#!/bin/bash

#
# Generate OpenVPN configs
#

TMP_PUSH_CONFIGFILE=$(mktemp -t vpn_push.XXXXXXX)
TMP_ROUTE_CONFIGFILE=$(mktemp -t vpn_route.XXXXXXX)
TMP_EXTRA_CONFIGFILE=$(mktemp -t vpn_extra.XXXXXXX)
TMP_EXTRA_CLIENT_CONFIGFILE=$(mktemp -t vpn_extra_client.XXXXXXX)

#Traceback on Error and Exit come from https://docwhat.org/tracebacks-in-bash/
set -eu

_showed_traceback=f

traceback() {
	# Hide the traceback() call.
	local -i start=$(( ${1:-0} + 1 ))
	local -i end=${#BASH_SOURCE[@]}
	local -i i=0
	local -i j=0

	echo "Traceback (last called is first):" 1>&2
	for ((i=${start}; i < ${end}; i++)); do
		j=$(( $i - 1 ))
		local function="${FUNCNAME[$i]}"
		local file="${BASH_SOURCE[$i]}"
		local line="${BASH_LINENO[$j]}"
		echo "     ${function}() in ${file}:${line}" 1>&2
	done
}

on_error() {
  local _ec="$?"
  local _cmd="${BASH_COMMAND:-unknown}"
  traceback 1
  _showed_traceback=t
  echo "The command ${_cmd} exited with exit code ${_ec}." 1>&2
}
trap on_error ERR


on_exit() {
  echo "Cleaning up before Exit ..."
  rm -f $TMP_PUSH_CONFIGFILE
  rm -f $TMP_ROUTE_CONFIGFILE
  rm -f $TMP_EXTRA_CONFIGFILE
  rm -f $TMP_EXTRA_CLIENT_CONFIGFILE
  local _ec="$?"
  if [[ $_ec != 0 && "${_showed_traceback}" != t ]]; then
    traceback 1
  fi
}
trap on_exit EXIT

# Convert 1.2.3.4/24 -> 255.255.255.0
cidr2mask()
{
    local i
    local subnetmask=""
    local cidr=${1#*/}
    local full_octets=$(($cidr/8))
    local partial_octet=$(($cidr%8))

    for ((i=0;i<4;i+=1)); do
        if [ $i -lt $full_octets ]; then
            subnetmask+=255
        elif [ $i -eq $full_octets ]; then
            subnetmask+=$((256 - 2**(8-$partial_octet)))
        else
            subnetmask+=0
        fi
        [ $i -lt 3 ] && subnetmask+=.
    done
    echo $subnetmask
}

# Used often enough to justify a function
getroute() {
    echo ${1%/*} $(cidr2mask $1)
}

usage() {
    echo "usage: $0 [-d]"
    echo "                  -u SERVER_PUBLIC_URL"
    echo "                 [-e EXTRA_SERVER_CONFIG ]"
    echo "                 [-E EXTRA_CLIENT_CONFIG ]"
    echo "                 [-f FRAGMENT ]"
    echo "                 [-n DNS_SERVER ...]"
    echo "                 [-p PUSH ...]"
    echo "                 [-r ROUTE ...]"
    echo "                 [-s SERVER_SUBNET]"
    echo
    echo "optional arguments:"
    echo " -2    Enable two factor authentication using Google Authenticator."
    echo " -a    Authenticate  packets with HMAC using the given message digest algorithm (auth)."
    echo " -c    Enable client-to-client option"
    echo " -C    A list of allowable TLS ciphers delimited by a colon (cipher)."
    echo " -d    Disable NAT routing and default route"
    echo " -D    Do not push dns servers"
    echo " -m    Set client MTU"
    echo " -N    Configure NAT to access external server network"
    echo " -t    Use TAP device (instead of TUN device)"
    echo " -T    Encrypt packets with the given cipher algorithm instead of the default one (tls-cipher)."
    echo " -z    Enable comp-lzo compression."
}

process_route_config() {
  local ovpn_route_config=''
  ovpn_route_config="$1"
  # If user passed "0" skip this, assume no extra routes
  [[ "$ovpn_route_config" == "0" ]] && break;
  echo "Processing Route Config: '${ovpn_route_config}'"
  [[ -n "$ovpn_route_config" ]] && echo "route $(getroute $ovpn_route_config)" >> "$TMP_ROUTE_CONFIGFILE"
}

process_push_config() {
  local ovpn_push_config=''
  ovpn_push_config="$1"
  echo "Processing PUSH Config: '${ovpn_push_config}'"
  [[ -n "$ovpn_push_config" ]] && echo "push $ovpn_push_config" >> "$TMP_PUSH_CONFIGFILE"
}

process_extra_config() {
  local ovpn_extra_config=''
  ovpn_extra_config="$1"
  echo "Processing Extra Config: '${ovpn_extra_config}'"
  [[ -n "$ovpn_extra_config" ]] && echo "$ovpn_extra_config" >> "$TMP_EXTRA_CONFIGFILE"

}

process_extra_client_config() {
  local ovpn_extra_config=''
  ovpn_extra_config="$1"
  echo "Processing Extra Client Config: '${ovpn_extra_config}'"
  [[ -n "$ovpn_extra_config" ]] && echo "$ovpn_extra_config" >> "$TMP_EXTRA_CLIENT_CONFIGFILE"
}

if [ "${DEBUG:-}" == "1" ]; then
  set -x
fi

set -e

if [ -z "${OPENVPN:-}" ]; then
  export OPENVPN="$PWD"
fi
if [ -z "${EASYRSA_PKI:-}" ]; then
    export EASYRSA_PKI="$OPENVPN/pki"
fi

OVPN_ENV=${OPENVPN}/ovpn_env.sh
OVPN_SERVER=192.168.255.0/24
OVPN_DEFROUTE=1
OVPN_NAT=0
OVPN_DNS=1
OVPN_DEVICE="tun"
OVPN_DEVICEN=0
OVPN_DNS_SERVERS=("8.8.8.8" "8.8.4.4")
TMP_DNS_SERVERS=()
OVPN_TLS_CIPHER=''
OVPN_CIPHER=''
OVPN_AUTH=''
OVPN_EXTRA_CONFIG=''
CUSTOM_ROUTE_CONFIG=''

# Import defaults if present
[ -r "$OVPN_ENV" ] && source "$OVPN_ENV"

# Parse arguments
while getopts ":a:e:E:C:T:r:s:du:cp:n:DNmf:tz2" opt; do
    case $opt in
        a)
            OVPN_AUTH="$OPTARG"
            ;;
        e)
            process_extra_config "$OPTARG"
            ;;
        E)
            process_extra_client_config "$OPTARG"
            ;;
        C)
            OVPN_CIPHER="$OPTARG"
            ;;
        T)
            OVPN_TLS_CIPHER="$OPTARG"
            ;;
        r)
            CUSTOM_ROUTE_CONFIG=1
            process_route_config "$OPTARG"
            ;;
        s)
            OVPN_SERVER=$OPTARG
            ;;
        d)
            OVPN_DEFROUTE=0
            ;;
        u)
            OVPN_SERVER_URL=$OPTARG
            ;;
        c)
            OVPN_CLIENT_TO_CLIENT=1
            ;;
        p)
            process_push_config "$OPTARG"
            ;;
        n)
            TMP_DNS_SERVERS+=("$OPTARG")
            ;;
        D)
            OVPN_DNS=0
            ;;
        N)
            OVPN_NAT=1
            ;;
        m)
            OVPN_MTU=$OPTARG
            ;;
        t)
            OVPN_DEVICE="tap"
            ;;
        z)
            OVPN_COMP_LZO=1
            ;;
        2)
            OVPN_OTP_AUTH=1
            ;;
        f)
            OVPN_FRAGMENT=$OPTARG
            ;;
        \?)
            set +x
            echo "Invalid option: -$OPTARG" >&2
            usage
            exit 1
            ;;
        :)
            set +x
            echo "Option -$OPTARG requires an argument." >&2
            usage
            exit 1
            ;;
    esac
done

# Create ccd directory for static routes
[ ! -d "${OPENVPN:-}/ccd" ] && mkdir -p ${OPENVPN:-}/ccd

# if dns servers were not defined with -n, use google nameservers
[ ${#TMP_DNS_SERVERS[@]} -gt 0 ] && OVPN_DNS_SERVERS=("${TMP_DNS_SERVERS[@]}")

# Server name is in the form "udp://vpn.example.com:1194"
if [[ "${OVPN_SERVER_URL:-}" =~ ^((udp|tcp|udp6|tcp6)://)?([0-9a-zA-Z\.\-]+)(:([0-9]+))?$ ]]; then
    OVPN_PROTO=${BASH_REMATCH[2]};
    OVPN_CN=${BASH_REMATCH[3]};
    OVPN_PORT=${BASH_REMATCH[5]};
else
    set +x
    echo "Common name not specified, see '-u'"
    usage
    exit 1
fi

# Apply defaults
[ -z "$OVPN_PROTO" ] && OVPN_PROTO=udp
[ -z "$OVPN_PORT" ] && OVPN_PORT=1194
[ -z "$CUSTOM_ROUTE_CONFIG" ] && process_route_config "192.168.254.0/24"

# Save extra client config from temp file only if temp file is not empty
if [ -s "$TMP_EXTRA_CLIENT_CONFIGFILE" ]; then
  OVPN_ADDITIONAL_CLIENT_CONFIG=$(cat $TMP_EXTRA_CLIENT_CONFIGFILE)
fi

export OVPN_SERVER OVPN_ROUTES OVPN_DEFROUTE
export OVPN_SERVER_URL OVPN_ENV OVPN_PROTO OVPN_CN OVPN_PORT
export OVPN_CLIENT_TO_CLIENT OVPN_PUSH OVPN_NAT OVPN_DNS OVPN_MTU OVPN_DEVICE
export OVPN_TLS_CIPHER OVPN_CIPHER OVPN_AUTH
export OVPN_COMP_LZO
export OVPN_OTP_AUTH
export OVPN_FRAGMENT
export OVPN_ADDITIONAL_CLIENT_CONFIG

# Preserve config
if [ -f "$OVPN_ENV" ]; then
    bak_env=$OVPN_ENV.$(date +%s).bak
    echo "Backing up $OVPN_ENV -> $bak_env"
    mv "$OVPN_ENV" "$bak_env"
fi

# Like `export | grep OVPN_ > "$OVPN_ENV"` but handles multiline variables
set +u
while read var ; do
  eval value=\$$var
  if [ -n "$value" ]; then
    echo "declare -x $var=\"$value\"" >> "$OVPN_ENV"
  else
    echo "declare -x $var" >> "$OVPN_ENV"
  fi
done < <(export | egrep -o '(OVPN_[^=]+)')
set -u

conf=${OPENVPN:-}/openvpn.conf
if [ -f "$conf" ]; then
    bak=$conf.$(date +%s).bak
    echo "Backing up $conf -> $bak"
    mv "$conf" "$bak"
fi

cat > "$conf" <<EOF
server $(getroute $OVPN_SERVER)
verb 3
key $EASYRSA_PKI/private/${OVPN_CN}.key
ca $EASYRSA_PKI/ca.crt
cert $EASYRSA_PKI/issued/${OVPN_CN}.crt
dh $EASYRSA_PKI/dh.pem
tls-auth $EASYRSA_PKI/ta.key
key-direction 0
keepalive 10 60
persist-key
persist-tun

proto $OVPN_PROTO
# Rely on Docker to do port mapping, internally always 1194
port 1194
dev $OVPN_DEVICE$OVPN_DEVICEN
status /tmp/openvpn-status.log

user nobody
group nogroup
EOF

#This was in the heredoc, we use the new function instead
process_push_config "block-outside-dns"

[ -n "$OVPN_TLS_CIPHER" ] && echo "tls-cipher $OVPN_TLS_CIPHER" >> "$conf"
[ -n "$OVPN_CIPHER" ] && echo "cipher $OVPN_CIPHER" >> "$conf"
[ -n "$OVPN_AUTH" ] && echo "auth $OVPN_AUTH" >> "$conf"

[ -n "${OVPN_CLIENT_TO_CLIENT:-}" ] && echo "client-to-client" >> "$conf"
[ -n "${OVPN_COMP_LZO:-}" ] && echo "comp-lzo" >> "$conf"

[ -n "${OVPN_FRAGMENT:-}" ] && echo "fragment $OVPN_FRAGMENT" >> "$conf"

[ "$OVPN_DNS" == "1" ] && for i in "${OVPN_DNS_SERVERS[@]}"; do
  process_push_config "dhcp-option DNS $i"
done

# Append route commands
echo -e "\n### Route Configurations Below" >> "$conf"
cat $TMP_ROUTE_CONFIGFILE >> "$conf"

# Append push commands
echo -e "\n### Push Configurations Below" >> "$conf"
cat $TMP_PUSH_CONFIGFILE >> "$conf"

# Optional OTP authentication support
if [ -n "${OVPN_OTP_AUTH:-}" ]; then
    echo -e "\n\n# Enable OTP+PAM for user authentication" >> "$conf"
    echo "plugin /usr/lib/openvpn/plugins/openvpn-plugin-auth-pam.so openvpn" >> "$conf"
    echo "reneg-sec 0" >> "$conf"
fi

echo -e "\n### Extra Configurations Below" >> "$conf"
cat $TMP_EXTRA_CONFIGFILE >> "$conf"

set +e

# Clean-up duplicate configs
if diff -q "${bak_env:-}" "$OVPN_ENV" 2>/dev/null; then
    echo "Removing duplicate back-up: $bak_env"
    rm -fv "$bak_env"
fi
if diff -q "${bak:-}" "$conf" 2>/dev/null; then
    echo "Removing duplicate back-up: $bak"
    rm -fv "$bak"
fi

echo "Successfully generated config"