// Modified from Google Developer Example, JDS 12/08

/**
 * 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');

  var months=['Jan','Feb','Mar','Apr','May','Jun',
	      'Jul','Aug','Sep','Oct','Nov','Dec'];
  var days=['Sun','Mon','Tue','Wed','Thu','Fri','Sat'];

  // Show Time 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 Mon D hh:mm(am|pm) 
    dateString = days[ld.getDay()] + ', ' + 
	months[ld.getMonth()] + ' ' + 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 =  months[parseInt(month, 10)-1] + ' ' + 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, maxcnt) {
  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');

  var TimeZone=feed.gCal$timezone.value;
  
  if (typeof feed.entry != 'undefined') {

      // loop through each event in the feed
      for (var i = 0; i < feed.entry.length && maxcnt > 0; i++) {
	  var entry = feed.entry[i];
	  // skip private (free/busy only) events, showing at most maxcnt.
	  if (entry['gCal$privateCopy'] && entry['gCal$privateCopy'].value) {
	      continue;
	  }
	  
	  maxcnt--;
	  var title = entry.title.$t;
	  var start = entry['gd$when'][0].startTime;
	  var where = entry['gd$where'][0].valueString;
	  if (where != "") { where = ", " + where; }
	  
	  // 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'];
		  if (typeof TimeZone != 'undefined') {
		      // Add our Time Zone info
		      entryLinkHref=
			  entryLinkHref.replace("?eid",
						"?ctz=America/New_York&eid");
		  }
	      }
	  }

	  var dateString = formatGCalTime(start);
	  var li = document.createElement('li');
	  
	  // 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);
	      li.appendChild(document.createTextNode(' - '+dateString+where));
	  } else {
	      li.appendChild(document.createTextNode(title+' - '+
						     dateString+where));
	  }	    
	  
	  // append the list item onto the unordered list
	  ul.appendChild(li);
      }
  }
  var li=document.createElement('li');
  var entryLink=document.createElement('a');
  entryLink.setAttribute('href','news/calendar.html');
  entryLink.appendChild(document.createTextNode('more events...'));
  li.appendChild(entryLink);
  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',5);
}