Inspections added

Utils/DateCalculator.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Linq;
+using GazpromApp.Enums;
+using GazpromApp.Models;
+using GazpromApp.ViewModels;
+
+namespace GazpromApp.Utils;
+
+public static class DateCalculator
+{
+    public static DateTime[] GetNearestDates(this InspectionViewModel inspection)
+    {
+        var today = DateTime.Today;
+
+        var firstFutureDate = AddPeriod(inspection.InspectionDate.DateTime, inspection.PeriodType, inspection.PeriodValue);
+
+        if (firstFutureDate > today)
+        {
+            return [inspection.InspectionDate.DateTime, firstFutureDate];
+        }
+
+        DateTime 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);
+
+        return [pastDate, futureDate];
+    }
+
+    private static DateTime AddPeriod(DateTime date, PeriodType periodType, float value)
+    {
+        return periodType switch
+        {
+            PeriodType.Day => date.AddDays(value),
+            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)
+            _ => throw new ArgumentException("Invalid period type")
+        };
+    }
+
+    private static DateTime SubtractPeriod(DateTime date, PeriodType periodType, float value)
+    {
+        return AddPeriod(date, periodType, -value);
+    }
+}