Stop repeated preview push notifications

server/QMax.Api/Services/MaxBridgeSyncService.cs

@@ -5,6 +5,7 @@ using QMax.Api.Data.Entities;
 using QMax.Api.Infrastructure.Hubs;
 using QMax.Api.Infrastructure.Max;
 using QMax.Api.Infrastructure.Storage;
+using System.Collections.Concurrent;
 using System.Text;
 
 namespace QMax.Api.Services;
@@ -15,6 +16,8 @@ public sealed class MaxBridgeSyncService(
     IHubContext<QMaxHub> hubContext,
     ILogger<MaxBridgeSyncService> logger)
 {
+    private static readonly ConcurrentDictionary<string, DateTimeOffset> PreviewNotifications = new();
+
     public async Task<int> SyncOnceAsync(CancellationToken cancellationToken)
     {
         try
@@ -268,7 +271,7 @@ public sealed class MaxBridgeSyncService(
 
         var previousPreview = chat.LastMessagePreview;
         var previousPreviewAt = chat.LastMessageAt;
-        var previewAt = ResolveListPreviewAt(update);
+        var previewAt = ResolveListPreviewAt(update, previousPreviewAt ?? chat.UpdatedAt);
         var samePreview = string.Equals(previousPreview, preview, StringComparison.Ordinal);
         var samePreviewAt = previousPreviewAt is not null &&
             Math.Abs((previousPreviewAt.Value - previewAt).TotalSeconds) < 1;
@@ -281,11 +284,13 @@ public sealed class MaxBridgeSyncService(
         chat.LastMessageAt = previewAt;
         chat.UpdatedAt = DateTimeOffset.UtcNow;
 
-        var shouldNotify = !chatWasCreated &&
+        var shouldNotifyCandidate = !chatWasCreated &&
             !string.IsNullOrWhiteSpace(previousPreview) &&
             update.LastMessageIsOutgoing != true &&
             update.Messages.Count == 0 &&
             IsFreshListPreview(update, previewAt);
+        var shouldNotify = shouldNotifyCandidate &&
+            RememberPreviewNotification(chat.Id, preview, previewAt);
 
         if (incrementUnread && shouldNotify)
         {
@@ -313,16 +318,36 @@ public sealed class MaxBridgeSyncService(
         return true;
     }
 
-    private static DateTimeOffset ResolveListPreviewAt(MaxChatUpdate update)
+    private static bool RememberPreviewNotification(Guid chatId, string preview, DateTimeOffset previewAt)
+    {
+        var now = DateTimeOffset.UtcNow;
+        if (PreviewNotifications.Count > 4096)
+        {
+            var cutoff = now.AddHours(-2);
+            foreach (var item in PreviewNotifications)
+            {
+                if (item.Value < cutoff)
+                {
+                    PreviewNotifications.TryRemove(item.Key, out _);
+                }
+            }
+        }
+
+        var previewMinute = previewAt.ToUniversalTime().Ticks / TimeSpan.TicksPerMinute;
+        var key = $"{chatId:N}|{previewMinute}|{preview.Trim().ToLowerInvariant()}";
+        return PreviewNotifications.TryAdd(key, now);
+    }
+
+    private static DateTimeOffset ResolveListPreviewAt(MaxChatUpdate update, DateTimeOffset? fallback = null)
     {
         return TryParseMoscowListTime(update.LastMessageTimeText, out var parsed)
             ? parsed
-            : update.LastMessageAt ?? update.UpdatedAt;
+            : fallback ?? (update.Messages.Count > 0 ? update.LastMessageAt : null) ?? update.UpdatedAt;
     }
 
     private static bool IsFreshListPreview(MaxChatUpdate update, DateTimeOffset previewAt)
     {
-        if (string.IsNullOrWhiteSpace(update.LastMessageTimeText))
+        if (!HasListClockTime(update.LastMessageTimeText))
         {
             return false;
         }
@@ -331,6 +356,11 @@ public sealed class MaxBridgeSyncService(
         return previewAt >= now.AddMinutes(-15) && previewAt <= now.AddMinutes(10);
     }
 
+    private static bool HasListClockTime(string? value)
+    {
+        return System.Text.RegularExpressions.Regex.IsMatch(value?.Trim() ?? "", @"\b\d{1,2}:\d{2}\b");
+    }
+
     private static bool TryParseMoscowListTime(string? value, out DateTimeOffset parsed)
     {
         parsed = default;