#!/bin/bash
#
# script: monitor_interface
#
# Monitors a given list of interfaces and add or remove static IP addresses to these interfaces.
# The list of interfaces is provided in the file '/var/local/emhttp/statics.ini'
# This file is maintained by the script 'create_network_ini' which keep track of all IP assignments.
#
# By removing static IP addresses from inactive interfaces, these interfaces do not longer interfere with wireless.
# In other words the wired connection can be pulled without consequences.
#
# Bergware - modified for Unraid OS, May 2025

FILE=/var/local/emhttp/statics.ini
SYSTEM=/sys/class/net

state(){
  cat $SYSTEM/$1/operstate 2>/dev/null
}

md5(){
  [[ -r $FILE ]] && md5sum $FILE | awk '{print $1;exit}'
}

switch(){
  local n status
  [[ -z $1 ]] && return 1
  status=3
  # state should stay different for at least 3 seconds
  for n in {1..3}; do
    [[ $(state $1) != $2 ]] && ((status--))
    sleep 1
  done
  [[ $status -eq 0 ]]
}

init(){
  PORT=(); STATE=();
  if [[ -r $FILE ]]; then
    # initialize values from file, maintained by 'create_network_ini'
    while IFS=$'\n' read -r ROW; do
      PORT+=("$ROW")
      STATE+=($(state ${ROW%% *}))
    done <$FILE
  fi
  MD5=$(md5)
}

while :; do
  # monitor file content changes
  [[ $MD5 != $(md5) ]] && init
  LAST=
  for i in ${!PORT[@]}; do
    INT=${PORT[$i]%% *}
    # did interface state change?
    if switch $INT ${STATE[$i]}; then
      NEW=$(state $INT)
      STATE[$i]=$NEW
      if [[ $NEW == up ]]; then
        ip addr add dev ${PORT[$i]}
      elif [[ $NEW == down && $INT != $LAST ]]; then
        ip addr flush scope global dev $INT
      fi
    fi
    LAST=$INT
  done
  # check every 3 seconds
  sleep 3
done &