# services/net_info.py
import subprocess
import json

def _run(cmd: list[str]) -> str:
    return subprocess.check_output(cmd, text=True).strip()

def _first_ipv4_cidr_from_ip_json(ip_json: dict) -> str | None:
    # Find first IPv4 on the interface
    for addr in ip_json.get("addr_info", []):
        if addr.get("family") == "inet" and addr.get("local") and addr.get("prefixlen") is not None:
            return f'{addr["local"]}/{addr["prefixlen"]}'
    return None

def get_iface_cidr(iface: str) -> str | None:
    # ip -j addr show dev eth0
    raw = _run(["ip", "-j", "addr", "show", "dev", iface])
    data = json.loads(raw)
    if not data:
        return None
    return _first_ipv4_cidr_from_ip_json(data[0])

def get_default_gw_for_iface(iface: str) -> str | None:
    lines = _run(["ip", "route", "show", "default", "dev", iface]).splitlines()
    for line in lines:
        parts = line.split()
        if parts and parts[0] == "default":
            try:
                idx = parts.index("via")
                return parts[idx + 1]
            except ValueError:
                continue
            except IndexError:
                continue
    return None

def get_eth0_dhcp_snapshot() -> dict:
    iface = "eth0"
    cidr = get_iface_cidr(iface) or ""
    gw   = get_default_gw_for_iface(iface) or ""
    if not cidr or not gw:
        raise RuntimeError("Could not determine eth0 CIDR and/or default gateway")
    return {"iface": iface, "cidr": cidr, "gw": gw}