#!/usr/bin/env bash
#
# detect_bridge.sh
#
# Detect whether there is a switch / Linux bridge between THIS host and a target host.
# - Usage: sudo ./detect_bridge.sh <target-ip-or-hostname> [interface]
# - Optional flags:
#     --mac-spoof   (runs an optional MAC-change test; disabled by default)
#
# Requires: bash, ip, ping, tcpdump, ethtool, arping, awk, grep, sed, date, awk, timeout
#           lldpctl if available (script will check).
#
# Notes:
# - Many methods require root (tcpdump, ethtool, arping). Run with sudo.
# - The script attempts safe tests first. MAC spoofing is optional and may disrupt traffic.
# - The script prints a summary and confidence estimate at the end.
#

set -euo pipefail
IFS=$'\n\t'

TARGET="$1"
IFACE="${2:-}"
MAC_SPOOF=false

# parse optional flags
for arg in "$@"; do
  if [ "$arg" = "--mac-spoof" ]; then
    MAC_SPOOF=true
  fi
done

# helper: detect default interface to reach target
detect_iface() {
  if [ -n "$IFACE" ]; then
    echo "$IFACE"
    return 0
  fi
  # Use 'ip route get' to find outgoing interface
  if route_info=$(ip route get "$TARGET" 2>/dev/null); then
    # route_info often contains "dev <iface>"
    dev=$(echo "$route_info" | awk '{for(i=1;i<=NF;i++){if($i=="dev"){print $(i+1);exit}}}')
    if [ -n "$dev" ]; then
      echo "$dev"
      return 0
    fi
  fi
  # fallback to first non-loopback up interface
  for dev in $(ls /sys/class/net); do
    if [ "$dev" != "lo" ] && [ -f "/sys/class/net/$dev/operstate" ] && grep -q "up" "/sys/class/net/$dev/operstate"; then
      echo "$dev"
      return 0
    fi
  done
  echo "eth0"
}

if ! command -v ip >/dev/null 2>&1; then
  echo "This script requires 'ip' (iproute2). Aborting." >&2
  exit 1
fi

IFACE=$(detect_iface)
echo "Target: $TARGET"
echo "Interface: $IFACE"
echo

# ensure we can resolve target ip
TARGET_IP=""
if [[ "$TARGET" =~ ^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
  TARGET_IP="$TARGET"
else
  if ! TARGET_IP=$(getent hosts "$TARGET" | awk '{print $1}' | head -n1); then
    echo "Failed to resolve target '$TARGET'." >&2
    exit 1
  fi
fi
echo "Resolved target IP: $TARGET_IP"
echo

# check for required commands and print warnings for optional commands
REQ_CMDS=(ip ping awk grep sed date)
for c in "${REQ_CMDS[@]}"; do
  if ! command -v "$c" >/dev/null 2>&1; then
    echo "Missing required command: $c" >&2
    exit 1
  fi
done

# optional commands
HAS_TCPDUMP=false
HAS_ETHTOOL=false
HAS_ARPING=false
HAS_LLDPC=false
HAS_TRACEROUTE=false

if command -v tcpdump >/dev/null 2>&1; then HAS_TCPDUMP=true; fi
if command -v ethtool >/dev/null 2>&1; then HAS_ETHTOOL=true; fi
if command -v arping >/dev/null 2>&1; then HAS_ARPING=true; fi
if command -v lldpctl >/dev/null 2>&1; then HAS_LLDPC=true; fi
if command -v traceroute >/dev/null 2>&1; then HAS_TRACEROUTE=true; fi

echo "Tool availability:"
echo "  tcpdump:  $HAS_TCPDUMP"
echo "  ethtool:  $HAS_ETHTOOL"
echo "  arping:   $HAS_ARPING"
echo "  lldpctl:  $HAS_LLDPC"
echo "  traceroute: $HAS_TRACEROUTE"
echo

# helper to run a command with a nice header
run_header() {
  echo
  echo "===== $1 ====="
}

# 1) interface->master check (fast & safe)
run_header "Interface master / bridge hint (ip link)"
ip link show dev "$IFACE" | sed -n '1,4p'
# Look for "master <bridge>" or "brd"
master=$(ip link show dev "$IFACE" 2>/dev/null | tr '\n' ' ' | sed 's/.*master \([^ ]*\).*/\1/;t;d')
if [ -n "$master" ]; then
  echo "Interface reports master: $master  -> This interface is enslaved to a bridge on this host (local bridge)."
else
  echo "No 'master' shown; interface is not a local bridge slave (or not reported)."
fi

# 2) check /sys/class/net/<if>/bridge (exists only when this host has a bridge device)
run_header "Check local bridge sysfs"
if [ -d "/sys/class/net/$IFACE/bridge" ]; then
  echo "/sys/class/net/$IFACE/bridge exists -> this host has a bridge device attached to $IFACE (local)."
else
  echo "No /sys/class/net/$IFACE/bridge -> local host is not the bridge owner for this interface."
fi

# 3) LLDP via lldpctl (if installed)
if $HAS_LLDPC; then
  run_header "LLDP via lldpctl (if lldpd installed) -- shows neighbor(s) when available"
  echo "(running: lldpctl -f keyvalue on $IFACE)"
  sudo lldpctl -f keyvalue "$IFACE" 2>/dev/null || echo "lldpctl produced no output or isn't running for $IFACE."
else
  run_header "LLDP: lldpctl not installed"
  echo "lldpctl not installed. You can install lldpd (Debian/Ubuntu: apt install lldpd) and restart it to try LLDP discovery."
fi

# 4) passive capture for STP/LLDP (tcpdump) - captures broadcast control frames
if $HAS_TCPDUMP; then
  run_header "Passive capture: look for STP BPDUs and LLDP frames (tcpdump, 6s capture)"
  echo "Capturing for 6 seconds on $IFACE for STP (01:80:c2:00:00:00) and LLDP (0x88cc)"
  TMPPCAP=$(mktemp /tmp/detect_bridge_pcap.XXXX.pcap)
  sudo timeout 6 tcpdump -i "$IFACE" -s 128 -w "$TMPPCAP" "ether dst 01:80:c2:00:00:00 or ether proto 0x88cc or ether multicast" >/dev/null 2>&1 || true
  if [ -s "$TMPPCAP" ]; then
    echo "Captured packets into $TMPPCAP. Decoding summary (tcpdump -r):"
    sudo tcpdump -n -r "$TMPPCAP" -e | sed -n '1,50p' || true
    # search for STP and LLDP keywords
    if sudo tcpdump -n -r "$TMPPCAP" -e | grep -i "stp\|bpdu" >/dev/null 2>&1; then
      echo "-> STP/BPDU frames observed. Very likely a bridge/switch present (could be Linux bridge running STP)."
    fi
    if sudo tcpdump -n -r "$TMPPCAP" -e | grep -i "LLDP" >/dev/null 2>&1; then
      echo "-> LLDP frames observed. This indicates a neighbor device is advertising (switch/bridge)."
    fi
  else
    echo "No control frames captured in 6s capture. That does NOT prove absence of a switch (some devices do not emit LLDP/STP)."
  fi
  rm -f "$TMPPCAP"
else
  run_header "Passive capture: tcpdump not available"
  echo "tcpdump missing. Install tcpdump and re-run to capture control frames (STP/LLDP)."
fi

# 5) ethtool PHY/link partner info
if $HAS_ETHTOOL; then
  run_header "ethtool: link/partner info"
  echo "(showing ethtool output for $IFACE)"
  sudo ethtool "$IFACE" || true
  echo
  echo "ethtool -a (autoneg/advertised/partner info) if supported:"
  sudo ethtool -a "$IFACE" 2>/dev/null || true
  echo
  echo "ethtool -S (driver stats) if supported:"
  sudo ethtool -S "$IFACE" 2>/dev/null || true
  echo
  echo "Notes: Some drivers expose PHY partner info; presence of a 'PHY' or 'link partner advertised' entry may hint at a switch PHY vs peer NIC."
else
  run_header "ethtool not available"
  echo "Install ethtool for PHY diagnostics (apt install ethtool)."
fi

# 6) ARP / neighbor and MAC lookup
run_header "ARP table and MAC OUI"
ip neigh show to "$TARGET_IP" | sed -n '1,50p' || true
arp_mac=$(ip neigh show to "$TARGET_IP" | awk '{print $5; exit}' || true)
if [ -n "$arp_mac" ]; then
  echo "Observed MAC for $TARGET_IP: $arp_mac"
  echo "OUI (first 3 octets): $(echo "$arp_mac" | awk -F: '{print toupper($1 $2 $3)}' | sed 's/\(..\)/\1:/g;s/:$//')"
else
  echo "No ARP entry yet. Try 'arping' or ping to populate ARP."
fi

# 7) arping test (if available) - see reply times, flooding behavior
if $HAS_ARPING; then
  run_header "arping: 5 probes to target (shows ARP replies and timing)"
  echo "(arping may require sudo)"
  sudo timeout 6 arping -c 5 -I "$IFACE" "$TARGET_IP" || true
else
  run_header "arping: not available"
  echo "Install arping to run ARP-level timing tests (apt install arping)."
fi

# 8) ping micro-latency test
run_header "ping micro-latency test: 100 pings, 10ms interval (if allowed)"
echo "(This measures latency distribution; software bridge often adds slightly higher microsecond latency.)"
ping_count=100
if ping -c 1 "$TARGET_IP" >/dev/null 2>&1; then
  ping -c "$ping_count" -i 0.01 "$TARGET_IP" | tail -n 5
  # compute stats quickly
  stats=$(ping -c "$ping_count" -i 0.01 -q "$TARGET_IP" 2>/dev/null | tail -n1 || true)
  echo "Ping summary: $stats"
else
  echo "Target is not responding to ICMP, skipping ping test."
fi

# 9) traceroute (may help if some IP hops exist)
if $HAS_TRACEROUTE; then
  run_header "traceroute (ICMP) to target (may not be useful for L2) -- 5 probes"
  traceroute -n -w 1 -q 1 "$TARGET_IP" || true
else
  run_header "traceroute not available"
fi

# 10) passive multicast sniff for other control frames (LLDP multicast 01:80:c2:00:00:0e etc)
if $HAS_TCPDUMP; then
  run_header "Passive: sniff for LLDP multicast (01:80:c2:00:00:0e) and other bridge groups"
  TMPLOG=$(mktemp /tmp/detect_bridge_log.XXXX.txt)
  sudo timeout 4 tcpdump -i "$IFACE" -s 160 -l -n 'ether multicast' 2>/dev/null | sed -n '1,200p' >"$TMPLOG" || true
  if [ -s "$TMPLOG" ]; then
    echo "Multicast control frames captured (sample):"
    sed -n '1,50p' "$TMPLOG"
    if grep -i "LLDP" "$TMPLOG" >/dev/null 2>&1; then
      echo "-> LLDP present."
    fi
    if grep -i "STP\|BPDU" "$TMPLOG" >/dev/null 2>&1; then
      echo "-> STP/BPDU present."
    fi
  else
    echo "No multicast control frames in short 4s sniff."
  fi
  rm -f "$TMPLOG"
fi

# 11) Attempt to infer switch by MAC learning / flood test (non-destructive)
# Method: send broadcast pings (ARP floods) and observe if any change in behavior
run_header "Broadcast/ARP flood test (gentle): send 3 ARP probes quickly and observe any flooding/delays"
if $HAS_ARPING; then
  echo "Sending 3 arping requests spaced tightly to observe behavior..."
  sudo timeout 4 arping -c 3 -I "$IFACE" "$TARGET_IP" >/dev/null 2>&1 || true
  echo "Check dmesg or bridge forwarding table on the local machine (if you manage it) for MAC learning events."
else
  echo "arping not available -> skipping."
fi

# 12) Optional: MAC-spoof learning probe (disabled by default)
if $MAC_SPOOF = true; then
  echo
  echo "***** MAC SPOOF TEST ENABLED *****"
  echo "This will temporarily change the MAC of $IFACE to a random value and send pings to see whether traffic is forwarded/learned by a bridge."
  echo "If you run this, you MUST ensure you can restore connectivity (script attempts to restore original MAC)."
  read -p "Continue with MAC spoof test? (y/N) " yn
  if [[ "$yn" =~ ^[Yy]$ ]]; then
    orig_mac=$(cat /sys/class/net/"$IFACE"/address)
    rand_mac=$(printf '02:%02x:%02x:%02x:%02x:%02x\n' $((RANDOM%256)) $((RANDOM%256)) $((RANDOM%256)) $((RANDOM%256)) $((RANDOM%256)))
    echo "Original MAC: $orig_mac"
    echo "Changing $IFACE to $rand_mac"
    sudo ip link set dev "$IFACE" down
    sudo ip link set dev "$IFACE" address "$rand_mac"
    sudo ip link set dev "$IFACE" up
    echo "Sending 5 pings to $TARGET_IP..."
    ping -c 5 "$TARGET_IP" || true
    echo "Restoring original MAC"
    sudo ip link set dev "$IFACE" down
    sudo ip link set dev "$IFACE" address "$orig_mac"
    sudo ip link set dev "$IFACE" up
    echo "MAC restored to $orig_mac"
  else
    echo "Skipping MAC spoof test."
  fi
else
  echo
  echo "(MAC spoof test disabled. To enable, re-run with --mac-spoof and be prepared for temporary link disruption.)"
fi

# 13) Synthesize findings and give a confidence score
run_header "Synthesis of observations and confidence"

score=0
notes=()

# If we saw STP/BPDU -> strong evidence
if $HAS_TCPDUMP && sudo tcpdump -n -c 1 -i "$IFACE" 'ether dst 01:80:c2:00:00:00' >/dev/null 2>&1; then
  score=$((score+40))
  notes+=("STP/BPDU frames were observed -> very likely a bridge/switch (possibly Linux bridge running STP).")
fi

# LLDP observed
if $HAS_TCPDUMP && sudo tcpdump -n -c 1 -i "$IFACE" 'ether proto 0x88cc' >/dev/null 2>&1; then
  score=$((score+40))
  notes+=("LLDP frames observed -> neighbor device is advertising (switch/bridge).")
elif $HAS_LLDPC; then
  # try lldpctl quick check
  if sudo lldpctl "$IFACE" 2>/dev/null | grep -q .; then
    score=$((score+40))
    notes+=("lldpctl shows LLDP neighbor on $IFACE -> neighbor device found (likely bridge/switch).")
  fi
fi

# ethtool hints: if ethtool prints "Link detected: yes" but partner info ambiguous; check for PHY entries
if $HAS_ETHTOOL; then
  if sudo ethtool "$IFACE" 2>/dev/null | grep -qi "Link detected: yes"; then
    # if driver exposes "Link partner" lines, count it as small hint
    if sudo ethtool "$IFACE" 2>/dev/null | grep -i "Link partner\|PHY" >/dev/null 2>&1; then
      score=$((score+5))
      notes+=("ethtool shows PHY/Link-partner info -> small hint the partner may be a switch PHY.")
    fi
  fi
fi

# ping/arp timings: if average ping latency > 0.2ms add small weight (depends on environment)
if ping -c 10 -i 0.01 -q "$TARGET_IP" >/dev/null 2>&1; then
  avg_ms=$(ping -c 10 -i 0.01 -q "$TARGET_IP" 2>/dev/null | tail -n1 | awk -F'/' '{print $5}')
  # if avg above threshold (0.2ms)
  avg_ms_f=$(printf "%.3f" "$avg_ms")
  avg_us=$(awk "BEGIN {print $avg_ms_f*1000}")
  if (( $(echo "$avg_us > 200" | bc -l) )); then
    score=$((score+5))
    notes+=("Ping avg ${avg_ms_f} ms (≈ ${avg_us%.*} µs) — slightly higher than direct NIC-NIC; could indicate software bridging, but not conclusive.")
  fi
fi

# ARP behavior: if ARP shows an intermediate device (rare), small weight
if [ -n "$arp_mac" ]; then
  # if arp_mac OUI seems vendor-like? we can't lookup vendor offline, but if OUI ends with 00:00:00 unlikely
  score=$((score+2))
  notes+=("ARP resolved target's MAC (${arp_mac}). (By itself this is expected and not a proof for/against a bridge.)")
fi

# ip link master: if interface is enslaved locally -> local bridge
if [ -n "$master" ]; then
  score=$((score+30))
  notes+=("Interface master indicates this host is attached to a local bridge ($master) — local bridge present.")
fi

# TTL/hops/traceroute: generally not useful, but check if traceroute shows multiple hops
if $HAS_TRACEROUTE; then
  hops=$(traceroute -n -q 1 -w 1 -m 3 "$TARGET_IP" 2>/dev/null | awk 'NR>1 {print $2}' | wc -l)
  if [ "$hops" -gt 1 ]; then
    score=$((score+2))
    notes+=("traceroute showed more than 1 hop (rare for pure L2) — inspect carefully.")
  fi
fi

# Cap score 0-100
if [ "$score" -gt 100 ]; then score=100; fi

echo "Score: $score / 100"
echo
echo "Notes:"
for n in "${notes[@]}"; do
  echo " - $n"
done

echo
if [ "$score" -ge 70 ]; then
  echo "Conclusion: HIGH confidence there is a switch/bridge between the hosts."
elif [ "$score" -ge 35 ]; then
  echo "Conclusion: MEDIUM confidence of a switch/bridge between hosts. Some signals found but not definitive."
else
  echo "Conclusion: LOW confidence. No strong evidence found; switch could still be present but silent (no LLDP/STP), or path may be direct."
fi

echo
echo "Recommendations:"
echo " - If you control the intermediate device, check 'brctl show' or 'bridge link' on that host."
echo " - Enable lldpd on the bridge (sudo apt install lldpd) and use lldpctl on both ends."
echo " - If tcpdump showed STP/BPDU or LLDP, that's the most direct evidence."
echo
echo "Done."