Improve word count: real-time updates, better perf, and formatted display

- Propagate TextChanging event through INotepadsCore/NotepadsCore so word
  count updates in real time as the user types, deletes, or pastes text
- Replace string.Split word counting with O(n) char iteration to avoid
  intermediate allocations on every keystroke for large files
- Format display as Words: 1,245 and Words: 1,245 | Selected: 132
  with locale-aware thousand separators

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: SushrutDhakal

src/Notepads/Core/INotepadsCore.cs

@@ -1,4 +1,4 @@
-// ---------------------------------------------------------------------------------------------
+// ---------------------------------------------------------------------------------------------
 //  Copyright (c) 2019-2024, Jiaqi (0x7c13) Liu. All rights reserved.
 //  See LICENSE file in the project root for license information.
 // ---------------------------------------------------------------------------------------------
@@ -31,6 +31,7 @@ public interface INotepadsCore
         event EventHandler<ITextEditor> TextEditorFontZoomFactorChanged;
         event EventHandler<ITextEditor> TextEditorEncodingChanged;
         event EventHandler<ITextEditor> TextEditorLineEndingChanged;
+        event EventHandler<ITextEditor> TextEditorTextChanging;
         event EventHandler<ITextEditor> TextEditorModeChanged;
         event EventHandler<ITextEditor> TextEditorMovedToAnotherAppInstance;
         event EventHandler<IReadOnlyList<IStorageItem>> StorageItemsDropped;

src/Notepads/Core/NotepadsCore.cs

@@ -1,4 +1,4 @@
-// ---------------------------------------------------------------------------------------------
+// ---------------------------------------------------------------------------------------------
 //  Copyright (c) 2019-2024, Jiaqi (0x7c13) Liu. All rights reserved.
 //  See LICENSE file in the project root for license information.
 // ---------------------------------------------------------------------------------------------
@@ -42,6 +42,7 @@ public class NotepadsCore : INotepadsCore
         public event EventHandler<ITextEditor> TextEditorFontZoomFactorChanged;
         public event EventHandler<ITextEditor> TextEditorEncodingChanged;
         public event EventHandler<ITextEditor> TextEditorLineEndingChanged;
+        public event EventHandler<ITextEditor> TextEditorTextChanging;
         public event EventHandler<ITextEditor> TextEditorModeChanged;
         public event EventHandler<ITextEditor> TextEditorMovedToAnotherAppInstance;
         public event EventHandler<IReadOnlyList<IStorageItem>> StorageItemsDropped;
@@ -199,6 +200,7 @@ public ITextEditor CreateTextEditor(
             textEditor.Loaded += TextEditor_Loaded;
             textEditor.Unloaded += TextEditor_Unloaded;
             textEditor.SelectionChanged += TextEditor_OnSelectionChanged;
+            textEditor.TextChanging += TextEditor_OnTextChanging;
             textEditor.FontZoomFactorChanged += TextEditor_OnFontZoomFactorChanged;
             textEditor.KeyDown += TextEditorKeyDown;
             textEditor.ModificationStateChanged += TextEditor_OnEditorModificationStateChanged;
@@ -238,6 +240,7 @@ public void DeleteTextEditor(ITextEditor textEditor)
             textEditor.Unloaded -= TextEditor_Unloaded;
             textEditor.KeyDown -= TextEditorKeyDown;
             textEditor.SelectionChanged -= TextEditor_OnSelectionChanged;
+            textEditor.TextChanging -= TextEditor_OnTextChanging;
             textEditor.FontZoomFactorChanged -= TextEditor_OnFontZoomFactorChanged;
             textEditor.ModificationStateChanged -= TextEditor_OnEditorModificationStateChanged;
             textEditor.ModeChanged -= TextEditor_OnModeChanged;
@@ -521,6 +524,12 @@ private void TextEditor_OnSelectionChanged(object sender, EventArgs e)
             TextEditorSelectionChanged?.Invoke(this, textEditor);
         }
 
+        private void TextEditor_OnTextChanging(object sender, EventArgs e)
+        {
+            if (!(sender is ITextEditor textEditor)) return;
+            TextEditorTextChanging?.Invoke(this, textEditor);
+        }
+
         private void TextEditor_OnFontZoomFactorChanged(object sender, EventArgs e)
         {
             if (!(sender is ITextEditor textEditor)) return;

src/Notepads/Views/MainPage/NotepadsMainPage.StatusBar.cs

@@ -173,18 +173,52 @@ private void UpdateWordCountIndicator(ITextEditor textEditor)
             if (!string.IsNullOrEmpty(selectedText))
             {
                 var selectedWordCount = CountWords(selectedText);
-                WordCountIndicator.Text = $"{selectedWordCount}/{totalWordCount} words";
+                WordCountIndicator.Text = string.Format(
+                    "Words: {0} | Selected: {1}",
+                    totalWordCount.ToString("N0", CultureInfo.CurrentCulture),
+                    selectedWordCount.ToString("N0", CultureInfo.CurrentCulture));
             }
             else
             {
-                WordCountIndicator.Text = $"{totalWordCount} words";
+                WordCountIndicator.Text = string.Format(
+                    "Words: {0}",
+                    totalWordCount.ToString("N0", CultureInfo.CurrentCulture));
             }
         }
 
+        /// <summary>
+        /// Counts words in the given text using character iteration for efficiency.
+        /// A word is defined as a contiguous sequence of non-whitespace characters.
+        /// </summary>
         private static int CountWords(string text)
         {
-            if (string.IsNullOrWhiteSpace(text)) return 0;
-            return text.Split(new[] { ' ', '\t', '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries).Length;
+            if (string.IsNullOrEmpty(text)) return 0;
+
+            int wordCount = 0;
+            bool inWord = false;
+
+            for (int i = 0; i < text.Length; i++)
+            {
+                if (char.IsWhiteSpace(text[i]))
+                {
+                    if (inWord)
+                    {
+                        wordCount++;
+                        inWord = false;
+                    }
+                }
+                else
+                {
+                    inWord = true;
+                }
+            }
+
+            if (inWord)
+            {
+                wordCount++;
+            }
+
+            return wordCount;
         }
 
         private void UpdateFontZoomIndicator(ITextEditor textEditor)

src/Notepads/Views/MainPage/NotepadsMainPage.xaml.cs

@@ -63,6 +63,7 @@ private INotepadsCore NotepadsCore
                 _notepadsCore.TextEditorMovedToAnotherAppInstance += OnTextEditorMovedToAnotherAppInstance;
                 _notepadsCore.TextEditorRenamed += (sender, editor) => { if (NotepadsCore.GetSelectedTextEditor() == editor) SetupStatusBar(editor); };
                 _notepadsCore.TextEditorSelectionChanged += (sender, editor) => { if (NotepadsCore.GetSelectedTextEditor() == editor) { UpdateLineColumnIndicator(editor); UpdateWordCountIndicator(editor); } };
+                _notepadsCore.TextEditorTextChanging += (_, editor) => { if (NotepadsCore.GetSelectedTextEditor() == editor) UpdateWordCountIndicator(editor); };
                 _notepadsCore.TextEditorFontZoomFactorChanged += (sender, editor) => { if (NotepadsCore.GetSelectedTextEditor() == editor) UpdateFontZoomIndicator(editor); };
                 _notepadsCore.TextEditorEncodingChanged += (sender, editor) => { if (NotepadsCore.GetSelectedTextEditor() == editor) UpdateEncodingIndicator(editor.GetEncoding()); };
                 _notepadsCore.TextEditorLineEndingChanged += (sender, editor) => { if (NotepadsCore.GetSelectedTextEditor() == editor) { UpdateLineEndingIndicator(editor.GetLineEnding()); UpdateLineColumnIndicator(editor); } };