Add time zones settings panel

SettingsWindow/TimeZoneWindow.xaml.cs

@@ -0,0 +1,43 @@
+using ChrisKaczor.Wpf.Validation;
+using System;
+using System.Windows;
+
+namespace WorldClockStatusWindow.SettingsWindow;
+
+public partial class TimeZoneWindow
+{
+    public TimeZoneWindow()
+    {
+        InitializeComponent();
+    }
+
+    public bool? Display(TimeZoneEntry timeZoneEntry, Window owner)
+    {
+        DataContext = timeZoneEntry;
+
+        TimeZoneComboBox.ItemsSource = TimeZoneInfo.GetSystemTimeZones();
+
+        Title = string.IsNullOrWhiteSpace(timeZoneEntry.Label) ? Properties.Resources.TimeZoneWindowAdd : Properties.Resources.TimeZoneWindowEdit;
+
+        Owner = owner;
+
+        return ShowDialog();
+    }
+
+    private void HandleOkayButtonClick(object sender, RoutedEventArgs e)
+    {
+        if (!this.IsValid())
+            return;
+
+        var timeZoneEntry = (TimeZoneEntry)DataContext;
+
+        if (!Data.TimeZoneEntries.Contains(timeZoneEntry))
+            Data.TimeZoneEntries.Add(timeZoneEntry);
+
+        Data.Save();
+
+        DialogResult = true;
+
+        Close();
+    }
+}