Calculate dates one year in the past or one year in the future

dateUtility

import Foundation
 
/// Return date that is exactly one year earlier than specified date
///
/// :param: date NSDate
/// :returns: NSDate that is one year before date
func oneYearBeforeDate(date: NSDate) -> NSDate {
    let offsetComponents = NSDateComponents()
    offsetComponents.year = -1
 
    let calendar = NSCalendar.currentCalendar()
    if let result = calendar.dateByAddingComponents(offsetComponents, toDate: date, options: NSCalendarOptions(0)) {
        return result
    }
    else {
        // This should never happen, but we'll try to handle it gracefully
        let secondsPerYear: NSTimeInterval = 60 * 60 * 24 * 365
        return date.dateByAddingTimeInterval(-secondsPerYear)
    }
}
 
/// Return date that is exactly one year later than specified date
///
/// :param: date NSDate
/// :returns: NSDate that is one year beyond date
func oneYearAfterDate(date: NSDate) -> NSDate {
    let offsetComponents = NSDateComponents()
    offsetComponents.year = 1
 
    let calendar = NSCalendar.currentCalendar()
    if let result = calendar.dateByAddingComponents(offsetComponents, toDate: date, options: NSCalendarOptions(0)) {
        return result
    }
    else {
        // This should never happen, but we'll try to handle it gracefully
        let secondsPerYear: NSTimeInterval = 60 * 60 * 24 * 365
        return date.dateByAddingTimeInterval(secondsPerYear)
    }
}