import shutil
import subprocess


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)
        return result.stdout
    except subprocess.CalledProcessError as e:
        print(f"Failed to list interfaces: {e}")
        return ""


def start_tcpdump():
    return None