New: App health displayed in UI

src/NzbDrone.Core/HealthCheck/HealthCheckService.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using NLog;
+using NzbDrone.Core.Configuration.Events;
+using NzbDrone.Core.Download;
+using NzbDrone.Core.Indexers;
+using NzbDrone.Core.Messaging.Commands;
+using NzbDrone.Core.Messaging.Events;
+using NzbDrone.Core.ThingiProvider.Events;
+
+namespace NzbDrone.Core.HealthCheck
+{
+    public interface IHealthCheckService
+    {
+        List<HealthCheck> PerformHealthCheck();
+    }
+
+    public class HealthCheckService : IHealthCheckService,
+                                      IExecute<CheckHealthCommand>,
+                                      IHandleAsync<ConfigSavedEvent>,
+                                      IHandleAsync<ProviderUpdatedEvent<IIndexer>>,
+                                      IHandleAsync<ProviderUpdatedEvent<IDownloadClient>>
+    {
+        private readonly IEnumerable<IProvideHealthCheck> _healthChecks;
+        private readonly IEventAggregator _eventAggregator;
+        private readonly Logger _logger;
+
+        public HealthCheckService(IEnumerable<IProvideHealthCheck> healthChecks, IEventAggregator eventAggregator, Logger logger)
+        {
+            _healthChecks = healthChecks;
+            _eventAggregator = eventAggregator;
+            _logger = logger;
+        }
+
+        public List<HealthCheck> PerformHealthCheck()
+        {
+            _logger.Trace("Checking health");
+            var result = _healthChecks.Select(c => c.Check()).Where(c => c != null).ToList();
+            
+            return result;
+        }
+
+        public void Execute(CheckHealthCommand message)
+        {
+            //Until we have stored health checks we should just trigger the complete event
+            //and let the clients check in
+            //Multiple connected clients means we're going to compute the health check multiple times
+            //Multiple checks feels a bit ugly, but means the most up to date information goes to the client
+            _eventAggregator.PublishEvent(new TriggerHealthCheckEvent());
+        }
+
+        public void HandleAsync(ConfigSavedEvent message)
+        {
+            _eventAggregator.PublishEvent(new TriggerHealthCheckEvent());
+        }
+
+        public void HandleAsync(ProviderUpdatedEvent<IIndexer> message)
+        {
+            _eventAggregator.PublishEvent(new TriggerHealthCheckEvent());
+        }
+
+        public void HandleAsync(ProviderUpdatedEvent<IDownloadClient> message)
+        {
+            _eventAggregator.PublishEvent(new TriggerHealthCheckEvent());
+        }
+    }
+}