refactor: Improve multi-line text selection logic and handling

gtm2.py

@@ -278,25 +278,41 @@ def draw_selection(stdscr, state):
         return
 
     start_x, start_y = state.selection_start_coord
-    _, end_y = state.selection_end_coord
+    end_x, end_y = state.selection_end_coord
     
-    y1, y2 = min(start_y, end_y), max(start_y, end_y)
-
     # Determine pane from where selection started
     pane = 'left' if start_x < state.divider_col else 'right'
-
     if pane == 'left':
-        x1, x2 = 0, state.divider_col - 1
+        pane_x1, pane_x2 = 0, state.divider_col - 1
     else: # right
-        x1, x2 = state.divider_col + 2, state.width - 1
+        pane_x1, pane_x2 = state.divider_col + 2, state.width - 1
+
+    # Determine drag direction to handle multi-line selection correctly
+    if start_y < end_y or (start_y == end_y and start_x <= end_x):
+        drag_start_x, drag_start_y = start_x, start_y
+        drag_end_x, drag_end_y = end_x, end_y
+    else: # upward drag or right-to-left on same line
+        drag_start_x, drag_start_y = end_x, end_y
+        drag_end_x, drag_end_y = start_x, start_y
+
+    for y in range(drag_start_y, drag_end_y + 1):
+        x1, x2 = -1, -1
+        if drag_start_y == drag_end_y: # single line selection
+            x1, x2 = drag_start_x, drag_end_x
+        elif y == drag_start_y: # first line of multi-line selection
+            x1, x2 = drag_start_x, pane_x2
+        elif y == drag_end_y: # last line of multi-line selection
+            x1, x2 = pane_x1, drag_end_x
+        else: # middle line of multi-line selection
+            x1, x2 = pane_x1, pane_x2
+        
+        # Clamp selection to pane boundaries
+        x1 = max(x1, pane_x1)
+        x2 = min(x2, pane_x2)
 
-    for y in range(y1, y2 + 1):
         try:
-            # chgat can fail at the bottom-right corner of the screen
+            if x1 < state.width and x1 <= x2:
-            if x1 < state.width:
+                length = x2 - x1 + 1
-                # `width-1` is the last valid column
-                end_col = min(x2, state.width - 1)
-                length = end_col - x1 + 1
                 if length > 0:
                     stdscr.chgat(y, x1, length, curses.A_REVERSE)
         except curses.error:
@@ -357,33 +373,54 @@ def copy_selection_to_clipboard(stdscr, state):
         return
 
     start_x, start_y = state.selection_start_coord
-    _, end_y = state.selection_end_coord
+    end_x, end_y = state.selection_end_coord
-
-    y1, y2 = min(start_y, end_y), max(start_y, end_y)
 
     # Determine pane from where selection started
     pane = 'left' if start_x < state.divider_col else 'right'
-
     if pane == 'left':
-        x1, x2 = 0, state.divider_col - 1
+        pane_x1, pane_x2 = 0, state.divider_col - 1
     else: # right
-        x1, x2 = state.divider_col + 2, state.width - 1
+        pane_x1, pane_x2 = state.divider_col + 2, state.width - 1
+
+    # Determine drag direction to handle multi-line selection correctly
+    if start_y < end_y or (start_y == end_y and start_x <= end_x):
+        drag_start_x, drag_start_y = start_x, start_y
+        drag_end_x, drag_end_y = end_x, end_y
+    else: # upward drag or right-to-left on same line
+        drag_start_x, drag_start_y = end_x, end_y
+        drag_end_x, drag_end_y = start_x, start_y
 
     height, width = stdscr.getmaxyx()
     selected_text_parts = []
 
-    for y in range(y1, y2 + 1):
+    for y in range(drag_start_y, drag_end_y + 1):
-        if 0 <= y < height:
+        if not (0 <= y < height):
-            line_str = ""
+            continue
-            end_col = min(x2, width - 1)
+
-            for x in range(x1, end_col + 1):
+        x1, x2 = -1, -1
+        if drag_start_y == drag_end_y: # single line selection
+            x1, x2 = drag_start_x, drag_end_x
+        elif y == drag_start_y: # first line of multi-line selection
+            x1, x2 = drag_start_x, pane_x2
+        elif y == drag_end_y: # last line of multi-line selection
+            x1, x2 = pane_x1, drag_end_x
+        else: # middle line of multi-line selection
+            x1, x2 = pane_x1, pane_x2
+        
+        # Clamp selection to pane boundaries and screen width
+        x1 = max(x1, pane_x1)
+        x2 = min(x2, pane_x2, width - 1)
+
+        line_str = ""
+        if x1 <= x2:
+            for x in range(x1, x2 + 1):
                 try:
                     char_and_attr = stdscr.inch(y, x)
                     char = char_and_attr & 0xFF
                     line_str += chr(char)
                 except curses.error:
                     line_str += " "
-            selected_text_parts.append(line_str.rstrip())
+        selected_text_parts.append(line_str)
 
     if selected_text_parts:
         text_to_copy = "\n".join(selected_text_parts)