function(elem)                   
  {

  if (( elem == undefined) || ( elem.offsetWidth == undefined ))
    return( 0 );

  value = elem.offsetWidth;
  if (isNaN(value))
    {
    value = 0;
    }

  return( value );
  }

fv_dragList.prototype.getDivHeight = function(elem) 
  {

  if (( elem == undefined) || ( elem.offsetHeight == undefined ))
    return( 0 );

  value = elem.offsetHeight;
  if (isNaN(value))
    {
    value = 25;
    }

  return( value );
  }

/**
* return list of draggable items
*/

fv_dragList.prototype.getListItems = function( itemTagName )
  {
  if ( itemTagName == undefined )
    {
    itemTagName = "div";
    }

  var listItems = this.listRoot.getElementsByTagName( itemTagName );

  return( listItems );
  }

// end of draglist class definition.

// -------------------------------------

/**
* add a new dragList to the list of draglists on this page
*
* This implementatoin supports multiple managed draglists on
* a single page. The index is contained in a global dragListIndex
* array that must be declared in the page.
*/

function addDragList( draglist )
  {
  dragListIndex[ draglist.dragListRootId ] = draglist;
  }

// -------------------------------------------------------

/**
* given a draggable div element, return the draglist it belongs to
*
* @see fv_draglist.prototype.setup
* @todo this should probably be a method inside the draglist class.
*/

function getDragList( elem )
  {

  // given a list item return the drag list it belongs to.

  var draglistContainer = elem.parentNode;

  var draglist = dragListIndex[ draglistContainer.id ];

  return( draglist );
  }