var NamespaceURIs = {
  "xlink": "http://www.w3.org/1999/xlink"
};

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 = Object.create(null);
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, namespace;

  if (!oldAttrs && !attrs) return;
  oldAttrs = oldAttrs || {};
  attrs = attrs || {};

  // update modified attributes, add new attributes
  for (key in attrs) {
    cur = attrs[key];
    old = oldAttrs[key];
    namespace = key.split(":")[0];
    if (old !== cur) {
      if(!cur && booleanAttrsDict[key])
        elm.removeAttribute(key);
      else if(key.match(/:/) && NamespaceURIs.hasOwnProperty(namespace))
        elm.setAttributeNS(NamespaceURIs[namespace], key, cur);
      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};