Basic push notification system for service alerts

Co-authored-by: Copilot <copilot@github.com>

1 files changed, 134 insertions, 0 deletions

diff --git a/src/Enmarcha.Backend/Services/PushNotificationService.cs b/src/Enmarcha.Backend/Services/PushNotificationService.cs
new file mode 100644
index 0000000..c9d79dc
--- /dev/null
+++ b/src/Enmarcha.Backend/Services/PushNotificationService.cs
@@ -0,0 +1,134 @@
+using Enmarcha.Backend.Configuration;
+using Enmarcha.Backend.Data;
+using Enmarcha.Backend.Data.Models;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Options;
+using System.Text.Json;
+using WebPush;
+
+namespace Enmarcha.Backend.Services;
+
+public interface IPushNotificationService
+{
+    Task SubscribeAsync(string endpoint, string p256dh, string auth);
+    Task UnsubscribeAsync(string endpoint);
+    Task SendAlertAsync(ServiceAlert alert);
+}
+
+public class PushNotificationService(
+    AppDbContext db,
+    IOptions<AppConfiguration> options,
+    ILogger<PushNotificationService> logger
+) : IPushNotificationService
+{
+    private readonly WebPushClient? _client = BuildClient(options.Value.Vapid);
+
+    private static WebPushClient? BuildClient(VapidConfiguration? vapid)
+    {
+        if (vapid is null) return null;
+        var client = new WebPushClient();
+        client.SetVapidDetails(vapid.Subject, vapid.PublicKey, vapid.PrivateKey);
+        return client;
+    }
+
+    public async Task SubscribeAsync(string endpoint, string p256dh, string auth)
+    {
+        var existing = await db.PushSubscriptions
+            .FirstOrDefaultAsync(s => s.Endpoint == endpoint);
+
+        if (existing is null)
+        {
+            db.PushSubscriptions.Add(new Data.Models.PushSubscription
+            {
+                Id = Guid.NewGuid(),
+                Endpoint = endpoint,
+                P256DhKey = p256dh,
+                AuthKey = auth,
+                CreatedAt = DateTime.UtcNow,
+            });
+        }
+        else
+        {
+            // Refresh keys in case they changed (e.g. after re-subscription)
+            existing.P256DhKey = p256dh;
+            existing.AuthKey = auth;
+        }
+
+        await db.SaveChangesAsync();
+    }
+
+    public async Task UnsubscribeAsync(string endpoint)
+    {
+        var subscription = await db.PushSubscriptions
+            .FirstOrDefaultAsync(s => s.Endpoint == endpoint);
+
+        if (subscription is not null)
+        {
+            db.PushSubscriptions.Remove(subscription);
+            await db.SaveChangesAsync();
+        }
+    }
+
+    public async Task SendAlertAsync(ServiceAlert alert)
+    {
+        if (_client is null)
+        {
+            logger.LogWarning("VAPID not configured — skipping push notification for alert {AlertId}", alert.Id);
+            return;
+        }
+
+        var now = DateTime.UtcNow;
+        var phase = alert.GetPhase(now);
+
+        alert.Version++;
+
+        if (phase == AlertPhase.PreNotice)
+            alert.PreNoticeNotifiedAt = now;
+        else if (phase == AlertPhase.Active)
+            alert.ActiveNotifiedAt = now;
+
+        var payload = JsonSerializer.Serialize(new
+        {
+            alertId = alert.Id,
+            version = alert.Version,
+            phase = phase.ToString(),
+            cause = alert.Cause.ToString(),
+            effect = alert.Effect.ToString(),
+            header = (Dictionary<string, string>)alert.Header,
+            description = (Dictionary<string, string>)alert.Description,
+            selectors = alert.Selectors.Select(s => s.Raw).ToList(),
+            eventStart = alert.EventStartDate,
+            eventEnd = alert.EventEndDate,
+        });
+
+        var subscriptions = await db.PushSubscriptions.ToListAsync();
+        var expired = new List<Data.Models.PushSubscription>();
+
+        foreach (var sub in subscriptions)
+        {
+            try
+            {
+                var pushSub = new WebPush.PushSubscription(sub.Endpoint, sub.P256DhKey, sub.AuthKey);
+                await _client.SendNotificationAsync(pushSub, payload);
+            }
+            catch (WebPushException ex) when (
+                ex.StatusCode is System.Net.HttpStatusCode.Gone or System.Net.HttpStatusCode.NotFound)
+            {
+                // Subscription expired or was revoked — remove it
+                expired.Add(sub);
+            }
+            catch (Exception ex)
+            {
+                logger.LogWarning(ex, "Failed to deliver push notification to endpoint {Endpoint}", sub.Endpoint[..Math.Min(40, sub.Endpoint.Length)]);
+            }
+        }
+
+        if (expired.Count > 0)
+        {
+            db.PushSubscriptions.RemoveRange(expired);
+            logger.LogInformation("Removed {Count} expired push subscription(s)", expired.Count);
+        }
+
+        await db.SaveChangesAsync();
+    }
+}