#!/bin/sh
set -e

. /usr/share/debconf/confmodule
db_version 2.0

action="$1"

umask 022


get_config_option() {
	option="$1"

	[ -f /etc/ssh/sshd_config ] || return

	# TODO: actually only one '=' allowed after option
	sed -E -n -e 's/[[:space:]]+/ /g' -e 's/[[:space:]]+$//' \
		-e 's/^[[:space:]]*'"$option"'[[:space:]=]+//Ip' \
		/etc/ssh/sshd_config
}


host_keys_required() {
	hostkeys="$(get_config_option HostKey)"
	if [ "$hostkeys" ]; then
		echo "$hostkeys"
	else
		# No HostKey directives at all, so the server picks some
		# defaults.
		echo /etc/ssh/ssh_host_ed25519_key
	fi
}


create_key() {
	msg="$1"
	shift
	hostkeys="$1"
	shift
	file="$1"
	shift

	if echo "$hostkeys" | grep -x "$file" >/dev/null && \
	   [ ! -f "$file" ] ; then
		printf %s "$msg"
		ssh-keygen -q -f "$file" -N '' "$@"
		echo
		if command -v restorecon >/dev/null 2>&1; then
			restorecon "$file" "$file.pub"
		fi
		ssh-keygen -l -f "$file.pub"
	fi
}


create_keys() {
	hostkeys="$(host_keys_required)"

	create_key "Creating SSH2 RSA key; this may take some time ..." \
		"$hostkeys" /etc/ssh/ssh_host_rsa_key -t rsa
	create_key "Creating SSH2 DSA key; this may take some time ..." \
		"$hostkeys" /etc/ssh/ssh_host_dsa_key -t dsa
	create_key "Creating SSH2 ECDSA key; this may take some time ..." \
		"$hostkeys" /etc/ssh/ssh_host_ecdsa_key -t ecdsa
	create_key "Creating SSH2 ED25519 key; this may take some time ..." \
		"$hostkeys" /etc/ssh/ssh_host_ed25519_key -t ed25519
}


new_config=

cleanup() {
	if [ "$new_config" ]; then
		rm -f "$new_config"
	fi
}


create_sshdconfig() {
	# XXX cjwatson 2016-12-24: This debconf template is very confusingly
	# named; its description is "Disable SSH password authentication for
	# root?", so true -> prohibit-password (the upstream default),
	# false -> yes.
	db_get openssh-server/permit-root-login
	permit_root_login="$RET"
	db_get openssh-server/password-authentication
	password_authentication="$RET"

	trap cleanup EXIT
	new_config="$(mktemp)"
	cp -aZ /usr/share/openssh/sshd_config "$new_config"
	if [ "$permit_root_login" != true ]; then
		sed -i 's/^#*PermitRootLogin .*/PermitRootLogin yes/' \
			"$new_config"
	fi
	if [ "$password_authentication" != true ]; then
		sed -i 's/^#PasswordAuthentication .*/PasswordAuthentication no/' \
			"$new_config"
	fi
	mkdir -pZ /etc/ssh
	ucf --three-way --debconf-ok \
		--sum-file /usr/share/openssh/sshd_config.md5sum \
		"$new_config" /etc/ssh/sshd_config
	ucfr openssh-server /etc/ssh/sshd_config
}

setup_sshd_user() {
	if ! getent passwd sshd >/dev/null; then
		adduser --quiet --system --no-create-home --home /run/sshd --shell /usr/sbin/nologin sshd
	fi
}

if [ "$action" = configure ]; then
	create_sshdconfig
	create_keys
	setup_sshd_user
	if dpkg --compare-versions "$2" lt-nl 1:7.9p1-5 && \
	   [ -f /etc/ssh/moduli.dpkg-bak ]; then
	    # Handle /etc/ssh/moduli being moved from openssh-client to
	    # openssh-server.  If there were no user modifications, then we
	    # don't need to do anything special here; but if there were,
	    # then the dpkg-maintscript-helper calls from openssh-client's
	    # maintainer scripts will have saved the old file as .dpkg-bak,
	    # which we now move back into place.
	    mv /etc/ssh/moduli.dpkg-bak /etc/ssh/moduli
	fi
	if dpkg --compare-versions "$2" lt-nl 1:9.1p1-1~ && \
	   deb-systemd-helper --quiet was-enabled ssh.socket && \
	   [ -d /run/systemd/system ]
	then
		# migrate to systemd socket activation.
		systemctl unmask ssh.service
		systemctl disable ssh.service
	fi
fi

#DEBHELPER#

db_stop

exit 0