#!/usr/bin/env bash

usage() {
   if [ -n "$1" ];then
      echo -e "\n   [ Error ]: $1"
   fi

cat<<EOF

   Usage: $(basename $0) YYYY-MM-DD

   $(basename $0) - Scripts shuts down this machine if the given date is the actual date.

                         The most common practice is, to use this script as cronjob.

EOF

exit 1
}

isValidDate() {
    DATE="${1}"

    # Autorized separator char ['space', '/', '.', '_', '-']
    SEPAR="([ \/._-])?"

    # Date format day[01..31], month[01,03,05,07,08,10,12], year[1900..2099]
    DATE_1="((([123][0]|[012][1-9])|3[1])${SEPAR}(0[13578]|1[02])${SEPAR}(19|20)[0-9][0-9])"

    # Date format day[01..30], month[04,06,09,11], year[1900..2099]
    DATE_2="(([123][0]|[012][1-9])${SEPAR}(0[469]|11)${SEPAR}(19|20)[0-9][0-9])"

    # Date format day[01..28], month[02], year[1900..2099]
    DATE_3="(([12][0]|[01][1-9]|2[1-8])${SEPAR}02${SEPAR}(19|20)[0-9][0-9])"

    # Date format day[29], month[02], year[1904..2096]
    DATE_4="(29${SEPAR}02${SEPAR}(19|20(0[48]|[2468][048]|[13579][26])))"

    # Date 29.02.2000
    DATE_5="(29${SEPAR}02${SEPAR}2000)"

    # Match the date in the Regex

    if [[ "${DATE}" =~ ^(${DATE_1}|${DATE_2}|${DATE_3}|${DATE_4}|${DATE_5})$ ]] ; then
      return 0
    else
      return 1
   fi
}

[ $# -ne "1" ] && usage "Wrong number of arguments"

_date=$1

IFS='-' read -a _val_arr <<< "$_date"

__year=${_val_arr[0]}
__month=${_val_arr[1]}
__day=${_val_arr[2]}

if ! isValidDate "${__day}-${__month}-${__year}" ; then
	usage "Invalid date: ${_date}"
fi

[[ "$(/bin/date +%Y-%m-%d)" == "$_date" ]] && /sbin/poweroff

exit 0