/**
 * Converts regular text into html by turning newlines into <br/> tags
 * and by finding URLS and adding <a href tags to them
 *
 * @param {string} regular text
 * @return {string} HTML text
 */
function htmlify(regularText)
{
//var urlRegexp = /(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?/gi;  //works in FF, fails in IE8
var urlRegexp = /(https?:\/\/)([\da-zA-Z\._-]+)\.([A-Za-z\.]{2,6})([\/\w\._-]*)\/?/g; //works in both FF3.6 and IE8
var tmp=regularText;
tmp=tmp.replace(urlRegexp, "<a target='_blank' href='$1$2.$3$4'>$1$2.$3$4</a>"); // replace URLs with actual hyperlinks
tmp=tmp.replace("\n\r","\n"); // replace newlines/carriage-returns in description with newline only
tmp=tmp.replace("\n\n","<p/>"); // replace double newlines in description with HTML paragraph
tmp=tmp.replace("\n","<br>"); // replace single newlines in description with HTML break
return tmp;
}


/**
 * 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 - 1, dateMonth, hours, mins);
    var gmtDateEpoch = originalDateEpoch + totalCorrMins * 1000 * 60;
    var ld = new Date(gmtDateEpoch);

    // date is originally in YYYY-MM-DD format
    // time is originally in a 24-hour format
    // this converts it to MM/DD hh:mm (AM|PM) 
    dateString = (ld.getMonth() + 1) + '/' + ld.getDate() + ' @ ' + 
        ((ld.getHours()>12)?(ld.getHours()-12):(ld.getHours()===0?12:
	ld.getHours())) + ':' + ((ld.getMinutes()<10)?('0' + 
	ld.getMinutes()):(ld.getMinutes())) + ' ' + 
	((ld.getHours()>=12)?'PM':'AM');
  } else {
    // if only a DATE was matched
    dateString =  parseInt(month, 10) + '/' + parseInt(dateMonth, 10);
  }
  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 description = htmlify(entry.content.$t);

    // 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 li = document.createElement('li');
		li.innerHTML = title + " : " + dateString + "<div style='margin-top:3px; font-size:smaller;'>" + description + "</div>";
		li.style.marginBottom='10px';
		
		/*
    // 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.setAttribute('target', 'puatl-caldetail');
      entryLink.appendChild(document.createTextNode(title));
      li.appendChild(entryLink);
      li.appendChild(document.createTextNode(' : ' + dateString + '<br/>' + description));
    } else {
      li.appendChild(document.createTextNode(title + ' : ' + dateString + '<br/>' + description));
    }	    
		*/
		
    // 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');
}