#!/usr/bin/python3
import subprocess
import os
from datetime import datetime, timezone
from typing import Optional


def generate_timestamp(fmt: Optional[str] = None, utc: bool = False) -> str:
    """Return a timestamp string.

    - If `fmt` is provided, return `datetime.strftime(fmt)`.
    - If `fmt` is None, return an ISO 8601 timestamp. When `utc` is True
      the timestamp ends with 'Z' (UTC). When `utc` is False it returns
      the local time ISO format.

    Examples:
      - `generate_timestamp()` -> '2025-11-20T12:34:56Z'
      - `generate_timestamp("%Y-%m-%d %H:%M:%S")` -> '2025-11-20 12:34:56'
    """
    if fmt:
        dt = datetime.now(timezone.utc) if utc else datetime.now()
        return dt.strftime(fmt)

    dt = datetime.now(timezone.utc) if utc else datetime.now()
    if utc:
        # force trailing Z for UTC instead of +00:00
        return dt.replace(tzinfo=timezone.utc).isoformat().replace('+00:00', 'Z')
    return dt.isoformat()

print(f"Starting system update at {generate_timestamp()}")
# Update package lists
print(f"{generate_timestamp()}: Updating package lists...")
subprocess.run(['sudo', 'apt', 'update'], check=True)
# Upgrade packages
print(f"{generate_timestamp()}: Upgrading packages...")
subprocess.run(['sudo', 'apt', 'upgrade', '-y'], check=True)

# Check if reboot is required
if os.path.exists('/var/run/reboot-required'):
    print(f"{generate_timestamp()}: Reboot required. Rebooting now...")
    subprocess.run(['sudo', 'reboot'])
else:
    print(f"{generate_timestamp()}: No reboot required.")