using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace Infrastructure.StockData;

/// <summary>
/// KST 기준 매일 지정 시각에 1회 실행되는 배치 베이스.
/// RunOnceAsync 가 false 를 반환하면 (예: T+1 데이터 미반영) RetryDelay 간격으로 MaxRetryCount 회 재시도 후 다음 날로 넘어간다.
/// </summary>
internal abstract class DailyScheduledService(ILogger logger) : BackgroundService
{
    protected static readonly TimeZoneInfo Kst = ResolveKst();

    protected ILogger Logger { get; } = logger;

    /// <summary>로그 프리픽스용 배치 이름</summary>
    protected abstract string JobName { get; }

    /// <summary>KST 실행 시각</summary>
    protected abstract TimeOnly TargetTime { get; }

    /// <summary>실패(false) 시 재시도 횟수 (기본 0 = 재시도 없음)</summary>
    protected virtual int MaxRetryCount => 0;

    /// <summary>재시도 간격</summary>
    protected virtual TimeSpan RetryDelay => TimeSpan.FromHours(2);

    /// <summary>1회 실행. true = 완료, false = 데이터 미반영 등으로 재시도 필요.</summary>
    protected abstract Task<bool> RunOnceAsync(DateOnly todayKst, CancellationToken ct);

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

    protected static TimeOnly ParseTime(string value, TimeOnly fallback)
    {
        return TimeOnly.TryParse(value, out var parsed) ? parsed : fallback;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        Logger.LogInformation("[{Job}] 서비스 시작 — 실행 시각(KST): {Time}", JobName, TargetTime);

        while (!stoppingToken.IsCancellationRequested)
        {
            var delay = NextDelay();
            Logger.LogInformation("[{Job}] 다음 실행까지 대기: {Delay}", JobName, delay);

            try
            {
                await Task.Delay(delay, stoppingToken);
            }
            catch (OperationCanceledException)
            {
                break;
            }

            for (var attempt = 0; attempt <= MaxRetryCount; attempt++)
            {
                if (stoppingToken.IsCancellationRequested)
                {
                    return;
                }

                var done = true;
                try
                {
                    done = await RunOnceAsync(DateOnly.FromDateTime(NowKst()), stoppingToken);
                }
                catch (OperationCanceledException)
                {
                    return;
                }
                catch (Exception ex)
                {
                    Logger.LogError(ex, "[{Job}] 실행 예외 (attempt {Attempt})", JobName, attempt + 1);
                }

                if (done || attempt == MaxRetryCount)
                {
                    break;
                }

                Logger.LogInformation("[{Job}] 데이터 미반영 — {Delay} 후 재시도 ({Attempt}/{Max})", JobName, RetryDelay, attempt + 1, MaxRetryCount);

                try
                {
                    await Task.Delay(RetryDelay, stoppingToken);
                }
                catch (OperationCanceledException)
                {
                    return;
                }
            }
        }
    }

    private TimeSpan NextDelay()
    {
        var nowKst = NowKst();
        var target = nowKst.Date.Add(TargetTime.ToTimeSpan());

        if (target <= nowKst)
        {
            target = target.AddDays(1);
        }

        return target - nowKst;
    }

    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");
    }
}