1 files changed, 75 insertions, 3 deletions
diff --git a/cmd2/cmd2.py b/cmd2/cmd2.py
index d817e461..baf511f3 100644
--- a/cmd2/cmd2.py
+++ b/cmd2/cmd2.py
@@ -50,7 +50,7 @@ from .clipboard import can_clip, get_paste_buffer, write_to_paste_buffer
 from .parsing import StatementParser, Statement
 
 # Set up readline
-from .rl_utils import rl_type, RlType, rl_get_point
+from .rl_utils import rl_type, RlType, rl_get_point, rl_set_prompt
 if rl_type == RlType.NONE:  # pragma: no cover
     rl_warning = "Readline features including tab completion have been disabled since no \n" \
                  "supported version of readline was found. To resolve this, install \n" \
@@ -3248,6 +3248,64 @@ Script should contain one command per line, just like command would be typed in
         # Redraw the prompt and input line
         rl_force_redisplay()
 
+    def update_prompt(self, new_prompt: str) -> None:
+        """
+        Used to display an important message to the user while they are at the prompt.
+        The current prompt and input lines are erased, then the alert is printed in their place, and
+        finally the prompt and input lines restored below the alert. To the user it appears as if
+        an alert message is printed above the prompt.
+
+        :param alert_msg: the message to display to the user
+        """
+        if rl_type == RlType.NONE:
+            return
+
+        import shutil
+        import colorama.ansi as ansi
+        from colorama import Cursor
+
+        visible_prompt = self.visible_prompt
+
+        # Get the size of the terminal
+        terminal_size = shutil.get_terminal_size()
+
+        # Figure out how many lines the prompt and user input take up
+        total_str_size = len(visible_prompt) + len(readline.get_line_buffer())
+        num_input_lines = int(total_str_size / terminal_size.columns) + 1
+
+        # Get the cursor's offset from the beginning of the first input line
+        cursor_input_offset = len(visible_prompt) + rl_get_point()
+
+        # Calculate what input line the cursor is on
+        cursor_input_line = int(cursor_input_offset / terminal_size.columns) + 1
+
+        # Create a string that will clear all input lines
+        terminal_str = ''
+
+        # Move the cursor down to the last input line
+        if cursor_input_line != num_input_lines:
+            terminal_str += Cursor.DOWN(num_input_lines - cursor_input_line)
+
+        # Clear each input line from the bottom up so that the cursor ends up on the original first input line
+        terminal_str += (ansi.clear_line() + Cursor.UP(1)) * (num_input_lines - 1)
+        terminal_str += ansi.clear_line()
+
+        # Move the cursor to the beginning of the line
+        terminal_str += '\r'
+
+        # Set the new prompt
+        rl_set_prompt(new_prompt)
+        self.prompt = new_prompt
+
+        # Write the string to the terminal
+        if rl_type == RlType.GNU:
+            sys.stdout.write(terminal_str)
+        elif rl_type == RlType.PYREADLINE:
+            readline.rl.mode.console.write(terminal_str)
+
+        # Redraw the prompt and input line
+        rl_force_redisplay()
+
     def alerter(self):
         import time
         while True:
@@ -3259,8 +3317,22 @@ Script should contain one command per line, just like command would be typed in
 
     def do_alert(self, args):
         import threading
-        printer = threading.Thread(target=self.alerter, daemon=True)
-        printer.start()
+        alert_thread = threading.Thread(target=self.alerter, daemon=True)
+        alert_thread.start()
+
+    def prompt_changer(self):
+        import time
+        counter = 1
+        while True:
+            time.sleep(1)
+            self.update_prompt("({:>3}) ".format(counter))
+            counter += 1
+
+    def do_update_prompt(self, args):
+        import threading
+        self.prompt = "(  0) "
+        change_thread = threading.Thread(target=self.prompt_changer, daemon=True)
+        change_thread.start()
 
     def cmdloop(self, intro: Optional[str]=None) -> None:
         """This is an outer wrapper around _cmdloop() which deals with extra features provided by cmd2.