// Source code from:  http://extjs.com/forum/showthread.php?t=21913&highlight=drag+drop+grid&page=5

Ext.namespace('Ext.ux.dd');

Ext.ux.dd.GridReorderDropTarget = function(grid, config) {
    this.target = new Ext.dd.DropTarget(grid.getEl(), {
        ddGroup: grid.ddGroup || 'GridDD'
        ,grid: grid
        ,gridDropTarget: this
        ,notifyDrop: function(dd, e, data){
          // determine the row
          var t = Ext.lib.Event.getTarget(e);
          var rindex = this.grid.getView().findRowIndex(t);
          if (rindex === false) return false;
          if (rindex == data.rowIndex) return false;
         
          // fire the before move/copy event
          if (this.gridDropTarget.fireEvent(this.copy?'beforerowcopy':'beforerowmove', this.gridDropTarget, data.rowIndex, rindex, data.selections) === false) return false;
         
          // update the store
          var ds = this.grid.getStore();
          if (!this.copy) {
              for(i = 0; i < data.selections.length; i++) {
                  ds.remove(ds.getById(data.selections[i].id));
              }
          }
          ds.insert(rindex,data.selections);
         
          // re-select the row(s)
          var sm = this.grid.getSelectionModel();
          if (sm) sm.selectRecords(data.selections);
         
          // fire the after move/copy event
          this.gridDropTarget.fireEvent(this.copy?'afterrowcopy':'afterrowmove', this.gridDropTarget, data.rowIndex, rindex, data.selections);
         
          return true;
        }
        ,notifyOver: function(dd, e, data) {
            var t = Ext.lib.Event.getTarget(e);
            var rindex = this.grid.getView().findRowIndex(t);
            if (rindex == data.rowIndex) rindex = false;

            return (rindex === false)? this.dropNotAllowed : this.dropAllowed;
        }
    });
    if (config) {
        Ext.apply(this.target, config);
        if (config.listeners) Ext.apply(this,{listeners: config.listeners});
    }

    this.addEvents({
        "beforerowmove": true
        ,"afterrowmove": true
        ,"beforerowcopy": true
        ,"afterrowcopy": true
    });

    Ext.ux.dd.GridReorderDropTarget.superclass.constructor.call(this);
};

Ext.extend(Ext.ux.dd.GridReorderDropTarget, Ext.util.Observable, {
    getTarget: function() {
        return this.target;
    }
    ,getGrid: function() {
        return this.target.grid;
    }
    ,getCopy: function() {
        return this.target.copy?true:false;
    }
    ,setCopy: function(b) {
        this.target.copy = b?true:false;
    }
});