using Domain.Entities.Paper.ValueObject;

namespace Application.Helpers;

/// <summary>
/// 모의투자 체결 규칙(KST) 계산 — 접수 시각에 따라 FillRule/TargetDate/CancelableUntil 을 확정한다 (d4 §③).
///   • 영업일 t &lt; 09:00 → 당일 시가 (CancelableUntil = 당일 09:00)
///   • 영업일 09:00 ≤ t &lt; 15:30 → 당일 종가 (CancelableUntil = 당일 15:30)
///   • t ≥ 15:30 또는 휴장일 → 다음 영업일 시가 (CancelableUntil = 익영업일 09:00)
/// 휴장일은 주말 + 호출자가 주입하는 MarketHoliday 집합으로 판정한다.
/// </summary>
public static class PaperTradingClock
{
    private static readonly TimeOnly MarketOpen = new(9, 0);
    private static readonly TimeOnly MarketClose = new(15, 30);

    private static readonly TimeZoneInfo Kst = ResolveKst();

    public static DateTime NowKst() => TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, Kst);

    public static DateTime ToUtc(DateTime kst)
    {
        var unspecified = DateTime.SpecifyKind(kst, DateTimeKind.Unspecified);
        return TimeZoneInfo.ConvertTimeToUtc(unspecified, Kst);
    }

    public static bool IsHoliday(DateOnly date, IReadOnlySet<DateOnly> holidays)
    {
        if (date.DayOfWeek is DayOfWeek.Saturday or DayOfWeek.Sunday)
        {
            return true;
        }

        return holidays.Contains(date);
    }

    /// <summary>date 이후(자기 자신 제외)의 다음 영업일.</summary>
    public static DateOnly NextBusinessDay(DateOnly date, IReadOnlySet<DateOnly> holidays)
    {
        var next = date.AddDays(1);
        while (IsHoliday(next, holidays))
        {
            next = next.AddDays(1);
        }
        return next;
    }

    /// <summary>date 로부터 N 영업일 뒤(자기 자신 제외). count &lt;= 0 이면 date 그대로. (예측 채점 DueDate 산정 — d2 §③)</summary>
    public static DateOnly AddBusinessDays(DateOnly date, int count, IReadOnlySet<DateOnly> holidays)
    {
        var result = date;
        for (var i = 0; i < count; i++)
        {
            result = NextBusinessDay(result, holidays);
        }
        return result;
    }

    /// <summary>date 가 영업일이면 그대로, 아니면 다음 영업일.</summary>
    public static DateOnly EnsureBusinessDay(DateOnly date, IReadOnlySet<DateOnly> holidays)
    {
        var d = date;
        while (IsHoliday(d, holidays))
        {
            d = d.AddDays(1);
        }
        return d;
    }

    /// <summary>
    /// 접수 시각(KST)으로 체결 계획을 산정한다. 반환은 (FillRule, TargetDate, CancelableUntilKst).
    /// CancelableUntilKst 는 KST 벽시계 기준 — 호출자가 ToUtc 로 변환해 저장한다.
    /// </summary>
    public static (PaperFillRule FillRule, DateOnly TargetDate, DateTime CancelableUntilKst) Plan(
        DateTime nowKst,
        IReadOnlySet<DateOnly> holidays)
    {
        var today = DateOnly.FromDateTime(nowKst);
        var timeOfDay = TimeOnly.FromDateTime(nowKst);

        if (!IsHoliday(today, holidays))
        {
            if (timeOfDay < MarketOpen)
            {
                // 당일 시가
                var cancelable = today.ToDateTime(MarketOpen);
                return (PaperFillRule.Open, today, cancelable);
            }

            if (timeOfDay < MarketClose)
            {
                // 당일 종가
                var cancelable = today.ToDateTime(MarketClose);
                return (PaperFillRule.Close, today, cancelable);
            }
        }

        // 15:30 이후 또는 휴장일 → 다음 영업일 시가
        var nextDay = NextBusinessDay(today, holidays);
        var cancelableUntil = nextDay.ToDateTime(MarketOpen);
        return (PaperFillRule.Open, nextDay, cancelableUntil);
    }

    private static TimeZoneInfo ResolveKst()
    {
        if (TimeZoneInfo.TryFindSystemTimeZoneById("Asia/Seoul", out var tz))
        {
            return tz;
        }

        if (TimeZoneInfo.TryFindSystemTimeZoneById("Korea Standard Time", out tz))
        {
            return tz;
        }

        // KST 는 DST 없음 — 고정 +9 fallback
        return TimeZoneInfo.CreateCustomTimeZone("KST", TimeSpan.FromHours(9), "KST", "KST");
    }
}