#!/bin/sh
set -eu

file=/dev/stdin
if [ -r "${1:-}" ] && [ -w "${1:-}" ]; then
  file="$1"
  shift
fi

date=
arg="${1:-}"
args="$*"
if [ -z "$arg" ]; then
  read -p 'When should I tickle you about this message? ' args
  arg="${args%% *}"
fi

if [ "$arg" = '-d' ] || [ $# -gt 1 ]; then
  shift
  date="$args"
else
  case "$arg" in
    *[0-9]w) date="now + ${arg%w} weeks 00:00";;
    *[0-9]m) date="now + ${arg%m} months 00:00";;
    *[0-9]d) date="now + ${arg%d} days 00:00";;
    *[0-9]h) date="now + ${arg%h} hours";;
    @[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9])
      date="@${arg#@}";;
    *' '*) date="$args";;
    *[!0-9]*) 
      echo "E: invalid argument: $arg" >&2
      exit 1
      ;;
    *) date="now + $arg days 00:00";;
  esac
fi

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

TMPFILE="$(tempfile -d /tmp -p tickle)"
trap "rm -f $TMPFILE" 0 1 2 3 4 5 6 7 8 10 11 12 13 14 15

formail -i "X-Tickle: $tickle" < $file \
  | formail -R X-Postponed X-Was-Postponed > $TMPFILE

[ -w "$file" ] && mv $TMPFILE $file

rm -f $TMPFILE
trap - 0 1 2 3 4 5 6 7 8 10 11 12 13 14 15