TimeZones.cs

using GeoTimeZone;
using NodaTime;
using NodaTime.Extensions;
using TimeZoneConverter;
using TimeZoneNames;

namespace Arex388.TimeZones;

/// <summary>
/// TimeZones object.
/// </summary>
public static class TimeZones {
	/// <summary>
	/// Returns all time zones for the current instant in time.
	/// </summary>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zones.</returns>
	public static IEnumerable<TimeZone> GetTimeZones(
		string languageCode = "en-US") {
		var instant = SystemClock.Instance.GetCurrentInstant();

		return GetTimeZones(instant, languageCode);
	}

	/// <summary>
	/// Returns all time zones for an instant in time.
	/// </summary>
	/// <param name="dateTime">The DateTimeOffset value to use for an instant in time.</param>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zones.</returns>
	public static IEnumerable<TimeZone> GetTimeZones(
		DateTimeOffset? dateTime,
		string languageCode = "en-US") {
		if (dateTime is null) {
			throw new ArgumentNullException(nameof(dateTime));
		}

		var instant = dateTime.Value.ToInstant();

		return GetTimeZones(instant, languageCode);
	}

	/// <summary>
	/// Returns all time zones for an instant in time.
	/// </summary>
	/// <param name="instant">The instant in time.</param>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zones.</returns>
	public static IEnumerable<TimeZone> GetTimeZones(
		Instant instant,
		string languageCode = "en-US") => DateTimeZoneProviders.Tzdb.Ids.Select(
		id => DateTimeZoneProviders.Tzdb[id]).Select(
		dtz => {
			var gotWindowsTimeZoneId = TZConvert.TryIanaToWindows(dtz.Id, out var windowsTimeZoneId);

			if (!gotWindowsTimeZoneId
				|| windowsTimeZoneId is null) {
				return null;
			}

			var isDaylightSavings = TimeZoneInfo.FindSystemTimeZoneById(windowsTimeZoneId).IsDaylightSavingTime(instant.ToDateTimeOffset());
			var abbreviation = TZNames.GetAbbreviationsForTimeZone(dtz.Id, languageCode);
			var offset = dtz.GetUtcOffset(instant);

			return new TimeZone {
				Abbreviation = (isDaylightSavings
					? abbreviation.Daylight
					: abbreviation.Standard) ?? dtz.Id,
				IanaId = dtz.Id,
				IsDaylightSavings = isDaylightSavings,
				UtcOffset = offset.ToFormattedString(),
				UtcOffsetTs = offset.ToTimeSpan(),
				WindowsId = windowsTimeZoneId
			};
		}).Where(
		tz => tz is not null);

	/// <summary>
	/// Returns the time zone by the specified latitude and longitude coordinate for the current instant in time.
	/// </summary>
	/// <param name="latitude">The coordinate's latitude.</param>
	/// <param name="longitude">The coordinate's longitude.</param>
	/// <returns>The time zone.</returns>
	public static TimeZone? GetTimeZoneByCoordinate(
		decimal latitude,
		decimal longitude) => GetTimeZoneByCoordinate((double)latitude, (double)longitude);

	/// <summary>
	/// Returns the time zone by the specified latitude and longitude coordinate for the current instant in time.
	/// </summary>
	/// <param name="latitude">The coordinate's latitude.</param>
	/// <param name="longitude">The coordinate's longitude.</param>
	/// <returns>The time zone.</returns>
	public static TimeZone? GetTimeZoneByCoordinate(
		double latitude,
		double longitude) => GetTimeZoneByCoordinate(new Coordinate {
			Latitude = latitude,
			Longitude = longitude
		});

	/// <summary>
	/// Returns the time zone by the specified latitude and longitude coordinate for the current instant in time.
	/// </summary>
	/// <param name="coordinate">The coordinate.</param>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zone.</returns>
	public static TimeZone? GetTimeZoneByCoordinate(
		ICoordinate coordinate,
		string languageCode = "en-US") {
		var ianaId = TimeZoneLookup.GetTimeZone(coordinate.Latitude, coordinate.Longitude);

		return GetTimeZoneByIanaId(ianaId.Result, languageCode);
	}

	/// <summary>
	/// Returns the time zone by the specified latitude and longitude coordinate for the current instant in time.
	/// </summary>
	/// <param name="latitude">The coordinate's latitude.</param>
	/// <param name="longitude">The coordinate's longitude.</param>
	/// <param name="dateTime">The DateTimeOffset value to use for an instant in time.</param>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zone.</returns>
	public static TimeZone? GetTimeZoneByCoordinate(
		decimal latitude,
		decimal longitude,
		DateTimeOffset? dateTime,
		string languageCode = "en-US") => GetTimeZoneByCoordinate((double)latitude, (double)longitude, dateTime, languageCode);

	/// <summary>
	/// Returns the time zone by the specified latitude and longitude coordinate for an instant in time.
	/// </summary>
	/// <param name="latitude">The coordinate's latitude.</param>
	/// <param name="longitude">The coordinate's longitude.</param>
	/// <param name="dateTime">The DateTimeOffset value to use for an instant in time.</param>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zone.</returns>
	public static TimeZone? GetTimeZoneByCoordinate(
		double latitude,
		double longitude,
		DateTimeOffset? dateTime,
		string languageCode = "en-US") {
		return GetTimeZoneByCoordinate(new Coordinate {
			Latitude = latitude,
			Longitude = longitude
		}, dateTime, languageCode);
	}

	/// <summary>
	/// Returns the time zone by the specified point coordinate for an instant in time.
	/// </summary>
	/// <param name="coordinate">The coordinate.</param>
	/// <param name="dateTime">The DateTimeOffset value to use for an instant in time.</param>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zone.</returns>
	public static TimeZone? GetTimeZoneByCoordinate(
		ICoordinate coordinate,
		DateTimeOffset? dateTime,
		string languageCode = "en-US") {
		var ianaId = TimeZoneLookup.GetTimeZone(coordinate.Latitude, coordinate.Longitude);

		return GetTimeZoneByIanaId(ianaId.Result, dateTime, languageCode);
	}

	/// <summary>
	/// Returns the time zone by the IANA id for the current instant in time.
	/// </summary>
	/// <param name="ianaId">The time zone's IANA id.</param>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zone.</returns>
	public static TimeZone? GetTimeZoneByIanaId(
		string ianaId,
		string languageCode = "en-US") => GetTimeZones(languageCode).FirstOrDefault(
		tz => tz?.IanaId == ianaId);

	/// <summary>
	/// Returns the time zone by the IANA id for an instant in time.
	/// </summary>
	/// <param name="ianaId">The time zone's IANA id.</param>
	/// <param name="dateTime">The DateTimeOffset value to use for an instant in time.</param>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zone.</returns>
	public static TimeZone? GetTimeZoneByIanaId(
		string ianaId,
		DateTimeOffset? dateTime,
		string languageCode = "en-US") => GetTimeZones(dateTime, languageCode).FirstOrDefault(
		tz => tz?.IanaId == ianaId);

	/// <summary>
	/// Returns the time zones by the Windows id for the current instant in time.
	/// </summary>
	/// <param name="windowsId">The time zones' Windows id.</param>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zones.</returns>
	public static IEnumerable<TimeZone> GetTimeZonesByWindowsId(
		string windowsId,
		string languageCode = "en-US") => GetTimeZones(languageCode).Where(
		tz => tz?.WindowsId == windowsId);

	/// <summary>
	/// Returns the time zones by the Windows id for the current instant in time.
	/// </summary>
	/// <param name="windowsId">The time zones' Windows id.</param>
	/// <param name="dateTime">The DateTimeOffset value to use for an instant in time.</param>
	/// <param name="languageCode">The language code to use. "en-US" by default.</param>
	/// <returns>The time zones.</returns>
	public static IEnumerable<TimeZone> GetTimeZonesByWindowsId(
		string windowsId,
		DateTimeOffset? dateTime,
		string languageCode = "en-US") => GetTimeZones(dateTime, languageCode).Where(
		tz => tz?.WindowsId == windowsId);
}