#!/usr/bin/env bash
set -euo pipefail


## CONSTANTS ##
readonly DATA_DIR="/etc/openvpn-data"
readonly EASYRSA_DIR="${DATA_DIR}/easyrsa"
readonly DATA_SERVER_DIR="${DATA_DIR}/server"
readonly DATA_CLIENT_DIR="${DATA_DIR}/client"


## HANDLE EXIT SIGNALS ##
trap trap_exit EXIT SIGINT SIGTERM
trap_exit(){
	if [[ "${openvpn_pid:+x}" ]]; then
		kill -- $openvpn_pid 2> /dev/null || true
		q=0
		while proc_running $openvpn_pid; do
			q=$(( q + 1 ))
			snore 1
			if [[ "$q" -ge 15 ]]; then
				echo "Sending kill to OpenVPN" 1>&2
				kill -s KILL -- $openvpn_pid 2> /dev/null || true
				break
			fi
		done
	fi
	exit 0
}



#
# LIB: Efficient sleep (does not create a new process).
#
snore(){
	local IFS
	[[ -n "${_snore_fd:-}" ]] || exec {_snore_fd}<> <(:)
	read ${1:+-t "$1"} -u $_snore_fd || true
}



#
# HELPER: Check whether given pid is running.
# 
# @param $1		Process ID.
# 
# @exit			0:		Process is running
#				1:		Process is not running.
#
proc_running(){
	# try reading state
	local state_path="/proc/$1/stat"
	[[ ! -f "$state_path" ]] && return 1
	local state
	state=$(cat "$state_path" 2> /dev/null | cut -d ' ' -f3) || return 1
	
	# parse state
	case "$state" in
		R|S|D|Z|W|W|P|I) return 0;;
		*) return 1;;
	esac
}



#
# HELPER: Initialize iptables rules.
#
iptables_init(){
	/sbin/iptables -t nat -I POSTROUTING -s 192.168.35.0/24 ! -d 192.168.35.0/24 -j MASQUERADE
	/sbin/iptables -I INPUT -i tun0 -j ACCEPT
	/sbin/iptables -I INPUT -p udp --dport 1194 -j ACCEPT
	/sbin/iptables -I INPUT -p tcp --dport 1194 -j ACCEPT
	/sbin/iptables -I FORWARD -s 192.168.35.0/24 -j ACCEPT
	/sbin/iptables -I FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
}



#
# HELPER: Set up easyrsa.
#
easyrsa_init(){
	## MAYBE CREATE VARS FILE ##
	if [[ ! -f "${EASYRSA_DIR}/vars" ]]; then
		touch "${EASYRSA_DIR}/vars"
	fi
}



#
# HELPER: Set up server keys.
#
easyrsa_server_keys_create(){
	## IGNORE IF EXISTING ##
	[[ -d "${EASYRSA_DIR}/pki" ]] && return 0
	
	
	## SET UP CA AND SERVER KEYS (EASYRSA) ##
	local prev_pwd="$PWD" && cd "$EASYRSA_DIR"
	
	# new pki
	/usr/bin/easyrsa --batch init-pki
	chmod 755 pki
	
	# create ca
	/usr/bin/easyrsa --batch --days=7300 build-ca nopass
	
	# generate server keys
	/usr/bin/easyrsa --batch --days=7300 build-server-full server nopass
	
	# generate crl
	/usr/bin/easyrsa --batch --days=7300 gen-crl
	chown nobody:nobody pki/crl.pem
	
	# restore pwd
	cd "$prev_pwd"
	
	# create symlinks
	ln -s ${EASYRSA_DIR}/pki/{ca.crt,private/ca.key,issued/server.crt,private/server.key,crl.pem} "${DATA_SERVER_DIR}"
	
	
	## OTHER KEYS ##
	# dh parameters from `IETF RFC 7919`
	echo "-----BEGIN DH PARAMETERS-----
MIIBCAKCAQEA//////////+t+FRYortKmq/cViAnPTzx2LnFg84tNpWp4TZBFGQz
+8yTnc4kmz75fS/jY2MMddj2gbICrsRhetPfHtXV/WVhJDP1H18GbtCFY2VVPe0a
87VXE15/V8k1mE8McODmi3fipona8+/och3xWKE2rec1MKzKT0g6eXq8CrGCsyT7
YdEIqUuyyOP7uWrat2DX9GgdT0Kj3jlN9K5W7edjcrsZCwenyO4KbXCeAvzhzffi
7MA0BM0oNC9hkXL+nOmFg/+OTxIy7vKBg8P+OxtMb61zO7X8vC7CIAXFjvGDfRaD
ssbzSibBsu/6iGtCOGEoXJf//////////wIBAg==
-----END DH PARAMETERS-----" > "${DATA_SERVER_DIR}/dh2048.pem"
	
	# tls-crypt key
	openvpn --genkey secret "${DATA_SERVER_DIR}/tls-crypt.key"
}



#
# HELPER: Set up openvpn server config file.
#
openvpn_config_init(){
	## IGNORE IF EXISTING ##
	[[ -f "${DATA_SERVER_DIR}/server.conf" ]] && return 0
	
	
	## WRITE SERVER CONFIG ##
	echo "port 1194
proto udp
server 192.168.35.0 255.255.255.0
dev tun
user nobody
group nogroup
topology subnet

ca ca.crt
cert server.crt
key server.key
dh dh2048.pem
crl-verify crl.pem
tls-crypt tls-crypt.key
auth SHA512

client-config-dir ${DATA_CLIENT_DIR}
ifconfig-pool-persist ipp.txt
keepalive 300 1500
persist-key
persist-tun

push \"dhcp-option DNS 1.1.1.1\"
push \"dhcp-option DNS 1.0.0.1\"
push \"redirect-gateway def1 bypass-dhcp\"
push \"block-outside-dns\"

verb 3" > "${DATA_SERVER_DIR}/server.conf"
}



## SET UP USED DIRECTORIES ##
mkdir -p "$DATA_DIR"
mkdir -p "$EASYRSA_DIR"
mkdir -p "$DATA_SERVER_DIR"
mkdir -p "$DATA_CLIENT_DIR"


## SET UP TUN DEVICE ##
mkdir -p /dev/net
[[ ! -c /dev/net/tun ]] && mknod /dev/net/tun c 10 200


## SET UP FW AND ROUTING ##
iptables_init


## INITIALIZE CONFIG ##
# set up easyrsa
easyrsa_init

# server keys
easyrsa_server_keys_create

# server config
openvpn_config_init


## RUN OPENVPN SERVER ##
/usr/sbin/openvpn --cd "${DATA_SERVER_DIR}" --config "${DATA_SERVER_DIR}/server.conf" & openvpn_pid=$!
wait $openvpn_pid