Timer program created using ChatGPT.

timer.py

#! /usr/bin/env python

"""
This program was created using ChatGPT (GPT4) with the following prompt:

    You are an expert python programmer. Create a command-line program that accepts
    a time interval as a string of "hours:minutes:seconds" and displays a small window
    in which the interval counts down by seconds. It should also display a progress bar
    that decreases each second until it reaches zero and the timer expires.
    Upon expiration, an audible tone should be created. Produce commented Python code.

Further prompts were:

    please edit the program so the remaining time is displayed as "hours:minutes:seconds".

    Use argparse to accept mandatory time interval and title and also an optional command 
    to be executed when the timer elapses.

After that, I manually edited the program to add an option to repeat the timer once it expired.
"""

import sys
import time
import argparse
import subprocess
import tkinter as tk
from tkinter import ttk
import playsound
import pathlib

# Function to update the timer and progress bar
def update_timer():
    remaining_time = int(timer_var.get())

    # Update the progress bar and timer label
    progress_bar['value'] = remaining_time
    timer_label.config(text=gmtime_str(remaining_time))

    if remaining_time <= 0:
        # Play an audible tone when the timer expires
        playsound.playsound(pathlib.Path.home() / "bin/notify.mp3")
        # Execute the optional command
        if args.command:
            subprocess.Popen(args.command, shell=True)
        root.destroy()
    else:
        root.after(1000, update_timer)
        timer_var.set(remaining_time - 1)

# Convert seconds to "HH:MM:SS" while removing any leading "00:". 
def gmtime_str(seconds):
    time_str = time.strftime("%H:%M:%S", time.gmtime(seconds))
    while time_str.startswith("00:"):
        time_str = time_str[len("00:"):]
    return time_str

# Convert the input time interval to seconds
def time_to_seconds(time_str):
    hms = map(int, time_str.split(':'))
    secs = 0
    for v in hms:
        secs = secs * 60 + v
    return secs

if __name__ == "__main__":
    # Parse command-line arguments
    parser = argparse.ArgumentParser(description="Countdown timer with optional command execution")
    parser.add_argument("time", help="Time interval in the format hours:minutes:seconds")
    parser.add_argument("-t", "--title", default="Countdown", help="Title for the countdown timer window")
    parser.add_argument("-c", "--command", help="Optional command to be executed when the timer elapses")
    parser.add_argument("-r", "--repeat", type=int, default=1, help="Reset the timer and repeat on expiration.")
    args = parser.parse_args()

    for _ in range(args.repeat):
        total_seconds = time_to_seconds(args.time)

        # Create the main window
        root = tk.Tk()
        root.title(args.title)

        # Create a label to display the timer
        timer_var = tk.StringVar()
        timer_var.set(total_seconds)
        timer_label = tk.Label(root, text=time.strftime("%H:%M:%S", time.gmtime(total_seconds)), font=("Helvetica", 24))
        timer_label.pack(pady=10)

        # Create a progress bar
        progress_bar = ttk.Progressbar(root, orient="horizontal", length=300, mode="determinate")
        progress_bar.pack(pady=10)
        progress_bar['maximum'] = total_seconds
        progress_bar['value'] = total_seconds

        # Start the countdown
        update_timer()

        # Run the main loop
        root.mainloop()