define(function(require, exports, module) {
'use strict';

var Caldav = require('ext/caldav');
var ICAL = require('ext/ical');
var IcalRecurExpansion = require('./ical_recur_expansion');
var Presets = require('common/presets');
var Responder = require('common/responder');
var debug = require('common/debug')('service/caldav');
var extend = require('common/extend');
var uuid = require('ext/uuid');

/* TODO: ugly hack to enable system XHR fix upstream in Caldav lib */
var xhrOpts = {
  /** system is required for cross domain XHR  */
  mozSystem: true,
  /** mozAnon is required to avoid system level popups on 401 status */
  mozAnon: true,
  /** enables use of mozilla only streaming api's when available */
  useMozChunkedText: true
};

Caldav.Xhr.prototype.globalXhrOptions = xhrOpts;

function Service(service) {
  Responder.call(this);

  this.service = service;
  this._initEvents();
}
module.exports = Service;

Service.prototype = {
  __proto__: Responder.prototype,

  /**
   * See: http://tools.ietf.org/html/rfc5545#section-3.7.3
   */
  icalProductId: '-//Mozilla//FirefoxOS',

  /**
   * See: http://tools.ietf.org/html/rfc5545#section-3.7.4
   */
  icalVersion: '2.0',

  _initEvents: function() {
    var events = [
      'noop',
      'getAccount',
      'findCalendars',
      'getCalendar',
      'streamEvents',
      'expandComponents',
      'expandRecurringEvent',
      'deleteEvent',
      'updateEvent',
      'createEvent'
    ];

    debug('Will listen for worker events...');
    events.forEach(function(e) {
      this.service.on(e, this);
    }, this);
  },

  handleEvent: function(e) {
    debug('Worker will fulfill', e.type, 'request...');
    this[e.type].apply(this, e.data);
  },

  /**
   * Builds an Caldav connection from an account model object.
   */
  _createConnection: function(account) {
    var params = extend({}, account);
    var preset = Presets[account.preset];

    if (
        preset &&
        preset.authenticationType &&
        preset.apiCredentials
    ) {
      switch (preset.authenticationType) {
        case 'oauth2':
          params.httpHandler = 'oauth2';
          // shallow copy the apiCredentials on the preset
          params.apiCredentials = extend({}, preset.apiCredentials);
          // the url in this case will always be tokenUrl
          params.apiCredentials.url = preset.apiCredentials.tokenUrl;
          break;
      }
    }

    var connection = new Caldav.Connection(params);
    return connection;
  },

  _requestHome: function(connection, url) {
    return new Caldav.Request.CalendarHome(
      connection,
      { url: url }
    );
  },

  _requestCalendars: function(connection, url) {
    var Finder = Caldav.Request.Resources;
    var Resource = Caldav.Resources.Calendar;

    var req = new Finder(connection, { url: url });

    req.addResource('calendar', Resource);
    req.prop(['ical', 'calendar-color']);
    req.prop(['caldav', 'calendar-description']);
    req.prop('current-user-privilege-set');
    req.prop('displayname');
    req.prop('resourcetype');
    req.prop(['calserver', 'getctag']);

    return req;
  },

  _requestEvents: function(connection, cal, options) {
    var Resource = Caldav.Resources.Calendar;
    var remoteCal = new Resource(connection, cal);
    var query = remoteCal.createQuery();

    query.prop('getetag');

    // only return VEVENT & VTIMEZONE
    var filterQuery = query.filter.setComp('VCALENDAR');
    var filterEvent = filterQuery.comp('VEVENT');

    if (options && options.startDate) {
      // convert startDate to unix ical time.
      var icalDate = new ICAL.Time();

      // ical uses seconds not milliseconds
      icalDate.fromUnixTime(options.startDate.valueOf() / 1000);
      filterEvent.setTimeRange({ start: icalDate.toICALString() });
    }

    // include only the VEVENT/VTIMEZONE in the data
    query.data.setComp('VCALENDAR');

    return query;
  },

  noop: function(callback) {
    callback({ ready: true });
  },

  getAccount: function(account, callback) {
    var url = account.entrypoint;
    debug('Fetching account from:', url);

    var connection = this._createConnection(account);
    var request = this._requestHome(connection, url);
    debug('Will issue calendar home request.');
    return request.send(function(err, data) {
      if (err) {
        debug('Error sending home request:', err);
        return callback(err);
      }

      debug('Received data:', data);
      var result = {};

      if (data.url) {
        result.calendarHome = data.url;
      }

      if (connection.oauth) {
        result.oauth = connection.oauth;
      }

      if (connection.user) {
        result.user = connection.user;
      }

      callback(null, result);
    });
  },

  _formatCalendar: function(cal) {
    var result = Object.create(null);

    result.id = cal.url;
    result.url = cal.url;
    result.name = cal.name;
    result.color = cal.color;
    result.description = cal.description;
    result.syncToken = cal.ctag;
    result.privilegeSet = cal.privilegeSet;

    return result;
  },

  findCalendars: function(account, callback) {
    var self = this;
    var url = account.calendarHome;
    var connection = this._createConnection(account);

    var request = this._requestCalendars(
      connection,
      url
    );

    request.send(function(err, data) {
      if (err) {
        callback(err);
        return;
      }

      var calendars = data.calendar;
      var results = {};
      var key;
      var item;

      for (key in calendars) {
        if (calendars.hasOwnProperty(key)) {
          item = calendars[key];
          var formattedCal = self._formatCalendar(
            item
          );

          // If privilegeSet is not present we will assume full permissions.
          // Its highly unlikey that it is missing however.
          if (('privilegeSet' in formattedCal) &&
              (formattedCal.privilegeSet.indexOf('read') === -1)) {

            // skip calendars without read permissions
            continue;
          }

          results[key] = formattedCal;
        }
      }
      callback(null, results);
    });
  },

  /**
   * Formats an alarm trigger
   * Returns the relative time for that trigger
   *
   * @param {ICAL.Property} trigger property.
   * @param {ICAL.Date} start date.
   */
  _formatTrigger: function(trigger, startDate) {
    var alarmTrigger;
    if (trigger.type == 'duration') {
      alarmTrigger = trigger.getFirstValue().toSeconds();
    } else {
      // Type is date-time
      alarmTrigger = trigger
        .getFirstValue()
        .subtractDate(startDate)
        .toSeconds();
    }

    return alarmTrigger;
  },

  /**
   * Formats an already parsed ICAL.Event instance.
   * Expects event to already contain exceptions, etc..
   *
   * @param {String} etag etag.
   * @param {String} url caldav url.
   * @param {String} ical raw ical string.
   * @param {ICAL.Event} event ical event.
   */
  _formatEvent: function(etag, url, ical, event) {
    var self = this;
    var exceptions = null;
    var key;

    if (event.exceptions) {
      exceptions = [];
      for (key in event.exceptions) {
        exceptions.push(this._formatEvent(
          etag,
          url,
          ical,
          event.exceptions[key]
        ));
      }

      if (!exceptions.length) {
        exceptions = null;
      }
    }

    var rid = event.recurrenceId;

    if (rid) {
      rid = this.formatICALTime(rid);
    }

    var resultAlarms = [];
    var alarms = event.component.getAllSubcomponents('valarm');
    alarms.forEach(function(instance) {
      var action = instance.getFirstPropertyValue('action');
      if (action && action === 'DISPLAY') {
        var triggers = instance.getAllProperties('trigger');
        var i = 0;
        var len = triggers.length;

        for (; i < len; i++) {

          var trigger = triggers[i];

          resultAlarms.push({
            action: action,
            trigger: self._formatTrigger(trigger, event.startDate)
          });
        }
      }
    });

    var result = {
      alarms: resultAlarms,
      syncToken: etag,
      url: url,
      id: event.uid,
      title: event.summary,
      recurrenceId: rid,
      isRecurring: event.isRecurring(),
      description: event.description,
      location: event.location,
      start: this.formatICALTime(event.startDate),
      end: this.formatICALTime(event.endDate),
      exceptions: exceptions
    };

    return result;
  },

  /**
   * Find and parse the display alarms for an event.
   *
   * @param {Object} details details for specific instance.
   */
  _displayAlarms: function(details) {
    var event = details.item;
    var comp = event.component;
    var alarms = comp.getAllSubcomponents('valarm');
    var result = [];

    var self = this;
    alarms.forEach(function(instance) {
      var action = instance.getFirstPropertyValue('action');
      if (action && action === 'DISPLAY') {
        // lets just assume we might have multiple triggers
        var triggers = instance.getAllProperties('trigger');
        var i = 0;
        var len = triggers.length;

        for (; i < len; i++) {
          result.push({
            action: action,
            trigger: self._formatTrigger(triggers[i], event.startDate)
          });
        }
      }
    });

    return result;
  },

  /**
   * Takes an ICAL.Time object and converts it
   * into the storage format familiar to the calendar app.
   *
   *    var time = new ICAL.Time({
   *      year: 2012,
   *      month: 1,
   *      day: 1,
   *      zone: 'PST'
   *    });
   *
   *    // time is converted to a MS
   *    // then its UTC offset is added
   *    // so the time is at UTC (offset 0) then the
   *    // offset is associated with that time.
   *
   *    var output = {
   *      utc: ms,
   *      offset: (+|-)ms,
   *      // zone can mostly be ignored except
   *      // in the case where the event is "floating"
   *      // in time and we need to convert the utc value
   *      // to the current local time.
   *      tzid: ''
   *    };
   */
  formatICALTime: function(time) {
    var zone = time.zone;
    var offset = time.utcOffset() * 1000;
    var utc = time.toUnixTime() * 1000;

    utc += offset;

    var result = {
      tzid: zone.tzid,
      // from seconds to ms
      offset: offset,
      // from seconds to ms
      utc: utc
    };

    if (time.isDate) {
      result.isDate = true;
    }

    return result;
  },

  /**
   * Formats a given time/date into a ICAL.Time instance.
   * Suitable for converting the output of formatICALTime back
   * into a similar representation of the original.
   *
   * Once a time instance goes through this method it should _not_
   * be modified as the DST information is lost (offset is preserved).
   *
   * @param {ICAL.Time|Object} time formatted ical time
   *                                    or output of formatICALTime.
   */
  formatInputTime: function(time) {
    if (time instanceof ICAL.Time) {
      return time;
    }

    var utc = time.utc;
    var tzid = time.tzid;
    var offset = time.offset;
    var result;

    if (tzid === ICAL.Timezone.localTimezone.tzid) {
      result = new ICAL.Time();
      result.fromUnixTime(utc / 1000);
      result.zone = ICAL.Timezone.localTimezone;
    } else {
      result = new ICAL.Time();
      result.fromUnixTime((utc - offset) / 1000);
      result.zone = ICAL.Timezone.utcTimezone;
    }

    if (time.isDate) {
      result.isDate = true;
    }

    return result;
  },

  /**
   * Parse an ical data/string into primary
   * event and exceptions.
   *
   * It is assumed there is only one primary event
   * (does not have a RECURRENCE-ID) in the ical content.
   *
   * @param {Object|String|ICAL.Event} ical vcalendar chunk (and exceptions).
   * @param {Function} callback node style callback [err, primary event].
   */
  parseEvent: function(ical, callback) {
    if (ical instanceof ICAL.Event) {
      callback(null, ical);
      return;
    }

    var parser = new ICAL.ComponentParser();
    var primaryEvent;
    var exceptions = [];

    parser.ontimezone = function(zone) {
      var id = zone.tzid;

      if (!ICAL.TimezoneService.has(id)) {
        ICAL.TimezoneService.register(id, zone);
      }
    };

    parser.onevent = function(item) {
      if (item.isRecurrenceException()) {
        exceptions.push(item);
      } else {
        primaryEvent = item;
      }
    };

    parser.oncomplete = function() {
      if (!primaryEvent) {
        //TODO: in the error handling pass we need to define
        //     path to log this information so we can determine
        //     the cause of failures.
        callback(new Error('ical parse error'));
        return;
      }
      exceptions.forEach(primaryEvent.relateException, primaryEvent);
      callback(null, primaryEvent);
    };

    //XXX: Right now ICAL.js is all sync so we
    //     can catch the errors this way in the future
    //     onerror will replace this.
    try {
      parser.process(ical);
    } catch (e) {
      callback(e);
    }
  },

  _defaultMaxDate: function() {
    var now = new Date();

    return new ICAL.Time({
      year: now.getFullYear(),
      // three months in advance
      // +1 because js months are zero based
      month: now.getMonth() + 6,
      day: now.getDate()
    });
  },

  /**
   * Expands a list recurring events by their component.
   *
   * It is expected for this function to receive an array
   * of items each structured as a icalComponent.
   *
   *    [
   *      { ical: '...', lastRecurrenceId: '..', iterator: '...' },
   *      ...
   *    ]
   *
   * @param {Array.<icalComponent>} components list of icalComponents.
   * @param {Calendar.Responder} stream to emit events.
   * @param {Object} options list of options.
   * @param {Object} options.maxDate maximum date to expand to.
   * @param {Function} callback only sends an error if fatal.
   */
  expandComponents: function(components, options, stream, callback) {
    var pending = components.length;

    function next() {
      if (!(--pending)) {
        callback();
      }
    }


    components.forEach(function(component) {
      var ical = component.ical;
      var localOpts = {
        maxDate: options.maxDate,
        iterator: component.iterator
      };

      if (component.lastRecurrenceId) {
        localOpts.minDate = component.lastRecurrenceId;
      }

      // expand each component
      this.expandRecurringEvent(ical, localOpts, stream,
                                function(err, iter, lastRecurId, uid) {

        if (err) {
          stream.emit('error', err);
          next();
          return;
        }

        stream.emit('component', {
          eventId: uid,
          lastRecurrenceId: lastRecurId,
          ical: ical,
          iterator: iter
        });

        next();
      });
    }, this);
  },

  /**
   * Options:
   *
   *  - iterator: (ICAL.RecurExpander) optional recurrence expander
   *              used to resume the iterator state for existing events.
   *
   *  - maxDate: if instance ends after this date stop expansion.
   *
   *
   * Returns:
   *
   *    [
   *      {
   *        start: { offset: inMS, utc: ms },
   *        endDate: // same format as start,
   *        recurrenceId: // id of specific recurrence.
   *        uid: // uid of event
   *        isException: // true when is exception to usual rule.
   *      },
   *      //...
   *    ]
   */
  expandRecurringEvent: function(component, options, stream, callback) {
    var self = this;
    var maxDate;
    var minDate = null;
    var now;

    if (options.minDate) {
      minDate = this.formatInputTime(options.minDate);
    }

    if (options.maxDate) {
      maxDate = this.formatInputTime(options.maxDate);
    }

    if (!('now' in options)) {
      options.now = ICAL.Time.now();
    }

    now = options.now;

    // convert to rich ical event
    this.parseEvent(component, function(err, event) {
      if (err) {
        callback(err);
        return;
      }

      var iter = IcalRecurExpansion.forEach(
        event,
        options.iterator,
        occuranceHandler,
        minDate,
        maxDate
      );

      function occuranceHandler(next) {
        var details = event.getOccurrenceDetails(next);
        var inFuture = details.endDate.compare(now);

        debug('alarm time',
              event.summary,
              'will add ' + String(inFuture),
              'start:', details.startDate.toJSDate().toString(),
              'end:', details.endDate.toJSDate().toString(),
              'now:', now.toJSDate().toString());

        var occurrence = {
          start: self.formatICALTime(details.startDate),
          end: self.formatICALTime(details.endDate),
          recurrenceId: self.formatICALTime(next),
          eventId: details.item.uid,
          isException: details.item.isRecurrenceException()
        };

        // only set alarms for those dates in the future...
        if (inFuture >= 0) {
          var alarms = self._displayAlarms(details);
          if (alarms) {
            occurrence.alarms = alarms;
          }
        }

        stream.emit('occurrence', occurrence);
      }

      var lastRecurrence;

      if (iter.complete) {
        // when the iterator is complete
        // last recurrence is false.
        // We use this to signify the end
        // of the iteration cycle.
        lastRecurrence = false;
      } else {
        // its very important all times used
        // for comparison are based on the recurrence id
        // and not the start date as those can change
        // with exceptions...
        lastRecurrence = self.formatICALTime(
          iter.last
        );
      }

      callback(
        null,
        iter.toJSON(),
        lastRecurrence,
        event.uid
      );
    });
  },

  /**
   * Handle a single caldav event response.
   *
   * @param {String} url location of event.
   * @param {Object} response caldav response object.
   * @param {Calendar.Responder} responder event emitter.
   * @param {Function} callback node style callback fired after event parsing.
   */
  _handleCaldavEvent: function(url, response, stream, callback) {
    var self = this;
    var etag = response.getetag;
    var event = response['calendar-data'];

    if (event.status != 200) {
      callback(new Error('non 200 status code "' + url + '"'));
      return;
    }

    // process event
    var ical = event.value;
    this.parseEvent(ical, function(err, event) {

      if (err) {
        callback(err);
        return;
      }

      var result = self._formatEvent(etag.value, url, ical, event);
      stream.emit('event', result);

      var options = {
        maxDate: self._defaultMaxDate(),
        now: ICAL.Time.now()
      };

      self.expandRecurringEvent(event, options, stream,
                                function(err, iter, lastRecurrenceId) {

        if (err) {
          callback(err);
          return;
        }

        if (!event.isRecurring()) {
          stream.emit('component', {
            eventId: result.id,
            isRecurring: false,
            ical: ical
          });
        } else {
          stream.emit('component', {
            eventId: result.id,
            lastRecurrenceId: lastRecurrenceId,
            ical: ical,
            iterator: iter
          });
        }

        callback(null);
      });
    });
  },

  streamEvents: function(account, calendar, options, stream, callback) {
    var self = this;
    var hasCompleted = false;
    var connection = this._createConnection(account);

    var cache = options.cached;

    // we don't need to pass this around anywhere.
    //delete options.cache;

    var request = this._requestEvents(connection, calendar, options);
    var pending = 0;

    function next(err) {
      if (err) {
        try {
          stream.emit('error', err);
        } catch (e) {
          console.error('Failed to transport err:', err.toString(), err.stack);
        }
      }

      if (!(--pending) && hasCompleted) {
        callback(null);
      }
    }

    function handleResponse(url, data) {
      if (!data || !data['calendar-data']) {
        // throw some error;
        console.error('Could not sync: ', url);
        return;
      }
      var etag = data.getetag.value;
      if (url in cache) {
        // don't need to track this for missing events.
        if (etag !== cache[url].syncToken) {
          pending++;
          self._handleCaldavEvent(url, data, stream, next);
        }

        delete cache[url];
      } else {
        pending++;
        self._handleCaldavEvent(url, data, stream, next);
      }
    }

    request.sax.on('DAV:/response', handleResponse);

    request.send(function(err) {
      hasCompleted = true;
      // when the request is completed stop listening
      // for sax events.
      request.sax.removeEventListener(
        'DAV:/response', handleResponse
      );

      if (err) {
        callback(err);
        return;
      }

      if (!pending) {
        var missing = [];

        for (var url in cache) {
          missing.push(cache[url].id);
        }

        // send missing events
        stream.emit('missingEvents', missing);

        // notify the requester that we have completed.
        callback();
      }
    });
  },

  _assetRequest: function(connection, url) {
    return new Caldav.Request.Asset(connection, url);
  },

  deleteEvent: function(account, calendar, event, callback) {
    var connection = this._createConnection(account);

    var req = this._assetRequest(connection, event.url);

    req.delete({}, function(err) {
      callback(err);
    });
  },

  addAlarms: function(component, alarms, account) {
    alarms = alarms || [];

    for (var i = 0; i < alarms.length; i++) {

      var valarm = new ICAL.Component('valarm');

      // valarm details
      valarm.addPropertyWithValue('action', alarms[i].action);
      valarm.addPropertyWithValue('description', 'This is an event reminder');
      var trigger = valarm.addPropertyWithValue('trigger',
        ICAL.Duration.fromSeconds(
          alarms[i].trigger
        )
      );
      trigger.setParameter('relative', 'START');
      component.addSubcomponent(valarm);

      // Check if we need to mirror the VALARM onto email
      if (this.mirrorAlarms(account)) {
        valarm = new ICAL.Component('valarm');
        valarm.addPropertyWithValue('action', 'EMAIL');
        valarm.addPropertyWithValue('description',
          'This is an event reminder');
        valarm.addPropertyWithValue('ATTENDEE', account.user);
        trigger = valarm.addPropertyWithValue('trigger',
          ICAL.Duration.fromSeconds(
            alarms[i].trigger
          )
        );
        trigger.setParameter('relative', 'START');
        component.addSubcomponent(valarm);
      }
    }
  },

  /**
   * Update absolute alarm times when the startDate changes.
   *
   * @param {ICAL.Time} originalDate of the event.
   * @param {ICAL.Event} event to update.
   */
  adjustAbsoluteAlarms: function(originalDate, event) {
    var alarms = event.component.getAllSubcomponents('valarm');

    alarms.forEach(function(alarm) {
      var trigger = alarm.getFirstProperty('trigger');
      var value = trigger.getValues()[0].clone();

      // absolute time
      if (value instanceof ICAL.Time) {
        // find absolute time difference
        var diff = value.subtractDateTz(originalDate);
        trigger.setValue(diff);
      }
    });
  },

  /**
   * Yahoo needs us to mirror all alarms as EMAIL alarms
   */
  mirrorAlarms: function(account) {
    return account && account.domain === 'https://caldav.calendar.yahoo.com';
  },

  createEvent: function(account, calendar, event, callback) {
    var connection = this._createConnection(account);
    var vcalendar = new ICAL.Component('vcalendar');
    var icalEvent = new ICAL.Event();

    // vcalendar details
    vcalendar.addPropertyWithValue('prodid', this.icalProductId);
    vcalendar.addPropertyWithValue('version', this.icalVersion);

    // text fields
    icalEvent.uid = uuid();
    icalEvent.summary = event.title;
    icalEvent.description = event.description;
    icalEvent.location = event.location;
    icalEvent.sequence = 1;

    // time fields
    icalEvent.startDate = this.formatInputTime(event.start);
    icalEvent.endDate = this.formatInputTime(event.end);

    // alarms
    this.addAlarms(icalEvent.component, event.alarms, account);

    vcalendar.addSubcomponent(icalEvent.component);

    var url = calendar.url + icalEvent.uid + '.ics';
    var req = this._assetRequest(connection, url);

    event.id = icalEvent.uid;
    event.url = url;
    event.icalComponent = vcalendar.toString();

    req.put({}, event.icalComponent, function(err, data, xhr) {
      if (err) {
        callback(err);
        return;
      }

      var token = xhr.getResponseHeader('Etag');
      event.syncToken = token;
      // TODO: error handling
      callback(err, event);
    });

  },

  /**
   * Updates a single caldav event.
   * Will handle updating both primary events and exceptions.
   *
   * @param {Object} account full account details.
   * @param {Object} calendar full calendar details.
   * @param {Object} eventDetails details to update the event.
   *  unmodified parsed ical component. (VCALENDAR).
   */
  updateEvent: function(account, calendar, eventDetails, callback) {
    var connection = this._createConnection(account);

    var icalComponent = eventDetails.icalComponent;
    var event = eventDetails.event;

    var self = this;
    var req = this._assetRequest(connection, event.url);

    // parse event
    this.parseEvent(icalComponent, function(err, icalEvent) {
      if (err) {
        callback(err);
        return;
      }

      var target = icalEvent;
      var vcalendar = icalEvent.component.parent;
      var originalStartDate = target.startDate;

      // find correct event
      if (event.recurrenceId) {
        var rid = self.formatInputTime(event.recurrenceId);
        rid = rid.toString();
        if (icalEvent.exceptions[rid]) {
          target = icalEvent.exceptions[rid];
        }
      }

      // vcalendar pieces
      vcalendar.updatePropertyWithValue('prodid', self.icalProductId);

      // text fields
      target.summary = event.title;
      target.description = event.description;
      target.location = event.location;

      if (!target.sequence) {
        target.sequence = 0;
      }

      target.sequence = parseInt(target.sequence, 10) + 1;

      // time fields
      target.startDate = self.formatInputTime(
        event.start
      );

      target.endDate = self.formatInputTime(
        event.end
      );

      // adjust absolute alarm time ( we do this before adding/changing our
      // new alarm times )
      self.adjustAbsoluteAlarms(originalStartDate, target);

      // We generally want to remove all 'DISPLAY' alarms
      // UNLESS we are dealing with a YAHOO account
      // Then we overwrite all alarms
      var alarms = target.component.getAllSubcomponents('valarm');
      alarms.forEach(function(alarm) {
        var action = alarm.getFirstPropertyValue('action');
        if (action === 'DISPLAY' || self.mirrorAlarms(account)) {
          target.component.removeSubcomponent(alarm);
        }
      });
      self.addAlarms(target.component, event.alarms, account);

      var vcal = target.component.parent.toString();
      event.icalComponent = vcal;

      req.put({}, vcal, function(err, data, xhr) {
        if (err) {
          callback(err);
          return;
        }

        var token = xhr.getResponseHeader('Etag');
        event.syncToken = token;
        // TODO: error handling
        callback(err, event);
      });
    });
  }
};

});