using System;

namespace IOL.Helpers
{
	public static class DateTimeHelpers
	{
		public static DateTime ToTimeZoneId(this DateTime value, string timeZoneId) {
			try {
				var cstZone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneId);
				return TimeZoneInfo.ConvertTimeFromUtc(value, cstZone);
			} catch (TimeZoneNotFoundException) {
				Console.WriteLine("The registry does not define the " + timeZoneId + " zone.");
				return default;
			} catch (InvalidTimeZoneException) {
				Console.WriteLine("Registry data on the " + timeZoneId + " zone has been corrupted.");
				return default;
			}
		}

		public static DateTime ToOsloTimeZone(this DateTime value) => ToTimeZoneId(value, "Europe/Oslo");

		public static DateTime StartOfWeek(this DateTime dt, DayOfWeek startOfWeek) {
			var diff = (7 + (dt.DayOfWeek - startOfWeek)) % 7;
			return dt.AddDays(-1 * diff).Date;
		}
	}
}