#!/usr/bin/env bash
# IPNotify notifies system owner when the system's external IP changes
# Copyright (C) 2018  Aaron Ball <nullspoon@oper.io>
#
# 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 <http://www.gnu.org/licenses/>.


# Write file to tmpfs location. This way the server reports its location on
# boot as the filesystem will be recreated at that time.
STATUSFILE="${STATUSFILE:-/tmp/$(basename ${0})-status}"

# SMTP connection string in smtp[s]://host:port format. This is used as the
# mail relay to send the report email.
SMTP="${SMTP:-}"

# Address the email should come from (eg: noreply@somehost.foo)
FROM="${FROM:-}"

# URI to query for the current external IP.
# NOTE: This URI should only contain the ip address. Any additional text (such
#       as query timestamps) will trigger an email every time the text changes,
#       not just when the returned IP changes.
QUERYURI="${QUERYURI}"

# Admin email address.
# Can be format user@web.com or "First Last <user@web.com>". Also supports
# comma and semicolon delimited emails for multiple admins.
ADMIN="${ADMIN:-}"


titlize() {
  local text="${@}"

  printf -- "%s\n" "${text}"
  printf -- '-%.0s' $(seq 1 ${#text})
  printf -- '\n'
}


prereq_verify() {
  # Required binaries:
  #   curl
  #   mailx
  #   traceroute

  # Validate GNU traceroute installation
  if [ -z "$(type -p traceroute)" ]; then
    printf "ERROR: GNU traceroute is required but could not be found.\n" >&2
    return 1
  fi
  if [ -z "$(traceroute -V | grep 'GNU inetutils')" ]; then
    printf "ERROR: GNU traceroute is required but another version is installed.\n" >&2
    return 1
  fi

  if [ -z "$(type -p curl)" ]; then
    printf "ERROR: Curl required but could not be found.\n" >&2
    return 1
  fi

  if [ -z "$(type -p mailx)" ]; then
    printf "ERROR: mailx is required but could not be found.\n" >&2
    return 1
  fi

  return 0
}


notify_user() {
  local admin="${1}"
  local newip="${2}"
  local smtp="${3}"
  local from="${4}"

  local email_domain=$(echo ${admin} | cut -d '@' -f 2)

  # Construct email body
  printf "To: ${admin}
Subject: [report] Server $(hostname) has changed IPs


This server, $(hostname), has changed IPS.

$(titlize New IP)

  ${newip}


$(titlize "ICMP Traceroute to ${email_domain}")
$(timeout 12 traceroute --type=icmp -m 20 -w 2 ${email_domain} 2>&1 | sed 's/^/  /')


$(titlize "Resolv.conf")
$(cat /etc/resolv.conf | sed 's/^/  /')


" | timeout 14 mailx -S "smtp=${smtp}" -r "${from}" -t "${admin}"

  return $?
}


validate_vars() {
  if [ -z "${QUERY}" ]; then
    printf "QUERY endpoint unset. Cannot determine external IP.\n" >&2
    return 1
  fi

  if [ -z "${SMTP}" ]; then
    printf "SMTP relay server unset (eg: SMTP=smtp://hostname:587)\n" >&2
    return 1
  fi

  if [ -z "${FROM}" ]; then
    printf "FROM address unset.\n" >&2
    return 1
  fi

  if [ -z "${ADMIN}" ]; then
    printf "ADMIN unset. No one to notify (eg: ADMIN=admin@website.com).\n" >&2
    return 1
  fi
}


main() {
  local config="${1:-}" # Config file containing global variables
  local curip           # Placeholder for current ip address (as returned by
                        # the query destination)
  local cacheip         # Cached ip address (if cache file exists)


  if [ -z "${config}" ]; then
    printf "Config file required\n" >&2
    return 1
  fi

  # Source the config file to load its variables
  source "${config}"

  # Validate all required programs are present (eg: mailx, traceroute, ping, etc)
  prereq_verify
  [ $? -gt 0 ] && return 1

  # Validate all required variables are set (eg: FROM, ADMIN, etc)
  validate_vars
  [ $? -gt 0 ] && return 1


  # Get the current real ip
  curip="$(curl --max-time 7 --location --insecure --silent ${QUERY})"

  if [ -z ${curip:-} ]; then
    printf "Current ip unknown. Cannot continue\n"
    return 2
  fi

  # Set ip to state file if none is found
  if [ ! -f "${STATUSFILE}" ]; then
    printf "IP status file not found. Creating\n"
    printf "${curip}" > "${STATUSFILE}"
    notify_user "${ADMIN}" "${curip}" "${SMTP}" "${FROM}"
    return 0
  fi

  cacheip="$(cat ${STATUSFILE})"

  # Cached ip and current ip don't match - email admin
  if [ "${cacheip:-}" != "${curip:-}" ]; then
    printf "Current ip does not match last recorded IP. Notifying admin.\n"
    notify_user "${ADMIN}" "${curip}" "${SMTP}" "${FROM}"

    if [ $? -eq 0 ]; then
      printf "${curip}" > "${STATUSFILE}"
      return 0
    fi
    printf "Could not send notification email.\n"
    printf "Something is probably still wrong. Skipping write of IP\n"
    return 1
  fi

  printf "Nothing to see here\n"
}

main ${@}