3 files changed, 73 insertions, 18 deletions

diff --git a/src/ui/controls/text_box.cpp b/src/ui/controls/text_box.cpp
index 30b9069a..54b2f7ab 100644
--- a/src/ui/controls/text_box.cpp
+++ b/src/ui/controls/text_box.cpp
@@ -67,16 +67,47 @@ namespace cru::ui::controls
         Control::OnKeyDownCore(args);
         if (args.GetVirtualCode() == VK_LEFT && caret_position_ > 0)
         {
-            ClearSelection();
-            caret_position_--;
+            if (IsKeyDown(VK_SHIFT))
+            {
+                if (GetCaretSelectionSide())
+                    ShiftLeftSelectionRange(-1);
+                else
+                    ShiftRightSelectionRange(-1);
+            }
+            else
+            {
+                const auto selection = GetSelectedRange();
+                if (selection.has_value())
+                {
+                    ClearSelection();
+                    caret_position_ = selection.value().position;
+                }
+                else
+                    caret_position_--;
+            }
             Repaint();
         }
 
         if (args.GetVirtualCode() == VK_RIGHT && caret_position_ < GetText().size())
         {
-            ClearSelection();
-            caret_position_++;
-            Repaint();
+            if (IsKeyDown(VK_SHIFT))
+            {
+                if (GetCaretSelectionSide())
+                    ShiftLeftSelectionRange(1);
+                else
+                    ShiftRightSelectionRange(1);
+            }
+            else
+            {
+                const auto selection = GetSelectedRange();
+                if (selection.has_value())
+                {
+                    ClearSelection();
+                    caret_position_ = selection.value().position + selection.value().count;
+                }
+                else
+                    caret_position_++;
+            }
         }
     }
 
@@ -138,4 +169,33 @@ namespace cru::ui::controls
         caret_position_ = position;
         Repaint();
     }
+
+    bool TextBox::GetCaretSelectionSide() const
+    {
+        const auto selection = TextRange::ToTwoSides(GetSelectedRange(), caret_position_);
+        if (selection.first == caret_position_)
+            return true;
+        if (selection.second == caret_position_)
+            return false;
+        assert(false);
+        return true;
+    }
+
+    void TextBox::ShiftLeftSelectionRange(const int count)
+    {
+        const auto selection_range_side = TextRange::ToTwoSides(GetSelectedRange(), caret_position_);
+        int new_left = selection_range_side.first + count;
+        new_left = new_left < 0 ? 0 : new_left; // at least 0
+        caret_position_ = new_left;
+        SetSelectedRange(TextRange::FromTwoSides(static_cast<unsigned>(new_left), selection_range_side.second));
+    }
+
+    void TextBox::ShiftRightSelectionRange(const int count)
+    {
+        const auto selection_range_side = TextRange::ToTwoSides(GetSelectedRange(), caret_position_);
+        int new_right = selection_range_side.second + count;
+        new_right = new_right < 0 ? 0 : new_right; // at least 0
+        caret_position_ = new_right;
+        SetSelectedRange(TextRange::FromTwoSides(selection_range_side.first, static_cast<unsigned>(new_right)));
+    }
 }
diff --git a/src/ui/controls/text_box.h b/src/ui/controls/text_box.h
index 540ac758..37e04835 100644
--- a/src/ui/controls/text_box.h
+++ b/src/ui/controls/text_box.h
@@ -36,7 +36,13 @@ namespace cru::ui::controls
         void OnKeyDownCore(events::KeyEventArgs& args) override final;
         void OnCharCore(events::CharEventArgs& args) override final;
 
-        void RequestChangeCaretPosition(unsigned position) override;
+        void RequestChangeCaretPosition(unsigned position) override final;
+
+    private:
+        // return true if left
+        bool GetCaretSelectionSide() const;
+        void ShiftLeftSelectionRange(int count);
+        void ShiftRightSelectionRange(int count);
 
     private:
         unsigned caret_position_ = 0;
diff --git a/src/ui/controls/text_control.cpp b/src/ui/controls/text_control.cpp
index ee5b253d..3c5d7c33 100644
--- a/src/ui/controls/text_control.cpp
+++ b/src/ui/controls/text_control.cpp
@@ -162,18 +162,7 @@ namespace cru::ui::controls
         {
             const auto hit_test_result = TextLayoutHitTest(text_layout_.Get(), args.GetPoint(this), false).value();
             RequestChangeCaretPosition(hit_test_result);
-            if (hit_test_result > mouse_down_position_)
-            {
-                selected_range_ = TextRange(mouse_down_position_, hit_test_result - mouse_down_position_);
-            }
-            else if (hit_test_result < mouse_down_position_)
-            {
-                selected_range_ = TextRange(hit_test_result, mouse_down_position_ - hit_test_result);
-            }
-            else
-            {
-                selected_range_ = std::nullopt;
-            }
+            selected_range_ = TextRange::FromTwoSides(hit_test_result, mouse_down_position_);
             Repaint();
         }
     }