Add time zones settings panel

TimeZoneEntry.cs

@@ -1,7 +1,61 @@
-namespace WorldClockStatusWindow;
+using System;
+using System.Collections;
+using System.ComponentModel;
+using System.Linq;
+using System.Text.Json.Serialization;
 
-public class TimeZoneEntry
+namespace WorldClockStatusWindow;
+
+public class TimeZoneEntry : INotifyDataErrorInfo
 {
-    public string Label { get; set; }
+    private readonly DataErrorDictionary _dataErrorDictionary;
+
+    public TimeZoneEntry()
+    {
+        _dataErrorDictionary = new DataErrorDictionary();
+        _dataErrorDictionary.ErrorsChanged += DataErrorDictionaryErrorsChanged;
+    }
+
+    private string _label;
+
+    public string Label
+    {
+        get => _label;
+        set
+        {
+            if (!ValidateLabel(value))
+                return;
+
+            _label = value;
+        }
+    }
+
     public string TimeZoneId { get; set; }
+
+    [JsonIgnore]
+    public bool HasErrors => _dataErrorDictionary.Any();
+
+    public IEnumerable GetErrors(string propertyName)
+    {
+        return _dataErrorDictionary.GetErrors(propertyName);
+    }
+
+    public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;
+
+    private void DataErrorDictionaryErrorsChanged(object sender, DataErrorsChangedEventArgs e)
+    {
+        ErrorsChanged?.Invoke(this, new DataErrorsChangedEventArgs(e.PropertyName));
+    }
+
+    private bool ValidateLabel(string newValue)
+    {
+        _dataErrorDictionary.ClearErrors(nameof(Label));
+
+        if (!string.IsNullOrWhiteSpace(newValue))
+            return true;
+
+        _dataErrorDictionary.AddError(nameof(Label), "Label cannot be empty");
+
+        return false;
+    }
 }