var booleanAttrs = ["allowfullscreen", "async", "autofocus", "autoplay", "checked", "compact", "controls", "declare", 
                "default", "defaultchecked", "defaultmuted", "defaultselected", "defer", "disabled", "draggable", 
                "enabled", "formnovalidate", "hidden", "indeterminate", "inert", "ismap", "itemscope", "loop", "multiple", 
                "muted", "nohref", "noresize", "noshade", "novalidate", "nowrap", "open", "pauseonexit", "readonly", 
                "required", "reversed", "scoped", "seamless", "selected", "sortable", "spellcheck", "translate", 
                "truespeed", "typemustmatch", "visible"];
    
var booleanAttrsDict = {};
for(var i=0, len = booleanAttrs.length; i < len; i++) {
  booleanAttrsDict[booleanAttrs[i]] = true;
}
    
function updateAttrs(oldVnode, vnode) {
  var key, cur, old, elm = vnode.elm,
      oldAttrs = oldVnode.data.attrs || {}, attrs = vnode.data.attrs || {};
  
  // update modified attributes, add new attributes
  for (key in attrs) {
    cur = attrs[key];
    old = oldAttrs[key];
    if (old !== cur) {
      // TODO: add support to namespaced attributes (setAttributeNS)
      if(!cur && booleanAttrsDict[key])
        elm.removeAttribute(key);
      else
        elm.setAttribute(key, cur);
    }
  }
  //remove removed attributes
  // use `in` operator since the previous `for` iteration uses it (.i.e. add even attributes with undefined value)
  // the other option is to remove all attributes with value == undefined
  for (key in oldAttrs) {
    if (!(key in attrs)) {
      elm.removeAttribute(key);
    }
  }
}

module.exports = {create: updateAttrs, update: updateAttrs};