add basic create and list reminder api

Budet-cho-bot/Helpers/Utility.cs

@@ -0,0 +1,58 @@
+using Budet_cho_bot.Models;
+using Newtonsoft.Json.Linq;
+using System.Linq;
+
+namespace Budet_cho_bot.Helpers;
+
+public static class Utility
+{
+    public static DateTime ParseDate(string message)
+    {
+        if (TimeSpan.TryParse(message, out var parsedTime) == false)
+        {
+            throw new ArgumentException("Хуйня твоё время");
+        }
+
+        var today = DateTime.Today; //returns xx/xx/xxxx 00:00:00, so adding time span would set correct daate
+        var date = today + parsedTime;
+        return date;
+    }
+
+    public static TimeSpan DeserializeTime(string token)
+    {
+        return Newtonsoft.Json.JsonConvert.DeserializeObject<TimeSpan>(token);
+    }
+
+    public static string PackTimetableIntoString(CronRecord[] timetable)
+    {
+        return string.Join(';', timetable.Select(x =>
+        {
+            var unixRunTime = x.LastRun.ToUniversalTime().ToUnixTimeSeconds();
+            var secondsPeriod = (int)(x.Period.TotalSeconds);
+            return $"{unixRunTime}:{secondsPeriod}:{x.IsOneShot}";
+        }));
+    }
+
+    public static CronRecord[] UnpackTimetableFromString(string timetable)
+    {
+        if(timetable == null)
+        {
+            return new CronRecord[0];
+        }
+
+        return timetable.Split(';').Select(x =>
+        {
+            var record = x.Split(':'); //crude but whatever
+            var lastRun = DateTimeOffset.FromUnixTimeSeconds(long.Parse(record[0]));
+            var period = TimeSpan.FromSeconds(long.Parse(record[1]));
+            bool oneShot = bool.Parse(record[2]);
+
+            return new CronRecord()
+            {
+                LastRun = lastRun,
+                Period = period,
+                IsOneShot = oneShot
+            };
+        }).ToArray();
+    }
+}