修复学业预警的按时定时任务

src/Jiaowu.Api/Infrastructure/Scheduling/WarningCheckWorker.cs

@@ -7,6 +7,8 @@ namespace Jiaowu.Api.Infrastructure.Scheduling;
 
 public sealed class WarningCheckWorker(IServiceScopeFactory scopeFactory, ILogger<WarningCheckWorker> logger) : BackgroundService
 {
+    private static readonly TimeZoneInfo ChinaTimeZone = ResolveChinaTimeZone();
+
     protected override async Task ExecuteAsync(CancellationToken ct)
     {
         while (!ct.IsCancellationRequested)
@@ -25,22 +27,32 @@ public sealed class WarningCheckWorker(IServiceScopeFactory scopeFactory, ILogge
 
     private static async Task RunAsync(AppDbContext db, CancellationToken ct)
     {
-        var now = DateTime.UtcNow;
-        var dow = (int)now.DayOfWeek == 0 ? 7 : (int)now.DayOfWeek;
-        var currentMinute = new DateTime(now.Year, now.Month, now.Day, now.Hour, now.Minute, 0, DateTimeKind.Utc);
+        var nowUtc = DateTime.UtcNow;
+        var chinaNow = TimeZoneInfo.ConvertTime(
+            new DateTimeOffset(nowUtc),
+            ChinaTimeZone);
+        var dow = (int)chinaNow.DayOfWeek == 0 ? 7 : (int)chinaNow.DayOfWeek;
+        var currentMinuteUtc = new DateTime(
+            nowUtc.Year,
+            nowUtc.Month,
+            nowUtc.Day,
+            nowUtc.Hour,
+            nowUtc.Minute,
+            0,
+            DateTimeKind.Utc);
 
         var rules = await db.WarningRules
             .Where(r => r.IsEnabled && r.AutoCheckEnabled &&
-                        r.CheckHour == now.Hour && r.CheckMinute == now.Minute &&
+                        r.CheckHour == chinaNow.Hour && r.CheckMinute == chinaNow.Minute &&
                         (r.CheckDayOfWeek == null || r.CheckDayOfWeek == dow))
             .ToListAsync(ct);
 
         foreach (var rule in rules)
         {
-            if (rule.LastCheckAt.HasValue && rule.LastCheckAt.Value >= currentMinute)
+            if (rule.LastCheckAt.HasValue && rule.LastCheckAt.Value >= currentMinuteUtc)
                 continue;
 
-            rule.LastCheckAt = now;
+            rule.LastCheckAt = nowUtc;
             await db.SaveChangesAsync(ct);
 
             var studentIds = await db.Students.Where(x => x.Status == StudentStatus.Active).Select(x => x.Id).ToListAsync(ct);
@@ -100,4 +112,23 @@ public sealed class WarningCheckWorker(IServiceScopeFactory scopeFactory, ILogge
         var gpa = grades.Average(x => x.GradePoint!.Value);
         return gpa < rule.Threshold ? new WarningRecord { StudentId = sid, Type = WarningType.LowGPA, TriggerValue = Math.Round(gpa, 2), Detail = $"平均绩点 {gpa:F2}，低于预警阈值 {rule.Threshold}。", AcademicTermId = termId } : null;
     }
+
+    private static TimeZoneInfo ResolveChinaTimeZone()
+    {
+        foreach (var id in new[] { "Asia/Shanghai", "China Standard Time" })
+        {
+            try
+            {
+                return TimeZoneInfo.FindSystemTimeZoneById(id);
+            }
+            catch (TimeZoneNotFoundException)
+            {
+            }
+            catch (InvalidTimeZoneException)
+            {
+            }
+        }
+
+        throw new InvalidOperationException("服务器未提供中国标准时间时区定义。");
+    }
 }