feat: Add change navigation with visual markers and keyboard shortcuts

gtm

@@ -132,9 +132,28 @@ class AppState:
     
     # Line wrapping settings
     wrap_lines: bool = True
+    
+    # Change navigation
+    change_positions: List[int] = field(default_factory=list)
+    current_change_idx: int = -1  # -1 means no change is selected
 
 # --- Actions (Controller) ---
 
+def calculate_change_positions(state: AppState) -> AppState:
+    """Calculate positions of all changes (additions and deletions) in the file."""
+    positions = []
+    # Add positions of added lines
+    for line_num, _ in state.added_lines:
+        if line_num not in positions:
+            positions.append(line_num)
+    # Add positions of deleted lines
+    for line_num, _ in state.deleted_lines:
+        if line_num not in positions:
+            positions.append(line_num)
+    # Sort positions
+    positions.sort()
+    return replace(state, change_positions=positions, current_change_idx=-1)
+
 def load_commit_content(state: AppState) -> AppState:
     if not state.commits:
         return state
@@ -173,12 +192,15 @@ def load_commit_content(state: AppState) -> AppState:
     
     right_scroll_offset = max(0, min(right_scroll_offset, max_scroll_new))
 
-    return replace(state,
+    new_state = replace(state,
         file_lines=file_lines,
         added_lines=added_lines,
         deleted_lines=deleted_lines,
         right_scroll_offset=right_scroll_offset
     )
+    
+    # Calculate change positions for navigation
+    return calculate_change_positions(new_state)
 
 def update_dimensions(state: AppState, height: int, width: int) -> AppState:
     return replace(state, height=height, width=width)
@@ -240,6 +262,82 @@ def draw_left_pane(stdscr, state):
         if display_index == state.selected_commit_idx:
             stdscr.attroff(curses.A_REVERSE)
 
+def jump_to_next_change(state: AppState) -> AppState:
+    """Jump to the next change after the current scroll position."""
+    if not state.change_positions:
+        return state
+    
+    # Find the next change after current position
+    current_pos = state.right_scroll_offset
+    next_idx = -1
+    for i, pos in enumerate(state.change_positions):
+        if pos > current_pos:
+            next_idx = i
+            break
+    
+    # If no next change found, wrap to the first change
+    if next_idx == -1 and state.change_positions:
+        next_idx = 0
+    
+    if next_idx != -1:
+        new_scroll = state.change_positions[next_idx]
+        return replace(state, right_scroll_offset=new_scroll, current_change_idx=next_idx)
+    return state
+
+def jump_to_prev_change(state: AppState) -> AppState:
+    """Jump to the previous change before the current scroll position."""
+    if not state.change_positions:
+        return state
+    
+    # Find the previous change before current position
+    current_pos = state.right_scroll_offset
+    prev_idx = -1
+    for i in range(len(state.change_positions) - 1, -1, -1):
+        if state.change_positions[i] < current_pos:
+            prev_idx = i
+            break
+    
+    # If no previous change found, wrap to the last change
+    if prev_idx == -1 and state.change_positions:
+        prev_idx = len(state.change_positions) - 1
+    
+    if prev_idx != -1:
+        new_scroll = state.change_positions[prev_idx]
+        return replace(state, right_scroll_offset=new_scroll, current_change_idx=prev_idx)
+    return state
+
+def draw_change_markers(stdscr, state):
+    """Draw markers in the scrollbar area to indicate where changes are located."""
+    if not state.change_positions or not (state.show_whole_diff or state.show_additions or state.show_deletions):
+        return
+    
+    right_start = 0 if not state.show_sidebar else state.divider_col + 2
+    right_width = state.width - right_start - 1
+    marker_col = right_start + right_width - 1
+    
+    # Calculate scaling factor for marker positions
+    total_lines = len(state.file_lines)
+    if total_lines <= 1:
+        return
+    
+    scale_factor = (state.height - 1) / total_lines
+    
+    # Draw markers
+    for i, pos in enumerate(state.change_positions):
+        marker_y = int(pos * scale_factor)
+        if 0 <= marker_y < state.height - 1:
+            # Determine marker color based on change type
+            is_addition = any(added_line_num == pos for added_line_num, _ in state.added_lines)
+            is_deletion = any(del_line_num == pos for del_line_num, _ in state.deleted_lines)
+            
+            attr = curses.color_pair(3) if is_addition else curses.color_pair(4)
+            marker_char = '>' if i == state.current_change_idx else '|'
+            
+            try:
+                stdscr.addch(marker_y, marker_col, marker_char, attr)
+            except curses.error:
+                pass
+
 def draw_right_pane(stdscr, state):
     # If sidebar is hidden, right pane starts at column 0
     right_start = 0 if not state.show_sidebar else state.divider_col + 2
@@ -415,9 +513,13 @@ def draw_status_bars(stdscr, state):
         if len(parts) >= 4:
             commit_message = parts[3]
     
-    # Add wrap indicator to commit message
+    # Add wrap indicator and change position to commit message
     wrap_indicator = " [W] " if state.wrap_lines else " [NW] "
-    commit_message = wrap_indicator + commit_message
+    change_indicator = ""
+    if state.change_positions and state.current_change_idx != -1:
+        change_indicator = f" [Change {state.current_change_idx + 1}/{len(state.change_positions)}] "
+    
+    commit_message = wrap_indicator + change_indicator + commit_message
     
     # Status bar percentages
     if len(state.file_lines) > 0:
@@ -492,6 +594,7 @@ def draw_ui(stdscr, state):
     draw_left_pane(stdscr, state)
     draw_right_pane(stdscr, state)
     draw_divider(stdscr, state)
+    draw_change_markers(stdscr, state)
     draw_status_bars(stdscr, state)
     draw_selection(stdscr, state)
     stdscr.refresh()
@@ -644,6 +747,12 @@ def handle_keyboard_input(key, state: AppState) -> AppState:
         return toggle_sidebar(state)
     elif key == ord('w'):
         return replace(state, wrap_lines=not state.wrap_lines)
+    elif key == ord('n'):
+        if state.focus == "right" and (state.show_whole_diff or state.show_additions or state.show_deletions):
+            return jump_to_next_change(state)
+    elif key == ord('p'):
+        if state.focus == "right" and (state.show_whole_diff or state.show_additions or state.show_deletions):
+            return jump_to_prev_change(state)
     elif key in [curses.KEY_LEFT, ord('h')]:
         if state.show_sidebar:
             return replace(state, focus="left")