install

#!/usr/bin/env bash

# verify permission
if [ "${EUID:-$(id -u)}" != 0 ]; then
    echo >&2 "error: permission denied"
    echo >&2 'installation requires root privileges'
    exit 1
fi

# go to script dir
cd "$(dirname "$(readlink -f "$0")")"

# add cron scheduled job
add_cron(){
    local name="${1}"
    local cmd="${2}"
    local motd="${3}"
    cron_file="/etc/cron.hourly/${name}"
    echo "[+] add cron in ${cron_file}"
    cat << EOF > "${cron_file}"
#!/usr/bin/env sh
${cmd} > "${motd}"
EOF
    chmod +x "${cron_file}"
}

# add systemd scheduled job
add_systemd(){
    local name="${1}"
    local cmd="${2}"
    local motd="${3}"
    local service_file="/etc/systemd/system/${name}.service"
    echo "[+] add service in ${service_file}"
    cat << EOF > "${service_file}"
[Unit]
Description=${name} executor
After=network.target
After=network-online.target

[Service]
Type=oneshot
ExecStart=${cmd}
StandardOutput=truncate:${motd}
StandardError=truncate:${motd}

[Install]
WantedBy=multi-user.target
EOF
    local timer_file="/etc/systemd/system/${name}.timer"
    echo "[+] add timer in ${timer_file}"
    cat << EOF > "${timer_file}"
[Unit]
Description=${name} timer

[Timer]
OnCalendar=hourly
AccuracySec=5s

[Install]
WantedBy=timers.target
EOF
    systemctl daemon-reload
    systemctl enable --now ${name}.timer
}

# parse args
while [[ "$1" =~ ^- && ! "$1" == "--" ]]; do
    case "$1" in
        -u|--user)      shift; user="$1";;
    esac
    shift
done

if [[ -z "${user}" ]]; then
    echo >&2 "error: no user specified"
    echo >&2 "usage: ./$(basename "${0}") --user <USER>"
    exit 1
fi

# get homedir
home="$(getent passwd "${user}" | cut -d: -f6)"

# search for job scheduler
motd="$(pwd)/data/motd"
if [[ -d /run/systemd/system ]]; then 
    add_systemd 'tinymotd' "$(pwd)/generate" "${motd}"
elif [[ -d /etc/cron.hourly ]]; then 
    add_cron 'tinymotd' "$(pwd)/generate" "${motd}"
else
    echo >&2 "error: no job scheduler method found"
    exit 1
fi

# add print
bashrc="${home}/.bashrc"
echo "[+] add motd load in ${bashrc}"
cat << EOF >> "${bashrc}"
# motd supervision
if [[ -f ${motd} ]]; then
    cat ${motd}
fi
EOF