/*==============================================================================
Ajax - Simple Ajax Support Library

DESCRIPTION:

This library defines simple cross-browser functions for rudimentary Ajax
support.

AUTHORS:

   Ingy döt Net <ingy@cpan.org>
   Kang-min Liu <gugod@gugod.org>

COPYRIGHT:

Copyright Ingy döt Net 2006. All rights reserved.

Ajax.js is free software.

This library is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at
your option) any later version.

This library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
General Public License for more details.

   http://www.gnu.org/copyleft/lesser.txt

=============================================================================*/

if (! this.Ajax) Ajax = function () {};
proto = Ajax.prototype;

Ajax.VERSION = '0.10';

// Allows one to override with something more drastic.
// Can even be done "on the fly" using a bookmarklet.
// As an example, the test suite overrides this to test error conditions.
proto.die = function(e) { throw(e) };

// The simple user interface function to GET. If no callback is used the
// function is synchronous.

Ajax.get = function(url, callback) {
   return (new Ajax()).get(
       { 'url': url, 'onComplete': callback }
   );
}

// The simple user interface function to POST. If no callback is used the
// function is synchronous.
Ajax.post = function(url, data, callback) {
   return (new Ajax()).post(
       { 'url': url, 'data': data, 'onComplete': callback }
   );
}

// Object interface
proto.get = function(params) {
   this._init_object(params);
   this.request.open('GET', this.url, Boolean(this.onComplete));
   return this._send();
}

proto.post = function(params) {
   this._init_object(params);
   this.request.open('POST', this.url, Boolean(this.onComplete));
   this.request.setRequestHeader(
       'Content-Type',
       'application/x-www-form-urlencoded'
   );
   return this._send();
}

// Set up the Ajax object with a working XHR object.
proto._init_object = function(params) {
   for (key in params) {
       if (! key.match(/^url|data|onComplete$/))
           throw("Invalid Ajax parameter: " + key);
       this[key] = params[key];
   }

   if (! this.url)
       throw("'url' required for Ajax get/post method");

   if (this.request)
       throw("Don't yet support multiple requests on the same Ajax object");

   this.request = new XMLHttpRequest();

   if (! this.request)
       return this.die("Your browser doesn't do Ajax");
   if (this.request.readyState != 0)
       return this.die("Ajax readyState should be 0");

   return this;
}

proto._send = function() {
   var self = this;
   if (this.onComplete) {
       this.request.onreadystatechange = function() {
           self._check_asynchronous();
       };
   }
   this.request.send(this.data);
   return Boolean(this.onComplete)
       ? this
       : this._check_synchronous();
}

// TODO Allow handlers for various readyStates and statusCodes.
// Make these be the default handlers.
proto._check_status = function() {
   if (this.request.status != 200) {
       return this.die(
           'Ajax request for "' + this.url +
           '" failed with status: ' + this.request.status
       );
   }
}

proto._check_synchronous = function() {
   this._check_status();
   return this.request.responseText;
}

proto._check_asynchronous = function() {
   if (this.request.readyState != 4) return;
   this._check_status();
   this.onComplete(this.request.responseText);
}

// IE support
if (window.ActiveXObject && !window.XMLHttpRequest) {
   window.XMLHttpRequest = function() {
       var name = (navigator.userAgent.toLowerCase().indexOf('msie 5') != -1)
           ? 'Microsoft.XMLHTTP' : 'Msxml2.XMLHTTP';
       return new ActiveXObject(name);
   }
}