#!/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 mDNS-resolves each responder (avahi-resolve, bounded
# per-IP timeout so one non-mDNS device can't stall the whole run), and dumps
# ip+mac+state+mdnsHostname 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

MDNS_DIR="$(mktemp -d)"
trap 'rm -rf "$MDNS_DIR"' EXIT

# `ip neigh show dev <iface>` output: "<ip> lladdr <mac> <state> [router]"
mapfile -t neighbors < <(ip neigh show dev "$IFACE")

i=0
for line in "${neighbors[@]}"; do
  read -r ip _ mac state _ <<< "$line"
  [[ "$ip" == *:* ]] && continue
  [[ -z "$mac" ]] && continue
  case "$state" in
    REACHABLE|STALE|DELAY|PERMANENT) ;;
    *) continue ;;
  esac
  (
    hostname=$(timeout 2 avahi-resolve -a "$ip" 2>/dev/null | awk '{print $2}')
    echo "${hostname:-}" > "$MDNS_DIR/$ip"
  ) &
  i=$((i + 1))
  if (( i % 32 == 0 )); then wait; fi
done
wait

TMP_FILE="$(mktemp)"
{
  echo "["
  first=1
  for line in "${neighbors[@]}"; do
    read -r ip _ mac state _ <<< "$line"
    [[ "$ip" == *:* ]] && continue
    [[ -z "$mac" ]] && continue
    case "$state" in
      REACHABLE|STALE|DELAY|PERMANENT) ;;
      *) continue ;;
    esac
    mdns=""
    [[ -f "$MDNS_DIR/$ip" ]] && mdns=$(cat "$MDNS_DIR/$ip")
    # Minimal JSON string escaping -- mDNS hostnames come from the network,
    # not a source we control.
    mdns="${mdns//\\/\\\\}"
    mdns="${mdns//\"/\\\"}"
    [[ $first -eq 0 ]] && echo ","
    first=0
    if [[ -n "$mdns" ]]; then
      printf '{"ip":"%s","mac":"%s","state":"%s","mdnsHostname":"%s"}' "$ip" "$mac" "$state" "$mdns"
    else
      printf '{"ip":"%s","mac":"%s","state":"%s"}' "$ip" "$mac" "$state"
    fi
  done
  echo
  echo "]"
} > "$TMP_FILE"

mv "$TMP_FILE" "$OUTPUT_FILE"