requestAccessWithCompletion.swift

private let healthStore = HKHealthStore()

/// Requests access to all the data types the app wishes to read/write from HealthKit.
/// On success, data is queried immediately and observer queries are set up for background
/// delivery. This is safe to call repeatedly and should be called at least once per launch.
func requestAccessWithCompletion(completion: @escaping AccessRequestCallback) {
	guard HKHealthStore.isHealthDataAvailable() else {
		debugPrint("Can't request access to HealthKit when it's not supported on the device.")
		return
	}

	let writeDataTypes = dataTypesToWrite()
	let readDataTypes = dataTypesToRead()

	healthStore.requestAuthorization(toShare: writeDataTypes, read: readDataTypes) { [weak self] (success: Bool, error: Error?) in
		guard let strongSelf = self else { return }
		if success {
			debugPrint("Access to HealthKit data has been granted")
			strongSelf.setUpBackgroundDeliveryForDataTypes(types: readDataTypes)
		} else {
			debugPrint("Error requesting HealthKit authorization: \(error)")
		}

		DispatchQueue.main.async {
			completion(success, error)
		}
	}
}