#!/usr/bin/env bash
set -euo pipefail

export LC_ALL=C

RUNTIME_DIR="${HARBOR_RUNTIME_DIR:-$HOME/.vpn-proxy-client/.runtime}"
STATE_FILE="$RUNTIME_DIR/network.json"
ROUTE_BIN="${HARBOR_ROUTE_BIN:-/sbin/route}"
ARP_BIN="${HARBOR_ARP_BIN:-/usr/sbin/arp}"
NETSTAT_BIN="${HARBOR_NETSTAT_BIN:-/usr/sbin/netstat}"

route_info="$($ROUTE_BIN -n get default 2>/dev/null || true)"
gateway="$(awk '/^[[:space:]]*gateway:/{print $2; exit}' <<<"$route_info")"
network_interface="$(awk '/^[[:space:]]*interface:/{print $2; exit}' <<<"$route_info")"

if [[ -z "$gateway" || -z "$network_interface" ]]; then
  read -r gateway network_interface < <(
    "$NETSTAT_BIN" -rn -f inet 2>/dev/null \
      | awk '$1 == "default" && $2 ~ /^[0-9]+\./ { print $2, $4; exit }'
  ) || true
fi

if [[ ! "$gateway" =~ ^([0-9]{1,3}\.){3}[0-9]{1,3}$ ]]; then
  gateway=""
  network_interface=""
fi
if [[ ! "$network_interface" =~ ^[a-zA-Z0-9._-]{1,32}$ ]]; then
  network_interface=""
fi

mac=""
if [[ -n "$gateway" ]]; then
  mac="$($ARP_BIN -n "$gateway" 2>/dev/null | awk '/ at /{print $4; exit}' || true)"
  if [[ ! "$mac" =~ ^[a-fA-F0-9]{2}(:[a-fA-F0-9]{2}){5}$ ]]; then
    mac=""
  else
    mac="$(printf '%s' "$mac" | tr '[:upper:]' '[:lower:]')"
  fi
fi

mkdir -p "$RUNTIME_DIR"
tmp="$(mktemp "${STATE_FILE}.XXXXXX")"
trap 'rm -f "$tmp"' EXIT
printf '{"gateway":"%s","interface":"%s","mac":"%s","observedAt":"%s"}\n' \
  "$gateway" "$network_interface" "$mac" "$(date -u '+%Y-%m-%dT%H:%M:%SZ')" > "$tmp"
mv "$tmp" "$STATE_FILE"