#!/bin/sh
#
# pdfcat - concatenate PDFs into one
#
# $Id$

add_empties=0

me=`basename "$0"`

Erm() { echo $@ 1>&2; }

Die() { echo fatal error: $@ 1>&2; exit 1; }

DieIfMissing()
{
  for x in "$@"
  do
     command -v "$x" >/dev/null || Die cannot find required executable $x
  done
}

while :
do
  case "$1" in
  -e) add_empties=1;;
  -h) Erm Usage: $me [-e] [pdffile1 [pdffile2 [...]]] > all.pdf; exit 0;;
  -*) Die unknown option: $1, use -h for help; exit 1;;
  *) break;;
  esac
  shift
done

DieIfMissing mktemp file pdflatex pdfinfo

d=`mktemp -d /tmp/$me-XXXXX`

[ -n "$d" ] || exit 1

# thank you, https://unix.stackexchange.com/questions/272872/concatenate-pdfs-but-extend-pdfs-to-be-even-number-of-pages

trap "rm -rf $d" INT QUIT HUP EXIT

cat <<ZZ > $d/all.tex
\documentclass{article}
\usepackage{pdfpages}
\begin{document}
ZZ

i=1

for f in "$@"
do
  if [ application/pdf != `file -b --mime-type "$f"` ]
  then
    Erm not accessible or no PDF, skipped: $f
    continue
  fi

  cp -p "$f" $d/$i.pdf

  printf '\includepdf[pages=-]{%s}\n' $i.pdf >> $d/all.tex

  if [ $add_empties = 1 ]
  then
    # add an empty page if their number is odd
    pages=`pdfinfo $d/$i.pdf | grep -oP '^Pages:\s*\K\d+'`
    if [ `expr "$pages" % 2` != 0 ]
    then
      printf '%s\n' "\newpage\null" >> $d/all.tex
    fi
  fi

  i=`expr $i + 1`
done

printf '\\end{document}\n' >> $d/all.tex

(
  cd $d &&
  pdflatex all >/dev/null 2>&1 &&
  { grep -q . all.pdf && cat all.pdf; }
)