countdown.swift

func countDownString(from date: Date, until nowDate: Date) -> String {
        let calendar = Calendar(identifier: .gregorian)
        let components = calendar
            .dateComponents([.day, .hour, .minute, .second]
                ,from: nowDate,
                 to: date)
        return String(format: "%02dd:%02dh:%02d:%02ds",
                      components.day ?? 00,
                      components.hour ?? 00,
                      components.minute ?? 00,
                      components.second ?? 00)
}