#!/bin/bash
# Configures a temporary VPN tunnel (using single-use keys) to a remote host
# using WireGuard: https://www.wireguard.com/
#
# Author: Matt Low <matt@mlow.ca>
#

HOST=$1
HOST_ADDR=$(echo ${HOST} | awk -F '@' '{ print $NF }')

RAND=$(tr -dc 'a-zA-Z0-9' < /dev/urandom | fold -w 8 | head -1)
INTERFACE_NAME=tun-${RAND}
SERVER_ADDR=10.99.255.1/24
CLIENT_ADDR=10.99.255.2/32
DNS=8.8.8.8
#INTERFACE_NAME=${INTERFACE_PFX}-${RAND}

echo "Generating keys..."
SERVER_KEY=$(wg genkey)
CLIENT_KEY=$(wg genkey)
SERVER_PUB=$(wg pubkey <<< ${SERVER_KEY})
CLIENT_PUB=$(wg pubkey <<< ${CLIENT_KEY})
PSK=$(wg genpsk)
echo "  Server pubkey: ${SERVER_PUB}"
echo "  Client pubkey: ${CLIENT_PUB}"

SERVER_LIB=$(cat << END
DEFAULT_IFACE=\$(awk '\$2 == 00000000 { print \$1 }' /proc/net/route)

exec_sudo() {
	echo "[#] \$@"
	sudo \$@ 2>/dev/null
}

deps() {
	if ! type -p wg iptables >/dev/null ; then
		echo "wireguard-tools or iptables missing, installing..."
		sudo apt install -y wireguard-tools iptables 2>/dev/null \
			|| sudo pacman -S --noconfirm wireguard-tools iptables 2>/dev/null \
			|| sudo dnf install -y wireguard-tools iptables 2>/dev/null
		if [ "\$?" -ne 0 ] ; then
			echo "Could not install wireguard-tools and/or iptables. Aborting."
			return 1
		fi
	fi
	return 0
}

enable_forwarding() {
	if sysctl net.ipv4.ip_forward | grep -q 0 ; then
		sudo sysctl -wq net.ipv4.ip_forward=1
		touch /tmp/vpnerator-ipfwd
	fi
}

remove_interface() {
	exec_sudo iptables -D FORWARD -i \$1 -j ACCEPT
	exec_sudo iptables -D FORWARD -o \$1 -j ACCEPT
	exec_sudo iptables -t nat -D POSTROUTING -s "${CLIENT_ADDR}" -o \${DEFAULT_IFACE} -j MASQUERADE
	exec_sudo ip link del dev \$1
}

cleanup() {
	if [ -f '/tmp/vpnerator-ipfwd' ] ; then
		sudo sysctl -wq net.ipv4.ip_forward=0
		rm /tmp/vpnerator-ipfwd
	fi

	EXIST_INTERFACE=\$(ip addr show to ${SERVER_ADDR} | head -1 | awk '{ print \$2 }' | cut -d':' -f1)
	if [ ! -z "\${EXIST_INTERFACE}" ] ; then
		if [ -z "\$(ip link show "\${EXIST_INTERFACE}" type wireguard)" ] ; then
			# bail if the existing interface isn't of type wireguard
			return 2
		fi

		remove_interface \${EXIST_INTERFACE}
		return 0
	elif ip link show ${INTERFACE_NAME} type wireguard > /dev/null 2>&1 ; then
		remove_interface ${INTERFACE_NAME}
		return 0
	fi
	return 1
}
END
)

echo
echo "Starting server..."
ssh -T ${HOST} /bin/bash << END
# include SERVER_LIB
${SERVER_LIB}

# Install depends
deps || exit 1

# Cleanup previous tunnel
cleanup
if [ "\$?" -eq 2 ] ; then
	echo "$SERVER_ADDR is already being used on the server."
	echo "Please choose another address."
	exit 1
fi

umask 0177

exec_sudo ip link add "${INTERFACE_NAME}" type wireguard

TMP=\$(mktemp)
cat << EOF > \${TMP}
[Interface]
ListenPort = 51820
PrivateKey = ${SERVER_KEY}

[Peer]
# foo
PublicKey = ${CLIENT_PUB}
PresharedKey = ${PSK}
AllowedIPs = ${CLIENT_ADDR}
EOF

exec_sudo wg setconf "${INTERFACE_NAME}" "\${TMP}"
rm "\${TMP}"

enable_forwarding

exec_sudo ip addr add "${SERVER_ADDR}" dev "${INTERFACE_NAME}"
exec_sudo ip link set mtu 1420 up dev "${INTERFACE_NAME}"

exec_sudo iptables -A FORWARD -i "${INTERFACE_NAME}" -j ACCEPT
exec_sudo iptables -A FORWARD -o "${INTERFACE_NAME}" -j ACCEPT
exec_sudo iptables -t nat -A POSTROUTING -s "${CLIENT_ADDR}" -o "\${DEFAULT_IFACE}" -j MASQUERADE

echo
sudo wg show "$INTERFACE_NAME"
END

if [ "$?" -ne 0 ]; then
    echo "Error starting server, aborting."
    exit 1
fi

umask 0177
FILE="/tmp/${INTERFACE_NAME}.conf"
cat << CONF > "${FILE}"
[Interface]
Address = ${CLIENT_ADDR}
PrivateKey = ${CLIENT_KEY}
DNS = ${DNS}

[Peer]
PublicKey = ${SERVER_PUB}
PresharedKey = ${PSK}
Endpoint = ${HOST_ADDR}:51820
AllowedIPs = 0.0.0.0/0, ::/0
CONF

echo
echo "Starting client..."
sudo wg-quick up "${FILE}"

sleep 1
echo
sudo wg show "${INTERFACE_NAME}"
echo
echo "Connected! SIGINT or Enter to disconnect and stop server."

# clear sensitive variables from memory
PSK=
CLIENT_KEY=
SERVER_KEY=

cleanup() {
	set -e
	echo
	echo "Stopping client..."
	sudo wg-quick down ${FILE}
	rm ${FILE}

	echo
	echo "Stopping server..."
	ssh -T ${HOST} /bin/bash <<- END
	${SERVER_LIB}

	cleanup || echo "Server was already shut down."
	END

	echo
	echo "Bye!"

	exit
}

trap cleanup INT TERM
read var
cleanup