Round Date to Second

RoundedSecond.swift

extension Date {
    var roundedToSecond: Date {
        let date = self
        let diff = 1000000000 - Calendar.current.component(.nanosecond, from: date)
        return Calendar.current.date(byAdding: .nanosecond, value: diff, to: date)!
    }
}

/// USAGE:
let roundedDate = Date().roundedToSecond /// zero nanoseconds

FYI This rounds down correctly if you change to the following line:

let diff = -Calendar.current.component(.nanosecond, from: date)

As is, the code adds an extra second.