#!/bin/sh

USAGE="Usage: compress-pdf [<in-pdf>] [<out-pdf>]
Compress PDF files using gs and compress."

usage() {
  echo "$USAGE"
  exit 0
}

die() {
  echo >&2 "error: $@"
  exit 1
}

# help option
case "$1" in
-h|--h|--help) usage ;;
esac

# check for dependencies
type gs &>/dev/null || die "dependency not found: gs
It is contained in the package: ghostscript
One of these may work for you:
    brew install ghostscript
    sudo apt-get install ghostscript"

# arguments
stream=0
infile=$1
outfile=$2

# are we streaming? if so use temp files.
if [ $# -eq 0 ]; then
  date=$(date +"%Y-%m-%dT%H:%M:%SZ")
  infile=$(mktemp "/tmp/compress-pdf.in.$date.XXXXXX.pdf")
  outfile=$(mktemp "/tmp/compress-pdf.out.$date.XXXXXX.pdf")
  stream=1

  echo >&2 "Awaiting pdf from stdin (stream mode)..."
  echo >&2 "If you meant to compress a file, use: $0 <file>"
  cat - >"$infile"
fi

# only one filename provided, default output filename.
if [ $# -eq 1 ]; then
  outfile=$(echo "$infile" | sed 's/\(.*\.\)\([^.]*\)/\1compressed.\2/')
fi

# if file does not exist, show usage.
if [ ! -f "$infile" ]; then
  die "'$infile' does not exist or is not a pdf file"
fi

# actually do the compression now \o/
echo >&2 "compressing $infile to $outfile..."
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.6 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile="$outfile" "$infile" >/dev/null

# if streaming, output the outfile, then remove the tmp files
if [ $stream -eq 1 ]; then
  cat "$outfile"
  rm "$infile"
  rm "$outfile"
fi