dragdrop.js

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    if(options.reverteffect)
      options_for_draggable.reverteffect = options.reverteffect;
    else
      if(options.ghosting) options_for_draggable.reverteffect = function(element) {
        element.style.top  = 0;
        element.style.left = 0;
      };

    if(options.endeffect)
      options_for_draggable.endeffect = options.endeffect;

    if(options.zindex)
      options_for_draggable.zindex = options.zindex;

    // build options for the droppables  
    var options_for_droppable = {
      overlap:     options.overlap,
      containment: options.containment,
      tree:        options.tree,
      hoverclass:  options.hoverclass,
      onHover:     Sortable.onHover
      //greedy:      !options.dropOnEmpty
    }
    
    var options_for_tree = {
      onHover:      Sortable.onEmptyHover,
      overlap:      options.overlap,
      containment:  options.containment,
      hoverclass:   options.hoverclass
    }

    // fix for gecko engine
    Element.cleanWhitespace(element); 

    options.draggables = [];
    options.droppables = [];

    // drop on empty handling
    if(options.dropOnEmpty || options.tree) {
      Droppables.add(element, options_for_tree);
      options.droppables.push(element);
    }

    (this.findElements(element, options) || []).each( function(e) {
      // handles are per-draggable
      var handle = options.handle ? 
        Element.childrenWithClassName(e, options.handle)[0] : e;    
      options.draggables.push(
        new Draggable(e, Object.extend(options_for_draggable, { handle: handle })));
      Droppables.add(e, options_for_droppable);
      if(options.tree) e.treeNode = element;
      options.droppables.push(e);      
    });
    
    if(options.tree) {
      (Sortable.findTreeElements(element, options) || []).each( function(e) {
        Droppables.add(e, options_for_tree);
        e.treeNode = element;
        options.droppables.push(e);
      });
    }

    // keep reference
    this.sortables[element.id] = options;

    // for onupdate
    Draggables.addObserver(new SortableObserver(element, options.onUpdate));

  },

  // return all suitable-for-sortable elements in a guaranteed order
  findElements: function(element, options) {
    return Element.findChildren(
      element, options.only, options.tree ? true : false, options.tag);
  },
  
  findTreeElements: function(element, options) {
    return Element.findChildren(
      element, options.only, options.tree ? true : false, options.treeTag);
  },

  onHover: function(element, dropon, overlap) {
    if(Element.isParent(dropon, element)) return;

    if(overlap > .33 && overlap < .66 && Sortable.options(dropon).tree) {
      return;
    } else if(overlap>0.5) {
      Sortable.mark(dropon, 'before');
      if(dropon.previousSibling != element) {
        var oldParentNode = element.parentNode;
        element.style.visibility = "hidden"; // fix gecko rendering
        dropon.parentNode.insertBefore(element, dropon);
        if(dropon.parentNode!=oldParentNode) 
          Sortable.options(oldParentNode).onChange(element);
        Sortable.options(dropon.parentNode).onChange(element);
      }
    } else {
      Sortable.mark(dropon, 'after');
      var nextElement = dropon.nextSibling || null;
      if(nextElement != element) {
        var oldParentNode = element.parentNode;
        element.style.visibility = "hidden"; // fix gecko rendering
        dropon.parentNode.insertBefore(element, nextElement);
        if(dropon.parentNode!=oldParentNode) 
          Sortable.options(oldParentNode).onChange(element);
        Sortable.options(dropon.parentNode).onChange(element);
      }
    }
  },
  
  onEmptyHover: function(element, dropon, overlap) {
    var oldParentNode = element.parentNode;
    var droponOptions = Sortable.options(dropon);
        
    if(!Element.isParent(dropon, element)) {
      var index;
      
      var children = Sortable.findElements(dropon, {tag: droponOptions.tag, only: droponOptions.only});
      var child = null;
            
      if(children) {
        var offset = Element.offsetSize(dropon, droponOptions.overlap) * (1.0 - overlap);
        
        for (index = 0; index < children.length; index += 1) {
          if (offset - Element.offsetSize (children[index], droponOptions.overlap) >= 0) {
            offset -= Element.offsetSize (children[index], droponOptions.overlap);
          } else if (offset - (Element.offsetSize (children[index], droponOptions.overlap) / 2) >= 0) {
            child = index + 1 < children.length ? children[index + 1] : null;
            break;
          } else {
            child = children[index];
            break;
          }
        }
      }
      
      dropon.insertBefore(element, child);
      
      Sortable.options(oldParentNode).onChange(element);
      droponOptions.onChange(element);
    }
  },

  unmark: function() {
    if(Sortable._marker) Element.hide(Sortable._marker);
  },

  mark: function(dropon, position) {
    // mark on ghosting only
    var sortable = Sortable.options(dropon.parentNode);
    if(sortable && !sortable.ghosting) return; 

    if(!Sortable._marker) {
      Sortable._marker = $('dropmarker') || document.createElement('DIV');
      Element.hide(Sortable._marker);
      Element.addClassName(Sortable._marker, 'dropmarker');
      Sortable._marker.style.position = 'absolute';
      document.getElementsByTagName("body").item(0).appendChild(Sortable._marker);
    }    
    var offsets = Position.cumulativeOffset(dropon);
    Sortable._marker.style.left = offsets[0] + 'px';
    Sortable._marker.style.top = offsets[1] + 'px';
    
    if(position=='after')
      if(sortable.overlap == 'horizontal') 
        Sortable._marker.style.left = (offsets[0]+dropon.clientWidth) + 'px';
      else
        Sortable._marker.style.top = (offsets[1]+dropon.clientHeight) + 'px';
    
    Element.show(Sortable._marker);
  },
  
  _tree: function(element, options, parent) {
    var children = Sortable.findElements(element, options) || [];
  
    for (var i = 0; i < children.length; ++i) {
      var match = children[i].id.match(options.format);

      if (!match) continue;
      
      var child = {
        id: encodeURIComponent(match ? match[1] : null),
        element: element,
        parent: parent,
        children: new Array,
        position: parent.children.length,
        container: Sortable._findChildrenElement(children[i], options.treeTag.toUpperCase())
      }
      
      /* Get the element containing the children and recurse over it */
      if (child.container)
        this._tree(child.container, options, child)
      
      parent.children.push (child);
    }

    return parent; 
  },

  /* Finds the first element of the given tag type within a parent element.
    Used for finding the first LI[ST] within a L[IST]I[TEM].*/
  _findChildrenElement: function (element, containerTag) {
    if (element && element.hasChildNodes)
      for (var i = 0; i < element.childNodes.length; ++i)
        if (element.childNodes[i].tagName == containerTag)
          return element.childNodes[i];
  
    return null;
  },

  tree: function(element) {
    element = $(element);
    var sortableOptions = this.options(element);
    var options = Object.extend({
      tag: sortableOptions.tag,
      treeTag: sortableOptions.treeTag,
      only: sortableOptions.only,
      name: element.id,
      format: sortableOptions.format
    }, arguments[1] || {});
    
    var root = {
      id: null,
      parent: null,
      children: new Array,
      container: element,
      position: 0
    }
    
    return Sortable._tree (element, options, root);
  },

  /* Construct a [i] index for a particular node */
  _constructIndex: function(node) {
    var index = '';
    do {
      if (node.id) index = '[' + node.position + ']' + index;
    } while ((node = node.parent) != null);
    return index;
  },

  sequence: function(element) {
    element = $(element);
    var options = Object.extend(this.options(element), arguments[1] || {});
    
    return $(this.findElements(element, options) || []).map( function(item) {
      return item.id.match(options.format) ? item.id.match(options.format)[1] : '';
    });
  },

  setSequence: function(element, new_sequence) {
    element = $(element);
    var options = Object.extend(this.options(element), arguments[2] || {});
    
    var nodeMap = {};
    this.findElements(element, options).each( function(n) {
        if (n.id.match(options.format))
            nodeMap[n.id.match(options.format)[1]] = [n, n.parentNode];
        n.parentNode.removeChild(n);
    });
   
    new_sequence.each(function(ident) {
      var n = nodeMap[ident];
      if (n) {
        n[1].appendChild(n[0]);
        delete nodeMap[ident];
      }
    });
  },
  
  serialize: function(element) {
    element = $(element);
    var options = Object.extend(Sortable.options(element), arguments[1] || {});
    var name = encodeURIComponent(
      (arguments[1] && arguments[1].name) ? arguments[1].name : element.id);
    
    if (options.tree) {
      return Sortable.tree(element, arguments[1]).children.map( function (item) {
        return [name + Sortable._constructIndex(item) + "[id]=" + 
                encodeURIComponent(item.id)].concat(item.children.map(arguments.callee));
      }).flatten().join('&');
    } else {
      return Sortable.sequence(element, arguments[1]).map( function(item) {
        return name + "[]=" + encodeURIComponent(item);
      }).join('&');
    }
  }
}

/* Returns true if child is contained within element */
Element.isParent = function(child, element) {
  if (!child.parentNode || child == element) return false;

  if (child.parentNode == element) return true;

  return Element.isParent(child.parentNode, element);
}

Element.findChildren = function(element, only, recursive, tagName) {    
  if(!element.hasChildNodes()) return null;
  tagName = tagName.toUpperCase();
  if(only) only = [only].flatten();
  var elements = [];
  $A(element.childNodes).each( function(e) {
    if(e.tagName && e.tagName.toUpperCase()==tagName &&
      (!only || (Element.classNames(e).detect(function(v) { return only.include(v) }))))
        elements.push(e);
    if(recursive) {
      var grandchildren = Element.findChildren(e, only, recursive, tagName);
      if(grandchildren) elements.push(grandchildren);
    }
  });

  return (elements.length>0 ? elements.flatten() : []);
}

Element.offsetSize = function (element, type) {
  if (type == 'vertical' || type == 'height')
    return element.offsetHeight;
  else
    return element.offsetWidth;
}