#!/bin/bash

name="pdf-concat"
version="1.0"
read -r -d '' help_message <<-EOF
	Concatenate PDF files
	Usage: pdf-concat [OPTIONS] TARGET [TARGET..]
	Options:
	 -b BACKEND,            select a PDF backend
	     --backend BACKEND
	 -d, --dump             print to STDOUT
	 -h, --help             print this message
	 -l, --list-backends    list available PDF backends
	 -o OUTPUT,             write to a file
	     --output OUTPUT
	 -q, --quiet            suppress error messages and prompts
	 -v, --verbose          show additional messages
	 -V, --version          print version number and exit
EOF

source /usr/local/lib/mylib.bash

select_backend() {
  if command -v pdfjam >/dev/null 2>&1; then
    /usr/bin/printf "pdfjam\n"
  fi
  if command -v pdfunite >/dev/null 2>&1; then
    /usr/bin/printf "pdfunite\n"
  fi
  if command -v gs >/dev/null 2>&1; then
    /usr/bin/printf "gs\n"
  fi
  if command -v pdftk >/dev/null 2>&1; then
    /usr/bin/printf "pdftk\n"
  fi
}

list_backends() {
  if command -v pdfjam >/dev/null 2>&1; then
    msg "pdfjam    Interface to the pdfpages package for LaTeX"
  fi
  if command -v pdfunite >/dev/null 2>&1; then
    msg "pdfunite  Utility built on FreeDesktop's Poppler library"
  fi
  if command -v gs >/dev/null 2>&1; then
    msg "gs        PostScript interpreter"
  fi
  if command -v pdftk >/dev/null 2>&1; then
    msg "pdftk     General-purpose PDF toolkit"
  fi
}

positional=()
quiet=0
verbose=0
dump=0
backend="$(select_backend)"
outfile=""
while [[ $# -gt 0 ]]; do
  case "$1" in

  -b|--backend)
    debug_msg "Setting backend option to ${2} (was ${backend})"
    dump="$2"
    shift; shift
    ;;

  -d|--dump)
    debug_msg "Setting dump option to 1 (was ${dump})"
    dump=1
    shift
    ;;

  -h|--help)
    help_msg
    shift
    ;;

  -l|--list-backends)
    list_backends
    shift
    ;;

  -o|--output)
    debug_msg "Setting outfile option to ${2} (was ${outfile})"
    outfile="$2"
    shift; shift
    ;;

  -q|--quiet)
    debug_msg "Setting quiet option to 1 (was ${quiet})"
    quiet=1
    shift
    ;;

  -v|--verbose)
    debug_msg "Setting verbose option to 1 (was ${verbose})"
    verbose=1
    shift
    ;;

  -V|--version)
    version_msg
    ;;

  *)
    debug_msg "Argument '${1}' added to positional array"
    positional+=("$1")
    shift
    ;;
  esac
done

# sanitize infiles
infiles=()
infiles_count=0
for target in "${positional[@]}"; do
  if [[ ! -f "$target" ]]; then
    error_msg "No such file '${target}'"
  else
    infiles+=("$target")
    infiles_count=1
  fi
done
if [[ "$infiles_count" -eq 0 ]]; then
  usage_msg
fi
infiles_string="$(/usr/bin/printf "%q " "${infiles[@]}")"

# sanitize outfile
if [[ -f "$outfile" ]]; then
  if ! prompt_overwrite "$outfile"; then
    error_msg "No valid output"
  fi
fi

# dispatch to backend
if [[ "$backend" -eq "pdfjam" ]]; then
  pdfjam -o "$outfile" $infiles_string
elif [[ "$backend" -eq "pdfunite" ]]; then
  pdfunite $infiles_string "$outfile"
elif [[ "$backend" -eq "gs" ]]; then
  gs -dNOPAUSE -dQUIET -dBATCH -sDEVICE=pdfwrite -sOutputFile="$outfile" $infiles_string
elif [[ "$backend" -eq "pdftk" ]]; then
  pdftk $infiles_string cat output "$outfile"
else
  error_msg "No valid backend"
fi