Ground work for Wino Calendar. (#475)

Wino Calendar abstractions.

Wino.Core.UWP/Dialogs/BaseAccountCreationDialog.cs

@@ -0,0 +1,52 @@
+using System.Threading;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Interfaces;
+
+namespace Wino.Dialogs
+{
+    public abstract class BaseAccountCreationDialog : ContentDialog, IAccountCreationDialog
+    {
+        public AccountCreationDialogState State
+        {
+            get { return (AccountCreationDialogState)GetValue(StateProperty); }
+            set { SetValue(StateProperty, value); }
+        }
+
+        public CancellationTokenSource CancellationTokenSource { get; private set; }
+
+        public static readonly DependencyProperty StateProperty = DependencyProperty.Register(nameof(State), typeof(AccountCreationDialogState), typeof(BaseAccountCreationDialog), new PropertyMetadata(AccountCreationDialogState.Idle));
+
+        // Prevent users from dismissing it by ESC key.
+        public void DialogClosing(ContentDialog sender, ContentDialogClosingEventArgs args)
+        {
+            if (args.Result == ContentDialogResult.None)
+            {
+                args.Cancel = true;
+            }
+        }
+
+        public void ShowDialog(CancellationTokenSource cancellationTokenSource)
+        {
+            CancellationTokenSource = cancellationTokenSource;
+
+            _ = ShowAsync();
+        }
+
+        public void Complete(bool cancel)
+        {
+            State = cancel ? AccountCreationDialogState.Canceled : AccountCreationDialogState.Completed;
+
+            // Unregister from closing event.
+            Closing -= DialogClosing;
+
+            if (cancel && !CancellationTokenSource.IsCancellationRequested)
+            {
+                CancellationTokenSource.Cancel();
+            }
+
+            Hide();
+        }
+    }
+}