powernap

#!/bin/bash

shopt -s extglob

# requires bash >=4.4
printf -v startTime '%(%H:%M)T'
printf -v startTimeTs '%(%s)T'

time="${1//[hms]}"
timeval="${1//[!hms]}"
dowarn=0

# convert always to seconds
case "$timeval" in
    h)
        ((time=time * 3600))
    ;;
    m)
        ((time=time * 60))
    ;;
esac

if (( time > 300 )); then
    dowarn=1
    ((sleepTime=time - 300))
else
    sleepTime="$time"
fi

printf 'powernap started at %s\n' "$startTime"
printf 'Your pc will poweroff at %s\n' "$( printf '%(%H:%M)T' "$((startTimeTs + time))" )"

sleep "$sleepTime"

if (( dowarn )); then
    notify-send --app-name=powernap --expire-time=300000 --urgency=critical "PC will shut down in 5m"
    echo "PC will shut down in 5m"
    echo sleep 5m
fi

poweroff