refactor: Improve diff parsing and display logic for deleted and added lines

gtm

@@ -24,49 +24,58 @@ def get_diff_info(current_commit, prev_commit, filename):
         # For the first commit, we can't compare with a previous one
         return [], []
     
-    # Get additions
-    cmd_additions = ['git', 'diff', '--unified=0', prev_commit, current_commit, '--', filename]
-    result_additions = subprocess.run(cmd_additions, capture_output=True, text=True)
+    # Use a more detailed diff format to better understand the changes
+    cmd = ['git', 'diff', prev_commit, current_commit, '--', filename]
+    result = subprocess.run(cmd, capture_output=True, text=True)
     
+    # Parse the diff output to extract added and deleted lines
+    lines = result.stdout.splitlines()
+    
+    # Store line changes with their positions
     added_lines = []
     deleted_lines = []
     
-    # Initialize variables outside the loop to avoid UnboundLocalError
-    start_line = 0
-    del_start = 0
+    # Track the current position in the new file
+    current_line_num = 0
+    deletion_offset = 0
     
-    for line in result_additions.stdout.splitlines():
-        # Parse the diff output to find line numbers of additions and deletions
+    # Parse the diff output
+    i = 0
+    while i < len(lines):
+        line = lines[i]
+        
+        # Parse hunk headers to get line numbers
         if line.startswith('@@'):
-            # Parse the hunk header to get line numbers
+            # Format is like @@ -a,b +c,d @@
             parts = line.split()
             if len(parts) >= 3:
-                # Format is like @@ -a,b +c,d @@
-                # We're interested in the +c,d part for additions
+                # Extract the starting line number in the new file
                 add_part = parts[2][1:]  # Remove the + sign
                 if ',' in add_part:
-                    start_line, count = map(int, add_part.split(','))
+                    current_line_num, _ = map(int, add_part.split(','))
                 else:
-                    start_line, count = int(add_part), 1
+                    current_line_num = int(add_part)
                 
-                # For deletions, we look at the -a,b part
-                del_part = parts[1][1:]  # Remove the - sign
-                if ',' in del_part:
-                    del_start, del_count = map(int, del_part.split(','))
-                else:
-                    del_start, del_count = int(del_part), 1
+                # Reset deletion offset for this hunk
+                deletion_offset = 0
+        
+        # Process added lines
         elif line.startswith('+') and not line.startswith('+++'):
-            # This is an added line
-            added_lines.append((start_line, line[1:]))
-            start_line += 1
+            added_lines.append((current_line_num, line[1:]))
+            current_line_num += 1
+        
+        # Process deleted lines
         elif line.startswith('-') and not line.startswith('---'):
-            # This is a deleted line
-            deleted_lines.append((del_start, line[1:]))
-            del_start += 1
+            # Store deleted lines with the position where they would have been
+            # in the new file (before the next line)
+            deleted_lines.append((current_line_num, line[1:]))
+            deletion_offset += 1
+        
+        # Process context lines
         elif not line.startswith('+') and not line.startswith('-') and not line.startswith('@@'):
-            # Context line, increment both counters
-            start_line += 1
-            del_start += 1
+            current_line_num += 1
+        
+        i += 1
     
     return added_lines, deleted_lines
 
@@ -167,12 +176,30 @@ def main(stdscr, filename, show_additions=False, show_deletions=False):
         # Draw file content (right pane) - more efficiently
         right_width = width - divider_col - 3
         
-        # First, collect all lines to display (regular and deleted)
+        # First, collect all lines to display (regular, added, and deleted)
         display_lines = []
         
+        # Create a map of line numbers to deleted lines for faster lookup
+        deleted_line_map = {}
+        if show_deletions:
+            for del_line_num, del_content in deleted_lines:
+                if del_line_num not in deleted_line_map:
+                    deleted_line_map[del_line_num] = []
+                deleted_line_map[del_line_num].append(del_content)
+        
+        # Process each visible line
         for i, line in enumerate(visible_lines):
             line_num = i + scroll_offset + 1  # 1-based line number
             
+            # First add any deleted lines that come before this line
+            if show_deletions and line_num in deleted_line_map:
+                for del_content in deleted_line_map[line_num]:
+                    display_lines.append({
+                        'type': 'deleted',
+                        'content': del_content,
+                        'line_num': line_num
+                    })
+            
             # Check if this is an added line
             is_added = False
             if show_additions:
@@ -187,22 +214,6 @@ def main(stdscr, filename, show_additions=False, show_deletions=False):
                 'content': line,
                 'line_num': line_num
             })
-            
-            # If showing deletions, check if there are deleted lines at this position
-            if show_deletions:
-                # Collect all deleted lines at this position
-                deleted_at_position = []
-                for del_line_num, del_line_content in deleted_lines:
-                    if del_line_num == line_num:
-                        deleted_at_position.append(del_line_content)
-                
-                # Add all deleted lines together after the current line
-                for del_content in deleted_at_position:
-                    display_lines.append({
-                        'type': 'deleted',
-                        'content': del_content,
-                        'line_num': line_num
-                    })
         
         # Now display all lines
         display_row = 0