#!/bin/env bash

#    WAN IP Checker - Whenever server WAN IP address changes, inform admins via email
#    Copyright (C) 2018  Pekka Helenius
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <https://www.gnu.org/licenses/>.

###########################################################

# A script for remote server environments which are behind
# dynamic (non-static) DHCP. Usually these dynamic IPs are 
# used in common household networks in non-corporate
# environments.

###########################################################

# Script requirements
#
# SSMTP

# https://wiki.archlinux.org/index.php/SSMTP
# Relevant conf files
# /etc/ssmtp/revaliases
# /etc/ssmtp/ssmtp.conf

# Because your email password is stored as cleartext in /etc/ssmtp/ssmtp.conf, it is important that this file
# is secure. By default, the entire /etc/ssmtp directory is accessible only by root and the mail group.
# The /usr/bin/ssmtp binary runs as the mail group and can read this file. There is no reason to add
# yourself or other users to the mail group.

###########################################################

# Some lines below are commented out because the timer is handled by systemd service file
# If you don't use provided systemd service file, re-enable the relevant lines below

function checkWANIP() {

  # Command to resolve the current IPv4 WAN address
  local WANIP_CURRENT="dig +short myip.opendns.com @resolver1.opendns.com"

############################

  # If we are connected to internet...
  # There's no point to do WAN IP check if we can't establish connection to WAN/Internet at all
  # In addition, do not generate any network related variables if the connection
  # can't be established. Therefore, include variable defitions inside this if statement.
  if [[ $(printf $(eval ${WANIP_CURRENT} &> /dev/null)$?) -eq 0 ]]; then

    # Check interval in minutes
  #  local CHECK_INTERVAL=5

############################

    # Cache/Log directory of the script
    local WANIP_DIR="$HOME"

    # Log file for checked/resolved IPv4 WAN addresses:
    local WANIP_LOG="$WANIP_DIR/.ip_wan.log"

    if [[ ! -d ${WANIP_DIR} ]]; then
      mkdir -p ${WANIP_DIR}
    fi

    if [[ ! -f ${WANIP_LOG} ]]; then
      printf 'Time\t\t\t\tWAN IPv4\n' > ${WANIP_LOG}
    fi

############################

    # Log file timestamp format
    local TIMESTAMP=$(date '+%d-%m-%Y, %X')

############################

    # Email to send notify to
    local EMAIL_RECIPIENT="mymail@hotmail.com"

    # Email subject/title
    local SUBJECT_EMAIL="WAN IP address change (Helsinki, $(tail -1 ${WANIP_LOG} | awk '{print $NF}') -> $(eval ${WANIP_CURRENT}))"

    # Email message/body contents
    local MESSAGE_EMAIL="${TIMESTAMP}: WAN address of the server (Helsinki) has been changed from $(tail -1 ${WANIP_LOG} | awk '{print $NF}') to $(eval ${WANIP_CURRENT})"

    # Message to server stdout
    local MESSAGE_STDOUT="$(echo ${TIMESTAMP}) - WAN address of this server has been changed from $(tail -1 ${WANIP_LOG} | awk '{print $NF}') to $(eval ${WANIP_CURRENT})"

############################

    # Email send command
    local MAIL_SEND="echo -e \"To: ${EMAIL_RECIPIENT}\nFrom: ${EMAIL_RECIPIENT}\nSubject: ${SUBJECT_EMAIL}\n\n${MESSAGE_EMAIL}\" | sendmail -v ${EMAIL_RECIPIENT}"

    # Log write command
    local LOG_WRITE="printf '%s %s\t\t%s\n' $(echo $TIMESTAMP) $(eval $WANIP_CURRENT) >> $WANIP_LOG"

############################

    # If the log file has no previous IPv4 entries
    if [[ $(cat $WANIP_LOG | wc -l) -le 1 ]]; then
      eval ${LOG_WRITE}
    fi

#  local i=0
#  while true; do

#    if [[ $i -ne 0 ]]; then
#      sleep $(( ${CHECK_INTERVAL} * 60 ))
#    fi

#    if [[ -f $WANIP_LOG ]]; then

      # The log file must include more than just the header line
    if [[ $(cat $WANIP_LOG | wc -l) -gt 1 ]]; then

      if [[ $(tail -1 $WANIP_LOG | awk '{print $NF}') != $(printf '%s' $(eval $WANIP_CURRENT)) ]]; then

        echo -e ${MESSAGE_STDOUT}
        eval ${MAIL_SEND}
        eval ${LOG_WRITE}

      fi
    fi
  fi
#    let i++
#  done
}

############################

checkWANIP