feat: periodic notice of whether the Backend is available or not

Author: Xiphereal

Desktop/App.xaml.cs

@@ -23,6 +23,7 @@ protected override void OnStartup(StartupEventArgs e)
         var services = new ServiceCollection();
 
         services.AddSingleton<MainWindow>();
+        services.AddSingleton<MainWindowViewModel>();
         services.AddSingleton<TaskCreation>();
         services.AddTransient<TaskCreationViewModel>();
         services.AddTransient<TaskListViewModel>();

Desktop/MainWindow.xaml

@@ -11,6 +11,7 @@
         <Grid.ColumnDefinitions>
             <ColumnDefinition Width="Auto" />
             <ColumnDefinition />
+            <ColumnDefinition Width="Auto" />
         </Grid.ColumnDefinitions>
         <StackPanel Grid.Column="0">
             <Label HorizontalAlignment="Center">Views</Label>
@@ -25,5 +26,6 @@
             </Menu>
         </StackPanel>
         <ContentControl Grid.Column="1" Name="Content" />
+        <Label Grid.Column="2" Content="{Binding BackendAvailability}" />
     </Grid>
 </Window>

Desktop/MainWindow.xaml.cs

@@ -7,9 +7,11 @@ public partial class MainWindow : Window
 {
     private readonly TaskListViewModel taskListViewModel;
 
-    public MainWindow(TaskListViewModel taskListViewModel)
+    public MainWindow(TaskListViewModel taskListViewModel, MainWindowViewModel viewModel)
     {
         this.taskListViewModel = taskListViewModel;
+        DataContext = viewModel;
+
         InitializeComponent();
         NavigateToTaskList();
     }

Desktop/MainWindowViewModel.cs

@@ -0,0 +1,43 @@
+using System.Windows.Threading;
+using Desktop.Common;
+using Desktop.Tasks;
+
+namespace Desktop;
+
+public class MainWindowViewModel : ViewModelBase
+{
+    private readonly IRemoteTaskRepository backend;
+
+    private static readonly TimeSpan CheckBackendAvailabilityInterval =
+        TimeSpan.FromSeconds(2);
+
+    private string backendAvailability = "Available";
+    private readonly DispatcherTimer periodicBackendAvailabilityCheckTimer;
+
+    public string BackendAvailability
+    {
+        get => backendAvailability;
+        set
+        {
+            backendAvailability = value;
+            OnPropertyChanged();
+        }
+    }
+
+    public MainWindowViewModel(IRemoteTaskRepository backend)
+    {
+        this.backend = backend;
+        periodicBackendAvailabilityCheckTimer = new DispatcherTimer
+        {
+            Interval = CheckBackendAvailabilityInterval
+        };
+        periodicBackendAvailabilityCheckTimer.Tick += async (_, _) =>
+            await CheckBackendAvailability();
+        periodicBackendAvailabilityCheckTimer.Start();
+    }
+
+    private async Task CheckBackendAvailability()
+    {
+        BackendAvailability = await backend.IsAvailable() ? "Available" : "Non available";
+    }
+}

Desktop/Tasks/BackendTaskRepository.cs

@@ -5,7 +5,7 @@
 
 namespace Desktop.Tasks;
 
-public class BackendTaskRepository : ITaskRepository
+public class BackendTaskRepository : ITaskRepository, IRemoteTaskRepository
 {
     private readonly HttpClient httpClient;
 
@@ -14,6 +14,22 @@ public BackendTaskRepository(HttpClient httpClient)
         this.httpClient = httpClient;
     }
 
+    public async Task<bool> IsAvailable()
+    {
+        try
+        {
+            var result = await httpClient.GetAsync("/health/");
+
+            result.EnsureSuccessStatusCode();
+
+            return true;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+
     public async Task<IReadOnlyList<Task>> All()
     {
         HttpResponseMessage getResult;

Desktop/Tasks/Extensions/ServiceCollectionExtensions.cs

@@ -25,5 +25,6 @@ public static void AddBackendTaskRepository(
             return httpClient;
         });
         services.AddSingleton<ITaskRepository, BackendTaskRepository>();
+        services.AddSingleton<IRemoteTaskRepository, BackendTaskRepository>();
     }
 }

Desktop/Tasks/IRemoteTaskRepository.cs

@@ -0,0 +1,6 @@
+namespace Desktop.Tasks;
+
+public interface IRemoteTaskRepository
+{
+    Task<bool> IsAvailable();
+}