tree controller implementation for sourceRoot

App.adviceListController = SC.ArrayController.create({
  
  sourceRoot: function() {
    var groups = {}, headings = [], group, adviceAry, ret ;
    var source = this.get('content') ;
    if (!source) return null ;
    
    source.forEach(function(advice) {
      if (group = advice.get('group')) {
        adviceAry = groups[group] ;
        if (!adviceAry) groups[group] = adviceAry = [] ;
        adviceAry.push(group);
        if (headings.indexOf(group) < 0) headings.push(group) ;
      }
    }, source);
    
    // once divided into kinds, create group nodes for each kind
    ret = [];
    headings.forEach(function(group) {
      adviceAry = groups[group];
      ret.push(SC.Object.create({
        displayName: "%@".fmt(group).loc(),
        isExpanded: YES,
        children: adviceAry
      }));
    });
    return SC.Object.create({ children: ret, isExpanded: YES });
  
  }.property('[]').cacheable()
  
});

App.adviceTreeController = SC.TreeController.create({
  
  contentBinding: 'App.adviceListController.sourceRoot',
  
  allowsEmptySelection : NO,
  allowsMultipleSelection : NO,
  
  treeItemChildrenKey: 'children',
  treeItemIsExpandedKey: 'isExpanded',
  treeItemIsGrouped: YES
  
});