#!/bin/bash

config=/etc/chrony.conf
keyfile=/etc/chrony.keys
chronyc=/usr/bin/chronyc
dhclient_servers=/var/lib/dhclient/chrony.servers.*
dhclient_added_servers=/var/lib/dhclient/chrony.added_servers
service_name=chronyd.service

get_key() {
    awk '/^[ \t]*'$1'\>/ { if ($3 == "") print "MD5", $2;
         else print $2, $3; exit }' < $keyfile
}

get_commandkeyid() {
    awk '/^[ \t]*commandkey\>/ { keyid=$2 } END { print keyid }' < $config
}

chrony_command() {
    commandkeyid=$(get_commandkeyid)
    [ -z "$commandkeyid" ] && return 1
    commandkey=$(get_key $commandkeyid)
    [ -z "$commandkey" ] && return 2

    authhash=${commandkey% *}
    password=${commandkey#* }

    $chronyc <<EOF
authhash $authhash
password $password
$1
EOF
}

generate_commandkey() {
    commandkeyid=$(get_commandkeyid)
    [ -z "$commandkeyid" ] && return 1
    commandkey=$(get_key $commandkeyid)
    [ -z "$commandkey" ] || return 0

    password=$(tr -c -d '0-9A-F' < /dev/urandom 2> /dev/null | head -c 40)
    [ ${#password} -eq 40 ] &&
        echo "$commandkeyid SHA1 HEX:$password" >> $keyfile
}

update_dhclient_added_servers() {
    new_servers=$(echo "$1" | sort -u)
    old_servers=$(cat $dhclient_added_servers 2> /dev/null)
    [ "$old_servers" = "$new_servers" ] && return 0
    [ -n "$new_servers" ] && echo "$new_servers" > $dhclient_added_servers ||
        rm -f $dhclient_added_servers
}

add_dhclient_servers() {
    shopt -s nullglob
    servers_files=($dhclient_servers)
    shopt -u nullglob
    (( ${#servers_files[*]} )) || return 0

    added_servers=$(
        cat $dhclient_added_servers 2> /dev/null
        cat ${servers_files[*]} |
            while read server serverargs; do
                chrony_command "add server $server $serverargs" &> /dev/null &&
                    echo "$server"
            done)
    update_dhclient_added_servers "$added_servers"
}

remove_dhclient_servers() {
    [ -f $dhclient_added_servers ] || return 0
    all_servers=$(
        cat $dhclient_servers 2> /dev/null |
            while read server serverargs; do
                echo "$server"
            done | sort -u)
    echo "$all_servers" | comm -23 $dhclient_added_servers - |
        while read server; do
            chrony_command "delete $server" &> /dev/null
        done
    added_servers=$(echo "$all_servers" | comm -12 $dhclient_added_servers -)
    update_dhclient_added_servers "$added_servers"
}

is_running() {
    systemctl is-active -q $service_name
}

case "$1" in
    generate-commandkey)
        generate_commandkey
        ;;
    add-dhclient-servers)
        add_dhclient_servers
        ;;
    remove-dhclient-servers)
        remove_dhclient_servers
        ;;
    is-running)
        is_running
        ;;
    command)
        is_running && chrony_command "$2"
        ;;
    forced-command)
        chrony_command "$2"
        ;;
    *)
        echo $"Usage: $0 {generate-commandkey|add-dhclient-servers|remove-dhclient-servers|is-running|command|forced-command}"
        exit 2
esac
exit $?