#!/bin/sh
#
# get-timestamp - helper script to obtain a timestamp from the user
#
# Copyright © 2008 martin f. krafft <madduck@madduck.net>
# Released under the terms of the Artistic Licence 2.0
#
set -eu

printf 'When should I tickle you about this message? ' >/dev/tty
read timespec </dev/tty

case "$timespec" in
  @[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]|*' '*)
    date="$timespec";;
  *[0-9]y) date="now + ${timespec%y} years 00:00";;
  *[0-9]m) date="now + ${timespec%m} months 00:00";;
  *[0-9]w) date="now + ${timespec%w} weeks 00:00";;
  *[0-9]d) date="now + ${timespec%d} days 00:00";;
  *[0-9]h) date="now + ${timespec%h} hours";;
  *[!0-9]*) 
    echo "E: invalid timespec: $timespec" >&2
    exit 1
    ;;
  *) date="now + $timespec days 00:00";;
esac

exec date +'%s (%c)' -d "$date"