import ipaddress
import shutil
import subprocess
from typing import Optional


def check_installed() -> bool:
    """Check if tcpdump is installed and available on the system path."""
    return shutil.which('tcpdump') is not None


def ensure_installed():
    """Ensure that tcpdump is installed, raise an error if not."""
    if not check_installed():
        raise RuntimeError('tcpdump is not installed. Please install it to continue.')


def list_interfaces() -> str:
    """List available network interfaces using tcpdump."""
    ensure_installed()
    try:
        result = subprocess.run(['tcpdump', '--list-interfaces'], capture_output=True, text=True, check=True)
        print(result.stdout)
    except subprocess.CalledProcessError as e:
        print(f'Failed to list interfaces: {e}')
        return ''


def is_valid_ipv4(ip: str) -> bool:
    try:
        ipaddress.IPv4Address(ip)
        return True
    except ValueError:
        return False

def str_to_ipv4(ip: str) -> (bool, Optional[ipaddress]):
    try:
        address = ipaddress.IPv4Address(ip)
        return address == ipaddress.IPv4Address(ip), address
    except ipaddress.AddressValueError:
        return False, None