feat: 添加推送通知功能，支持订阅和发送通知

Service/NotificationService.cs

@@ -0,0 +1,93 @@
+using WebPush;
+
+namespace Service;
+
+public interface INotificationService
+{
+    Task<string> GetVapidPublicKeyAsync();
+    Task SubscribeAsync(PushSubscriptionEntity subscription);
+    Task SendNotificationAsync(string message, string? url = null);
+}
+
+public class NotificationService(
+    IPushSubscriptionRepository subscriptionRepo,
+    IConfiguration configuration,
+    ILogger<NotificationService> logger) : INotificationService
+{
+    private NotificationSettings GetSettings()
+    {
+        var settings = configuration.GetSection("NotificationSettings").Get<NotificationSettings>();
+        if (settings == null)
+        {
+            // Fallback or throw. For now, let's return empty to avoid crashing if not configured, 
+            // but logging error is better.
+            logger.LogWarning("NotificationSettings not configured");
+            return new NotificationSettings();
+        }
+        return settings;
+    }
+
+    public Task<string> GetVapidPublicKeyAsync()
+    {
+        return Task.FromResult(GetSettings().PublicKey);
+    }
+
+    public async Task SubscribeAsync(PushSubscriptionEntity subscription)
+    {
+        var existing = await subscriptionRepo.GetByEndpointAsync(subscription.Endpoint);
+        if (existing != null)
+        {
+            existing.P256DH = subscription.P256DH;
+            existing.Auth = subscription.Auth;
+            existing.UpdateTime = DateTime.Now;
+            await subscriptionRepo.UpdateAsync(existing);
+        }
+        else
+        {
+            await subscriptionRepo.AddAsync(subscription);
+        }
+    }
+
+    public async Task SendNotificationAsync(string message, string? url = null)
+    {
+        var settings = GetSettings();
+        if (string.IsNullOrEmpty(settings.PublicKey) || string.IsNullOrEmpty(settings.PrivateKey))
+        {
+            logger.LogWarning("VAPID keys not configured, skipping notification");
+            return;
+        }
+
+        var vapidDetails = new VapidDetails(settings.Subject, settings.PublicKey, settings.PrivateKey);
+        var webPushClient = new WebPushClient();
+
+        var subscriptions = await subscriptionRepo.GetAllAsync();
+        var payload = System.Text.Json.JsonSerializer.Serialize(new
+        {
+            title = "System Notification",
+            body = message,
+            url = url ?? "/",
+            icon = "/pwa-192x192.png"
+        });
+
+        foreach (var sub in subscriptions)
+        {
+            try
+            {
+                var pushSubscription = new PushSubscription(sub.Endpoint, sub.P256DH, sub.Auth);
+                await webPushClient.SendNotificationAsync(pushSubscription, payload, vapidDetails);
+            }
+            catch (WebPushException ex)
+            {
+                if (ex.StatusCode == System.Net.HttpStatusCode.Gone || ex.StatusCode == System.Net.HttpStatusCode.NotFound)
+                {
+                    await subscriptionRepo.DeleteAsync(sub.Id);
+                }
+                logger.LogError(ex, "Error sending push notification to {Endpoint}", sub.Endpoint);
+            }
+            catch (Exception ex)
+            {
+                logger.LogError(ex, "Error sending push notification to {Endpoint}", sub.Endpoint);
+            }
+        }
+    }
+}