How to format time intervals for user display (social network like) in swift?

If you are targeting newer OS versions (iOS 13.5+, OS X 10.15+), you can use RelativeDateTimeFormatter:

let formatter = RelativeDateTimeFormatter()
formatter.dateTimeStyle = .named

for d in [-12600.0, -90000.0, -900.0, 13500.0] {
    let str = formatter.localizedString(fromTimeInterval: d)
    print("\(d): \(str)")
}

// Output
-12600.0: 3 hours ago
-90000.0: yesterday
-900.0: 15 minutes ago
13500.0: in 3 hours

---

For older OS versions, use DateComponentFormatter, available since iOS 8:

func format(duration: TimeInterval) -> String {
    let formatter = DateComponentsFormatter()
    formatter.allowedUnits = [.day, .hour, .minute, .second]
    formatter.unitsStyle = .abbreviated
    formatter.maximumUnitCount = 1

    return formatter.string(from: duration)!
}

for d in [12600.0, 90000.0, 900.0, 13500.0] {
    let str = format(duration: d)
    print("\(d): \(str)")
}

This prints:

12600.0: 4h
90000.0: 1d
900.0: 15m
13500.0: 4h

Just in case anyone wants it.. Swift 4

extension TimeInterval {
    func format(using units: NSCalendar.Unit) -> String? {
        let formatter = DateComponentsFormatter()
        formatter.allowedUnits = units
        formatter.unitsStyle = .abbreviated
        formatter.zeroFormattingBehavior = .pad

        return formatter.string(from: self)
    }
}

Example usage:

let value:TimeInterval =  12600.0
print("\(value.format(using: [.hour, .minute, .second])!)")

and the result will be:

3h 30m 0s