Deleting Calendar Rules in Microsoft Dynamics CRM 2016

/// <summary>
/// Clears the calender rules.
/// </summary>
/// <param name="service">The service.</param>
/// <param name="bookableResourceId">The bookable resource identifier.</param>
/// <param name="startDate">The start date.</param>
/// <param name="endDate">The end date.</param>
public static void ClearCalenderRules(IOrganizationService service, Guid bookableResourceId, DateTime startDate, DateTime endDate)
{
    using (var context = new CrmServiceContext(service))
    {
        var bookableResource = context.BookableResourceSet.Where(b => b.Id == bookableResourceId).FirstOrDefault();

        if (bookableResource?.CalendarId != null)
        {

            Entity entity = service.Retrieve("calendar", bookableResource.CalendarId.Id, new ColumnSet(true));
            EntityCollection entityCollection = (EntityCollection)entity.Attributes["calendarrules"];

            int num = 0;
            List<int> list = new List<int>();
            foreach (Entity current in entityCollection.Entities)
            {
                DateTime dateTime2 = Convert.ToDateTime(current["starttime"]);
                if (dateTime2 >= startDate && dateTime2 <= endDate)
                {
                    list.Add(num);
                }

                num++;
            }

            list.Sort();
            list.Reverse();

            for (int i = 0; i < list.Count; i++)
            {
                entityCollection.Entities.Remove(entityCollection.Entities[list[i]]);
            }

            entity.Attributes["calendarrules"] = entityCollection;
            service.Update(entity);
        }
    }
}