namespace MiaoJiZhang.Api.Services;

public static class ChinaClock
{
    private static readonly Lazy<TimeZoneInfo> Zone = new(() =>
    {
        try
        {
            return TimeZoneInfo.FindSystemTimeZoneById("Asia/Shanghai");
        }
        catch (TimeZoneNotFoundException)
        {
            return TimeZoneInfo.FindSystemTimeZoneById("China Standard Time");
        }
    });

    public static DateTime Now => ToLocal(DateTime.UtcNow);

    public static DateTime ToLocal(DateTime utc) =>
        TimeZoneInfo.ConvertTimeFromUtc(
            DateTime.SpecifyKind(utc, DateTimeKind.Utc),
            Zone.Value);

    public static DateTime ToUtc(DateTime local) =>
        TimeZoneInfo.ConvertTimeToUtc(
            DateTime.SpecifyKind(local, DateTimeKind.Unspecified),
            Zone.Value);

    public static (DateTime Start, DateTime End) WeekRangeUtc(DateTime localDate)
    {
        var date = DateTime.SpecifyKind(localDate.Date, DateTimeKind.Unspecified);
        var offset = ((int)date.DayOfWeek + 6) % 7;
        var start = date.AddDays(-offset);
        return (ToUtc(start), ToUtc(start.AddDays(7)));
    }

    public static (DateTime Start, DateTime End) MonthRangeUtc(int year, int month)
    {
        var start = new DateTime(year, month, 1);
        return (ToUtc(start), ToUtc(start.AddMonths(1)));
    }

    public static (DateTime Start, DateTime End) YearRangeUtc(int year)
    {
        var start = new DateTime(year, 1, 1);
        return (ToUtc(start), ToUtc(start.AddYears(1)));
    }
}