Rounding time

RoundedTime.swift

private func nearestPotentialStartTime(toTime time: NSDate) -> NSDate {
    let calendar = NSCalendar.currentCalendar()
    let components = calendar.components([.Era, .Year, .Month, .Day, .Hour, .Minute], fromDate: time)
    
    let minutes = components.minute
    let nextStartMark = (minutes % startInterval) + startInterval
    let previousStartMark = nextStartMark - startInterval
    
    let previousDelta = abs(minutes - previousStartMark)
    let nextDelta = abs(minutes - nextStartMark)
    
    components.minute = previousDelta <= nextDelta ? previousStartMark : nextStartMark
    return calendar.dateFromComponents(components)!
}