Converting date between timezones swift
<p>I have a date stored on my online server database which is in <code>GMT</code>. I load the date and convert it to the user's timezone using the following code : </p>

<pre><code> if let messagedate = oneitem["timestamp"] as? String {
     let dateFormatter = NSDateFormatter()
     dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
     let date = dateFormatter.dateFromString(messagedate)
     let source_timezone = NSTimeZone(abbreviation: "GMT")
     let local_timezone = NSTimeZone.systemTimeZone()
     let source_EDT_offset = source_timezone?.secondsFromGMTForDate(date!)
     let destination_EDT_offset = local_timezone.secondsFromGMTForDate(date!)
     let time_interval : NSTimeInterval = Double(destination_EDT_offset - source_EDT_offset!)


     let final_date = NSDate(timeInterval: time_interval, sinceDate: date!)
     curr_item.date = final_date
 }
</code></pre>

<p>Now I need to convert the date back to <code>GMT</code> in order to communicate it to the server, however I'm not sure how to convert it back to <code>GMT</code>.</p>