#!/bin/bash
# Runs on the CT122 host (not in a container) via the homelab-monitor-discover
# systemd timer. Real ARP entries live in the host's network namespace, not an
# isolated Docker bridge network, so this has to run here rather than inside
# the api container — see docs/device-discovery.md.
#
# Pings every address in the subnet (ICMP only, no port scanning) to populate
# the ARP cache, then dumps ip+mac+state pairs as JSON. The API service reads
# this file and does known/unknown labeling using config/hosts.yaml.
set -euo pipefail

SUBNET_PREFIX="${SUBNET_PREFIX:-192.168.1}"
OUTPUT_FILE="${OUTPUT_FILE:-/opt/homelab-monitor/data/devices-raw.json}"
IFACE="${IFACE:-eth0}"

mkdir -p "$(dirname "$OUTPUT_FILE")"

for i in $(seq 1 254); do
  ping -c 1 -W 1 "${SUBNET_PREFIX}.${i}" >/dev/null 2>&1 &
  # cap concurrency so we don't fork 254 pings at once
  if (( i % 32 == 0 )); then wait; fi
done
wait

TMP_FILE="$(mktemp)"
{
  echo "["
  first=1
  # `ip neigh show dev <iface>` output: "<ip> lladdr <mac> <state> [router]"
  while read -r ip _ mac state _; do
    [[ "$ip" == *:* ]] && continue  # skip IPv6 (link-local neighbor entries)
    [[ -z "$mac" ]] && continue
    case "$state" in
      REACHABLE|STALE|DELAY|PERMANENT) ;;
      *) continue ;;
    esac
    [[ $first -eq 0 ]] && echo ","
    first=0
    printf '{"ip":"%s","mac":"%s","state":"%s"}' "$ip" "$mac" "$state"
  done < <(ip neigh show dev "$IFACE")
  echo
  echo "]"
} > "$TMP_FILE"

mv "$TMP_FILE" "$OUTPUT_FILE"