Date extension to display the date in relative terms (e.g. "5 hours ago").

Date+Relative.swift

// Adapted from http://stackoverflow.com/a/1248

private let minuteInterval: TimeInterval = 60
private let hourInterval: TimeInterval = 60 * minuteInterval
private let dayInterval: TimeInterval = 24 * hourInterval
private let monthInterval: TimeInterval = 30 * dayInterval

extension Date {

    var relative: String {
        // Adapted from http://stackoverflow.com/a/1248
        let delta = timeIntervalSinceNow * -1

        switch delta {
        case _ where delta < 0:
            return "in the future"

        case _ where delta < 1 * minuteInterval:
            let seconds = relativeComponents.second ?? 0
            return seconds == 1 ? "one second ago" : "\(seconds) seconds ago"

        case _ where delta < 2 * minuteInterval:
            return "a minute ago"

        case _ where delta < 45 * minuteInterval:
            let minutes = relativeComponents.minute ?? 0
            return "\(minutes) minutes ago"

        case _ where delta < 90 * minuteInterval:
            return "an hour ago"

        case _ where delta < 24 * hourInterval:
            let hours = relativeComponents.hour ?? 0
            return "\(hours) hours ago"

        case _ where delta < 48 * hourInterval:
            return "yesterday"

        case _ where delta < 30 * dayInterval:
            let days = relativeComponents.day ?? 0
            return "\(days) days ago"

        case _ where delta < 12 * monthInterval:
            let months = relativeComponents.month ?? 0
            return months <= 1 ? "one month ago" : "\(months) months ago"

        default:
            let years = relativeComponents.year ?? 0
            return years <= 1 ? "one year ago" : "\(years) years ago"
        }
    }

    private var relativeComponents: DateComponents {
        return Calendar.current.dateComponents(
            [.year, .month, .day, .hour, .minute, .second],
            from: self,
            to: Date() // now
        )
    }
}