using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using SPMS.Domain.Entities;
using SPMS.Infrastructure.Persistence;

namespace SPMS.Infrastructure.Workers;

public class DeadTokenCleanupWorker : BackgroundService
{
    private readonly IServiceScopeFactory _scopeFactory;
    private readonly ILogger<DeadTokenCleanupWorker> _logger;

    private static readonly TimeZoneInfo KstZone = TimeZoneInfo.FindSystemTimeZoneById("Asia/Seoul");
    private const int BatchSize = 1000;
    private const double SafetyThreshold = 0.5;

    public DeadTokenCleanupWorker(
        IServiceScopeFactory scopeFactory,
        ILogger<DeadTokenCleanupWorker> logger)
    {
        _scopeFactory = scopeFactory;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("DeadTokenCleanupWorker 시작");

        while (!stoppingToken.IsCancellationRequested)
        {
            var delay = CalculateDelayUntilNextSunday();
            _logger.LogInformation("DeadTokenCleanupWorker 다음 실행까지 {Delay} 대기", delay);

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

            try
            {
                await CleanupAsync(stoppingToken);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "DeadTokenCleanupWorker 정리 중 오류 발생");
            }
        }
    }

    private TimeSpan CalculateDelayUntilNextSunday()
    {
        var nowKst = TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, KstZone);
        var daysUntilSunday = ((int)DayOfWeek.Sunday - (int)nowKst.DayOfWeek + 7) % 7;
        var nextRun = nowKst.Date.AddDays(daysUntilSunday).AddHours(3);

        if (nextRun <= nowKst)
            nextRun = nextRun.AddDays(7);

        return nextRun - nowKst;
    }

    private async Task CleanupAsync(CancellationToken stoppingToken)
    {
        using var scope = _scopeFactory.CreateScope();
        var context = scope.ServiceProvider.GetRequiredService<AppDbContext>();

        var cutoffUtc = DateTime.UtcNow.AddDays(-7);

        var targetCount = await context.Set<Device>()
            .CountAsync(d => !d.IsActive && d.UpdatedAt < cutoffUtc, stoppingToken);

        var totalCount = await context.Set<Device>()
            .CountAsync(stoppingToken);

        _logger.LogInformation("DeadTokenCleanupWorker 삭제 대상: {TargetCount}개 / 전체: {TotalCount}개",
            targetCount, totalCount);

        if (targetCount == 0)
        {
            _logger.LogInformation("DeadTokenCleanupWorker 삭제 대상 없음");
            await WriteSystemLogAsync(context, 0, stoppingToken);
            return;
        }

        // 안전장치: 삭제 대상이 전체의 50% 초과 시 중단
        if (totalCount > 0 && (double)targetCount / totalCount > SafetyThreshold)
        {
            _logger.LogWarning(
                "DeadTokenCleanupWorker 안전 장치 발동! 삭제 대상({TargetCount})이 전체({TotalCount})의 50% 초과. 삭제를 중단합니다.",
                targetCount, totalCount);
            await WriteSystemLogAsync(context, 0, stoppingToken,
                $"안전 장치 발동: 삭제 대상 {targetCount}개 / 전체 {totalCount}개 (50% 초과)");
            return;
        }

        // 배치 삭제 (1000건씩, 트랜잭션 없음)
        var totalDeleted = 0;
        int deletedInBatch;

        do
        {
            deletedInBatch = await context.Database.ExecuteSqlRawAsync(
                "DELETE FROM Device WHERE is_active = false AND updated_at < {0} LIMIT 1000",
                new object[] { cutoffUtc },
                stoppingToken);

            totalDeleted += deletedInBatch;

            if (deletedInBatch > 0)
                _logger.LogInformation("DeadTokenCleanupWorker 배치 삭제: {BatchCount}건 (누적: {TotalDeleted}건)",
                    deletedInBatch, totalDeleted);
        } while (deletedInBatch > 0 && !stoppingToken.IsCancellationRequested);

        await WriteSystemLogAsync(context, totalDeleted, stoppingToken);

        _logger.LogInformation("DeadTokenCleanupWorker 정리 완료: {TotalDeleted}건 삭제", totalDeleted);
    }

    private static async Task WriteSystemLogAsync(
        AppDbContext context, int deletedCount,
        CancellationToken stoppingToken, string? extraDetails = null)
    {
        var details = extraDetails ?? $"비활성 토큰 정리 완료: {deletedCount}건 삭제";

        context.Set<SystemLog>().Add(new SystemLog
        {
            Action = "DeadTokenCleanup",
            Details = details,
            CreatedAt = DateTime.UtcNow
        });
        await context.SaveChangesAsync(stoppingToken);
    }
}