Get duration of a `SKProduct` in Apple Subscriptions

Question

The backend for my app needs two things along with receipt validation to ensure a user has access to a subscription. A subscriptionStartTimestamp and a subscriptionDuration. I was wondering if SKProduct offers something like this, and I stumbled upon SKProduct.subscriptionPeriod which contains a numberOfUnits and a unit. This unit could be day, month or other stuff.

Then another question hit me; "does Apple always consider a month 30 days?", "what about leap years?". How can I found a subscriptionDuration for a SKProduct?

Answer 1

I found this.

According to the answer mention above, I designed a function which takes a SKProduct and returns a duration for the subscription.

private func subscriptionDuration(product: SKProduct) -> TimeInterval {

    let currentDate = Date()
        
    guard let subscriptionPeriod = product.subscriptionPeriod else {
        return 0
    }
    
    let numberOfUnits = subscriptionPeriod.numberOfUnits
    let unit = subscriptionPeriod.unit
    
    var calendarComponent: Calendar.Component? = nil
    
    switch unit {
        
    case .day:
        calendarComponent = .day
        
    case .month:
        calendarComponent = .month
        
    case .week:
        calendarComponent = .weekOfYear
        
    case .year:
        calendarComponent = .year
        
    default:
        break
        
    }
    
    guard let component = calendarComponent else {
        return 0
    }
    
    let calendar = Calendar(identifier: .iso8601)
    
    guard let newDate = calendar.date(byAdding: component, value: numberOfUnits, to: currentDate) else {
        return 0
    }
    
    return newDate.timeIntervalSince1970 - currentDate.timeIntervalSince1970
}