#!/bin/sh
set -eu

eval mailfile="\${$#}"
editor=
for i in "$@"; do
  # strip last argument from editor, yuk
  case "$i" in
    ("$mailfile") break;;
    (*) editor="${editor:+$editor }$i";;
  esac
done

tmpfile=$(mktemp --tmpdir reuse.XXXXXXXXXX)
cleanup() { rm -f "$tmpfile"; trap - 1 2 3 4 5 6 7 8 10 11 12 13 14 15; }
trap cleanup 1 2 3 4 5 6 7 8 10 11 12 13 14 15

formail -I Subject: < "$mailfile" | \
  formail -I In-Reply-To: | \
  sed -e '/^$/,/^-- /d' | \
  sed -e '/^Bcc:/aSubject: ' > "$tmpfile"
cat "$tmpfile" > "$mailfile"

cleanup

if [ -n "$editor" ]; then
  eval exec "$editor" "$mailfile"

# the last three replicate mutt's default (cf. manual)
elif [ -n "$VISUAL" ]; then
  eval exec "$VISUAL" "$mailfile"
elif [ -n "$EDITOR" ]; then
  eval exec "$EDITOR" "$mailfile"
fi
exec /usr/bin/editor "$mailfile"