namespace JSMR.Infrastructure.Common.Time;

public interface ITimeProvider
{
    DateTimeOffset Now();
    DateTimeOffset Local(int year, int month, int day, int hour);
    DateTimeOffset Local(DateTimeOffset offset);
}

public abstract class TimeProvider : ITimeProvider
{
    protected abstract string Id { get; }
    protected abstract string[] TimeZoneIds { get; }

    private readonly IClock _clock;
    private readonly TimeZoneInfo _timeZone;

    public TimeProvider(IClock clock)
    {
        _clock = clock;
        _timeZone = ResolveTimeZone();
    }

    private TimeZoneInfo ResolveTimeZone()
    {
        foreach (string timeZoneId in TimeZoneIds)
        {
            if (TimeZoneInfo.TryFindSystemTimeZoneById(timeZoneId, out TimeZoneInfo? timeZoneInfo))
                return timeZoneInfo;
        }

        throw new TimeZoneNotFoundException($"Unable to resolve time zone for: {Id} ({string.Join(" / ", TimeZoneIds)})");
    }

    public DateTimeOffset Now() => TimeZoneInfo.ConvertTime(_clock.UtcNow, _timeZone);
    public DateTimeOffset Local(DateTimeOffset offset) => TimeZoneInfo.ConvertTime(offset, _timeZone);

    public DateTimeOffset Local(int year, int month, int day, int hour)
    {
        DateTime local = new(year, month, day, hour, 0, 0, DateTimeKind.Unspecified);
        TimeSpan offset = _timeZone.GetUtcOffset(local);

        return new DateTimeOffset(local, offset);
    }

    public DateTimeOffset CurrentScanAnchor()
    {
        DateTimeOffset now = Now();
        DateTimeOffset midnight = Local(now.Year, now.Month, now.Day, 0);
        DateTimeOffset fourPm = Local(now.Year, now.Month, now.Day, 16);

        return now >= fourPm ? fourPm : midnight;
    }

    public DateTimeOffset PreviousScanAnchor(DateTimeOffset scanAnchorTokyo)
    {
        // Normalize to Tokyo (no-op if already)
        var a = TimeZoneInfo.ConvertTime(scanAnchorTokyo, _timeZone);
        return a.Hour == 16
            ? Local(a.Year, a.Month, a.Day, 0)
            : Local(a.AddDays(-1).Year, a.AddDays(-1).Month, a.AddDays(-1).Day, 16);
    }
}

public class TokyoTimeProvider(IClock clock) : TimeProvider(clock)
{
    protected override string Id => "Tokyo Standard Time";
    protected override string[] TimeZoneIds => ["Tokyo Standard Time", "Asia/Tokyo"];
}