Convert Firebase Firestore Timestamp to Date (Swift)?

Question

I have a date saved in a Firestore field as a timestamp that I want to convert to a Date in Swift:

June 19,2018 at 7:20:21 PM UTC-4

I tried the following but I get an error:

let date = Date(timeIntervalSince1970: postTimestamp as! TimeInterval)

Error:

Could not cast value of type 'FIRTimestamp' (0x104fa8b98) to 'NSNumber'

The reason why I want to convert to Date is so that I can use this Date extension to mimic timestamps you see on Instagram posts:

extension Date {
    func timeAgoDisplay() -> String {
        let secondsAgo = Int(Date().timeIntervalSince(self))

        let minute = 60
        let hour = 60 * minute
        let day = 24 * hour
        let week = 7 * day

        if secondsAgo < minute {
            return "\(secondsAgo) seconds ago"
        } else if secondsAgo < hour {
            return "\(secondsAgo / minute) minutes ago"
        } else if secondsAgo < day {
            return "\(secondsAgo / hour) hours ago"
        } else if secondsAgo < week {
            return "\(secondsAgo / day) days ago"
        }

        return "\(secondsAgo / week) weeks ago"
    }
}

Solution

Either do:

let date = postTimestamp.dateValue()

or you could do:

let date = Date(timeIntervalSince1970: postTimestamp.seconds)

See the Timestamp reference documentation.