function dayBefore(date) {
  var remtxt = date;
  function consume(retxt) {
    var match = remtxt.match(new RegExp('^' + retxt));
    if (match) {
      remtxt = remtxt.substring(match[0].length);
      return match[0];
    }
    return '';
  }

  var year = consume('\\d{4}');
  consume('-?');
  var month = consume('\\d{2}');
  consume('-?');
  var dateMonth = consume('\\d{2}') - 1 ;
  if(dateMonth<10) {
    dateMonth = '0' + dateMonth;
  }
  return year + '-' + month + '-' + dateMonth;
}

/**
 * Converts an xs:date or xs:dateTime formatted string into the local
timezone
 * and outputs a human-readable form of this date or date/time.
 *
 * @param {string} gCalTime is the xs:date or xs:dateTime formatted string
 * @return {string} is the human-readable date or date/time string
 */
function formatGCalTime(gCalTime) { 
  // text for regex matches
  var remtxt = gCalTime;

  function consume(retxt) {
    var match = remtxt.match(new RegExp('^' + retxt));
    if (match) {
      remtxt = remtxt.substring(match[0].length);
      return match[0];
    }
    return '';
  }

  // minutes of correction between gCalTime and GMT
  var totalCorrMins = 0;

  var year = consume('\\d{4}');
  consume('-?');
  var month = consume('\\d{2}');
  consume('-?');
  var dateMonth = consume('\\d{2}');
  var timeOrNot = consume('T');

  // if a DATE-TIME was matched in the regex 
  if (timeOrNot == 'T') {
    var hours = consume('\\d{2}');
    consume(':?');
    var mins = consume('\\d{2}');
    consume('(:\\d{2})?(\\.\\d{3})?');
    var zuluOrNot = consume('Z');

    // if time from server is not already in GMT, calculate offset
    if (zuluOrNot != 'Z') {
      var corrPlusMinus = consume('[\\+\\-]');
      if (corrPlusMinus != '') {
        var corrHours = consume('\\d{2}');
        consume(':?');
        var corrMins = consume('\\d{2}');
        totalCorrMins = (corrPlusMinus=='-' ? 1 : -1) * 
            (Number(corrHours) * 60 + 
	    (corrMins=='' ? 0 : Number(corrMins)));
      }
    } 

    // get time since epoch and apply correction, if necessary
    // relies upon Date object to convert the GMT time to the local
    // timezone
    var originalDateEpoch = Date.UTC(year, month, dateMonth, hours, mins);
    var gmtDateEpoch = originalDateEpoch + totalCorrMins * 1000 * 60;
    var ld = new Date(gmtDateEpoch);

 	dateString = 
	((ld.getDate()<10)?('0' + ld.getDate()):(ld.getDate())) + '.' 
	+ ((ld.getMonth()==0)?'12': ((ld.getMonth()<10)?('0' + ld.getMonth()):(ld.getMonth()))) + '.' 
 //tu poprawilem kiedy 0daje '12'
	+ (parseInt(year)) + '  ' 
	+ ((ld.getHours()<10)?('0' + (ld.getHours()+0)):(ld.getHours()+0)) + ':' 
 // //bylo +1zmienilem na +0//adrian
	+ ((ld.getMinutes()<10)?('0' + ld.getMinutes()):(ld.getMinutes()));
  } else {
    // if only a DATE was matched
    dateString =  dateMonth + '.' + month + '.' + year ;
  }
  return dateString;
}

/**
 * Creates an unordered list of events in a human-readable form
 *
 * @param {json} root is the root JSON-formatted content from GData
 * @param {string} divId is the div in which the events are added
 */ 
function listEvents(root, divId) {
  var feed = root.feed;
  var events = document.getElementById(divId);

  if (events.childNodes.length > 0) {
    events.removeChild(events.childNodes[0]);
  }	  

  // create a new unordered list
  var ul = document.createElement('ul');

  // loop through each event in the feed
  for (var i = 0; i < feed.entry.length; i++) {
    var entry = feed.entry[i];
    var title = entry.title.$t;
    var start = entry['gd$when'][0].startTime;
    var end = entry['gd$when'][0].endTime;
    if(end.length<11) {
      end = dayBefore(end);
    } 
    var where = entry['gd$where'][0].valueString;


    // get the URL to link to the event
    for (var linki = 0; linki < entry['link'].length; linki++) {
      if (entry['link'][linki]['type'] == 'text/html' &&
          entry['link'][linki]['rel'] == 'alternate') {
        var entryLinkHref = entry['link'][linki]['href'];
      }
    }

    var dateString = formatGCalTime(start);
    var dateEndString = formatGCalTime(end);
    var li = document.createElement('li');
    var br = document.createElement('br');
    
    // if we have a link to the event, create an 'a' element
    if (typeof entryLinkHref != 'undefined') {
      entryLink = document.createElement('a');
      entryLink.setAttribute('href', entryLinkHref);
      entryLink.appendChild(document.createTextNode(title));
      li.appendChild(entryLink);
	br = document.createElement('br');
      li.appendChild(br);
      li.appendChild(document.createTextNode(dateString + ' - ' +
dateEndString));
	br = document.createElement('br');
	li.appendChild(br);
      li.appendChild(document.createTextNode(where));
    } else {
	br = document.createElement('br');
      li.appendChild(document.createTextNode(title));
      li.appendChild(br);
      li.appendChild(document.createTextNode(dateString + ' - ' +
dateEndString));
	br = document.createElement('br');
	li.appendChild(br);
      li.appendChild(document.createTextNode(where));
    }	    

    // append the list item onto the unordered list
    ul.appendChild(li);
  }
  events.appendChild(ul);
}

/**
 * Callback function for the GData json-in-script call
 * Inserts the supplied list of events into a div of a pre-defined name
 * 
 * @param {json} root is the JSON-formatted content from GData
 */ 
function insertAgenda(root) {
  listEvents(root, 'agenda');
}