at

#!/bin/bash

if [[ "$1" == "-h" ]]; then
	echo >&2 "Usage: $0 [ -h | -v ] when < sh_script"
	echo >&2 "With -v flag $0 mails script output if it's not empty even if exit code is zero."
	exit 0
fi

spool=
for spool_root in /{var/spool,dev}/shm /tmp; do
	if [[ -d "${spool_root}" ]]; then
		spool="${spool_root}/at"
		break
	fi
done
if [[ ! "$spool" ]]; then
	echo >&2 "Unable to find reliable enough spool-path, exiting"
	exit 1
fi

if [[ "$1" == "-v" ]]; then
	verbose=true
	shift
else verbose=
fi

timeout=$(( $(date +%s -d "$*") - $(date +%s) ))
if [[ $timeout -lt 0 ]]; then
	echo >&2 "Timeout is in the past: $(date -d "$*"), exiting"
	exit 1
fi

[[ ! -d "$spool" ]] && mkdir "$spool" && chmod 1777 "$spool"

umask 077
spool_file="$(mktemp --tmpdir="$spool" at.XXXXX)"
cat >"$spool_file"
echo "$(date): $@" >"${spool_file}.sched"

(
	sleep "$timeout"

	rm -f "${spool_file}.out"
	sh "$spool_file" >>"${spool_file}.out" 2>&1
	ERR=$?

	[[ $ERR -gt 0 || ( $verbose && -s "${spool_file}.out" ) ]] &&\
		cat "${spool_file}.out" | mailx -s "Delayed command output (exit code: $ERR)" "$USER"

	rm -f "$spool_file" "${spool_file}.pid" "${spool_file}.out" "${spool_file}.sched"
	rmdir "$spool" 2>/dev/null
) &

echo $! >"${spool_file}.pid"
pgrep -F "${spool_file}.pid" >/dev/null || rm -f "${spool_file}.pid"

disown
exit 0