From 5d1e5d97c2bf4d99e83a21c7e314761942e09ac8 Mon Sep 17 00:00:00 2001
From: Sergey Mikolaitis <blasterloremaster@gmail.com>
Date: Tue, 3 Jan 2023 23:04:21 +0300
Subject: [PATCH] [Text] [Selection] fix double click selection on word end
 position

---
 src/Avalonia.Controls/SelectableTextBlock.cs |  6 ++-
 src/Avalonia.Controls/TextBox.cs             |  6 ++-
 src/Avalonia.Controls/Utils/StringUtils.cs   | 49 ++++++++++++++++++++
 3 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Controls/SelectableTextBlock.cs b/src/Avalonia.Controls/SelectableTextBlock.cs
index b343439f98..f4c4d54951 100644
--- a/src/Avalonia.Controls/SelectableTextBlock.cs
+++ b/src/Avalonia.Controls/SelectableTextBlock.cs
@@ -300,7 +300,11 @@ namespace Avalonia.Controls
 
                         _wordSelectionStart = SelectionStart;
 
-                        SelectionEnd = StringUtils.NextWord(text, index);
+                        if (!StringUtils.IsEndOfWord(text, index))
+                        {
+                            SelectionEnd = StringUtils.NextWord(text, index);
+                        }
+                        
                         break;
                     case 3:
                         _wordSelectionStart = -1;
diff --git a/src/Avalonia.Controls/TextBox.cs b/src/Avalonia.Controls/TextBox.cs
index 1bdec878d9..9a2ee12dc3 100644
--- a/src/Avalonia.Controls/TextBox.cs
+++ b/src/Avalonia.Controls/TextBox.cs
@@ -1475,7 +1475,11 @@ namespace Avalonia.Controls
 
                         _wordSelectionStart = SelectionStart;
 
-                        SelectionEnd = StringUtils.NextWord(text, index);
+                        if (!StringUtils.IsEndOfWord(text, index))
+                        {
+                            SelectionEnd = StringUtils.NextWord(text, index);
+                        }
+
                         break;
                     case 3:
                         _wordSelectionStart = -1;
diff --git a/src/Avalonia.Controls/Utils/StringUtils.cs b/src/Avalonia.Controls/Utils/StringUtils.cs
index b2e56434b2..6c459d7985 100644
--- a/src/Avalonia.Controls/Utils/StringUtils.cs
+++ b/src/Avalonia.Controls/Utils/StringUtils.cs
@@ -67,6 +67,55 @@ namespace Avalonia.Controls.Utils
             }
         }
 
+        public static bool IsEndOfWord(string text, int index)
+        {
+            if (index >= text.Length)
+            {
+                return true;
+            }
+
+            var codepoint = new Codepoint(text[index]);
+        
+            if (!codepoint.IsWhiteSpace)
+            {
+                return false;
+            }
+            // A 'word' starts with an AlphaNumeric or some punctuation symbols immediately
+            // preceeded by lwsp.
+            if (index > 0)
+            {
+                var nextCodePoint = new Codepoint(text[index + 1]);
+
+                if (nextCodePoint.IsBreakChar)
+                {
+                    return true;
+                }
+            }
+
+            switch (codepoint.GeneralCategory)
+            {
+                case GeneralCategory.LowercaseLetter:
+                case GeneralCategory.TitlecaseLetter:
+                case GeneralCategory.UppercaseLetter:
+                case GeneralCategory.DecimalNumber:
+                case GeneralCategory.LetterNumber:
+                case GeneralCategory.OtherNumber:
+                case GeneralCategory.DashPunctuation:
+                case GeneralCategory.InitialPunctuation:
+                case GeneralCategory.OpenPunctuation:
+                case GeneralCategory.CurrencySymbol:
+                case GeneralCategory.MathSymbol:
+                    return false;
+
+                // TODO: How do you do this in .NET?
+                // case UnicodeCategory.OtherPunctuation:
+                //    // words cannot start with '.', but they can start with '&' or '*' (for example)
+                //    return g_unichar_break_type(buffer->text[index]) == G_UNICODE_BREAK_ALPHABETIC;
+                default:
+                    return true;
+            }
+        }
+
         public static int PreviousWord(string text, int cursor)
         {
             if (string.IsNullOrEmpty(text))