/*
 * http://www.sitepoint.com/article/build-your-own-ajax-web-apps/2
 */

function Ajax() {
  this.req = null;
  this.url = null;
  this.method = 'GET';
  this.async = true;
  this.status = null;
  this.statusText = '';
  this.postData = null;
  this.readyState = null;
  this.responseText = null;
  this.responseXML = null;
  this.handleResp = null;
  this.responseFormat = 'text', // 'text', 'xml', or 'object'
  this.mimeType = null;

  this.init = function() {
    if (!this.req) {
      try {
        // Try to create object for Firefox, Safari, IE7, etc.
        this.req = new XMLHttpRequest();
      } catch (e) {
        try {
          // Try to create object for later versions of IE.
          this.req = new ActiveXObject('MSXML2.XMLHTTP');
        } catch (e) {
          try {
            // Try to create object for early versions of IE.
            this.req = new ActiveXObject('Microsoft.XMLHTTP');
          }
          catch (e) {
            // Could not create an XMLHttpRequest object.
            return false;
          }
        }
      }
    }
    return this.req;
  };

  this.doReq = function() {
    if (!this.init()) {
      alert('Could not create XMLHttpRequest object.');
      return;
    }
    this.req.open(this.method, this.url, this.async);

    if (this.mimeType) {
      try {
        req.overrideMimeType(this.mimeType);
      } catch (e) {
        // couldn't override MIME type  --  IE6 or Opera?
      }
    } 

    var self = this; // Fix loss-of-scope in inner function
    this.req.onreadystatechange = function() {
      if (self.req.readyState == 4) {
        switch (self.responseFormat) {
          case 'text':
            resp = self.req.responseText;
            break;
          case 'xml':
            resp = self.req.responseXML;
            break;
          case 'object':
            resp = req;
            break;
        }
        if (self.req.status >= 200 && self.req.status <= 299) {
          self.handleResp(resp);
        } else {
          self.handleErr(resp);
        } 
      }
    };

    this.req.send(this.postData);
  };

  this.setMimeType = function(mimeType) {
    this.mimeType = mimeType;
  };

  this.handleErr = function() {
    var errorWin;
    try {
      errorWin = window.open('', 'errorWin');
      errorWin.document.body.innerHTML = this.responseText;
    } catch (e) {
      alert('An error occurred, but the error message cannot be '
       + 'displayed. This is probably because of your browser\'s '
       + 'pop-up blocker.\n'
       + 'Please allow pop-ups from this web site if you want to '
       + 'see the full error messages.\n'
       + '\n'
       + 'Status Code: ' + this.req.status + '\n'
       + 'Status Description: ' + this.req.statusText);
    }
  };

  this.setHandlerErr = function(funcRef) {
    this.handleErr = funcRef;  
  }

  this.setHandlerBoth = function(funcRef) {
    this.handleResp = funcRef;
    this.handleErr = funcRef;
  };

  this.abort = function() {
    if (this.req) {
      this.req.onreadystatechange = function() { };
      this.req.abort();
      this.req = null;
    }
  };

  this.doGet = function(url, hand, format) {
    this.url = url;
    this.handleResp = hand;
    this.responseFormat = format || 'text';
    this.doReq();
  };
}