#! /usr/bin/env nix-shell
#! nix-shell -i bash -p ghostscript -p coreutils
#
# Local Variables:
# mode: sh
# End:
#

workdir=
keep_workdir=false
output=-

function usage {
    cat <<EOF
usage: merge-pdf [options] files...

options:
  -o FILE    write result to FILE (default: -)
EOF
}

function cleanup {
    if [ x"${keep_workdir}" != x"true" ]; then
        if [ -d "${workdir}" ]; then
            rm -rf "${workdir}"
        fi
    fi
}

trap "cleanup" EXIT

while getopts ":ho:k" o; do
   case "$o" in
       h)
           usage
           exit 0
           ;;
       o)
           output="$OPTARG"
           ;;
       k)
           keep_workdir=true
           ;;
       *)
           usage
           exit 1
           ;;
   esac
done

shift $((OPTIND - 1))

workdir=$(mktemp -d)

echo >&2 "[INFO] Putting temporary files into ${workdir}"

files=()
for f; do
    fname=$(basename "$f" .pdf)
    of="${workdir}/${fname}.ps"
    echo >&2 "[PS  ] \"${f}\" -> \"${of}\""
    pdf2ps "$f" "${of}" >&/dev/null
    files+=("$of")
done

echo >&2 "[PDF ] combining ${#files[@]} file(s) into ${output}"

gs -dNOPAUSE -sDEVICE=pdfwrite \
    -dPDFSETTINGS=/prepress \
    -sPAPERSIZE=a4 \
    -sFIXEDMEDIA \
    -sOUTPUTFILE="${output}" \
    -dBATCH \
    "${files[@]}" >&/dev/null