How to subtract 30 minutes from a timeinterval in Swift?

Question

I have made an App with a datePicker and 2 buttons - "Check in" and "Check out". I did the calculation between the two timestamps in hours and minutes. Now I want to subtract 30 minutes from that time interval, IF the "Check in" is before 12:00.

This is my code so far:

var start = Date()

var end = Date()

class ViewController: UIViewController {

@IBOutlet weak var timeWheel: UIDatePicker!
@IBOutlet weak var workLabel: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()
}

@IBAction func checkIn(_ sender: Any) {
    start = timeWheel.date
    workLabel.text = ""
}

@IBAction func checkOut(_ sender: Any) {
    end = timeWheel.date
    let difference = Calendar.current.dateComponents([.hour, .minute], from: start, to: end)
    workLabel.text = "\(difference.hour ?? 0) timer og \(difference.minute ?? 0) minutter"
}
}

---

Got any suggestions ?

Answer 1

Before calculating the difference get the hour component of start and check if it's less than 12. If yes subtract the 30 minutes and then do the math

@IBAction func checkOut(_ sender: Any) {
    end = timeWheel.date
    let calendar = Calendar.current
    let startHour = calendar.component(.hour, from: start)
    let startDate = startHour < 12 ? calendar.date(byAdding: .minute, value: 30, to: start)! : start
    let difference = calendar.dateComponents([.hour, .minute], from: startDate, to: end)
    workLabel.text = "\(difference.hour!) timer og \(difference.minute!) minutter"
}

Forces unwrapping the components is perfectly fine as both components were clearly requested.