Swift convert time to time ago

I’ll just update the Truongky’s answer for Swif 3:

extension Date {

func getElapsedInterval() -> String {

    let interval = Calendar.current.dateComponents([.year, .month, .day], from: self, to: Date())

    if let year = interval.year, year > 0 {
        return year == 1 ? "\(year)" + " " + "year ago" :
            "\(year)" + " " + "years ago"
    } else if let month = interval.month, month > 0 {
        return month == 1 ? "\(month)" + " " + "month ago" :
            "\(month)" + " " + "months ago"
    } else if let day = interval.day, day > 0 {
        return day == 1 ? "\(day)" + " " + "day ago" :
            "\(day)" + " " + "days ago"
    } else {
        return "a moment ago"

    }

}
}

If you prefer a localizable response instead of only english this code will do the work

extension Date {
func getElapsedInterval() -> String {

    var calendar = Calendar.current
    calendar.locale = Locale(identifier: Bundle.main.preferredLocalizations[0]) 
// IF THE USER HAVE THE PHONE IN SPANISH BUT YOUR APP ONLY SUPPORTS I.E. ENGLISH AND GERMAN
// WE SHOULD CHANGE THE LOCALE OF THE FORMATTER TO THE PREFERRED ONE 
// (IS THE LOCALE THAT THE USER IS SEEING THE APP), IF NOT, THIS ELAPSED TIME 
// IS GOING TO APPEAR IN SPANISH

    let formatter = DateComponentsFormatter()
    formatter.unitsStyle = .full
    formatter.maximumUnitCount = 1
    formatter.calendar = calendar

    var dateString: String?

    let interval = calendar.dateComponents([.year, .month, .weekOfYear, .day], from: self, to: Date())

    if let year = interval.year, year > 0 {
        formatter.allowedUnits = [.year] //2 years
    } else if let month = interval.month, month > 0 {
        formatter.allowedUnits = [.month] //1 month
    } else if let week = interval.weekOfYear, week > 0 {
        formatter.allowedUnits = [.weekOfMonth] //3 weeks
    } else if let day = interval.day, day > 0 {
        formatter.allowedUnits = [.day] // 6 days
    } else {
        let dateFormatter = DateFormatter()
        dateFormatter.locale = Locale(identifier: Bundle.main.preferredLocalizations[0]) //--> IF THE USER HAVE THE PHONE IN SPANISH BUT YOUR APP ONLY SUPPORTS I.E. ENGLISH AND GERMAN WE SHOULD CHANGE THE LOCALE OF THE FORMATTER TO THE PREFERRED ONE (IS THE LOCALE THAT THE USER IS SEEING THE APP), IF NOT, THIS ELAPSED TIME IS GOING TO APPEAR IN SPANISH
        dateFormatter.dateStyle = .medium
        dateFormatter.doesRelativeDateFormatting = true

        dateString = dateFormatter.string(from: self) // IS GOING TO SHOW 'TODAY'
    }

    if dateString == nil {
        dateString = formatter.string(from: self, to: Date())
    }

    return dateString!
}