Round time to nearest thirty seconds - swift

Question

I have an app that presents data that expires every 30 seconds (precisely, at h/m/s 11:30:00, 11:30:30, 11:31:00, etc).
I can get the current time, but I am unsure on how to calculate the time between now and the nearest thirty seconds.
Anything I've found is in Objective-C, and I've been unable to convert it.
Here's what I tried:
func nearestThirtySeconds() -> Date? {
var components = NSCalendar.current.dateComponents([.second], from: self)
let second = components.second ?? 30
components.second = second >= 30 ? 60 - second : -second
return Calendar.current.date(byAdding: components, to: self)
}
But this returns the nearest minute (I think, it always returns a definite minute)
Any ideas?

Answer 1

You can round the seconds to the nearest multiple of 30,
and then add the difference between the rounded and the original
value to the date:
extension Date {
func nearestThirtySeconds() -> Date {
let cal = Calendar.current
let seconds = cal.component(.second, from: self)
// Compute nearest multiple of 30:
let roundedSeconds = lrint(Double(seconds) / 30) * 30
return cal.date(byAdding: .second, value: roundedSeconds - seconds, to: self)!
}
}
That should be good enough to display the rounded time, however it
is not exact: A Date includes also fractional seconds, so
for example "11:30:10.123" would become "11:30:00.123" and not "11:30:00.000". Here is another approach which solves that problem:
extension Date {
func nearestThirtySeconds() -> Date {
let cal = Calendar.current
let startOfMinute = cal.dateInterval(of: .minute, for: self)!.start
var seconds = self.timeIntervalSince(startOfMinute)
seconds = (seconds / 30).rounded() * 30
return startOfMinute.addingTimeInterval(seconds)
}
}
Now seconds is the time interval since the start of the current minute
(including fractional seconds). That interval is rounded to the nearest
multiple of 30 and added to the start of the minute.

Answer 2

I used the answer by Martin R to write a more generic version to round by any time period.
Answer is outdated and only works with time, check gist for the latest version.
https://gist.github.com/casperzandbergenyaacomm/83c6a585073fd7da2e1fbb97c9bcd38a
extension Date {
func rounded(on amount: Int, _ component: Calendar.Component) -> Date {
let cal = Calendar.current
let value = cal.component(component, from: self)
// Compute nearest multiple of amount:
let roundedValue = lrint(Double(value) / Double(amount)) * amount
let newDate = cal.date(byAdding: component, value: roundedValue - value, to: self)!
return newDate.floorAllComponents(before: component)
}
func floorAllComponents(before component: Calendar.Component) -> Date {
// All components to round ordered by length
let components = [Calendar.Component.year, .month, .day, .hour, .minute, .second, .nanosecond]
guard let index = components.index(of: component) else {
fatalError("Wrong component")
}
let cal = Calendar.current
var date = self
components.suffix(from: index + 1).forEach { roundComponent in
let value = cal.component(roundComponent, from: date) * -1
date = cal.date(byAdding: roundComponent, value: value, to: date)!
}
return date
}
}
To round to x minutes you need to also floor the seconds so this also contains the floor method I wrote.
How to use:
let date: Date = Date() // 10:16:34
let roundedDate0 = date.rounded(on: 30, .second) // 10:16:30
let roundedDate1 = date.rounded(on: 15, .minute) // 10:15:00
let roundedDate2 = date.rounded(on: 1, .hour) // 10:00:00

Answer 3

There's a Cocoapod called 'SwiftDate' that is great for date formatting and manipulation that can applied to your Date() instance.
Example of how to use the date rounding method:
let date = Date() // 2018-10-01 23:05:29
date.dateRoundedAt(at: .toFloor5Mins) // 2018-10-01 23:05:00
date.dateRoundedAt(at: .toCeil5Mins) // 2018-10-01 23:10:00
date.dateRoundedAt(at: .toFloorMins(1)) // 2018-10-01 23:05:00
date.dateRoundedAt(at: .toCeilMins(1)) // 2018-10-01 23:06:00
(For reference, check out the documentation at https://cocoapods.org/pods/SwiftDate)

Answer 4

let now = Date()
var timeInterval = now.timeIntervalSinceReferenceDate
timeInterval += 30 - timeInterval.truncatingRemainder(dividingBy: 30)
let rounded = Date(timeIntervalSinceReferenceDate: timeInterval)
print("\(now) rounded to nearest 30 seconds is \(rounded)")