feat: Add --diff-additions and --diff-deletions options with line highlighting

gtm

@@ -4,6 +4,7 @@ import curses
 import os
 import subprocess
 import sys
+import argparse
 
 VERSION = "2025-06-07"
 
@@ -17,7 +18,55 @@ def get_file_at_commit(commit_hash, filename):
     result = subprocess.run(cmd, capture_output=True, text=True)
     return result.stdout.splitlines()
 
-def main(stdscr, filename):
+def get_diff_info(current_commit, prev_commit, filename):
+    """Get diff information between two commits for a file"""
+    if not prev_commit:
+        # 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)
+    
+    added_lines = []
+    deleted_lines = []
+    
+    for line in result_additions.stdout.splitlines():
+        # Parse the diff output to find line numbers of additions and deletions
+        if line.startswith('@@'):
+            # Parse the hunk header to get line numbers
+            parts = line.split()
+            if len(parts) >= 3:
+                # Format is like @@ -a,b +c,d @@
+                # We're interested in the +c,d part for additions
+                add_part = parts[2][1:]  # Remove the + sign
+                if ',' in add_part:
+                    start_line, count = map(int, add_part.split(','))
+                else:
+                    start_line, count = int(add_part), 1
+                
+                # 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
+        elif line.startswith('+') and not line.startswith('+++'):
+            # This is an added line
+            added_lines.append((start_line, line[1:]))
+            start_line += 1
+        elif line.startswith('-') and not line.startswith('---'):
+            # This is a deleted line
+            deleted_lines.append((del_start, line[1:]))
+            del_start += 1
+        elif not line.startswith('+') and not line.startswith('-') and not line.startswith('@@'):
+            # Context line, increment both counters
+            start_line += 1
+            del_start += 1
+    
+    return added_lines, deleted_lines
+
+def main(stdscr, filename, show_additions=False, show_deletions=False):
     curses.curs_set(0)
     curses.mousemask(curses.ALL_MOUSE_EVENTS)
     curses.mouseinterval(0)
@@ -28,6 +77,8 @@ def main(stdscr, filename):
         curses.use_default_colors()  # Use terminal's default colors
         curses.init_pair(1, 5, 7)  # Focused status bar
         curses.init_pair(2, curses.COLOR_WHITE, 8)   # Unfocused status bar
+        curses.init_pair(3, curses.COLOR_GREEN, -1)  # Added lines
+        curses.init_pair(4, curses.COLOR_RED, -1)    # Deleted lines
         
     # Initialize key variable
     key = 0
@@ -45,6 +96,17 @@ def main(stdscr, filename):
     commit_hash = commits[selected_commit].split()[0]
     file_lines = get_file_at_commit(commit_hash, filename)
     
+    # Get previous commit hash for diff
+    prev_commit_hash = None
+    if selected_commit < len(commits) - 1:
+        prev_commit_hash = commits[selected_commit + 1].split()[0]
+    
+    # Get diff information if needed
+    added_lines = []
+    deleted_lines = []
+    if show_additions or show_deletions:
+        added_lines, deleted_lines = get_diff_info(commit_hash, prev_commit_hash, filename)
+    
     # Enable nodelay for smoother scrolling
     stdscr.nodelay(True)
     
@@ -57,6 +119,14 @@ def main(stdscr, filename):
             commit_hash = commits[selected_commit].split()[0]
             file_lines = get_file_at_commit(commit_hash, filename)
             
+            # Update diff information when commit changes
+            prev_commit_hash = None
+            if selected_commit < len(commits) - 1:
+                prev_commit_hash = commits[selected_commit + 1].split()[0]
+            
+            if show_additions or show_deletions:
+                added_lines, deleted_lines = get_diff_info(commit_hash, prev_commit_hash, filename)
+            
         max_scroll = max(0, len(file_lines) - (height - 1))
         scroll_offset = min(scroll_offset, max_scroll)
         visible_lines = file_lines[scroll_offset:scroll_offset + height - 1]
@@ -95,7 +165,33 @@ def main(stdscr, filename):
         for i, line in enumerate(visible_lines):
             # Only draw what fits in the window
             if i < height - 1:
-                stdscr.addnstr(i, divider_col + 2, line, right_width)
+                line_num = i + scroll_offset + 1  # 1-based line number
+                
+                # Check if this is an added line
+                is_added = False
+                if show_additions:
+                    for added_line_num, _ in added_lines:
+                        if added_line_num == line_num:
+                            is_added = True
+                            break
+                
+                # Display the line with appropriate formatting
+                if is_added:
+                    stdscr.addstr(i, divider_col + 2, "+ ", curses.color_pair(3))
+                    stdscr.addnstr(i, divider_col + 4, line, right_width - 2, curses.color_pair(3))
+                else:
+                    stdscr.addnstr(i, divider_col + 2, line, right_width)
+                
+                # Display deleted lines if enabled
+                if show_deletions:
+                    # Check if there are deleted lines after the current line
+                    for del_line_num, del_line_content in deleted_lines:
+                        if del_line_num == line_num:
+                            # Only show if we have space
+                            if i + 1 < height - 1:
+                                i += 1  # Move to next line for displaying the deleted content
+                                stdscr.addstr(i, divider_col + 2, "- ", curses.color_pair(4))
+                                stdscr.addnstr(i, divider_col + 4, del_line_content, right_width - 2, curses.color_pair(4))
 
         # Status bars for both panes
         visible_height = height - 1  # Reserve 1 line for the status bar
@@ -226,30 +322,37 @@ def show_help():
     print("A \"Git Time Machine\" for viewing file history.")
     print()
     print("Usage:")
-    print("\tgtm FILENAME")
+    print("\tgtm [OPTIONS] FILENAME")
     print()
-    print("Flags:")
+    print("Options:")
+    print("\t--diff-additions\thighlight newly added lines in green")
+    print("\t--diff-deletions\tshow deleted lines in red")
     print("\t-v, --version\tshow version number")
     print("\t-h, --help\tshow this help")
 
 if __name__ == "__main__":
-    if len(sys.argv) == 2:
-        if sys.argv[1] == "-v" or sys.argv[1] == "--version":
-            print(f"gtm version {VERSION}")
-            sys.exit(0)
-        elif sys.argv[1] == "-h" or sys.argv[1] == "--help":
-            show_help()
-            sys.exit(0)
-        
-        filename = sys.argv[1]
-        
-        # Check if the file exists
-        if not os.path.isfile(filename):
-            print(f"Error: File '{filename}' does not exist")
-            sys.exit(1)
-            
-        curses.wrapper(main, filename)
-    else:
+    parser = argparse.ArgumentParser(add_help=False, description="A Git Time Machine for viewing file history.")
+    parser.add_argument("--diff-additions", action="store_true", help="Highlight newly added lines in green")
+    parser.add_argument("--diff-deletions", action="store_true", help="Show deleted lines in red")
+    parser.add_argument("-v", "--version", action="store_true", help="Show version number")
+    parser.add_argument("-h", "--help", action="store_true", help="Show help information")
+    parser.add_argument("filename", nargs="?", help="File to view history for")
+    
+    args = parser.parse_args()
+    
+    if args.version:
+        print(f"gtm version {VERSION}")
+        sys.exit(0)
+    elif args.help or not args.filename:
         show_help()
+        sys.exit(0 if args.help else 1)
+    
+    filename = args.filename
+    
+    # Check if the file exists
+    if not os.path.isfile(filename):
+        print(f"Error: File '{filename}' does not exist")
         sys.exit(1)
+        
+    curses.wrapper(main, filename, args.diff_additions, args.diff_deletions)