RetryCloudKitOperation.swift

/// Helper method to retry a CloudKit operation when its error suggests it
///
/// - Parameters:
///   - error: The error returned from a CloudKit operation
///   - block: A block to be executed after a delay if the error is recoverable
/// - Returns: If the error can't be retried, returns the error
func retryCloudKitOperationIfPossible(with error: Error?, block: @escaping () -> ()) -> Error? {
    guard let effectiveError = error as? CKError else {
        // not a CloudKit error or no error present, just return the original error
        return error
    }
    
    guard let retryAfter = effectiveError.retryAfterSeconds else {
    // CloudKit error, can't  be retried, return the error
        return effectiveError
    }

    // CloudKit operation can be retried, schedule `block` to be executed later
    
    DispatchQueue.main.asyncAfter(deadline: .now() + retryAfter) {
        block()
    }
    
    return nil
}