# services/local_net.py
import subprocess
import re

def _sh(cmd):
    out = subprocess.check_output(cmd, text=True)
    return out

def get_eth0_dhcp_snapshot():
    """
    Returns {'iface':'eth0','cidr':'X.X.X.X/YY','ip':'X.X.X.X','prefixlen':YY,'gw':'A.B.C.D'}
    Raises on failure.
    """
    iface = "eth0"

    # ip -o -4 addr show dev eth0 | awk '{print $4}'
    addrs = _sh(["/sbin/ip", "-o", "-4", "addr", "show", "dev", iface]).strip()
    if not addrs:
        addrs = _sh(["ip", "-o", "-4", "addr", "show", "dev", iface]).strip()

    m = re.search(r"\s(\d+\.\d+\.\d+\.\d+/\d+)\s", addrs)
    if not m:
        raise RuntimeError(f"No IPv4 address on {iface}")
    cidr = m.group(1)
    ip = cidr.split("/")[0]
    prefixlen = int(cidr.split("/")[1])

    # ip route show default dev eth0 | awk '/default/ {print $3}'
    routes = _sh(["/sbin/ip", "route", "show", "default", "dev", iface])
    if not routes:
        routes = _sh(["ip", "route", "show", "default", "dev", iface])

    m2 = re.search(r"default via (\d+\.\d+\.\d+\.\d+)", routes)
    gw = m2.group(1) if m2 else ""

    return {
        "iface": iface,
        "cidr": cidr,
        "ip": ip,
        "prefixlen": prefixlen,
        "gw": gw
    }