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

namespace Monitor.Backend.Application;

/// <summary>保留清理：原始段文件（持续任务与按需测试保留期不同）、各层指标、事件。保留期来自 settings，可以在线修改。</summary>
public sealed partial class RetentionService : BackgroundService
{
    private static readonly TimeSpan s_interval = TimeSpan.FromHours(1);

    private readonly IRawStore _raw;
    private readonly IMetricStore _metrics;
    private readonly IEventStore _events;
    private readonly IAuthStore _auth;
    private readonly IHostStore _hosts;
    private readonly SettingsService _settings;
    private readonly LoginRateLimiter _limiter;
    private readonly TimeProvider _time;
    private readonly ILogger<RetentionService> _logger;

    public RetentionService(IRawStore raw, IMetricStore metrics, IEventStore events, IHostStore hosts, IAuthStore auth, SettingsService settings, LoginRateLimiter limiter, TimeProvider time, ILogger<RetentionService> logger)
    {
        _raw = raw;
        _metrics = metrics;
        _events = events;
        _hosts = hosts;
        _auth = auth;
        _settings = settings;
        _limiter = limiter;
        _time = time;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            try
            {
                await RunOnceAsync(stoppingToken);
                await Task.Delay(s_interval, _time, stoppingToken);
            }
            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
            {
                return;
            }
            catch (Exception ex)
            {
                // 后台循环不能因为一次失败而退出
                LogFailed(ex);
                await Task.Delay(TimeSpan.FromMinutes(5), _time, stoppingToken);
            }
        }
    }

    /// <summary>执行一轮清理（也供测试直接调用）。</summary>
    public async Task RunOnceAsync(CancellationToken ct)
    {
        DateTimeOffset now = _time.GetUtcNow();
        long nowMs = now.ToUnixTimeMilliseconds();
        DateOnly today = DateOnly.FromDateTime(now.UtcDateTime);
        int rawDays = await _settings.GetIntAsync(SettingsService.RawDays, ct);
        int testDays = await _settings.GetIntAsync(SettingsService.TestRawDays, ct);

        await _raw.DeleteExpiredAsync(today.AddDays(-rawDays), today.AddDays(-testDays), ct);
        await _metrics.DeleteOlderThanAsync(MetricLevel.S10, nowMs - (await _settings.GetIntAsync(SettingsService.Metric10sHours, ct) * Steps.Hour), ct);
        await _metrics.DeleteOlderThanAsync(MetricLevel.M1, nowMs - (await _settings.GetIntAsync(SettingsService.Metric1mDays, ct) * Steps.Day), ct);
        await _metrics.DeleteOlderThanAsync(MetricLevel.M5, nowMs - (await _settings.GetIntAsync(SettingsService.Metric5mDays, ct) * Steps.Day), ct);
        await _events.DeleteOlderThanAsync(nowMs - (await _settings.GetIntAsync(SettingsService.EventDays, ct) * Steps.Day), ct);
        await _hosts.DeleteOlderThanAsync(nowMs - (await _settings.GetIntAsync(SettingsService.HostDays, ct) * Steps.Day), ct);
        await _auth.DeleteExpiredSessionsAsync(nowMs, ct);
        _limiter.Prune();
    }

    [LoggerMessage(Level = LogLevel.Error, Message = "retention pass failed")]
    private partial void LogFailed(Exception exception);
}