Code clean up

Utils/DateCalculator.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Linq;
 using GazpromApp.Enums;
-using GazpromApp.Models;
 using GazpromApp.ViewModels;
 
 namespace GazpromApp.Utils;
@@ -19,11 +18,11 @@ public static class DateCalculator
             return [inspection.InspectionDate.DateTime, firstFutureDate];
         }
 
-        DateTime futureDate = Enumerable.Range(1, int.MaxValue)
+        var futureDate = Enumerable.Range(1, int.MaxValue)
             .Select(i => AddPeriod(inspection.InspectionDate.DateTime, inspection.PeriodType, inspection.PeriodValue * i))
             .First(d => d > today);
 
-        DateTime pastDate = SubtractPeriod(futureDate, inspection.PeriodType, inspection.PeriodValue);
+        var pastDate = SubtractPeriod(futureDate, inspection.PeriodType, inspection.PeriodValue);
 
         return [pastDate, futureDate];
     }
@@ -36,6 +35,7 @@ public static class DateCalculator
             PeriodType.Week => date.AddDays(value * 7),
             PeriodType.Month => date.AddDays(value * 30.436875), // Avg days/month
             PeriodType.Year => date.AddDays(value * 365.2425), // Avg days/year (incl. leap years)
+            PeriodType.Unknown => throw new ArgumentException("Invalid period type"),
             _ => throw new ArgumentException("Invalid period type")
         };
     }