There Are Only Two Roles of Code 1

there-are-only-two-roles-of-code-1.cs

public class Calculator
   {
       private readonly IStorageService storageService;
       private List<int> history = new List<int>();
       private int sessionNumber = 1;
       private bool newSession;
 
       public Calculator(IStorageService storageService)
       {
           this.storageService = storageService;
       }
 
       public int Add(int firstNumber, int secondNumber)
       {
           if(newSession)
           {
               sessionNumber++;
               newSession = false;
           }
 
           var result = firstNumber + secondNumber;
           history.Add(result);
 
           return result;
       }
 
       public List<int> GetHistory()
       {
           if (storageService.IsServiceOnline())
               return storageService.GetHistorySession(sessionNumber);
 
           return new List<int>();
       }
 
       public int Done()
       {
           if (storageService.IsServiceOnline())
           {
               foreach(var result in history)
                   storageService.Store(result, sessionNumber);
           }
           newSession = true;
           return sessionNumber;
       }
   }