// global xmlhttprequest object
var xmlHttp = false;
var callfunc = "";


/** AJAX functions **/

// constants
var REQUEST_GET		= 0;
var REQEST_POST		= 2;
var REQUEST_HEAD	= 1;
var REQUEST_XML		= 3;



/**
 * instantiates a new xmlhttprequest object
 *
 * @return xmlhttprequest object or false
 */
function getXMLRequester( )
{
	var xmlHttp = false;
			
	// try to create a new instance of the xmlhttprequest object		
	try
	{
		// Internet Explorer
		if( window.ActiveXObject )
		{
			for( var i = 5; i; i-- )
			{
				try
				{
					// loading of a newer version of msxml dll (msxml3 - msxml5) failed
					// use fallback solution
					// old style msxml version independent, deprecated
					if( i == 2 )
					{
						xmlHttp = new ActiveXObject( "Microsoft.XMLHTTP" );	
					}
					// try to use the latest msxml dll
					else
					{
						
						xmlHttp = new ActiveXObject( "Msxml2.XMLHTTP." + i + ".0" );
					}
					break;
				}
				catch( excNotLoadable )
				{						
					xmlHttp = false;
				}
			}
		}
		// Mozilla, Opera und Safari
		else if( window.XMLHttpRequest )
		{
			xmlHttp = new XMLHttpRequest();
		}
	}
	// loading of xmlhttp object failed
	catch( excNotLoadable )
	{
		xmlHttp = false;
	}
	return xmlHttp ;
}


/**
 * sends a http request to server
 *
 * @param strSource, String, datasource on server, e.g. data.php
 *
 * @param strData, String, data to send to server, optionally
 *
 * @param intType, Integer,request type, possible values: REQUEST_GET, REQUEST_POST, REQUEST_XML, REQUEST_HEAD default REQUEST_GET
 *
 * @param strData, Integer, ID of this request, will be given to registered event handler onreadystatechange', optionally
 *
 * @return String, request data or data source
 */
function sendRequest( strSource, strData, intType, intID, callfunc )
{
	if( !strData )
		strData = '';

	// default type (0 = GET, 1 = xml, 2 = POST )
	if( isNaN( intType ) )
		intType = 0; // GET

	// previous request not finished yet, abort it before sending a new request
	if( xmlHttp && xmlHttp.readyState )
	{
		xmlHttp.abort( );
		xmlHttp = false;
	}
		
	// create a new instance of xmlhttprequest object
	// if it fails, return
	if( !xmlHttp )
	{
		xmlHttp = getXMLRequester( );
		if( !xmlHttp )
			return;
	}
	
	// parse query string
	if( intType != 1 && ( strData && strData.substr( 0, 1 ) == '&' || strData.substr( 0, 1 ) == '?' ) )
		strData = strData.substring( 1, strData.length );

	// data to send using POST
	var dataReturn = strData ? strData : strSource;
	
	switch( intType )
	{
		case 1:	// xml
			strData = "xml=" + strData;
		case 2: // POST
			// open the connection 
			xmlHttp.open( "POST", strSource, true );
			xmlHttp.setRequestHeader( 'Content-Type', 'application/x-www-form-urlencoded' );
			xmlHttp.setRequestHeader( 'Content-length', strData.length );
			break;
		case 3: // HEAD
			// open the connection 
			xmlHttp.open( "HEAD", strSource, true );
			strData = null;
			break;
		default: // GET
			// open the connection 
			var strDataFile = strSource + (strData ? '?' + strData : '' );
			xmlHttp.open( "GET", strDataFile, true );
			strData = null;
	}
	
	// set onload data event-handler
	xmlHttp.onreadystatechange = new Function( "", "processResponse( '" + intID + "', '" + callfunc + "' )" ); ;

	// send request to server
	xmlHttp.send( strData );	// param = POST data
	
	return dataReturn;
}
	

/**
 * process the response data from server
 *
 * @param intID, Integer, ID of this response
 */
function processResponse( intID, callfunc )
{
	// status 0 UNINITIALIZED open() has not been called yet.
	// status 1 LOADING send() has not been called yet.
	// status 2 LOADED send() has been called, headers and status are available.
	// status 3 INTERACTIVE Downloading, responseText holds the partial data.
	// status 4 COMPLETED Finished with all operations.
	switch( xmlHttp.readyState )
	{
		// uninitialized
		case 0:
		// loading
		case 1:
		// loaded
		case 2:
		// interactive
		case 3:
			break;
		// complete
		case 4:	
			// check http status
			if( xmlHttp.status == 200 )	// success
			{
				processData( xmlHttp, intID, callfunc );
			}
			// loading not successfull, e.g. page not available
			else
			{
				if( window.handleAJAXError )
					handleAJAXError( xmlHttp, intID );
				//else alert( "ERROR\n HTTP status = " + xmlHttp.status + "\n" + xmlHttp.statusText ) ;
			}
	}
}

// process data from server
function processData( xmlHttp, intID, callfunc )
{
	if(intID!='') document.getElementById(intID).innerHTML = xmlHttp.responseText;
	eval(callfunc);
}

/** End AJAX functions **/