Refactor: extract selected_text_range and supporting functions

paint.py

@@ -476,6 +476,25 @@ class Selection:
         document.copy_region(source=self.contained_image, source_region=source_region, target_region=target_region, mask=self.mask)
 
 
+def offset_to_text_index(textbox: Selection, offset: Offset) -> int:
+    """Converts an offset in the textbox to an index in the text."""
+    assert textbox.textbox_mode, "offset_to_text_index called on non-textbox selection"
+    return offset.y * textbox.region.width + offset.x
+
+def text_index_to_offset(textbox: Selection, index: int) -> Offset:
+    """Converts an index in the text to an offset in the textbox."""
+    assert textbox.textbox_mode, "text_index_to_offset called on non-textbox selection"
+    return Offset(index % textbox.region.width, index // textbox.region.width)
+
+def selected_text_range(textbox: Selection) -> Generator[Offset, None, None]:
+    """Yields all offsets within the text selection."""
+    assert textbox.textbox_mode, "selected_text_range called on non-textbox selection"
+    start = offset_to_text_index(textbox, textbox.text_selection_start)
+    end = offset_to_text_index(textbox, textbox.text_selection_end)
+    for i in range(min(start, end), max(start, end) + 1):
+        yield text_index_to_offset(textbox, i)
+
+
 debug_region_updates = False
 
 ansi_escape_pattern = re.compile(r"(\N{ESC}\[[\d;]*[a-zA-Z])")
@@ -2760,26 +2779,11 @@ class PaintApp(App[None]):
             textbox = self.image.selection
             assert textbox.contained_image is not None, "Textbox mode should always have contained_image, to edit as text."
 
-            def offset_to_text_index(offset: Offset) -> int:
-                """Converts an offset in the textbox to an index in the text."""
-                return offset.y * textbox.region.width + offset.x
-            
-            def text_index_to_offset(index: int) -> Offset:
-                """Converts an index in the text to an offset in the textbox."""
-                return Offset(index % textbox.region.width, index // textbox.region.width)
-
-            def selected_text_range() -> Generator[Offset, None, None]:
-                """Yields all offsets within the text selection."""
-                start = offset_to_text_index(textbox.text_selection_start)
-                end = offset_to_text_index(textbox.text_selection_end)
-                for i in range(min(start, end), max(start, end) + 1):
-                    yield text_index_to_offset(i)
-
             def delete_selected_text() -> None:
                 """Deletes the selected text, if any."""
                 assert textbox.contained_image is not None, "Textbox mode should always have contained_image, to edit as text." # Come on, Pyright.
                 # Delete the selected text.
-                for offset in selected_text_range():
+                for offset in selected_text_range(textbox):
                     textbox.contained_image.ch[offset.y][offset.x] = " "
                 textbox.textbox_edited = True
                 # Move the cursor to the start of the selection.