iOS Swift extension to get GMT time offset string

OffsetStringFromGMT.swift

extension NSTimeZone {
    func offsetStringFromGMT() -> String {
        var offsetSeconds = secondsFromGMT
        var offsetString = "+00:00"
        var offsetSymbol = "+"
        var offsetHoursLeadString = "0"
        var offsetMinutesLeadString = "0"
        if offsetSeconds < 0 {
            offsetSymbol = "-"
            offsetSeconds = (offsetSeconds * -1)
        }
        var offsetHours = Int(offsetSeconds / 3600)
        var offsetMinutes = offsetSeconds - (offsetHours * 3600)
        if offsetHours > 10 {
            offsetHoursLeadString = ""
        }
        if offsetMinutes > 10 {
            offsetMinutesLeadString = ""
        }
        offsetString = String(format: "%@%@%i:%@%i", offsetSymbol, offsetHoursLeadString, offsetHours, offsetMinutesLeadString, offsetMinutes)
        return offsetString
    }
}