namespace NoticeBoard.Infrastructure;

/// <summary>
/// Single source of "now" for Meow expiry checks, so the picker (browser wall-clock,
/// no time zone info) and the server's comparison always agree on what "now" means.
///
/// Configured once at startup from the "TimeZone" setting (an IANA id like
/// "Australia/Melbourne", or "UTC"). Leaving it blank falls back to the host
/// machine's own local time zone — the original IIS behaviour, unchanged.
/// </summary>
public static class Clock
{
    private static TimeZoneInfo _timeZone = TimeZoneInfo.Local;

    public static void Configure(string? timeZoneId)
    {
        if (string.IsNullOrWhiteSpace(timeZoneId))
        {
            _timeZone = TimeZoneInfo.Local;
            return;
        }

        try
        {
            _timeZone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneId);
        }
        catch (TimeZoneNotFoundException)
        {
            // Unknown id (e.g. tzdata missing, or a typo) — UTC is a safe, unambiguous fallback.
            _timeZone = TimeZoneInfo.Utc;
        }
        catch (InvalidTimeZoneException)
        {
            _timeZone = TimeZoneInfo.Utc;
        }
    }

    /// <summary>Current time in the configured server time zone — directly comparable to a stored ExpiresAt value.</summary>
    public static DateTime Now => TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, _timeZone);
}