Basic push notification system for service alerts

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

1 files changed, 77 insertions, 0 deletions

diff --git a/src/Enmarcha.Backend/Services/AlertPhaseNotificationHostedService.cs b/src/Enmarcha.Backend/Services/AlertPhaseNotificationHostedService.cs
new file mode 100644
index 0000000..5cbbaee
--- /dev/null
+++ b/src/Enmarcha.Backend/Services/AlertPhaseNotificationHostedService.cs
@@ -0,0 +1,77 @@
+using Enmarcha.Backend.Data;
+using Microsoft.EntityFrameworkCore;
+
+namespace Enmarcha.Backend.Services;
+
+/// <summary>
+/// Background service that automatically sends push notifications when a service alert
+/// transitions into the PreNotice or Active phase without having been notified yet.
+/// Runs every 60 seconds and also immediately on startup to handle any missed transitions.
+/// </summary>
+public class AlertPhaseNotificationHostedService(
+    IServiceScopeFactory scopeFactory,
+    ILogger<AlertPhaseNotificationHostedService> logger) : IHostedService, IDisposable
+{
+    private Timer? _timer;
+
+    public Task StartAsync(CancellationToken cancellationToken)
+    {
+        // Run immediately, then every 60 seconds
+        _timer = new Timer(_ => _ = RunAsync(), null, TimeSpan.Zero, TimeSpan.FromSeconds(60));
+        return Task.CompletedTask;
+    }
+
+    private async Task RunAsync()
+    {
+        try
+        {
+            using var scope = scopeFactory.CreateScope();
+            var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
+            var pushService = scope.ServiceProvider.GetRequiredService<IPushNotificationService>();
+
+            var now = DateTime.UtcNow;
+
+            // Find alerts that are published and not yet hidden, but haven't been notified
+            // for their current phase (PreNotice: published but event not yet started;
+            // Active: event in progress).
+            var alertsToNotify = await db.ServiceAlerts
+                .Where(a =>
+                    a.PublishDate <= now && a.HiddenDate > now &&
+                    (
+                        // PreNotice: published, event hasn't started, no prenotice notification sent yet
+                        (a.EventStartDate > now && a.PreNoticeNotifiedAt == null) ||
+                        // Active: event started and not finished, no active notification sent yet
+                        (a.EventStartDate <= now && a.EventEndDate > now && a.ActiveNotifiedAt == null)
+                    ))
+                .ToListAsync();
+
+            if (alertsToNotify.Count == 0) return;
+
+            logger.LogInformation("Sending push notifications for {Count} alert(s)", alertsToNotify.Count);
+
+            foreach (var alert in alertsToNotify)
+            {
+                try
+                {
+                    await pushService.SendAlertAsync(alert);
+                }
+                catch (Exception ex)
+                {
+                    logger.LogError(ex, "Error sending push notification for alert {AlertId}", alert.Id);
+                }
+            }
+        }
+        catch (Exception ex)
+        {
+            logger.LogError(ex, "Unexpected error in {ServiceName}", nameof(AlertPhaseNotificationHostedService));
+        }
+    }
+
+    public Task StopAsync(CancellationToken cancellationToken)
+    {
+        _timer?.Change(Timeout.Infinite, 0);
+        return Task.CompletedTask;
+    }
+
+    public void Dispose() => _timer?.Dispose();
+}