#!/usr/bin/env python3

# vim: set ft=python:

import datetime
import ipaddress
import os
import sys
import sys.path


def generate_hosts_entry(ip_address_str, hostnames):
    """
    Generates a string formatted for /etc/hosts after validating the IP address.

    Args:
        ip_address_str (str): The IP address string.
        hostnames (list): A list of hostname strings.

    Returns:
        str: A formatted string for /etc/hosts, or None if validation fails.
    """
    try:
        # Validate the IP address
        ip = ipaddress.ip_address(ip_address_str)
    except ValueError:
        print(f"Error: '{ip_address_str}' is not a valid IP address.", file=sys.stderr)
        return None

    # Join hostnames with spaces
    hostnames_str = " ".join(hostnames)

    # Return the formatted line
    return f"{ip}    {hostnames_str}"


def append_hosts_entry(entry, hosts_file="/etc/hosts"):
    when = datetime.datetime.now().strftime("%Y-%m-%d %H:%M")
    try:
        with open(hosts_file, "a") as fp:
            fp.write(f"# Added by add_hosts_entry {when}\n{entry}\n")
        return True
    except PermissionError:
        if os.geteuid() == 0:
            print(f"Error: failed opening {hosts_file} for writing.",
                  file=sys.stderr)
            return False
        return relaunch_with_sudo()


def relaunch_with_sudo():
    script_abspath = os.path.abspath(sys.argv[0])
    os.execvp("sudo", [script_abspath] + sys.argv[1:])


if __name__ == "__main__":
    # Check for correct number of arguments
    if len(sys.argv) < 3:
        print("Usage: python3 generate_hosts_entry.py <ip_address> <hostname1> [hostname2 ...]", file=sys.stderr)
        sys.exit(1)

    ip_to_add = sys.argv[1]
    hostnames_to_add = sys.argv[2:]

    # Generate the entry
    entry = generate_hosts_entry(ip_to_add, hostnames_to_add)
    if not entry:
        sys.exit(1)
    if not append_hosts_entry(entry):
        sys.exit(1)