#!/bin/bash
#
# Script to change IKEv2 VPN server address
#
# The latest version of this script is available at:
# https://github.com/hwdsl2/setup-ipsec-vpn
#
# Copyright (C) 2022 Lin Song <linsongui@gmail.com>
#
# This work is licensed under the Creative Commons Attribution-ShareAlike 3.0
# Unported License: http://creativecommons.org/licenses/by-sa/3.0/
#
# Attribution required: please include my name in any derivative and let me
# know how you have improved it!

export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
SYS_DT=$(date +%F-%T | tr ':' '_')

exiterr() { echo "Error: $1" >&2; exit 1; }
bigecho() { echo "## $1"; }

check_ip() {
  IP_REGEX='^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$'
  printf '%s' "$1" | tr -d '\n' | grep -Eq "$IP_REGEX"
}

check_dns_name() {
  FQDN_REGEX='^([a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z]{2,}$'
  printf '%s' "$1" | tr -d '\n' | grep -Eq "$FQDN_REGEX"
}

check_root() {
  if [ "$(id -u)" != 0 ]; then
    exiterr "Script must be run as root. Try 'sudo bash $0'"
  fi
}

check_os() {
  os_type=centos
  rh_file="/etc/redhat-release"
  if grep -qs "Red Hat" "$rh_file"; then
    os_type=rhel
  fi
  if grep -qs "release 7" "$rh_file"; then
    os_ver=7
  elif grep -qs "release 8" "$rh_file"; then
    os_ver=8
    grep -qi stream "$rh_file" && os_ver=8s
    grep -qi rocky "$rh_file" && os_type=rocky
    grep -qi alma "$rh_file" && os_type=alma
  elif grep -qs "Amazon Linux release 2" /etc/system-release; then
    os_type=amzn
    os_ver=2
  else
    os_type=$(lsb_release -si 2>/dev/null)
    [ -z "$os_type" ] && [ -f /etc/os-release ] && os_type=$(. /etc/os-release && printf '%s' "$ID")
    case $os_type in
      [Uu]buntu)
        os_type=ubuntu
        ;;
      [Dd]ebian)
        os_type=debian
        ;;
      [Rr]aspbian)
        os_type=raspbian
        ;;
      [Aa]lpine)
        os_type=alpine
        ;;
      *)
cat 1>&2 <<'EOF'
Error: This script only supports one of the following OS:
       Ubuntu, Debian, CentOS/RHEL 7/8, Rocky Linux, AlmaLinux,
       Amazon Linux 2 or Alpine Linux
EOF
        exit 1
        ;;
    esac
    if [ "$os_type" = "alpine" ]; then
      os_ver=$(. /etc/os-release && printf '%s' "$VERSION_ID" | cut -d '.' -f 1,2)
      if [ "$os_ver" != "3.14" ] && [ "$os_ver" != "3.15" ]; then
        exiterr "This script only supports Alpine Linux 3.14/3.15."
      fi
    else
      os_ver=$(sed 's/\..*//' /etc/debian_version | tr -dc 'A-Za-z0-9')
    fi
  fi
}

check_libreswan() {
  ipsec_ver=$(ipsec --version 2>/dev/null)
  if ( ! grep -qs "hwdsl2 VPN script" /etc/sysctl.conf && ! grep -qs "hwdsl2" /opt/src/run.sh ) \
    || ! printf '%s' "$ipsec_ver" | grep -q "Libreswan"; then
cat 1>&2 <<'EOF'
Error: This script can only be used with an IPsec server created using:
       https://github.com/hwdsl2/setup-ipsec-vpn
EOF
    exit 1
  fi
}

check_ikev2() {
  if ! grep -qs "conn ikev2-cp" /etc/ipsec.d/ikev2.conf; then
cat 1>&2 <<'EOF'
Error: You must first set up IKEv2 before changing IKEv2 server address.
       See: https://git.io/ikev2
EOF
    exit 1
  fi
}

check_utils_exist() {
  command -v certutil >/dev/null 2>&1 || exiterr "'certutil' not found. Abort."
}

abort_and_exit() {
  echo "Abort. No changes were made." >&2
  exit 1
}

confirm_or_abort() {
  printf '%s' "$1"
  read -r response
  case $response in
    [yY][eE][sS]|[yY])
      echo
      ;;
    *)
      abort_and_exit
      ;;
  esac
}

check_cert_exists() {
  certutil -L -d sql:/etc/ipsec.d -n "$1" >/dev/null 2>&1
}

check_ca_cert_exists() {
  check_cert_exists "IKEv2 VPN CA" || exiterr "Certificate 'IKEv2 VPN CA' does not exist. Abort."
}

get_server_address() {
  server_addr_old=$(grep -s "leftcert=" /etc/ipsec.d/ikev2.conf | cut -f2 -d=)
  [ -z "$server_addr_old" ] && server_addr_old=$(grep -s "leftcert=" /etc/ipsec.conf | cut -f2 -d=)
  check_ip "$server_addr_old" || check_dns_name "$server_addr_old" || exiterr "Could not get current VPN server address."
}

show_welcome() {
cat <<EOF
Welcome! Use this script to change this IKEv2 VPN server's address. A new server
certificate will be generated if necessary.

Current server address: $server_addr_old

EOF
}

get_server_ip() {
  bigecho "Trying to auto discover IP of this server..."
  public_ip=${VPN_PUBLIC_IP:-''}
  check_ip "$public_ip" || public_ip=$(dig @resolver1.opendns.com -t A -4 myip.opendns.com +short)
  check_ip "$public_ip" || public_ip=$(wget -t 3 -T 15 -qO- http://ipv4.icanhazip.com)
}

enter_server_address() {
  echo "Do you want IKEv2 VPN clients to connect to this server using a DNS name,"
  printf "e.g. vpn.example.com, instead of its IP address? [y/N] "
  read -r response
  case $response in
    [yY][eE][sS]|[yY])
      use_dns_name=1
      echo
      ;;
    *)
      use_dns_name=0
      echo
      ;;
  esac
  if [ "$use_dns_name" = "1" ]; then
    read -rp "Enter the DNS name of this VPN server: " server_addr
    until check_dns_name "$server_addr"; do
      echo "Invalid DNS name. You must enter a fully qualified domain name (FQDN)."
      read -rp "Enter the DNS name of this VPN server: " server_addr
    done
  else
    get_server_ip
    echo
    read -rp "Enter the IPv4 address of this VPN server: [$public_ip] " server_addr
    [ -z "$server_addr" ] && server_addr="$public_ip"
    until check_ip "$server_addr"; do
      echo "Invalid IP address."
      read -rp "Enter the IPv4 address of this VPN server: [$public_ip] " server_addr
      [ -z "$server_addr" ] && server_addr="$public_ip"
    done
  fi
}

check_server_address() {
  if [ "$server_addr" = "$server_addr_old" ]; then
    echo >&2
    echo "Error: IKEv2 server address is already '$server_addr'. Nothing to do." >&2
    abort_and_exit
  fi
}

confirm_changes() {
cat <<EOF

You are about to change this IKEv2 VPN server's address.
Read the important notes below before continuing.

===========================================

Current server address: $server_addr_old
New server address:     $server_addr

===========================================

*IMPORTANT*
After running this script, you must manually update the server address
on any existing IKEv2 client devices. For iOS clients, you'll need to
export and re-import client configuration using the IKEv2 helper script.

EOF
  printf "Do you want to continue? [Y/n] "
  read -r response
  case $response in
    [yY][eE][sS]|[yY]|'')
      echo
      ;;
    *)
      abort_and_exit
      ;;
  esac
}

create_server_cert() {
  if check_cert_exists "$server_addr"; then
    bigecho "Server certificate '$server_addr' already exists, skipping..."
  else
    bigecho "Generating server certificate..."
    if [ "$use_dns_name" = "1" ]; then
      certutil -z <(head -c 1024 /dev/urandom) \
        -S -c "IKEv2 VPN CA" -n "$server_addr" \
        -s "O=IKEv2 VPN,CN=$server_addr" \
        -k rsa -g 3072 -v 120 \
        -d sql:/etc/ipsec.d -t ",," \
        --keyUsage digitalSignature,keyEncipherment \
        --extKeyUsage serverAuth \
        --extSAN "dns:$server_addr" >/dev/null 2>&1 || exiterr "Failed to create server certificate."
    else
      certutil -z <(head -c 1024 /dev/urandom) \
        -S -c "IKEv2 VPN CA" -n "$server_addr" \
        -s "O=IKEv2 VPN,CN=$server_addr" \
        -k rsa -g 3072 -v 120 \
        -d sql:/etc/ipsec.d -t ",," \
        --keyUsage digitalSignature,keyEncipherment \
        --extKeyUsage serverAuth \
        --extSAN "ip:$server_addr,dns:$server_addr" >/dev/null 2>&1 || exiterr "Failed to create server certificate."
    fi
  fi
}

update_ikev2_conf() {
  bigecho "Updating IKEv2 configuration..."
  if ! grep -qs '^include /etc/ipsec\.d/\*\.conf$' /etc/ipsec.conf; then
    echo >> /etc/ipsec.conf
    echo 'include /etc/ipsec.d/*.conf' >> /etc/ipsec.conf
  fi
  sed -i".old-$SYS_DT" \
      -e "/^[[:space:]]\+leftcert=/d" \
      -e "/^[[:space:]]\+leftid=/d" /etc/ipsec.d/ikev2.conf
  if [ "$use_dns_name" = "1" ]; then
    sed -i "/conn ikev2-cp/a \  leftid=@$server_addr" /etc/ipsec.d/ikev2.conf
  else
    sed -i "/conn ikev2-cp/a \  leftid=$server_addr" /etc/ipsec.d/ikev2.conf
  fi
  sed -i "/conn ikev2-cp/a \  leftcert=$server_addr" /etc/ipsec.d/ikev2.conf
}

restart_ipsec_service() {
  bigecho "Restarting IPsec service..."
  mkdir -p /run/pluto
  service ipsec restart 2>/dev/null
}

print_client_info() {
cat <<EOF

Successfully changed IKEv2 server address!

EOF
}

ikev2changeaddr() {
  check_root
  check_os
  check_libreswan
  check_ikev2
  check_utils_exist
  check_ca_cert_exists
  get_server_address

  show_welcome
  enter_server_address
  check_server_address
  confirm_changes

  create_server_cert
  update_ikev2_conf
  if [ "$os_type" = "alpine" ]; then
    ipsec auto --replace ikev2-cp >/dev/null
  else
    restart_ipsec_service
  fi
  print_client_info
}

## Defer until we have the complete script
ikev2changeaddr "$@"

exit 0