var m2AjaxParameters = 'm2Parameters';
var m2AjaxMarkerUrlParameter =  'm2MarkerId';

/*
** An m2Ajax allows HTML fragments to be loaded into a DOM Node
**
** @param _containerNode -  DOM node to contain loaded fragments
** @param _name - optional descriptive _name to be included in the _name of 
**               generated tags
*/
m2Ajax = function(_containerNode, _name) {
  this._containerNode = _containerNode;
  this._options = new Object();
  this._options.asynchronous = true;
  this._options.evalScripts = true;
  this._markerTag = 'div';
  this._parameters = new Object();
  this.onError = this.defaultErrorAction;

  this._name = "m2ajax";
  if (_name) {
   this._name = _name;
  }
}

/*
** Specifies the type of the Marker and replace element
** Defaults to 'div'
**
** @param tag - _name of HTML tag element, e.g. 'div', 'span'
**
** @return self
*/
m2Ajax.prototype.setMarkerTagType = function(_tag) {
  this._markerTag = _tag;
  return this;
}

/*
** Sets an action to be performed when the fragment is loaded
**
** @param action - function to call
**
** @return self
*/
m2Ajax.prototype.setOnComplete = function(_action) {
  this._options['onComplete'] = _action;
  return this;
}

/*
** Sets an action to be performed when the fragment fails to be loaded
** The action should expect 2 parameters
**   markerDiv
**   transport (an XMLHttpRequest or equivaltent)
**
** The default action puts an error message in the marker div
**
** @param action - function to call
**
** @return self
*/
m2Ajax.prototype.setOnError = function(_action) {
  this.onError = _action;
  return this;
}


/*
** Specifies a parameter to be passed to fragment
**
** @param _name - _name of parameter
** @param value - value of parameter
**
** @return self
*/
m2Ajax.prototype.setParameter = function(_name, _value) {
  this._parameters[_name] = _value;
  return this;
}

/*
** Loads the fragment into the container node
**
** @return DOM node that will contain the loaded fragment
*/
m2Ajax.prototype.setChild = function(_fragmentUrl) {
  var _markerNode = null;

  // search for previous marker node and reuse if its avalaible
  for (var i = 0; i < this._containerNode.childNodes.length; i++) {
    var node = this._containerNode.childNodes[i];
    var id = new String(node.id);
    if (node.nodeName.toUpperCase() == this._markerTag.toUpperCase()
      && id.indexOf(this._name) == 0) {
      _markerNode = node;
    }
  }

  if (!_markerNode) {
    _markerNode = this._createMarkerNode();
    this._containerNode.appendChild(_markerNode);
  }

  this.loadMarkerNode(_markerNode, _fragmentUrl, this._options);

  return _markerNode;
}


/*
** Appends the content returned by 'fragmentUrl' to the container
** associated with this m2Ajax
**
** @param _fragmentUrl - url of fragment to load
**
** @return DOM node that will contain loading fragment
*/
m2Ajax.prototype.appendChild = function(_fragmentUrl) {

  var _markerNode = this._createMarkerNode();
  this._containerNode.appendChild(_markerNode);

  this.loadMarkerNode(_markerNode, _fragmentUrl, this._options);

  return _markerNode;
}


/*
** Loads the specified markerNode with 'fragmentUrl'
** Adds parameters to the url to inform the fragment of the marker id
** and indicuate the request is an ajax request - m2ajax=1
**
** @param fragmentUrl - url of fragment to load
**
** @return DOM node that will contain loading fragment
*/
m2Ajax.prototype.loadMarkerNode = function(_markerNode, _fragmentUrl) {
  // attach parameters to div object - nasty, but simple
  _markerNode[m2AjaxParameters] = this._parameters

  var seperator = '?';
  if (_fragmentUrl.indexOf("?") > 0) {
    seperator = '&';
  }
  _fragmentUrl = _fragmentUrl + seperator + m2AjaxMarkerUrlParameter 
     + '=' + _markerNode.id;
  _fragmentUrl = _fragmentUrl + '&m2ajax=1';

  this._options['onFailure'] = function(transport) { 
    this.onError(_markerNode, transport);
  }

  var _updater = new Ajax.Updater(_markerNode.id, _fragmentUrl, this._options);
}

/*
** Removes the specified child node
*/
m2Ajax.prototype.removeChild = function(_markerNode) {
  this._containerNode.removeChild(_markerNode);
}

/*
** Removes all child nodes
*/
m2Ajax.prototype.removeAllChildren = function() {
  while (this._containerNode.hasChildNodes()) {
    this._containerNode.removeChild(this._containerNode.firstChild);
  }
}


m2Ajax.prototype._createMarkerNode = function() {
  var _markerNodeId = this._generateMarkerNodeId();

  var _markerNode = document.createElement(this._markerTag);
  _markerNode.setAttribute("id", _markerNodeId);

  return _markerNode;
}

m2Ajax.prototype._defaultErrorAction = function(markerDiv, transport) {
  markerDiv.innerHTML  = '<span style="color: red">m2Ajax error: '
    + transport.status + ' -- ' + transport.statusText + '</span>';
}

m2Ajax.prototype._generateMarkerNodeId = function() {
 return this._name + "-" +
   (new Date()).getTime() + "-" + Math.floor(Math.random() * 999999);
}


/*
** Allows an m2AjaxFragment to interact with its loader
**
** @param markerId - the id of the marker, passed as a url parameter
**       'm2MarkerId' to the fragment.
**       (it is expected you will use server side processing to get the
**        id from the fragment url)
*/
m2AjaxFragment = function(_markerId) {
  this.markerDiv = document.getElementById(_markerId);
}

/*
** @return the marker div for this fragment
*/
m2AjaxFragment.prototype.getMarkerDiv = function() {
  return this.markerDiv;
}

/*
** Deletes the Marker div and all its content associated with this Fragment.
*/
m2AjaxFragment.prototype.deleteDiv = function() {
  this.markerDiv.parentNode.removeChild(this.markerDiv);
}

/*
** @return the value associated with the javascript m2Ajax parameter '_name'
**         or null if not defined
*/
m2AjaxFragment.prototype.getParameter = function(_name) {
  if (!this.markerDiv || !this.markerDiv[m2AjaxParameters]) {
    return null;
  }

  return this.markerDiv[m2AjaxParameters][_name];
}