Customized Scheduler + Saved Kavita+ Details (#2644)

Kavita.Common/Helpers/CronHelper.cs

@@ -0,0 +1,22 @@
+using System;
+using Cronos;
+
+namespace Kavita.Common.Helpers;
+
+public static class CronHelper
+{
+    public static bool IsValidCron(string cronExpression)
+    {
+        // NOTE: This must match Hangfire's underlying cron system. Hangfire is unique
+        try
+        {
+            CronExpression.Parse(cronExpression);
+            return true;
+        }
+        catch (Exception ex)
+        {
+            /* Swallow */
+            return false;
+        }
+    }
+}